Prescott, Hillary A.: The Crystal Structures and Thermal Behavior of Hydrogen Monofluorophosphates and Basic Monofluorophosphates with Alkali Metal and N-containing Cations

30

Kapitel 4. The Crystal Structures and their Hydrogen Bonding

The crystal structures of the hydrogen monofluorophosphates and basic monofluorophosphates presented here were determined with single crystal X-ray diffraction. The distinction between oxygen and fluorine in the crystal structure was accomplished crystallographically by first refining the structure to a low R1-factor while treating all of the atoms on the phosphorus atom as oxygen. Fluorine was then assigned a position on each unique phosphorus atom based on typical P-O/F bond lengths and the location of hydrogen atoms: long distance to phosphorus and no hydrogen atom in its vicinity. The existence of the P-F bond(s) in the structures was supported by NMR and elemental analysis.

The basic structural unit is a distorted (H)PO3F tetrahedron with P-O and P-F bond lengths that vary. P-O distances in the hydrogen monofluorophosphates differ depending on the hydrogen donor/acceptor functions of the oxygen atoms. In general, two shorter P-OA distances (around 1.5 Å) are found for the oxygen atoms acting as hydrogen acceptors in the hydrogen bond system. Oxygen atoms not involved in hydrogen bonding exhibit shorter interatomic distances to phosphorus. A longer P-ODH bond (ap1.55 Å) is observed for the H donor oxygen atom. The P-F distance, for the most part, is longer than the P-OA and P-ODH bonds, but shorter than P-F lengths found in the basic


31

monofluorophosphates. This is due to changes in the P-O bonding. In the structures of the basic monofluorophosphates, all of the oxygen atoms are hydrogen acceptors (OA); therefore, three P-O bonds have similar distances around 1.5 Å. The P-F distance of about 1.6 Å is longer than the P-F lengths found in the hydrogen monofluorophosphates.

Hydrogen bonding is observed in both the hydrogen monofluorophosphates and basic monofluorophosphates investigated here. Three basic types of hydrogen bonds were observed in the structures. Two weak hydrogen bonds, Ow-H···O(w) and/or N-H···O, connect the (H)PO3F tetrahedra to crystal water (Ow) and/or the N-containing cation in both the hydrogen monofluorophosphate and monofluorophosphate structures. Hydrogen bonds of medium strength are more of an exception and will be discussed, when appropriate. Strong or very strong O-H···O bonds link the HPO3F tetrahedra to one another in the acid salts. The acid salts were classified according to the structural pattern of these bridged HPO3F tetrahedra for a discussion and systematic comparision with the hydrogen sulfates. Infinite chains, branched chains, isolated dimers, cyclic dimer, or cyclic tetramers were found in the structures of the hydrogen monofluorophosphates dependent on cation size. The units were then inter-linked by either metal-oxygen/fluorine coordination or weak hydrogen bonds with the crystal water or the cations containing nitrogen.

The crystal structures and their hydrogen bonding are described and compared in the following. Selected crystallographic data from Appendix A.1, the fluoride analysis, when available (Sect. 2.1 and 2.3), and the total bond valency for fluorine, VF, (Sect. 2.1) are given for each compound/structure in the appropriate section. Atomic coordinates and the equivalent isotropic displacement parameters are listed in Appendix A.2. The bond lengths and hydrogen bonding are provided in each section for that particular compound with supplementary data in Appendix A.3.

4.1 The Structures with Infinite Chains

Infinite chains of HPO3F tetrahedra were found in the crystal structures of the hydrogen monofluorophosphates with the smaller cations, sodium and diethylammonium, and the piperazinium cation (Tab. 1 and A1). In the structures of NaHPO3F·2.5H2O [81] and [NH2Et2]HPO3F, zigzag chains of HPO3F tetrahedra run parallel to the b-axis (angPPPNa = 72°, angPPPDiet = 164°). In comparison, the HPO3F tetrahedra in the piperazinium structure are connected to each other in the c-direction with angPPPPip = 101°. The sodium and piperazinium structures are both monoclinic, whereas the diethylammonium salt


32

crystallizes in the orthorhombic space group Pbca.

Tab. 1 Selected crystallographic data

Formula

NaHPO3F·2.5H2O*<1>

[NH2Et2]HPO3F

[PipzH2][HPO3F]2

Formula weight

167.01

173.12

286.11

Crystal system

Monoclinic

Orthorhombic

Monoclinic

Space group

C2/c

Pbca

P21/c

Crystal Size

0.8 x 0.4 x 0.4

0.4 x 0.2 x 0.1

0.6 x 0.4 x 0.1

A

19.112(4)

12.892(4)

6.020(2)

b

5.341(1)

9.530(3)

13.012(3)

C

12.727(3)

13.555(4)

7.285(2)

â

110.18(3)

90

95.09(3)

V/Å3, Z

1219.4(4), 8

1665.4(9), 8

568.4(3), 2

rhocalc./g·cm -3

1.819

1.381

1.672

R1 [I>2sigma(I)]

0.0277

0.0288

0.0251

Analysis

 

 

 

F (50 mL H2O)

0.3

0.03

-

F (Seel)

9.2

11.65

-

F (calcd)

11.38

10.97

-

VF

0.95

0.95

0.95

4.1.1 NaHPO3F·2.5H2O

The sodium compound, NaHPO3F·2.5 H2O [81], was the only hydrate determined for the alkali metal hydrogen monofluorophosphate (Tab. A9, Fig. 1, Tab. 2 ). The asymmetric unit contains one Na atom, one HPO3F tetrahedron, and three molecules of water. The Na atom is octahedrally coordinated by four water molecules (Ow4, Ow5, Ow5´, and Ow6) and two O atoms from the tetrahedron (O1 and O1´) with an average Na-O bond length of 2.406 Å (Tab. 2). The NaO6 octahedra alternately share one edge involving Ow5 and Ow5´ and one face defined by Ow6, O1, and O1´ to form chains running along the c-axis. The HPO3F tetrahedron has two short P-OA bonds (1.481(1) Å for P-O1 and 1.503(1) Å for P-O2), a P-ODH (1.563(2) Å for P-O3), and a long P-F bond (1.564(1) Å). The P-O lengths reflect the function of the oxygen atom in the hydrogen bond system as an H acceptor (O1 and O2) or a donor (O3).

Tab. 2 Bond lengths in NaHPO3F·2.5H2O (Å)

 

d

 

d

 

d

Na-Ow5

2.388(2)

Na-O1

2.397(2)

P-O1

1.481(2)

Na-Ow6

2.392(2)

Na-Ow4

2.403(2)

P-O2

1.503(2)

Na-Ow

2.395(2)

Na-O1´

2.458(2)

P-O3

1.563(2)

 

 

 

 

P-F

1.564(2)


33

In the hydrogen bond system (Tab. 3), the HPO3F-tetrahedra are connected to each other by one short hydrogen bond O3-H1···O2 (2.566(2) Å), which form columns around the crystallographic 21 axis at {¼, y, ¼} (Fig. 1). These columns run in the b-direction as zigzag chains of P-tetrahedra. They are held together by weaker hydrogen bonds (2.791(2) to 2.972(2) Å) with the water molecules to form a three-dimensional network. The hydrogen bond, Ow6-H6A···O1, bridges the chains of HPO3F-tetrahedra together in the a-direction. Hydrogen bonds also link the chains parallel to the c-axis. The Ow atoms act mainly as donors in the hydrogen bonds: Ow4-H4A···O2, Ow4-H4B···Ow3, Ow5-H5B···O2, and Ow5-H5A···Ow4. The F atom is not involved in the hydrogen bonding and has a bond valency of 0.95 for the bond to P (Tab. 1). The P-F vertex of the tetrahedron points away from the NaO6 octahedra (Fig. 1).

Tab. 3 Hydrogen bonding in NaHPO3F·2.5H2O (Å, °)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O3-H1···O2

0.84(3)

1.73(3)

2.566(2)

173(3)

Ow4-H4A···O3

0.83(3)

2.17(3)

2.972(2)

164(3)

Ow4-H4B···O2

0.76(3)

2.10(3)

2.838(3)

165(3)

Ow5-H5A···Ow4

0.86(3)

1.94(3)

2.791(2)

171(3)

Ow5-H5B···O2

0.86(3)

2.03(3)

2.880(3)

170(3)

Ow6-H6A···O1

0.84(3)

2.14(3)

2.910(3)

152(3)

Fig. 1 Structure of NaHPO3F·2.5H2O looking down the b-axis. The chains of [NaO6] units running in the c-direction at x = 0 and ½ are represented by gray octahedra. H···O bonds are indicated by dashed lines. The P atoms are blue; F atoms are red; H atoms are small open cirles; O atoms are larger open circles.


34

4.1.2 [NH2(CH2CH3)2]HPO3F

The structure of diethylammonium hydrogen monofluorophosphate (Tab. A10, Fig. 2a, b, and c) made up of one crystallographically independent [NH2Et2]+ cation and HPO3F- anion is quite symmetrical due to the high orthorhombic symmetry. Two N-C distances (1.495(3) and 1.496(3) Å) (Tab. 4) are found in the [NH2Et2]+ cation with equidistant C-C lengths of 1.503(3) Å. The C-H distances range from 0.91(3) to 0.99(2) Å. The cations were found grouped together in layers parallel to the ac-plane at b = ¼ and ¾ (Fig. 2b and c). The HPO3F tetrahedra demonstrates typical P-O and P-F bond lengths with two short P-OA distances (1.476(1) and 1.485(1) Å) and two long bonds for P-ODH and P-F of 1.545(1) and 1.566(1) Å, respectively (Tab. 4).

Tab. 4 Bond lengths in [NH2Et2]HPO3F (Å)

 

d

 

d

 

d

 

d

P1-O1

1.476(1)

N-C1

1.495(3)

C1-H4

0.93(2)

C3-H9

0.96(2)

P1-O2

1.485(1)

N-C3

1.496(3)

C1-H5

0.97(2)

C3-H10

0.96(2)

P1-O3

1.545(1)

C1-C2

1.503(3)

C2-H6

0.91(3)

C4-H11

0.98(3)

P1-F1

1.566(1)

C3-C4

1.503(3)

C2-H7

0.96(2)

C4-H12

0.99(3)

 

 

 

 

C2-H8

0.98(2)

C4-H13

0.99(2)

Fig. 2 Structure of [NH2Et2]HPO3F (a) Ball-and-stick representation looking down the c-axis. The N atoms are green; C atoms are black. The zigzag chains of HPO3F tetrahedra run parallel to b at x = ¼ and ¾. Dashed lines indicate the H···O bonds. The hydrogen atoms on carbon have been omitted for clarity. (b) Perspective view down the b-axis showing the orientation of HPO3F tetrahedra relative to the P-F bond and their linkage to each other via the [NH2Et2]+ ions. (c) Perspective view of the [NH2Et2]+ layers parallel to the ac-plane at y = ¼ and ¾ with the P-F axis between them.


