A N-Heterocyclic Carbene-Stabilized Coinage Metal-Chalcogenide Framework with Tunable Optical Properties

A new class of coinage-metal chalcogenide compounds [Au4M4(mu(3)-E)(4)(IPr)(4)] (M = Ag, Au; E = S, Se, Te) has been synthesized from the combination of N-hetero cyclic carbene-ligated gold(I) trimethylsilyl-chalcogenolates [(IPr)AuESiMe3] and ligand-supported metal acetates. Phosphorescence is observed from these clusters in glassy 2-methyltetrahydrofuran and in the solid state at 77 K, with emission energies that depend on the selection of metal/chalcogen ion composition. The ability to tune the emission is attributed to electronic transitions of mixed ligand-to-metal-metal-charge-transfer (IPr -> AuM2) and interligand (IPr -> E) phosphorescence character, as revealed by time-dependent density functional theory computations.N-heterocyclic carbenes (NHCs) have been applied as ancillary ligands in the synthesis of luminescent gold(I) chalcogenide clusters and this approach allows for unprecedented selectivity over the metal and chalcogen ions present within a stable octanuclear framework.