Crystal structures and properties of [Au(phen){(CN)0.92Br0.08}2]Br and [Au(phen)(CN){(CN)0.82Br0.18}]·0.5trans-[Au(CN)2Br2]·0.5Br·phen (phen = 1,10-phenanthroline) obtained by disproportionation of five-co-ordinate bromodicyano(1,10-phenanthroline)gold(III). Two examples of secondary co-ordination and CN/Br disorder in square-planar gold(III) complexes

Abstract

The disproportionation of neutral five-co-ordinate [Au(phen)(CN)₂Br](phen = 1,10-phenanthroline) in dimethylformamide (dmf) gives a conducting solution from which two charged species, [Au(phen){(CN)_0.92Br_0.08}₂]Br (1) and [Au(phen)(CN){(CN)_0.82Br_0.18}]·0.5trans-[Au(CN)₂Br₂]·0.5Br·phen (2), have been separated and characterized by single-crystal X-ray analysis. Crystals of (1) are orthorhombic, space group Fmm2, Z= 4 with a= 6.515(1), b= 11.76(2), c= 18.666(2)Å. Crystals of (2) are triclinic, space group P, Z= 2 with a= 9.149(3), b= 9.263(3), c= 15.485(5), α= 93.58(2), β= 105.10(2), γ= 95.49(2)°. The structures have been solved from three-dimensional counter data by Patterson and Fourier methods and refined by full-matrix least squares to R 0.031 and 0.044 for 729 and 2 701 observed reflections respectively. The co-ordination of the cation in both compounds is square planar with two positions occupied by the two N atoms of the phenanthroline ligand. In compound (1) the other two cis positions are occupied by equivalent CN groups substituted in 8% of cases by Br. In compound (2) one position is occupied by a CN group and the other by a CN group in 82% and Br in 18% of cases. Secondary co-ordination is shown by both the complex cations with Br^– at distances intermediate between bond and contact lengths, which gives rise to tetragonal bipyramidal and nearly square-pyramidal structures for (1) and (2) respectively.