35

The hydrogen bond system (Tab. 5) consists of one short O-H···O bond (O3···O2 2.529(2) Å) and two longer hydrogen bonds (N···O 2.761(2) and 2.837(2) Å). The O···O bridge links the HPO3F tetrahedra to zigzag chains along the b-axis (Fig. 2b). These chains are connected to each other by N···O bonds, N-H2···O1 and N-H3···O1´, with each O1 atom hydrogen-bonded to two different [NH2Et2]+ ions. Although the O1 atom is a twofold hydrogen acceptor in the structure, the P-O1 length is slightly shorter than the P-O2 bond probably due to weaker hydrogen interactions with O1. Each HPO3F tetrahedra is fixed in the structure by hydrogen bonds to its three oxygen vertices. The fourth vertex of the tetrahedron (P-F axis) lies between the layers of [NH2Et2]+ ions (Fig. 2c) with the F atom not participating in any other bonds.

Tab. 5 Hydrogen bonding in [NH2Et2]HPO3F (Å, °)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O3-H1···O2

0.72(2)

1.81(2)

2.529(2)

173(2)

N-H2···O1

0.90(2)

1.86(2)

2.761(2)

176(2)

N-H3···O1

0.92(2)

2.00(2)

2.837(2)

151(2)

4.1.3 [NH2(CH2CH2)2NH2][HPO3F]2

The piperazinium structure was the only one determined, in which the cation was a nitrogen heterocycle. The structure of one unique HPO3F tetrahedron and one-half of a unique piperazinium cation (Tab. A11, Fig. 3a and b) is less symmetrical when compared to that of [NH2Et2]HPO3F. The piperazinium cations (PipzH22+) are centered around centers of symmetry at {½, ½, 0} (Fig. 3a) with the HPO3F tetrahedra located in between.

Tab. 6 Bond lengths in [PipzH2][HPO3F]2 (Å)

 

d

 

d

 

d

P-O1

1.483(1)

N-C1

1.493(2)

C1-H5

0.92(2)

P-O2

1.505(1)

N-C2

1.493(2)

C2-H6

0.92(2)

P-O3

1.549(1)

C1-C2

1.512(2)

C2-H7

0.82(2)

P-F

1.564(1)

C1-H4

0.93(2)

 

 

Bond distances (Tab. 6) are comparable to those found in [NH2Et2]HPO3F. The [PipzH2]2+ cation has two N-C distances of 1.493(2) with a C-C bond length of 1.512(2) Å. C-H bonds are between 0.82(2) and 0.93(2) Å. The P-ODH and P-F bonds with lengths of 1.549(1) and 1.564(1) Å are similar to those found in [NH2Et2]HPO3F, whereas the P-OA distances vary with values of 1.483(1) for O1 and 1.505(1) Å for O2. The P-O2 bond is longer than typical P-OA distances, due to the twofold hydrogen acceptor function of O2 in


36

the structure.

Three hydrogen bonds build up a structure of interconnected HPO3F chains running in the c-direction (Tab. 7, Fig. 3a). The zigzag chains of HPO3F tetrahedra are formed by one short hydrogen bond, O3-H1···O2, (2.541(2) Å). They are then linked together by one weaker N···O hydrogen bond, N-H2···O2, with a length of 2.822(2) Å and a shorter N···O bridge, N-H3···O1 (2.677(2) Å). The short distance of the N···O1 bond could be caused by the fact that the O1 atom is only involved in one hydrogen bond as an acceptor. Layers of the [PipzH2]2+ cations are located parallel to the c-axis at x = ½ with the P-F bond pointed in the opposite direction (Fig. 3b).

Tab. 7 Hydrogen bonding in [PipzH2][HPO3F]2 (Å, °)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O3-H1···O2

0.73(2)

1.82(2)

2.541(2)

168(3)

N-H2···O2

0.86(2)

1.97(2)

2.822(2)

170(2)

N-H3···O1

0.83(2)

1.85(2).

2.677(2)

172(2)

Fig. 3 Structure of [PipzH2][HPO3F]2 (a) View along the a-axis with the zigzag HPO3F chains parallel to the c-direction. (b) Polyhedral representation of the HPO3F tetrahedra looking down the b-axis. The layer of [PipzH22+] ions is shown at x = ½ with the P-F axis of tetrahedron pointed in the opposite direction.

4.2 The Structure with Branched Chains

Branched chains of HPO3F tetrahedra were only found in the KHPO3F structure (Tab. 8 and A2). The structure consists of infinite chains of three different HPO3F tetrahedra with one branched HPO3F tetrahedron. The structure exhibited twinning which was not


37

surprising due to the beta angle close to 90°. A R1-factor of about 20% was reached after solving and refining the structure in the monoclinic space group, P21. After refinement with the TWIN correction for a pseudo-orthorhombic symmetry, a R1-factor of 2.14% was achieved with a 0.465:0.535 population ratio for the two orientations.

Tab. 8 Selected crystallographic data

Formula

KHPO3F

Formula weight

138.08

Crystal system

Monoclinic

Space group

P21

Crystal Size

0.1 x 0.1 x 0.1

a

7.273(1)

B

14.086(3)

c

7.655(2)

â

90.13(3)

V3, Z

784.2(3), 8

rhocalc./g·cm -3

2.339

R1 [I>2sigma(I)]

0.0214

VF (F1, F2, F3, F4)

1.09, 1.01, 1.07, 1.15

4.2.1 KHPO3F

The KHPO3F structure is composed of four crystallographically unique units of K+ and HPO3F- ions (Tab. A12, Fig. 4). The potassium atoms, K1, K3, and K4, have an eightfold coordination with both oxygen and fluorine atoms, whereas the K2 atom is only coordinated by seven atoms (1F + 6O). Average K-O lengths are 2.888, 2.814, 2.845, and 2.940 Å for K1, K2, K3, and K4, respectively (Tab. A30). The K1, K2, and K3, atoms located in the vicinity of one of the O-O edges of the HPO3F tetrahedra of P1, P2, and P3 (Fig. 4) are each bonded to one fluorine atom with K-F lengths of 2.757(3), 3.075(4), and 2.762(3) Å, respectively. The K4 atom positioned near the O-F edge of the HPO3F tetrahedron of P4 is coordinated by three F atoms with an average K-F length of 2.925 Å.

Tab. 9 P-O and P-F bond lengths in KHPO3F (Å)

 

d

 

d

 

d

 

d

P1-O1

1.483(3)

P2-O4

1.471(4)

P3-O7

1.479(4)

P4-O10

1.463(4)

P1-O2

1.489(4)

P2-O5

1.487(4)

P3-O8

1.504(4)

P4-O11

1.512(4)

P1-O3

1.555(4)

P2-O6

1.568(4)

P3-O9

1.556(3)

P4-O12

1.545(4)

P1-F1

1.565(3)

P2-F2

1.585(3)

P3-F3

1.574(3)

P4-F4

1.568(3)

The four HPO3F tetrahedra vary slightly in their P-O, P-OH, and P-F lengths (Tab. 9). The P-OA bonds found in the HPO3F tetrahedra with P1 have similar lengths of 1.483(3) and 1.489(4) Å; both of these oxygen atoms, O1 and O2, act as hydrogen acceptors in the structure. In the HPO3F tetrahedra with P3 and P4, only one of the oxygen atoms acts as a


38

hydrogen acceptor, O8 and O11, with longer P-O bond lengths of 1.504(4) and 1.512(4) Å respectively, whereas the oxygen atoms, O4, O5, O7, and O10, are not involved in hydrogen bonding and have shorter P-O distances between 1.463(4) and 1.487(4) Å. The HPO3F tetrahedron of P2 due to the absence of a hydrogen acceptor does not have a characteristic P-OA distance. The P-ODH bond distances with the oxygen atoms, O3, O6, O9, and O12, range from 1.545(4) to 1.568(4) Å. The P-F bond is the longest bond in each tetrahedron with lengths between 1.565(3) and 1.585(3) Å. The fluorine atoms, F2 and F3, are bonded to one phosphorus and one potassium atom, whereas the F1 and F4 atoms are involved in two K-F and one P-F bonds (Tab. A30).

Tab. 10 Hydrogen bonding in KHPO3F (Å, °)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O3-H1···O11

0.73(2)

1.93(4)

2.590(5)

150(9)

O6-H2···O2

0.80(9)

1.8(1)

2.544(5)

175(9)

O9-H3···O1

0.93(6)

1.60(6)

2.520(5)

169(6)

O12-H4···O8

0.91(6)

1.60(6)

2.497(5)

169(5)

Four short O-H···O hydrogen bonds build up zigzag chains of the three HPO3F tetrahedra with the P1, P3, and P4 atoms. These O-H···O bonds have O···O lengths between 2.497(5) and 2.590(5) Å. Each of these tetrahedra has one hydrogen donor and at least one hydrogen acceptor oxygen (Tab. 10). The chains run along b around the crystallographic 21 axis (Fig. 4). The fourth tetrahedra (P2, O4, O5, O6, F2) is connected to the HPO3F tetrahedra of P1 with the hydrogen bond, O6-H2···O2, to create a branched chain.

Fig. 4 Structure of KHPO3F viewed along the c-axis showing a branched chain of HPO3F tetrahedra, which runs parallel to b around the crystallographic 21 axis at x = ½. Dashed lines indicate the H···O bonds. The K atoms are green.


39

4.3 The Structure with Isolated Dimers

The structure of K3[H(PO3F)2] uniquely featured isolated dimers of [H(PO3F)2] units (Tab. 11 and A2). The [H(PO3F)2] unit consisted of two equivalent PO3F tetrahedra hydrogen-bonded to each other by a symmetrically-disordered hydrogen bond.

Tab. 11 Selected crystallographic data

Formula

K3[H(PO3F)2]

Formula weight

314.25

Crystal system

Monoclinic

Space group

C2/c

Crystal Size

0.9 x 0.8 x 0.2

a

7.973(3)

b

11.635(4)

c

9.668(4)

â

113.52(4)

V3, Z

822.3(5), 4

rhocalc./g·cm -3

2.538

R1 [I>2sigma(I)]

0.0581

Analysis

 

F (50 mL H2O)

11.9

F (calcd)

6.05

VF

1.14

4.3.1 K3[H(PO3F)2]

The structure of the potassium hydrogen monofluorophosphate, K3[H(PO3F)2] (Tab. A13, Fig. 5), was the only one characterized with a H/PO3F ratio of 0.5. The space group, C2/c, yielded a structure model with a R1-factor over 6%. A decrease in the R1-factor was achieved after the hydrogen atom initially found on the center of symmetry was assigned a general position within the hydrogen bond geometry.

