A novel anionic gold-indium cluster compound: Synthesis and molecular and electronic structure

The insertion of InBr into the Au-Br bond of [(Ph3P)AuBr] in tetrahydrofuran (thf) in the presence of [(CH2PPh2)(2)] (dppe) leads to the formation of an orange complex [(dppe)(2)Au](+)[(dppe)(2)Au3In3Br7(thf)](-), 2. Analytical, spectroscopic, and X-ray structural investigations showed that this product is an anionic analogue of a neutral chloride complex [(dppe)(2)Au3In3Cl6(thf)(3)], 1, prepared recently. Both complexes have an Au(3)ln(3) cluster core of approximate C-2v symmetry with one extremely short Au-Au bond [Au1-Au3 2.575(1) Angstrom] as part of a quasilinear array P1-Au1-Au3-P4, suggesting the presence of a bis(phosphine) complex of the neutral Au-2 molecule as part of the cluster. The third gold atom (Au2) is then assigned oxidation state +1. To gain deeper insight into the structure and bonding of this novel class of gold cluster compounds, regarding mainly the peculiar cluster geometry, the charge distribution, and the oxidation states, a series of scalar relativistic all-electron density functional (DF) calculations on model systems has been performed. As a model for 1, the neutral cluster {Au-3(PH3)(4)[InCl2- (H2O)](3)} was studied. For the examination of the geometry of complexes 1 and 2, the cluster Au-3(PH3)(4)I-3 has been considered as a further simplified model, where iodine replaces the InX2(thf) units. Experimental and calculated cluster geometries agree satisfactorily, and the formal oxidation states of the gold atoms (0 for Au1 and Au3, +1 for Au2) could be confirmed, but for the In centers no interpretable differences of the Mulliken charges were found.