Homopolynuclear TlI and heteropolynuclear AuI-TlI complexes with organodiselone ligands: Activation of luminescence by intermetallic interactions

Abstract

The organodiselone ligands 1,1-bis(3-methyl-4-imidazolin-2-selone)methane (L1) and 1,2-bis(3-methyl-4-imidazolin-2-selone)ethane (L2) have been used for the synthesis of homopolynuclear TlI [{Tl(L)}PF6]n·(mMeCN)n [L = L1, m = 1 (1); L = L2, m = 0 (2)] and discrete heteropolynuclear [Tl{Au(C6Cl5)2}(L)] [L = L1 (3), L2 (4)] complexes. The crystal structures of complexes 1 and 3 have been determined through X-ray diffraction studies. Complex 1 consists of alternating thallium(I) centres and bidentate Se-donor ligands that result in polymeric chains. The crystal structure of 3 is formed by [Tl(L1)]+ cations and [Au(C6Cl5)2]– anions joined together by an unsupported Au···Tl interaction. Compounds 3 and 4 are luminescent in the solid state at room temperature and at 77 K with lifetimes in the nanosecond range. DFT and time-dependent (TD)-DFT calculations have been carried out on different model systems including the free ligand L1, a representative model of complex 1 and a model system of complex 3. The character of the frontier molecular orbitals and the TD-DFT prediction of the absorption spectra are used to explain the origin of the luminescence of complexes 3 and 4 as an admixture of metal–metal (Au–Tl)-to-ligand charge transfer (MMLCT) and intraligand (IL) transitions as observed experimentally.