Tab. 12 Bond lengths in K3[H(PO3F)2] (Å)

 

d

 

d

 

d

 

d

 

d

K1-O1

2.729(4)

K1-O3´

2.860(4)

K2-O1

2.846(4)

K2-O1´

2.953(5)

P1-O1

1.487(4)

K1-O1´

2.729(4)

K1-F

3.096(4)

K2-O2

2.915(5)

K2-O2´´

3.084(5)

P1-O2

1.492(4)

K1-O2

2.785(4)

K1-F´

3.096(4)

K2-O2´

2.936(5)

K2-O3

3.150(5)

P1-O3

1.543(4)

K1-O2´

2.785(4)

 

 

K2-F

2.942(4)

K2-F´

3.181(4)

P1-F1

1.594(3)

K1-O3

2.860(4)

 

 

K2-O1

2.948(5)

 

 

 

 

The asymmetric unit consists of two potassium atoms, one PO3F tetrahedron, and a disordered hydrogen atom. The K1 atom has a special position on the crystallographic C2 axis (Fig. 5). The potassium atoms, K1 and K2, are bonded to a total of eight and nine oxygen and fluorine atoms, respectively, with average K-O/F lengths of 2.868 (for K1) and 2.995 Å (for K2) (Tab. 12). The PO3F tetrahedron has two P-O bonds with distances


40

of 1.487(4) and 1.492(4) Å (Tab. 12). These oxygen atoms, O1 and O2, coordinate the two K+ ions and do not participate in hydrogen bonding. The O3 atom, which is a half donor and half acceptor in the structure has a distance of 1.543(4) Å to phosphorus. This length is longer than other P-OH distances for oxygen atoms involved in a hydrogen bond as a donor and acceptor (½D + ½A) possibly due to further coordination of O3 to the potassium cations. The P-F bond with a length of 1.594(3) Å is also longer than those found in the other hydrogen monofluorophosphates and most likely caused by its extended coordination with four K atoms.

The hydrogen bond system consists of one short, symmetrically-disordered hydrogen bond, O3-H···O3´, (2.451(8) Å) (Tab. 13). This O-H···O bond links two equivalent PO3F tetrahedra together to form an isolated dimer with the formula: H(PO3F)2. These dimers are positioned around centers of symmetry. Layers of K atoms and two tetrahedra of two separate dimers alternate along the b-axis (Fig. 5).

Tab. 13 Hydrogen bonding in K3[H(PO3F)2] (Å, °)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O3-H···O3´

0.75(2)

1.72(4)

2.451(8)

166(20)

Fig. 5 View of the K3[H(PO3F)2] structure looking down the a-axis. The HO3´ bond is indicated with dashed lines. The isolated dimers of [H(PO3F)2] are shown positioned around centers of symmetry at {½, ½, ½} with the O1-O2 edges of the PO3F tetrahedra overlapping each other.

4.4 The Structures with Cyclic Dimers

Cyclic dimers of hydrogen-bonded HPO3F tetrahedra were also observed in the crystal structures of the hydrogen monofluorophosphates. This type of dimer was found in the


41

hydrogen monofluorophosphate structures with cesium [78] and the N-containing cations, [NHEt3]+, [C(NH2)2]+, and N,N´-dmuH+ (Tab. 14, A3, and A4). The cyclic dimers in the cesium and triethylammonium structures were formed by disordered hydrogen bonds.

Tab. 14 Selected crystallographic data

Formula

CsHPO3F

[NHEt3]HPO3F

[C(NH2)3]HPO3F

[N,N´-dmuH]HPO3F

Formula weight

231.89

201.18

159.07

188.10

Crystal system

Monoclinic

Monoclinic

Monoclinic

Monoclinic

Space group

C2/m

P21/n

P21/c

P21/c

Crystal Size

0.4 x 0.2 x 0.1

0.5 x 0.4 x 0.2

0.24 x 0.08 x 0.04

0.5 x 0.2 x 0.1

a

14.478(8)

10.735(3)

6.780(1)

5.435(1)

b

5.929(3)

8.214(2)

10.089(2)

17.634(4)

c

5.413(2)

11.755(3)

9.389(2)

8.507(2)

â

103.30(4)

91.15(3)

105.77(3)

100.47(3)

V3, Z

452.2(4), 4

1036.3(5), 4

618.1(2), 4

801.7(3), 4

rhocalc./g·cm -3

3.406

1.289

1.709

1.558

R1 [I>2sigma(I)]

0.0155

0.0387

0.0449

0.0383

Analysis

 

 

 

 

F (50 mL H2O)

-

0.1

0.8

0.5

F (Seel)

8.1

9.2

11.1

9.4

F (calcd)

8.19

9.44

11.94

10.10

VF

1.04

0.95

0.98

0.97

4.4.1 CsHPO3F

The crystal structure of cesium hydrogen monofluorophosphate consists of one crystallographically unique cesium atom and one HPO3F tetrahedron (Tab. A14). The HPO3F- anions are hydrogen-bonded to each other via one unique hydrogen bond to form cyclic dimers with cesium atoms between them (Fig. 6). The cesium, phosphorus, fluorine, and oxygen (O1) atoms are situated on the mirror plane, which gives the structure a symmetrical simplicity.

The cesium atom has a tenfold coordination with one fluorine and nine oxygen atoms with Cs-X distances between 3.030(3) and 3.379(2) Å (Tab. 15). In the HPO3F-tetrahedron, two different P-O bonds with lengths of 1.477(3) (P-O1) and 1.528(2) Å (P-O2) are observed with a longer distance of 1.577(2) Å between P and F. The O1 atom with a short distance to P does not participate in hydrogen bonding. The distance from phosphorus to the half protonated oxygen atom, O2, is between typical P-OA and P-ODH lengths.

Tab. 15 Bond lengths in CsHPO3F (Å)

 

d

 

d

 

d

Cs-O1

3.030(3)

Cs-O2´

3.315(2)

P-O1

1.477(3)

Cs-O1´

3.159(1)

Cs-O2´´

3.363(2)

P-O2

1.528(2)

Cs-O1´´

3.159(1)

Cs-O2´´´

3.363(2)

P-F

1.577(2)

Cs-F

3.194(3)

Cs-O2´´´´

3.379(2)

 

 

Cs-O2

3.315(2)

Cs-O2´´´´´

3.379(2)

 

 


42

The disordered hydrogen bond, O2-H···O2´, with a O···O distance of 2.527(2) Å (Fig. 6, Tab. 16) links two HPO3F tetrahedra with each other to form cyclic dimers. The oxygen atom, O2, acts as a half hydrogen donor and half acceptor (½ D + ½ A) on the basis of the disordered hydrogen position. Therefore, the tetrahedron can be more accurately written as [PO(OH1/2)2F].

Tab. 16 Hydrogen bonding in CsHPO3F (Å, °)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O2-H···O2´

0.74(2)

1.84(4)

2.527(2)

153.9(1)

Fig. 6 Structure of CsHPO3F viewed along the c-axis showing the cyclic dimers of HPO3F tetrahedra. The Cs atoms are green. Dashed lines indicate the H···O2´ bond.

4.4.2 [NH(CH2CH3)3]HPO3F

The triethylammonium structure contains one unique [NHEt3]+ cation and one HPO3F- anion (Tab. A15, Fig. 7a and b). Cyclic dimers are formed in the structure by a disordered hydrogen bond. The [NHEt3]+ cation has N-C lengths between 1.498(3) and 1.532(2) Å with C-C distances varying from 1.461(4) Å for C1-C2 to 1.521(3) Å for C5-C6 (Tab. 17). The C-H bonds have an average length of 1.00 Å (Tab. A31). A typical length of 1.566(2) Å is observed in the structure for the P-F distance, whereas inconsistencies are found in the P-O bond lengths. A very short P-OA distance of 1.452(2) Å is found for the P-O1 bond. The other P-O distances of 1.511(2) (P-O2) and 1.532(2) (P-O3) are much longer between P-OA and P-ODH lengths. These deviations in the interatomic distances are caused by the ½D + ½A function of the O2 and O3 atoms. The average P-O½D+½A length is 1.523 Å.


43

Tab. 17 P-X, N-C, and C-C bond lengths in [NHEt3]HPO3F (Å)

 

d

 

d

 

d

P-O1

1.452(2)

N-C1

1.498(2)

C3-C4

1.494(3)

P-O2

1.511(2)

N-C3

1.532(2)

C5-C6

1.521(3)

P-O3

1.534(2)

N-C5

1.522(3)

 

 

P-F

1.566(2)

C1-C2

1.461(4)

 

 

Fig. 7 Structure of [NHEt3]HPO3F (a) Ball-and-stick representation viewed along the b-axis. The hydrogen atoms on carbon have been omitted for clarity. Dashed lines indicate the H···O bonds. (b) Another view of the structure down the c-axis showing the O-H···O bonds with the disordered hydrogen position. (c) Polyhedral representation of the HPO3F tetrahedra along the a-axis showing the direction of the P-F axis relative to the layers of [NHEt3]+ ions at z = ¼ and ¾.

The HPO3F tetrahedra are linked to each other to form cyclic dimers in the structure via a short hydrogen bond between O2 and O3, in which the hydrogen atom has a disordered position (Fig. 7a). The tetrahedron can consequently be expressed as [PO(OH½)2F]. The disordered hydrogen bond, O2-H1B···O3´and O3-H1A···O2´, has a length of 2.515(2) Å (Tab. 18, Fig. 7b). The cyclic dimers are fixed in the structure by a second hydrogen bond, N-H2···O1 (2.622 Å). Each of the three oxygen vertices of the [PO(OH½)2F] tetrahedron are hydrogen-bonded to either a second tetrahedron or the [NHEt3]+ cation shown in Fig. 7a.


44

The fluorine atom on the fourth vertex of the tetrahedron located between the layers of cations at z = ¼ and ¾ does not participate in additional bonding (Fig. 7c).

Tab. 18 Hydrogen bonding in [NHEt3]HPO3F (Å, °)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O2-H1A···O3

0.72(4)

1.81(4)

2.515(2)

167(4)

O3-H1B···O2

0.74(2)

1.80(3)

2.515(2)

162(7)

N-H2···O1

0.84(3)

1.78(3)

2.622(2)

169(2)

4.4.3 [C(NH2)3]HPO3F

In the guanidinium hydrogen monofluorophosphate structure, one crystallographically independent unit of a [C(NH2)3]+ cation and a HPO3F- anion are found (Tab. A16, Fig. 8). The guanidinium cation has C-N lengths between 1.310(4) and 1.339(4) Å. N-H distances vary from 0.78(4) to 0.87(4) Å (Tab. 20). P-OA lengths of 1.480(2) and 1.479(3) Å are found for the P-O1 and P-O2 bonds, respectively. The P-O3 and P-F have lengths of 1.531(3) and 1.544(3) Å (Tab. 19).

Tab. 19 Bond lengths in [C(NH2)3]HPO3F (Å)

 

d

 

d

P-O1

1.480(2)

C-N1

1.339(4)

P-O2

1.479(3)

C-N2

1.310(4)

P-O3

1.531(3)

C-N3

1.325(4)

P-F

1.544(3)

 

 

Fig. 8 Ball-and-stick representation of the [C(NH2)3]HPO3F structure viewed along the a-axis. The cyclic dimers of HPO3F tetrahedra are shown linked by the short hydrogen bond, O3-H1···O2. The N-H···O hydrogen bonds are not shown for clarity.


