Binuclear Copper(I) Compounds with N‐Heterocyclic Thiolate and Diphosphane Ligands: Effects of Thiolate Ligands on Solid‐State Molecular Structures and Luminescence Properties

Abstract

A series of four photoluminescent binuclear copper(I) compounds bearing phosphorus and sulfur donor atom ligands have been synthesized from reactions of copper(I) halides with the diphosphane dppe [1,2‐bis(diphenylphoshino)ethane] and the anions of three different N‐heterocyclic thiols, namely 5‐methyl‐1,3,4‐thiadiazole‐2‐thiol, 1‐phenyl‐1H‐tetrazole‐5‐thiol and ethyl 2‐thiouracil‐5‐carboxylate. Depending on the nature of the N‐heterocyclic thiol, the resulting compounds adopt two different structural motifs, having either a dppe‐bridged core, that is, [Cu2(κ‐S‐thiolate)2(dppe)2(µ‐dppe)], or a bis(thiolate)‐bridged core, that is, [Cu2(µ‐S‐thiolate)2(dppe)2], with a Cu2(µ‐S)2 cluster‐type core. The stabilization of the latter type of structure is rationalized by the presence of intramolecular hydrogen‐bonding interactions developed between two bridging N‐heterocyclic thiolate ligands positioned at the same side of the Cu2(µ‐S)2 core, which lead to short Cu···Cu interactions (ca. 2.6 Å), as it is evidenced by X‐ray crystallography studies and supported by Density‐Functional Theory (DFT) calculations. All compounds are photoluminescent and, upon UV‐light irradiation, they exhibit emission maxima ranging from about 470 to 510 nm, depending on the structural and geometric characteristics of the complexes. According to DFT calculations, the photoluminescence properties of the dppe‐bridged binuclear compounds originate from excited states having mainly a (M+L)LCT character, which result from [dCuI+π(thiolate)]→π*(phosphane) electronic transitions, while in the case of the thiolate‐bridged, cluster‐like binuclear compound the emitting excited states are also influenced by the short Cu···Cu interactions and appear to have also CC contributions in addition to an MLCT character. Furthermore, in the case of the dppe‐bridged binuclear complexes, the influence of the electronic nature of the thiolate group on the observed emission wavelength is demonstrated.