Double Jahn-Teller Distortion in AuGe Complexes Leading to a Dual Blue-Orange Emission.

The tetrahedral AuI complexes [Au(GeCl3 )L3 ] (L=PMe3  (1), PMe2 Ph (2), PMePh2  (3), PPh3  (4)) were synthesized by in situ treatment of the [Au(GeCl3 )(tht)] complex with three equivalents of the corresponding tertiary phosphine. The crystal structures of complexes 1 and 3 have been determined through X-ray diffraction studies and show [GeCl3 ]- fragments bonded to the corresponding [Au(PR3 )3 ]+ units through covalent bonds, leading to a tetrahedral coordination environment for gold. Complexes 3 and 4 show dual phosphorescence in the solid state at 77 K and, in the case of complex 4, an interesting room-temperature mechanochromism effect is observed. Correlated MP2, SCS-MP2, SCS-CC2, and ONIOM MP2/UFF calculations suggest the existence of two largely distorted and thermally connected triplet excited states (T1 and T2 ) for a model system of complex 4. The AuP3 + moiety can be distorted in two different planes leading to the two triplet excited states T1 and T2 , leaving the GeCl3 - unit almost unaltered. The emissions of these phosphorescent AuI GeII complexes is mainly ascribed to a metal (gold)-centered (3 MC) transition with some contribution from the [GeCl3 ]- fragments.