45

The hydrogen bond system (Tab. 20) in the guanidinium structure involves one short O-H···O hydrogen bond and longer N-H····O bridges. The hydrogen bond, O3-H1···O2, with a length of 2.562(4) Å connects the HPO3F tetrahedra to cyclic dimers. The dimers are interlinked to each other by the long N-H···O bridges. Only the nitrogen atoms, N2 and N3, participate in N···O bonds with a range of lengths from 2.920(4) to 3.042(4) Å (Tab. 20). The hydrogen atoms, H2 and H3, on N1 are not involved in hydrogen bonding in the structure. The O1 atom is involved in three N···O hydrogen bonds, whereas O2 participates in the short O···O bond and one long N···O bridge as a hydrogen acceptor.

Tab. 20 Hydrogen bonding in [C(NH2)3]HPO3F (Å, °)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O3-H1···O2

0.81(5)

1.77(5)

2.562(4)

166(5)

N1-H2

0.84(5)

 

 

 

N1-H3

0.85(5)

 

 

 

N2-H4···O2

0.81(4)

2.17(4)

2.920(4)

155(3)

N2-H5···O1

0.79(4)

2.18(5)

2.934(4)

161(4)

N3-H6···O1

0.78(4)

2.14(4)

2.898(4)

163(3)

N3-H7···O1

0.87(4)

2.27(4)

3.042(4)

149(3)

4.4.4 {HOC[NH(CH3)]2}HPO3F

In the structure of the N,N´-dimethyluronium (N,N´-dmuH) hydrogen monofluorophosphate, a crystallographic unique set of one [N,N´-dmuH]+ ion and one HPO3F- anion build up a structure of interconnected cyclic dimers (Tab. A17, Fig. 9). The uronium carbon atom is bonded to one oxygen atom (1.303(3) Å) and two nitrogen atoms (average distance of 1.323 Å) (Tab. 21). Longer N-C bonds are observed between the nitrogen atoms and the methyl groups with lengths of 1.445(3) and 1.466(3) Å. The average C-H length in the structure is 0.94 Å with N-H distances of 0.79(3) and 0.83(3) Å (Tab. 22). The HPO3F tetrahedron has two short P-OA lengths of 1.498(2) and 1.492(2) Å with a P-ODH distance of 1.542(2) Å. The P-F bond length is 1.554(2) Å.

Tab. 21 Bond lengths in [N,N´-dmuH]HPO3F (Å)

 

d

 

d

 

d

P-O1

1.498(2)

C1-N1

1.321(3)

C2-H6

0.89(3)

P-O2

1.492(2)

C1-N2

1.325(3)

C2-H7

0.94(3)

P-O3

1.542(2)

N1-C2

1.445(3)

C3-H8

0.97(4)

P-F

1.554(2)

N2-C3

1.466(3)

C3-H9

0.93(5)

C1-O4

1.303(3)

C2-H5

0.99(3)

C3-H10

0.92(4)

The hydrogen bond system in the uronium salt consists of two short O-H···O bonds and two longer N-H···O bridges (Fig.9, Tab. 22). The hydrogen bond, O3-H1···O2, with a


46

length of 2.562(2) Å links the HPO3F tetrahedra to cyclic dimers. The second short hydrogen bond, O4-H2···O1, (2.488(2) Å) is between the carbonyl oxygen atom, O4, and the HPO3F tetrahedron. It and the weaker N-H···O bonds with lengths of 2.884(3) and 2.942(3) Å connect the dimers to each other. The fluorine atoms are located near the inert part of the organic cation on the ac-plane at about y = 0 and ½. Layers of the uronium cations are situated at y = ¼ and ¾ in a parallel plane (Fig. 9).

Tab. 22 Hydrogen bonding in [N,N´-dmuH]HPO3F (Å, °)

D-H···A

d (D-H)

d (H···A)

d (D···A)

angOHO

O3-H1···O2

0.88(4)

1.70(4)

2.562(2)

168(4)

O4-H2···O1

0.97(3)

1.52(4)

2.488(2)

173(3)

N1-H3···O2

0.79(3)

2.10(3)

2.884(3)

171(3)

N2-H4···O1

0.83(3)

2.16(3)

2.942(3)

158(2)

Fig. 9 Cyclic dimers of HPO3F tetrahedra in the structure of [N,N´-dmuH]HPO3F viewed down the a-axis. Dashed lines indicate the H···O bonds. Hydrogen atoms on carbon are not shown for clarity.


47

4.5 The Structures with Cyclic Tetramers

Tetramers were formed in the structures with ammonium and rubidium (Tab. 23 and A5). In the case of ammonium, two modifications, á- and â-NH4HPO3F [77], were found with cyclic tetrameric units of HPO3F tetrahedra. Cyclic tetramers were also formed in alpha-RbHPO3F isostructural to the alpha-NH4HPO3F structure.

Tab. 23 Selected crystallographic data

Formula

á-NH4HPO3F

â-NH4HPO3F

alpha-RbHPO3F

Formula weight

117.02

117.02

184.45

Crystal system

0.4 x 0.1 x 0.1

0.7 x 0.6 x 0.4

0.8 x 0.2 x 0.1

Space group

Monoclinic

Triclinic

Monoclinic

Crystal Size

P21/n

Pî

P21/n

a

7.4650(7)

7.481(1)

7.465(2)

b

15.586(2)

7.511(1)

15.551(8)

c

7.5785(9)

7.782(1)

7.563(4)

á

90

84.31(1)

90

â

108.769(9)

84.20(3)

105.38(5)

gamma

90

68.67(2)

90

V3, Z

834.9(2), 8

404.31(9), 4

846.5(7), 8

rhocalc./gcm -3

1.862

1.922

2.894

R1 [I>2sigma(I)]

0.0376

0.0254

0.0365

Analysis

 

 

 

F (50 mL H2O)

14.2

0.4

1.1

F (Seel)

-

15.7

9.4

F (calcd)

16.24

16.24

10.30

VF (F1, F2)

0.96, 0.95

0.96, 0.95

1.08, 1.12

4.5.1 alpha-NH4HPO3F

The á-NH4HPO3F structure contains two crystallographically independent NH4+ cations and HPO3F- anions (Tab. A18, Fig. 10). The NH4+ cations have an average N-H bond length of 0.85 Å (Tab. 25). P-OA lengths vary from 1.487(2) to1.492(2) with P-ODH lengths of 1.545(2) and 1.550(2) Å. The P-F bond lengths observed are 1.558(2) and 1.566(2) Å (Tab. 24).

Tab. 24 Bond lengths in alpha-NH4HPO3F and beta-NH4HPO3F (310 K) (Å)

 

á-NH4HPO3F

â-NH4HPO3F

 

á-NH4HPO3F

â-NH4HPO3F

P1-O1

1.492(2)

1.486(1)

P2-O4

1.490(2)

1.483(1)

P1-O2

1.487(2)

1.483(1)

P2-O5

1.491(2)

1.488(1)

P1-O3

1.545(2)

1.547(1)

P2-O6

1.550(2)

1.546(1)

P1-F1

1.558(2)

1.563(1)

P2-F2

1.566(2)

1.568(1)

The hydrogen bond system consists of short O-H···O and longer N-H···O bonds. The shorter hydrogen bonds, O3-H1···O5 and O6-H2···O2, link two pairs of nonequivalent HPO3F tetrahedra together to form cyclic tetramers (Fig. 10). They have lengths of


48

2.535(3) and 2.508(3) Å (Tab. 25). The weaker N-H···O bonds connect the tetramers to each other with N···O distances between 2.800(3) and 2.951(4) Å. The ammonia hydrogen atom, H10, is not involved in the hydrogen bond system. The compound has a calculated density of 1.862 g·cm-3. No O-H···F or N-H···F bonds are found in the structure, although a very short distance of 2.731 Å exists between F1 and F2 (ang P1F1F2 = 118 ° and ang P2F2F1 = 159°). An H atom was not located between these two F atoms.

Tab. 25 Hydrogen bonding in á-NH4HPO3F (Å, º)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O3-H1···O5

0.74(2)

1.82(2)

2.535(3)

166(5)

O6-H2···O2

0.87(4)

1.64(4)

2.508(3)

174(4)

N1-H3···O4

0.92(3)

2.04(3)

2.932(4)

164(3)

N1-H4···O1

0.80(4)

2.22(4)

2.951(4)

152(3)

N1-H5···O1

0.87(4)

2.02(4)

2.863(4)

161(3)

N1-H6···O2

0.84(4)

2.10(4)

2.917(4)

163(3)

N2-H7···O1

0.90(4)

1.99(4)

2.876(4)

164(3)

N2-H8···O4

0.81(4)

2.01(4)

2.800(3)

167(3)

N2-H9···O4

0.84(5)

2.01(5)

2.842(4)

174(4)

N2-H10

0.83(4)

 

 

 

Fig. 10 Structure of á-NH4HPO3F viewed along the c-axis with the NH4+ ions and the cyclic tetramers of HPO3F tetrahedra. Dashed lines indicate the H···O bonds. N-HO bonds are not shown for clarity.

4.5.2 beta-NH4HPO3F

The beta-NH4HPO3F structure was measured at both 180 (Tab. A19) and 310 K (Tab. A20) [77]. The measurement at 310 K probably due to improved crystal quality yielded a more precise structure model than the 180 K measurement. Only slight differences were observed between the two structure refinements [77]; therefore, only the data from the 310 K measurement is presented and discussed here.

The structure contains crystallographically unique units of two NH4+ cations and two


49

HPO3F- anions (Fig. 11). An average N-H bond length of 0.86 Å is found in the structure (Tab. 26). P-OA lengths are between 1.483(1) to1.488(1) Å with P-ODH lengths of 1.547(1) and 1.546(1) Å (Tab. 24). The P-F bond has distances of 1.563(1) and 1.568(1) Å.

Short O-H···O and weaker N-H···O bonds make up the hydrogen bond system. The short O-H···O bonds, O3-H1···O5 and O6-H2···O2, link two pairs of the unique HPO3F tetrahedra to cyclic tetramers (Fig. 11, Tab. 26); they have distances of 2.568(2) and 2.539(2) Å, respectively. The tetramers are interconnected with weaker N-H···O bonds (2.881(2)-3.043(2) Å). All of the ammonium hydrogen atoms participate in hydrogen bonds. The structure had a calculated density of 1.922 g·cm-3.

Tab. 26 Hydrogen bonding in beta-NH4HPO3F at 310 K (Å, º)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O3-H1···O5

0.73(3)

1.85(3)

2.568(2)

169(3)

O6-H2···O2

0.75(3)

1.79(3)

2.539(2)

174(4)

N1-H3···O1

0.88(2)

2.02(2)

2.895(2)

169(2)

N1-H4···O4

0.84(3)

2.06(3)

2.881(2)

165(2)

N1-H5···O1

0.83(3)

2.13(3)

2.919(2)

160(2)

N1-H6···O2

0.88(3)

2.15(3)

2.899(2)

142(2)

N2-H7···O4

0.84(3)

2.07(3)

2.904(2)

176(2)

N2-H8···O4

0.82(3)

2.27(3)

3.043(2)

159(2)

N2-H9···O5

0.90(3)

2.15(3)

3.004(2)

159(2)

N2-H10···O1

0.89(2)

2.07(2)

2.964(2)

175(2)

Fig. 11 View of â-NH4HPO3F looking down the b-axis with the tetramerically hydrogen-bonded phosphorus tetrahedra and the NH4+ ions. The H···O bonds are indicated by dashed lines. N-HO bonds are not shown for clarity.


