Structure and Luminescence Studies of Salts of the Helical Dication, [Au 2 (μ-bis(diphenylphosphine)ethane) 2 ] 2+ and Comparison with Salts of [Au 2 (μ-bis(diphenylphosphine)propane) 2 ] 2 .

Six salts ([Au 2 (μ-dppe) 2 ](BF 4 ) 2 ·CHCl 3 , [Au 2 (μ-dppe) 2 ](BF 4 ) 2 ·1,2-Cl 2 C 2 H 4 , [Au 2 (μ-dppe) 2 ](PF 6 ) 2 ·CHCl 3 , [Au 2 (μ-dppe) 2 ](PF 6 ) 2 , [Au 2 (μ-dppe) 2 ](SbF 6 ) 2 , and [Au 2 (μ-dppe) 2 ](OTf) 2 ·2CHCl 3 ), (dppe is bis(diphenylphosphine)ethane) containing the dication, [Au 2 (μ-dppe) 2 ] 2+ , have been prepared and structurally characterized by single-crystal X-ray crystallography. Unlike the three-coordinate dppe-bridged dimers, Au 2 X 2 (μ-dppe) 2 (X = Br, I), which show considerable variation in the distance between the gold(I) ions over the range 3.0995(10) to 3.8479(3) Å in various solvates, the structure of the helical dication, [Au 2 (μ-dppe) 2 ], in the new salts is remarkably consistent with the Au···Au separation falling in the narrow range 2.8787(9) to 2.9593(5) Å. In the solid state, the six crystals display a green luminescence both at room temperature and at 77 K, which has been assigned as phosphorescence. However, solutions of the dication are not luminescent. Salts containing the analogous dication [Au 2 (μ-dppp) 2 ](PF 6 ) 2 (dppp is bis(diphenylphosphine)propane) have been prepared to determine whether the longer bridging ligand might also twist into a helical shape. These salts include [Au 2 (μ-dppp) 2 ](OTf) 2 (OTf is triflate) and three crystalline forms of [Au 2 (μ-dppp) 2 ](PF 6 ) 2 : the solvate [Au 2 (μ-dppp) 2 ](PF 6 ) 2 ·(CHCl 3 ) and two polymorphs of the unsolvated salt. None of these crystals are luminescent, but all contain a similar dication, [Au 2 (μ-dppp) 2 ] 2+ , that contains two nearly parallel, linear P-Au-P groups and a long separation between the gold ions that varies from 5.3409(4) to 5.6613(6)Å.