The compounds [Se(AuPPh3)2] and [Se(Au2dppf)] are good precursors for the synthesis of highly aurated selenium-centered derivatives. Thus the reaction of [Se(AuPPh3)2] with various molar ratios of [Au(OTf)PPh3] affords the homoleptic species [Se(AuPPh3) n ](OTf) n - 2 (n = 3−6). Similarly, the treatment of [Se(Au2dppf)] with various stoichiometric ratios of [Au2(OTf)2(μ-dppf)] gives the polynuclear derivatives [(Au2dppf){Se(Au2dppf)}2](OTf)2, [Se(Au2dppf)2](OTf)2, and [Se(Au2dppf)3](OTf)4. The compounds [Au{Se(AuPPh3)2}2]ClO4 and [Au{Se(Au2dppf)}2]ClO4 have been obtained by reaction of the precursors with [Au(tht)2]ClO4 in a molar ratio of 2:1. Some of these derivatives have been characterized by X-ray diffraction studies and show unusual geometries, associated with gold−gold interactions. The latter have been studied theoretically using [Se(AuPH3) n ]( n -2)+ (n = 2−6) models at the HF and MP2 levels with quasi-relativistic pseudopotentials. There is a good agreement between experimental and theoretical geometries.

The gold(I) compounds [Se(AuPPh 3 ) 2 ] and [Se{Au 2 (µ-dppf)}] (dppf ) 1,1′-bis(diphenylphosphino)ferrocene) react with 1 and 2 equiv of [Au(C 6 F 5 ) 3 OEt 2 ] to give the mixed gold(I)-gold-have been characterized by X-ray diffraction studies. They show dissimilar Au(I)‚ ‚‚Au(III) distances, indicating the presence of weak interactions. Quasi-relativistic pseudopotential calculations on [Se(AuPH 3 ) 2 (AuR 3 )], [Se(AuPH 3 )(AuR 3 ) 2 ] -(R ) -H, -CH 3 ), and [{Se(AuPH 3 )} 2 {Au(CH 3 ) 2 } 2 ] models have been performed at Hartree-Fock and secondorder Møller-Plesset perturbation theory levels. There is a good agreement between experimental and theoretical geometries at the MP2 level. Scheme 1 a a Legend: (i) MeOH, Na2CO3; (ii) [Au(C6F5)3OEt2]; (iii) 2 [Au(C6F5)3OEt2]; (iv) [Au(C6F5)2Cl]2.

The first gold complex, [Se(AuPPh 3 ) 4 ](CF 3 SO 3 ) 2 , with a m 4selenido ligand has been prepared; the crystal structure reveals a square pyramidal geometry with short gold-gold interactions.