50

4.5.3 alpha-RbHPO3F

The alpha-RbHPO3F structure (Tab. A21, Fig. 12) isotypic to alpha-NH4HPO3F (Fig. 10) has two crystallographic unique units of Rb+ and HPO3F- ions (Fig. 12). The Rb atoms are coordinated with a total of nine oxygen and fluorine atoms, Rb1 (8 O + 1 F) and Rb2 (6 O + 3 F), with average lengths of 3.057 and 3.049 Å, respectively (Tab. A32). The HPO3F tetrahedra have three different P-O bonds: P-O, P-OA, and P-ODH. The P-O bonds are short with lengths of 1.477(5) and 1.479(5) Å for O1 and O4, respectively, which are only involved in the Rb coordination (Tab. 27). The O2 and O5 atoms act as hydrogen acceptors in the hydrogen bonds and have interatomic distances to phosphorus of 1.499(4) and 1.493(4) Å (P-OA). The P-ODH distances are practically identical for the HPO3F tetrahedra with 1.556(5) and 1.557(6) Å, whereas the P-F bond lengths vary between the tetrahedra: 1.571(4) and 1.586(4) Å.

Tab. 27 P-O and P-F bond lengths in alpha-RbHPO3F (Å)

 

d

 

d

P1-O1

1.477(5)

P2-O4

1.479(5)

P1-O2

1.499(4)

P2-O5

1.493(4)

P1-O3

1.556(5)

P2-O6

1.557(6)

P1-F1

1.571(4)

P2-F2

1.586(4)

Fig. 12 Structure of alpha-RbHPO3F looking down the c-axis with the Rb+ ions and the cyclic tetramers of hydrogen-bonded HPO3F tetrahedra. Dashed lines indicate the H···O bonds. The Rb atoms are green.


51

The hydrogen bond system consists of two short O-H···O hydrogen bonds, which connect the tetrahedra to cyclic tetramers identical to those found in alpha-NH4HPO3F. The bonds, O3-H1···O5 and O6-H2····O2, have lengths of 2.561(6) and 2.486(7) Å (Tab.28).

Tab. 28 Hydrogen bonding in alpha-RbHPO3F (Å, °)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O3-H1···O5

0.75(2)

1.83(3)

2.561(5)

160(10)

O6-H2···O2

0.8(1)

1.7(1)

2.486(7)

169(9)

4.6 The Complex Structures and Hydrates

More complex structures were found for compositions other than MHPO3F (Tab. 29 and Tab. 30, A6, and A7). Structures with mixed cations were determined for compounds with Cs+ and NH4+ ions and Na+ and [N(CH3)4]+ ions. Both HPO3F and PO3F tetrahedra were observed in the structure with cesium and ammonium, Cs3(NH4)2(HPO3F)3(PO3F) [78]. Structures of basic salts were determined for: the decahydrate of Na2PO3F [81], Na5[N(CH3)4](PO3F)3·18H2O, and [C(NH2)3]2PO3F (Tab. 30). The structures described here are more complex and can not be described by a certain type of structural feature formed by the hydrogen-bonded HPO3F tetrahedra.

Tab. 29 Selected crystallographic data

Formula

Cs3(NH4)2(HPO3F)3(PO3F)

[N(CH3)4]HPO3F·H2O

Formula weight

829.72

191.14

Crystal system

Monoclinic

Cubic

Space group

P21/c

P213

Crystal Size

0.6 x 0.6 x 0.6

0.8 x 0.8 x 0.24

a

20.619(4)

9.691(2)

b

12.076(2)

9.691(2)

c

15.856(3)

9.691(2)

â

102.58(2)

90

V3, Z

3853(1), 8

910.1(3), 4

rhocalc./gcm -3

2.860

1.395

R1 [I>2sigma(I)]

0.0466

0.0239

Analysis

 

 

F (50 mL H2O)

8.2

0.2

F (Seel)

-

9.5

F (calcd)

9.16

9.94

VF

1.04-1.09

0.96


52

Tab. 30 Selected crystallographic data

Formula

Na2PO3F·10H2O

Na5[N(CH3)4](PO3F)3·18H2O

[C(NH2)3]2PO3F

Formula weight

324.11

807.3

218.15

Crystal system

Monoclinic

Triclinic

Monoclinic

Space group

P21/c

Pî

Cm

Crystal Size

0.5 x 0.5 x 0.4

0.4 x 0.2 x 0.1

0.6 x 0.5 x 0.4

a

11.380(3)

6.438(2)

13.201(3)

b

10.234(2)

13.438(4)

7.291(1)

c

13.051(4)

19.520(5)

11.680(2)

á

90

89.38(3)

90

â

106.49(3)

88.84(3)

119.72(3)

gamma

90

88.18(3)

90

V3, Z

1457.4(7), 4

1687.5(8), 6

976.3(3), 4

rhocalc./gcm -3

1.477

1.589

1.484

R1 [I>2sigma(I)]

0.0266

0.0306

0.0424

Analysis

 

 

 

F (50 mL H2O)

-

0

3.5

F (Seel)

-

6.5

10.7

F (calcd)

-

7.06

8.71

VF

0.91

0.92, 0.94, 0.94

0.94, 0.95

4.6.1 Cs3(NH4)2(HPO3F)3(PO3F)

The structure of Cs3(NH4)2(HPO3F)3(PO3F) (Tab. A22 and A23, Fig. 13a and b) is made up of a complex network of HPO3F and PO3F tetrahedra held together by cesium atoms and hydrogen bonds. The PO3F tetrahedron (P8, O22, O23, O24, F8) is disordered around the P-F axis (Tab. 31). The three disordered oxygen atoms have two orientations with occupancies refined to 0.65(2) and 0.35(2) for the major and minor components, respectively. The asymmetric unit contains six Cs+ and four NH4+ cations and two PO3F2- and six HPO3F- anions. Two types of hydrogen bonds, O-H···O and N-H···O, link the different structural units together to form a three-dimensional structure (Fig. 13b). Five of the six crystallographically independent cesium atoms are coordinated by twelve atoms (fluorine and oxygen). The cesium atom, Cs1, has an elevenfold coordination. The Cs-O and Cs-F distances range from 3.005(6) to 3.750(6) Å (Tab. A33).

Tab. 31 P-O and P-F bond lengths in Cs3(NH4)2(HPO3F)3PO3F (Å) for the PO3F tetrahedra

 

d

 

d

 

d

P7-O19

1.503(5)

P8-O22

1.49(1)

P8-O22A

1.50(2)

P7-O20

1.487(5)

P8-O23

1.43(1)

P8-O23A

1.53(2)

P7-O21

1.490(5)

P8-O24

1.52(1)

P8-O24A

1.49(1)

P7-F7

1.574(4)

P8-F8

1.544(5)

 

 

Two different types of PO3F tetrahedra are found in the structure for the eight crystallographically independent tetrahedra. The P-O bond lengths vary depending on the type of tetrahedron. The PO3F tetrahedron of P7 with three short P-O bonds (average


53

length of 1.493 Å) and one long P-F bond (1.574(4) Å) is a PO3F tetrahedron (Tab. 31). The bonding of the PO3F tetrahedron of P8 with three short P-O lengths is difficult to discuss because of the higher esd‘s caused by tetrahedral disordering. All of the oxygen atoms of the two PO3F tetrahedra were hydrogen acceptors (OA) in O···O (Tab. 33) and N···O hydrogen bonds (Tab. A34).

Tab. 32 P-O and P-F bond lengths in Cs3(NH4)2(HPO3F)3PO3F (Å) for the HPO3F tetrahedra

 

d

 

d

 

d

P1-O1

1.482(5)

P2-O4

1.488(5)

P3-O7

1.481(5)

P1-O2

1.480(6)

P2-O5

1.480(6)

P3-O8

1.474(5)

P1-O3

1.544(5)

P2-O6

1.544(6)

P3-O9

1.559(5)

P1-F1

1.580(4)

P2-F2

1.571(5)

P3-F3

1.576(5)

 

 

 

 

 

 

P4-O10

1.486(5)

P5-O13

1.468(6)

P6-O16

1.473(6)

P4-O11

1.482(5)

P5-O14

1.477(5)

P6-O17

1.479(5)

P4-O12

1.551(5)

P5-O15

1.538(6)

P6-O18

1.547(6)

P4-F4

1.577(4)

P5-F5

1.559(6)

P6-F6

1.568(5)

The other six tetrahedra (Tab. 32) have only two short P-OA bonds (average length: 1.479 Å) instead of three and are characterized as HPO3F tetrahedra. The two oxygen atoms with short P-OA lengths in the HPO3F tetrahedra are hydrogen acceptors in the N-H···O hydrogen bonds. The third oxygen atom in each of these six HPO3F tetrahedra has a long interatomic distance to P, which is between 1.538(6) and 1.559(5) Å (O3, O6, O9, O12, O15, and O18) with an average length of 1.547 Å. These oxygen atoms are protonated and participate in hydrogen bonding to the PO3F tetrahedra as hydrogen donors (OD) (Tab. 33). The P-F bonds range from 1.559(6) to 1.580(4) Å (Tab. 32).

