Homopolynuclear T1I and Heteropolynuclear AuI-T1I Complexes with Organodiselone Ligands: Activation of Luminescence by Intermetallic Interactions

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 T1(I) [{T1(L)} PF6](n)center dot(mMeCN)(n) [L = L1, m = 1 (1); L = L2, m = 0 (2)] and discrete heteropolynuclear [T1{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 [T1(L1)](+) cations and [Au(C6Cl5)(2)](-) anions joined together by an unsupported Au center dot center dot center dot T1 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-T1)-to-ligand charge transfer (MMLCT) and intraligand (IL) transitions as observed experimentally.