Equilibrium and kinetic studies of (2, 2': 6', 2'-terpyridine) gold (III) complexes. Preparation and crystal structure of [Au(terpy)(OH)][ClO_4]_2

摘要

Kinetic and equilibrium studies of the processes (1) and (2) (terpy=2, 2': 6', 2"-terpyridine) have been carried out in [Au(terpy)Cl]~(2+)+H_2O reversible [Au(terpy) (OH)_2]~(3+)+Cl~- (1) [Au(terpy)OH_2]~(3+) reversible [Au(terpy) (OH)]~(2+)+H~+ (2) water at 25 deg C, I=0.1 mol dm~(-3) (LiClO_4). Owing to the high charge of the metal center, the [Au(terpy)OH_2]~(3+) cation behaves as a strong acid (K_a>=0.8 mol dm~(-3)) and dissociates completely into the corresponding hydroxo species, which can be isolated in the solid state as its perchlorate. The crystal structure of [Au(terpy)(OH)][ClO_4]_2 has been determined by the single-crystal X-ray diffraction technique. It consists of SP (square planar) [Au(terpy)OH]~(2+) cations having Au-N distances of 2.009 (5), 2.008 (4) and 1.949 (4) A and an Au-OH distance, the first experimentally determined, of 2.000 (4)A. The SP geometry is expanded to distorted tetragonal bipyramidal (TBPY) by linking the two perchlorate anions with Au-O distances of 3.023 (8) and 3.069 (8) A, which are intermediate between bonding and van der Waals interactions. The secondary co-ordination phenomenon in gold (III) SP complexes is reviewed and a possible reason for its occurrence proposed.