Tab. 33 O-H···O hydrogen bonding in Cs3(NH4)2(HPO3F)3PO3F (Å, °)

 

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O3-H1···O20

0.65(5)

1.88(4)

2.501(7)

162(6)

O6-H2···O22A

0.68(6)

1.88(5)

2.50(1)

140(10)

O6-H2···O22

0.68(6)

1.95(5)

2.47(2)

155(7)

O9-H3···O21

0.68(4)

1.88(4)

2.531(8)

176(7)

O12-H4···O19

0.7(1)

1.8(1)

2.503(7)

160(10)

O15-H5···O24

0.69(5)

1.88(7)

2.57(2)

150(10)

O15-H5···O24A

0.69(5)

1.70(7)

2.37(2)

156(5)

O18-H6···O23

0.69(7)

1.80(9)

2.44(1)

150(10)

O18-H6···O23A

0.69(7)

1.98(7)

2.67(2)

167(13)

A total of 22 O···O and N···O hydrogen bonds create an elaborate three-dimensional network in the structure (Fig. 13b). The O-H···O bonds are short with lengths between 2.44(1) and 2.67(2) Å and connect the HPO3F tetrahedra to the PO3F tetrahedra (Tab. 33). The N-H···O bonds (2.735(8)-2.86(2) Å; Tab. A34) then interlink these groups


54

Fig. 13 Projection of the Cs3(NH4)2(HPO3F)3(PO3F) structure along the c-axis. Only one orientation (major component) of the disordered P8 tetrahedron is shown. (a) The Cs atoms are large green circles; smaller green circles represent the N atoms. The hydrogen bonds are not shown for clarity. (b) The hydrogen-bonded layers of (NH4)2PO3F and HPO3F-tetrahedra are shown in and around the ac-plane. The Cs atoms, H atoms, and N-H···O bonds are not shown for clarity. Dashed lines indicate the H···O bonds between the PO3F and HPO3F tetrahedra.

of HPO3F and PO3F tetrahedra; these bonds are not shown in Fig. 13b. In general, the structure of Cs3(NH4)2(HPO3F)3(PO3F) can be considered as two sets of structural units: 2 NH4+ and PO3F2-(I) and Cs+ and HPO3F-(II). The I units are found very close to the ac-plane at y = ¼ and ¾, whereas the units of II are arranged between them around parallel planes at y = 0 and ½ (Fig. 13b). For every complete set of I, there are three sets of II, thus the compound can be written as: 3CsHPO3F·(NH4)2PO3F. These layers, alternate in the b-direction and are linked together by hydrogen bonds. Each of the PO3F-tetrahedra (I) is hydrogen-bonded to three HPO3F tetrahedra of II. Taking the strongest interaction in the structure, O-H···O, into consideration, the structure can also be characterized by thick, alternating layers parallel to the bc-plane shown in Fig. 13b. The thick layers running in the b-direction both have the composition of 3CsHPO3F·(NH4)2PO3F, but are


55

crystallographically different. The layer centered around x = ½ consists of the disordered PO3F tetrahedron of P8 hydrogen-bonded to the HPO3F tetrahedra of P2, P5, and P6 with the N1, N2, and Cs4-6 atoms. The second layer at x = 0 includes the (H)PO3F tetrahedra of P1, P3, P4, and P7, and the atoms, N3, N4, and Cs1-3. The layers have two different orientations for their three hydrogen bonds. Two of the hydrogen bonds on the PO3F tetrahedron of P7 have a similar orientation to the ac-plane, whereas the third branches out to the other side of the PO3F plane. The hydrogen bonds between the PO3F tetrahedron of P8 and the HPO3F units, on the other hand, are all directed to the same side of the plane. This is not affected by the disordering in the PO3F tetrahedra of P8 except for a slight rotation of the bonds around the P-F bond.

4.6.2 [N(CH3)4]HPO3F·H2O

The tetramethylammonium hydrogen monofluorophosphate monohydrate (Tab. A24) was found to contain the following crystallographically independent units: one HPO3F tetrahedron, one molecule of crystal water, and one [NMe4]+ cation. Its structure (Fig. 14a and b) is quite unique due to its cubic symmetry. The phosphorus, fluorine, oxygen (Ow2 and Ow2A), nitrogen, and carbon (C1) atoms all have special postions on the crystallographic C3 axis (Fig. 14a). The threefold symmetry in the structure is shown in Fig. 14b looking down the crystallographic C3 axis. Disordered oxygen and hydrogen positions were observed for both the PO3F tetrahedron and the molecule of crystal water. The tetrahedron was disordered around the P-F axis with two orientations. The occupancies of the major and minor components were refined to 0.888(4) and 0.112(4), respectively (O1 and O1A). The position of the oxygen atom of the crystal water, Ow2, was also disordered with the same occupancies for the major and minor components. The hydrogen positions given represent the corresponding hydrogen atom, H5A or H5B, for the major orientation of the oxygen atom, O1 or Ow2, respectively. The minor components of the hydrogen atom positions were neglected. Only the major component of the disordered oxygen and hydrogen positions is discussed and shown in Fig. 14a and b.

The [NMe4]+ cation contains two different N-C bonds with lengths of 1.496(3) and 1.493(1) Å (Tab. 34) with an average C-H distance of 0.945 Å. The HPO3F tetrahedron has one short P-O length of 1.500(1) Å (O1) and one long P-F bond with a distance of 1.563(1) Å.


56

Tab. 34 Bond lengths in [N(CH3)4]HPO3F·H2O (Å)

 

d

 

d

P-O1

1.500(1)

C1-H1

0.94(2)

P-F

1.563(1)

C2-H2

0.96(2)

P-O1A

1.485(8)

C2-H3

0.93(2)

N-C1

1.496(3)

C2-H4

0.95(2)

N-C2

1.493(1)

O1A-H5A

1.07(9)

 

 

Ow2A-H5B

0.92(3)

Fig. 14 Structure of [N(CH3)4]HPO3F·H2O (a) Ball-and-stick representation of the HPO3F tetrahedra with the molecule of crystal water and [NMe4]+ ions viewed along the a-axis. The minor component of the oxygen positions of the PO3F tetrahedron and crystal water is not shown. The HO bonds are indicated by dashed lines. (b) View looking down the crystallographic C3 axis. The molecule of crystal water, [NMe4]+ cation, and HPO3F- anion are centered on this axis.

The hydrogen bond system consists of one disordered hydrogen bond between the molecule of crystal water and the disordered oxygen atom on phosphorus. The hydrogen bond, O1-H5A···Ow2 and Ow2-H5B···O1, has an O···O distance of 2.637(2) Å. (Tab. 35). Shorter O···O distances of 2.551(2) and 2.499(8) Å are observed between these H donor oxygen atoms and the minor components of the disordered oxygen atoms. Each molecule of crystal water is hydrogen-bonded to three equivalent HPO3F tetrahedra (Fig. 14a).

Tab. 35 Hydrogen bonding in [N(CH3)4]HPO3F·H2O (Å, °)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O1-H5A···Ow2

0.65(9)

2.02(9)

2.637(2)

160(11)

Ow2-H5B···O1

0.70(3)

1.94(3)

2.637(2)

174(3)


57

4.6.3 Na2PO3F·10H2O

The Na2PO3F·10H2O structure [81] (Tab. A25, Fig. 15a and b) contains the following crystallographically independent atoms and units: two Na atoms, one PO3F tetrahedron, and ten molecules of water. Eight of the ten Ow atoms participate in the octahedral coordination of the Na atoms. The two alternating NaO6 octahedra are linked together by edge-sharing (Ow6-Ow7 and Ow8-Ow9) to form chains parallel to the c-axis. The Na-O bond lengths range from 2.380(1) to 2.473(1) Å (Tab. 36). The PO3F-tetrahedron has three short P-O bonds with an average length of 1.508 Å and one long P-F bond (1.6082(9) Å) typical for bonding in a PO3F tetrahedron.

Tab. 36 Bond lengths in Na2PO3F10H2O (Å)

 

d

 

d

 

d

Na1-Ow5

2.380(1)

Na2-Ow6

2.373(1)

P-O1

1.5130(9)

Na1-Ow8

2.398(1)

Na2-Ow8

2.400(1)

P-O2

1.5069(9)

Na1-Ow6

2.433(1)

Na2-Ow11

2.426(1)

P-O3

1.505(1)

Na1-Ow4

2.445(1)

Na2-Ow7

2.439(1)

P-F

1.6082(9)

Na1-Ow7

2.450(1)

Na2-Ow9

2.440(1)

 

 

Na1-Ow9

2.473(1)

Na2-Ow10

2.464(1)

 

 

Tab. 37 Hydrogen bonding in Na2PO3F·10H2O (Å, °)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

Ow4-H4A···O1

0.76(2)

2.26(2)

3.023(2)

177(2)

Ow4-H4B···Ow10

0.78(2)

2.03(2)

2.790(2)

163(2)

Ow5-H5A···O3

0.83(2)

1.90(2)

2.727(1)

174(2)

Ow5-H5B···Ow11

0.85(3)

1.95(3)

2.790(2)

170(2)

Ow5-H5C···Ow11

0.79(7)

1.98(7)

2.771(2)

171(5)

Ow6-H6A···O2

0.83(2)

1.93(2)

2.753(1)

173(2)

Ow6-H6B···Ow13

0.82(2)

2.03(2)

2.827(2)

165(2)

Ow7-H7A···O3

0.83(3)

2.14(3)

2.952(2)

168(2)

Ow7-H7B···Ow12

0.82(2)

2.03(2)

2.851(1)

177(2)

Ow8-H8A···O2

0.80(2)

1.99(2)

2.767(2)

167(2)

Ow8-H8B···Ow12

0.85(2)

1.94(2)

2.783(2)

175(2)

Ow9-H9A···F

0.79(2)

2.21(2)

3.003(2)

176(2)

Ow9-H9B···Ow13

0.81(2)

2.03(2)

2.841(2)

176(2)

Ow10-H10A···O2

0.82(2)

1.99(2)

2.793(2)

164(2)

Ow10-H10B···Ow4

0.80(3)

2.07(2)

2.836(2)

162(2)

Ow11-H11A···O1

0.78(2)

2.16(2)

2.927(2)

167(2)

Ow11-H11B···Ow5

0.83(4)

1.96(4)

2.771(2)

163(2)

Ow11-H11C···Ow5

1.05(6)

1.84(6)

2.790(2)

149(5)

Ow12-H12A···O1

0.87(2)

1.94(2)

2.802(2)

174(2)

Ow12-H12B···O3

0.80(2)

1.97(2)

2.760(2)

175(2)

Ow13-H13A···F

0.83(2)

1.90(2)

2.837(2)

172(2)

Ow13-H13B···O1

0.84(2)

2.08(2)

2.718(2)

149(2)


58

Fig. 15 Structure of Na2PO3F·10H2O (a) View of one layer along the b-axis. The chains of NaO6 and connected PO3F tetrahedra run along the c-axis. Only the hydrogen bonds, Ow-H···F, and the Ow-HO bonds between the PO3F tetrahedra and the Ow12/Ow13 molecules are shown. (b) Projection of the two tetramers along the b-axis. The hydrogen bonds and anchoring bonds to the Na and O1 - O3 atoms are shown with the indicated centers of symmetry.

The elaborate system of 20 hydrogen bonds, Ow-H···O(w) and Ow-H···F, forms a three-dimensional network with hydrogen atoms supplied by the molecules of crystal water. The hydrogen bonds have lengths between 2.718(2) and 3.023(2) Å (Tab. 37). The acceptor O atoms of the PO3F-tetrahedron, namely O1, O2, and O3, are hydrogen-bonded to 3, 3, and 4 molecules of crystal water, respectively (Tab. 37). The F atom only participates in two hydrogen bonds to Ow9 and Ow13. The eight water molecules, Ow4-Ow11, are hydrogen-


59

bonded to one of the O/F atoms in the tetrahedron and one Ow atom. The Ow12 and Ow13 water molecules, which are not involved in the Na coordination, connect two PO3F tetrahedra to each other parallel to the c-axis (Fig. 15a). The cyclic tetramers are formed by water molecules, Ow4 with Ow10 and Ow5 with Ow11 via hydrogen bonding around the centers of symmetry at (½, ½, ½) and (0, 0, ½) (Fig. 15b). The hydrogen bonds, Ow4-H4B···Ow10 and Ow10-H10B···Ow4, form one tetramer. In the second tetramer between Ow5 and Ow11, two disordered hydrogen bonds connect the water molecules to each other. The relative occupancies for the disordered hydrogen positions were refined to values of 0.67 for H5B and H11B and 0.33 for H5C and H11C and then fixed. The disordered bonds are Ow5-H5B···Ow11 and Ow11-H11B···Ow5 with the minor components H11C and H5C, respectively (Fig. 15b). Both hydrogen-bonded ring systems are fixed in the structure by bonds to Na atoms and O atoms of the PO3F-tetrahedra.

