Binding of a TlCl Entity by a Tetragold Tetramercaptothiacalixarene Metalloligand via Metallophilic Interactions

Abstract

p-tert-Butyltetramercaptotetrathiacalix[4]arene was used as a coordination platform to synthesize and investigate gold(I) complexes with varying nuclearity. Aiming at the corresponding tetranuclear complex through salt metathesis it was found capable of binding a neutral, molecular TlCl entity by metallophilic interactions, as shown by structural and theoretical investigations. These Interactions lead to photoluminescence at low temperatures (see figure). The successive auration of p-tert-butyltetramercaptotetrathiacalix[4]arene, H4(MTC[4]), with gold(I) phosphine units was investigated. Through deprotonation with NaOMe, followed by salt metathesis reactions with (PR3)AuCl (R=Me, Ph) complexes with two and three [(PR3)Au]+ moieties could be prepared and isolated, namely [(Ph3PAu)2H2(MTC[4])] and [(Me3PAu)3H(MTC[4])]. In [(Me3PAu)3H(MTC[4])] two gold atoms already come close enough to undergo aurophilic interactions. To introduce a fourth [(PR3)Au]+ entity TlOEt had to be used for the deprotonation, which led to the finding that four gold atoms organised by the (MTC[4])4− coordination platform are able to bind and stabilize a TlCl entity, yielding [(Me3PAu)4TlCl(MTC[4])]. As evidenced by structural and theoretical investigations the binding occurs through strong metallophilic interactions, which lead to photoluminescence at low temperatures.