Synthesis and Structures of Bis- and Tris-(triphenylarsine)gold(i) Iodides

The title compounds [(Ph3As)(2)AuI] and [(Ph3As)(3)AuI] have been crystallized from equimolar solutions of Bu4NAuI2 and AsPh3 in dimethylformamide and structurally characterized by single crystal X-ray diffraction studies. [(Ph3As)(2)AuI] crystallizes in space group C2/c, Z 4, and is isomorphous with other [(Ph3E)(2)MX] (MX=coinage metal(i) salt) arrays, with the Au-I bond being disposed on a crystallographic 2-axis: Au-I, As 2.7008(2), 2.4337(2) angstrom, As-Au-As, I 125.736(8)degrees, 117.132(4)degrees (153K). [(Ph3As)(3)AuI] crystallizes as a triclinic phase in space group CH19340_IE1.gif, Z 4, and is isomorphous with [(Ph3Sb)(3)CuI] and [(Ph3P)(3)AgI]: Au-As 2.4847-2.5049(10), Au-I 2.8518(8), 2.8597(7) angstrom with As-Au-As, I 109.67(3)-115.97(3)degrees, 101.33(2)-106.85(3)degrees. A second '[(Ph3As)(3)AuI]' product was obtained as a co-crystalline phase in space group P2(1)/n containing [(Ph3As)(3)AuI], and [(Ph3As)(2)AuI] accompanied by an additional unbound Ph3As molecule, i.e. [(Ph3As)(3)AuI][(Ph3As)(2)AuIPh3As], with structural parameters closely similar to those for the corresponding separate [(Ph3As)(3)AuI] and [(Ph3As)(2)AuI] complexes described above. Comparison of the bond lengths for these and related complexes show that they are generally consistent with the 'gold is smaller than silver' phenomenon caused by relativistic orbital contraction effects in gold, but the results also show that the magnitude of this effect is dependent on the nature of the metal-ligand bonds involved, and on changes in the metal coordination environment, which can in some circumstances yield trends in which the effect on particular bonds is partially masked or even reversed.