4.6.4 Na5[N(CH3)4](PO3F)3·18H2O

The triclinic structure of sodium tetramethylammonium monofluorophosphate (Tab. A26 and A27) with 18 molecules of crystal water is composed of an elaborate three-dimensional network of O-H···O hydrogen bonds, which forms channels along the a-axis for the [NMe4]+ cations (Fig. 16a and b). The assymetric unit contains five Na atoms, one [NMe4]+ cation, three PO3F2- anions, and the molecules of crystal water. The hydrogen positions of the methyl groups were calculated. The compound is a basic salt with Ow-H···O(w) hydrogen bonds. The Na atoms are octahedrally coordinated solely by oxygen atoms to form trimeric units of [Na3O13] and isolated dimeric units of [Na2O8]. Na-O distances range from 2.283(2) to 2.674(2) Å except for the bond Na5-Ow13 with a length of 2.801(2) Å (Tab. A35). Average Na-O distances (Tab. 38) are comparable for all five of the NaO6 octahedra despite the short Na5-Ow25 and long Na5-Ow13 bonds.

Tab. 38 Avg. Na-O bond lengths in Na5[N(CH3)4](PO3F)3·18H2O (Å)

 

d

Na1

2.449

Na2

2.404

Na3

2.446

Na4

2.441

Na5

2.447

The [Na3O13] units in the structure build up infinite chains with the three NaO6 octahedra, Na1, Na2, and Na3, running in the b-direction at z = ½. The Na1 and Na3 octahedra are


60

connected to equivalent octahedra by edge-sharing on centers of symmetry with the oxygen atoms, O16/O16´ (for Na1) and O28/O28´ (for Na3) (Fig. 16a). The third NaO6 octahedron, Na2, connects these Na1 and Na3 "dimers" to each other by face-sharing. The faces are defined by the oxygen atoms: O18, O12, O19 for Na1 and O14, O17, O19 for Na3. The second unit of Na atoms, [Na2O8], is somewhat questionable based on the vertex-sharing involving four common atoms (O13, O23, O24, O26). This unit consists of the Na4 and Na5 octahedra, which are linked by oxygen atoms to one another to form isolated dimers located around the center of symmetry at (½, ½, 0) (Fig. 16a). The Na-Na interatomic distance in these dimers is 3.272 Å. One of the four atoms shared is that of the oxygen atom, Ow13, which has an exceptionally long distance to Na5 (2.801(2) Å) compared to the other structures with NaO6 units. The NaO6 octahedron of Na5 also has the shortest Na-O distance in the structure: 2.283(2) Å for Na5-Ow25. An interesting feature of this NaO6 octahedron is that one of the PO3F oxygen atoms, O4, is involved in the Na coordination (Fig. 16a), while one of the molecules of crystal water, Ow15, does not participate in the metal coordination.

The [NMe4]+ cation (Fig. 16b) has N-C bonds with distances between 1.494(4) and 1.506(3) Å and a calculated C-H bond length of 0.98 Å for the methyl groups (Tab. A35). The three PO3F tetrahedra each have three short P-OA distances between 1.498(2) and 1.518(2) Å with an average length of 1.509 Å ( Tab. 39 ). These distances correspond to a PO3F tetrahedron, in which all of the oxygen atoms are hydrogen acceptors in the hydrogen bond system. Two different interatomic distances of 1.580(2) and 1.599(2) are found between the P and F atoms in the structure. The long P-F bond (1.599(1) Å) explains the significantly shorter P-O1 length of 1.498(2) Å in the PO3F tetrahedron of P1.

Tab. 39 P-O and P-F bond lengths in Na5[N(CH3)4](PO3F)3·18H2O (Å)

 

d

 

d

 

d

P1-O1

1.498(2)

P2-O4

1.507(2)

P3-O7

1.505(2)

P1-O2

1.504(2)

P2-O5

1.510(2)

P3-O8

1.508(2)

P1-O3

1.517(2)

P2-O6

1.512(2)

P3-O9

1.518(2)

P1-F1

1.599(2)

P2-F2

1.580(2)

P3-F3

1.580(2)

The hydrogen bond system of predominantly longer O-H···O bonds (Tab. A36, Fig. 16b) creates a complicated three-dimensional network with channels for the [NMe4]+ cations. The Ow-H···O(w) hydrogen bonds have O···O distances ranging from 2.706(3) to 2.988(3) Å with an exceptionally short bond, Ow27-H27A···O3: O···O distance of 2.677(3) Å. Two hydrogen atoms, H19B and H26A, are not involved in hydrogen bonds. The oxygen atoms,


61

OA, from the PO3F tetrahedra except for O4 and O8 participate in 2-3 hydrogen bonds. The O4 atom is not only involved in two hydrogen bonds, but also bonded to the Na5 atom; the oxygen atom, O8, is a fourfold hydrogen acceptor. The water molecules, Ow11, Ow13, and Ow20-Ow22, are both hydrogen donors and acceptors and coordinate the Na+ cations. The Ow15 atom functions as an hydrogen acceptor and donor in four hydrogen bonds, but does not coordinate a Na atom. All of the other Ow atoms coordinate the Na+ ions and act exclusively as hydrogen donors in the structure.

Fig. 16 Structure of Na5[N(CH3)4](PO3F)3·18H2O (a) Ball-and-stick representation along the a-axis. The infinite chains of [Na3O13] are shown running in the b-direction with the isolated dimers [Na2O8]. The hydrogen atoms were omitted and hydrogen bonds are not shown for clarity. The Na atoms are gray. (b) OwO(w) hydrogen bonding indicated by dashed lines. The organic cations are seen in the channels at (x, ¼, ¾) and (x, ¾, ¼). The hydrogen atoms have been omitted for clarity.

The most interesting feature of this structure is the formation of channels at (x, ¼, ¼) and (x, ¾, ¾) (Fig. 16b) for the [NMe4]+ cations. These channels are formed by the NaO6 octahedra and the PO3F tetrahedra connected indirectly to each other via hydrogen bonds to crystal water. The channels can be characterized by the P-F vertex of the three PO3F tetrahedra directed towards the organic cation. The other three oxygen vertices face outwards to participate in the hydrogen bonding. The size of the channel can be estimated


62

by the F···O and F···F interatomic distances, 5.47 for F1···O22, 5.75 for F1···O25, 3.171 for F1···F2, 2.96 for F1···F3, and 4.70 Å for F2···F3, not considering the covalent radii. Fluorine's nonparticipation in hydrogen bonding is very well demonstrated by this structure.

4.6.5 [C(NH2)3]2PO3F

The guanidinium monofluorophosphate structure with the space group Cm (Tab. A28) consists of PO3F tetrahedra hydrogen-bonded to the guandinium cations via N-H···O bonds. The asymmetric unit consists of three [C(NH2)3]+ cations and two PO3F2- anions (Fig. 17a and b). The atoms: P1, P2, F1, F2, C1, C2, O1, O3, N2 and N3, all have special positions on the mirror plane.

Fig. 17 Structure of [C(NH2)3]2PO3F (a) Ball-and-stick representation looking down the b-axis. Dashed lines indicate the H···O hydrogen bonds. The hydrogen atoms have been omitted for clarity. (b) Polyhedral representation of the HPO3F tetrahedra along the a-axis showing the P-F bond orientation relative to the hydrogen bonds.


63

The guanidinium cations have C-N distances between 1.310(7) and 1.334(4) Å with an average length of 1.324 Å (Tab. 40). The N-H bond lengths had an average distance of 0.86 Å (Tab. 41). Short P-O bonds with similar lengths were found in each PO3F tetrahedra: 1.505(3) and 1.509(2) for the P1 tetrahedra and 1.504(2) Å for the P2 tetrahedra. In comparison with the P-O bonds, the distance between P and F vary between the tetrahedra with lengths of 1.575(3) and 1.567(3) Å.

Tab. 40 Bond lengths in [C(NH2)3]2PO3F (Å)

 

d

 

d

 

d

 

 

 

d

P1-O1

1.505(3)

P2-O3

1.504(4)

C1-N1

1.334(4)

C2-N4

1.330(4)

C3-N7

1.324(5)

P1-O2

1.509(2)

P2-O4

1.504(2)

C1-N2

1.310(7)

C3-N5

1.326(5)

 

 

P1-F1

1.575(3)

P2-F2

1.567(3)

C2-N3

1.327(7)

C3-N6

1.318(5)

 

 

The hydrogen bond system of N-H···O bridges is somewhat complicated, because of the three different guanidinium cations in the structure. Long N-H···O bonds with N···O distances between 2.820(4) and 3.128(4) Å connect the PO3F tetrahedra to the guanidinium cations (Tab. 41, Fig. 17a). These N···O bridges build up a three-dimensional network of hydrogen bonds (Fig. 17b). The direction of the P-F axis in the PO3F tetrahedra of P1 is quite easy to recognize. Here, the bond is pointed directly towards the carbon atom of the C1 guanidinium cation where no hydrogen bonds are found (Fig. 17b). The P-F bond in the PO3F tetrahedra of P2 lies between the hydrogen bonds, O3···N1 and O3···N7 as shown in Fig. 17b.

Tab. 41 Hydrogen bonding in [C(NH2)3)]2PO3F (Å, °)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

N1-H1A···O3

0.86(2)

2.06(2)

2.911(4)

175(4)

N1-H1B···O2

0.84(2)

2.24(3)

2.989(4)

148(4)

N2-H2···O4

0.87(2)

2.02(2)

2.884(3)

175(4)

N3-H3···O2

0.86(2)

2.07(2)

2.914(4)

166(4)

N4-H4A···O2

0.90(4)

2.05(4)

2.920(4)

162(4)

N4-H4B···O1

0.85(2)

2.10(2)

2.942(4)

171(5)

N5-H5A···O2

0.85(2)

2.19(3)

2.978(4)

155(5)

N5-H5B···O4

0.86(2)

2.10(2)

2.949(4)

168(4)

N6-H6A···O1

0.87(7)

2.18(7)

3.000(5)

158(6)

N6-H6B···O4

0.87(2)

1.96(2)

2.820(4)

169(4)

N7-H7A···O3

0.86(2)

2.18(2)

3.007(5)

163(5)

N7-H7B···O4

0.86(2)

2.37(3)

3.128(4)

148(4)

4.7 The Structure of beta-RbHPO3F

The structural clarification of beta-RbHPO3F has been somewhat problematic. A first single crystal X-ray diffraction measurement yielded a basic structural model for the P21/n space


64

group with a R1-factor over 5%. One disordered hydrogen position was found between two equivalent oxygen atoms with an occupancy of 0.5. A lower R1-factor of 3.64% was achieved by a second measurement; however, the second hydrogen atom could not be found.

