Synthesis, structure, and photophysical studies of luminescent two- and three-dimensional gold-thallium supramolecular arrays

The reactions of tetrahydrofuran solutions of NBu4[AuR2] (R = C6F5, C6Cl5) with TIPF6 and 4,4'-bipyridine lead to the synthesis of the luminescent materials [Tl(bipy)](2)[Au(C6F5)(2)](2) 1 and [Tl(bipy)][Tl(bipy)(0.5)(thf)][Au(C6Cl5)(2)](2) 2 in high yield. The structures of these complexes, as analyzed by X-ray diffraction, consist of planar polymers formed by repetition of Tl-Au-Au-Tl (1) or Tl-Au-Tl'-Au (2) moieties linked through bidentate bridging bipy ligands. In complex 1 these layers are associated via Tl...F contacts between atoms of adjacent planes, whereas in complex 2 each two polymeric layers are linked through additional bridging bipy molecules, Both complexes are strongly luminescent at room temperature and at 77 K in the solid state, losing this characteristic in solution even at high concentrations. The luminescence is attributed to interactions between metal atoms which are strongly affected by their structural dispositions. DFT calculations are in accord with the observed experimental behavior, showing the nature of the orbitals involved in each transition. Detailed analyses reveal a substantial participation of the metals in the transition giving rise to the emission maxima, and also other more energetic bands in which the ligands are involved and which also give rise to these emissions. The obtained theoretical excitation spectra clearly match the experimental results.