19F, 31P, and 1H MAS NMR spectra showed two separate signals for the F, P, and H nuclei with signal ratios of 3:7, 4:6, and 3:7, respectively (Appendix A.4). Two doublets in both the 19F and 31P spectra confirmed the presence of two nonequivalent PO3F tetrahedra in the structure. A singulet at 0.7 ppm with an area of 5% was also found in the 31P spectrum for the phosphate impurity. The 1H spectrum showed one broad signal at 13.0 ppm for a hydrogen atom involved in a strong hydrogen bond (60-70%) and one sharp signal at 5.9 ppm for a weakly bonded hydrogen atom (30-40%). The 1H signal ratio of ca. 2:1 correlated with that of phosphorus. Based on these results showing two nonequivalent PO3F tetrahedra, the single crystal data was then solved and refined for the noncentrosymmetric space groups, Pn and P21. Both refinements included strong correlations of the heavier atoms and difficulties were encountered when the displacement parameters were refined anisotropically. Thus, the centrosymmetric space group was assumed to be correct. The different P and F surroundings found by the MAS NMR measurements can most likely be explained by a statistical O/F disordering of the O3 and F positions on phosphorus, which generates two different phosphorus tetrahedra. Second harmonic generation measurements could help determine whether the structure is centrosymmetric or noncentrosymmetric, but could not be carried out within the scope of this thesis.

Tab. 42 Selected crystallographic data

Formula

beta-RbHPO3F

Formula weight

184.45

Crystal system

Monoclinic

Space group

P21/n

Crystal Size

0.2 x 0.2 x 0.2

a

7.5157(8)

b

7.7244(7)

c

7.5582(8)

â

104.29(1)

V3, Z

425.21(7), 4

rhocalc./gcm -3

2.877

R1 [I>2sigma(I)]

0.0352

Analysis

 

F (50 mL H2O)

0.5

F (Seel)

9.3

F (calcd)

10.30

VF

1.07

Thus, the P21/n structure was refined further with an O/F disorder in both the F and O3


65

positions on phosphorus based on the NMR measurements and implied by the almost identical bond lengths of 1.539(4) (P-O3) and 1.540(5) Å (P-F). The relative occupancies for these positions were refined and fixed as 0.7 and 0.3 for O3/F (major component) and FA/O3A (minor component), respectively, which correspond to the signal ratios found in the MAS NMR spectra. The R1-factor decreased to 3.52% (Tab. 42 and A8). A short distance was found between the O3 and F positions.

The structure of beta-RbHPO3F (Tab. A29, Fig. 18) has one unique Rb atom and one HPO3F tetrahedron. The Rb atom has an eightfold coordination with bonds to seven oxygen atoms and one fluorine atom. Distances range from 2.868(4) to 3.358(4) Å (Tab. 43). The HPO3F tetrahedron has a P-F distance that strongly deviates from those in the structures described previously (Tab. 43). The bond between the P and O1 atoms has a length of 1.485(4) typical for oxygen atoms only participating in the metal coordination in the structure. The exact functions of the other O atoms in the structure is more difficult to define. The P-OH½ bond (O2) has a length of 1.513(4) Å. This atom, O2, is involved in the only hydrogen bond found in the structure with a disordered hydrogen position (occupancy 0.5) as a hydrogen acceptor and donor (½A + ½D). The other positions on phosphorus, O3/FA and F/O3A, have almost identical interatomic distances to the P atom of 1.538(4) and 1.541(4) Å, respectively. These distances are relatively long for a P-O bond and very short for a P-F bond, when compared to the other structures. This is probably due to the O/F disorder.

Tab. 43 Bond lengths in beta-RbHPO3F (Å)

 

d

 

d

 

d

Rb-O1

2.868(4)

Rb-O2

3.049(4)

P-O1

1.485(4)

Rb-O1´

2.882(4)

Rb-O3´/FA´

3.054(4)

P-O2

1.513(4)

Rb-O1´´

2.966(4)

Rb-O2´

3.154(4)

P-O3/FA

1.538(4)

Rb-O3/FA

2.973(4)

Rb-F/O3A

3.358(4)

P-F/O3A

1.541(4)

The hydrogen bond system (Tab. 44) consists of one short, symmetrically-disordered hydrogen bond between two equivalent HPO3F tetrahedra. An O2···O2´ distance of 2.560(8) Å was found. A second hydrogen bond between the O3/FA and F/O3A positions of two HPO3F tetrahedra is implied by the short distance between these two positions shown by the red dashed lines in Fig. 18. The O3/FA and F/O3A positions have a distance of 2.672(6) Å with the following angles: angPFO3 = 115.9(2)° and angPO3F = 130.9(2)°. These values strongly indicate a hydrogen bond, yet a hydrogen atom could not be found. Thus, a new type of structure is formed that has not been observed for either the metal hydrogen phosphates or the pure monofluorophosphates.


66

Tab. 44 Hydrogen bonding in beta-RbHPO3F (Å, °)

D-H···A

d(D-H)

d(H···A)

d(D···A)

angD-H···A

O2-H···O2´

0.75(2)

1.84(6)

2.560(8)

160(20)

O3···F

 

 

2.672(6)

 

Fig. 18 View of the structure of beta-RbHPO3F looking down the a-axis. The black dashed lines indicate the symmetrically-disordered HO bond between H and O2´. The implied hydrogen bond between the O3/FA and the F/O3A positions (indicated by the red-outlined open circles) is shown with red dashed lines. The Rb atoms are green.

4.8 Summary

The crystal structures of the hydrogen monofluorophosphates and basic monofluorophosphates were determined for the alkali metal and N-containing cations. The structures vary in their structural features, but have similarities in their bonding overall, which are summarized here.

Infinite chains of hydrogen-bonded HPO3F tetrahedra (Sect. 4.1) are found in the structures of NaHPO3F·2.5H2O (Na), [NH2Et2]HPO3F, and [PipzH2]HPO3F. The zigzag chains are held together by longer hydrogen bonds, Ow-H···O(w) (Na) and N-H···O (Diet and Pipz). The sodium atom is octahedrally coordinated solely with oxygen atoms to form chains of NaO6 octahedra. In all three structures, the P-F vertex of the tetrahedron is pointed away from the hydrogen bond system.

The potassium compounds feature unique structural patterns of branched chains in KHPO3F and isolated dimers in K3[H(PO3F)2] (Sect. 4.2 and 4.3). In KHPO3F, three different, short and very short O-H···O bonds form chains of HPO3F tetrahedra with a


67

short O-H···O bond between the chain and the branched tetrahedron The isolated dimers in K3[H(PO3F)2] are made up of two equivalent PO3F tetrahedra bonded to each other via a strong, symmetrically-disordered O-H···O bond. The potassium cations have a 7-9 coordination with both oxygen and fluorine atoms.

In comparison to the structural patterns in the potassium structures, structures with cyclic dimers (Sect. 4.4) have been found in numerous compounds with Cs, [NEt3], [C(NH2)3], and [N,N´-dmu] as cations. Short O-H···O hydrogen bonds link the HPO3F tetrahedra to dimers; disordered hydrogen positions are only observed in CsHPO3F and [NHEt3]HPO3F. The HPO3F dimers are then fixed by the Cs coordination in CsHPO3F and longer N-H···O bonds in the other structures. The Cs atom is coordinated by O and F atoms. In the structures with N-containing cations, the P-F bond is pointed either between layers of cations in [NHEt3]HPO3F or towards the inert part of the cation: the C atom in [C(NH2)3]HPO3F or a methyl group in [N,N´-dmuH]HPO3F.

The alpha and beta-modifications of NH4 and the structure of alpha-RbHPO3F isotypic to alpha-NH4HPO3F are made up of cyclic tetramers (Sect. 4.5). These tetramers are defined by two unique HPO3F tetrahedra connected alternately to tetramers with two short, unique O-H···O bonds. The tetrameric units are bonded to each other in the structure by either longer N-H···O or Rb-X bonds. The Rb+ ion has a nine-fold coordination with O and F atoms.

The complex structures described in Sect. 4.6 feature structural aspects not observed in the hydrogen monofluorophosphates with the composition, MHPO3F. In the Cs3(NH4)2(HPO3F)3(PO3F), tetrahedra of PO3F and HPO3F are found with short O-H···O bonds linking them together. The hydrate structures, [N(CH3)4]HPO3F·H2O, Na2PO3F·10H2O, and Na5[N(CH3)4](PO3F)3·18H2O, vary as much in their compositions as in their systems of hydrogen bonds. A hydrogen bond with a disordered hydrogen position is found between the HPO3F tetrahedra and the Ow atom in [NMe4]HPO3F·H2O. In the Na2PO3F·10H2O structure with Ow-H···O(w) bonds, the fluorine atom acts as a two-fold hydrogen acceptor in long Ow-H···F bonds. Both of these bonds have lengths similar to those found for the weaker N-H···O and Ow-H···O(w) hydrogen bonds. The elaborate hydrogen bond system in the structure of the mixed salt, Na5[NMe4](PO3F)3·18H2O, forms channels for the [NMe4]+ ions with the P-F bond directed towards the inert C atom of the cation. The structure of [C(NH2)3]2PO3F is rather asymmetrical with two nonequivalent PO3F tetrahedra hydrogen-bonded to three [C(NH2)3]+ ions with longer N-H···O bonds.


68

The beta-modification of RbHPO3F is the only structure found with O/F disordering. Here, one symmetrically-disordered hydrogen bond held two equivalent PO3F tetrahedra together. A suspiciously short distance is observed between the O/F disordered position on phosphorus, but the corresponding hydrogen atom could not be located.

In general, three types of hydrogen bonding are found in the structures. Short and very short hydrogen bonds link the (H)PO3F tetrahedra to one another, while longer hydrogen bonds are found between the (H)PO3F tetrahedra and the crystal water or cations containing nitrogen. Hydrogen bonds with lengths in between are found for a N-H···O bond in [PipzH2]HPO3F and [NHEt3]HPO3F and Ow-H···O and Ow-H···Ow bonds in Na/[NMe4], Na2PO3F·10H2O, and [NMe4]HPO3F·H2O. Fluorine is involved in two hydrogen bonds in the Na2PO3F·10H2O structure as a hydrogen acceptor. This is not observed in any other structure. In several structures, single hydrogen atoms do not participate in the hydrogen bond system: two hydrogen atoms in [C(NH2)3]HPO3F and Na5[N(CH3)4](PO3F)3·18H2O and one hydrogen atom in the alpha-NH4HPO3F.

The total calculated bond valency of fluorine, VF, varies in the compounds. The VF values are between 0.94 and 0.97 for the structures with N-containing cations in comparison to the alkali metal structures, in which VF is 0.91 for Na2PO3F·10H2O and 0.95 (Na) to 1.15 (K) for the MHPO3F compounds with M = Na, K, Rb, and Cs. This difference is also demonstrated by the mixed salts, Cs3(NH4)2(HPO3F)3(PO3F) and Na5[N(CH3)4](PO3F)3·18H2O, with fluorine valencies of 1.04-1.09 and 0.92-0.94, respectively.


Fußnoten:

<1>

* The data was refined postpublication.


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