Kinetics and equilibria in the hydrolysis of [Pt(terpy)Cl]Cl; Crystal and molecular structure of [Pt(terpy)OH]ClO4 center dot H2O (terpy=2,2 '-6,2 ''-terpyridine)

The cationic platinum(II) complex [Pt(terpy)CI](+) (terpy = 2,2'-6',2"-terp yridine), monomer in water at low concentrations (<1.5 x 10(-5) mol dm(-3)) , undergoes basic and acid hydrolysis. The equilibrium constant for the aci d hydrolysis is 1.4 x 10(-5) mol dm(-3) {25<degrees>C, [CH3SO3H] =0.1 mol d m(-3)}. Basic hydrolysis (pH>10) leads to the complete formation of [Pt(ter py)(OH)](+) with a two terms rate law, k(obs) = k(1) + k(2)[OH-] (k(1) = 2. 24 x 10(-2) s(-1), k(2) = 0.7 mol(-1) dm(3) s(-1)). The mechanism of substi tution is discussed and the system is compared to that of the congener [Ft( dien)Cl](+) species (dien = 1,5-diamino-3-aza-pentane). The crystal structu re of [Pt(terpy)OH]-ClO4.H2O has been determined: monoclinic, space group P 2(1)(/)n, a = 7.937(1), b = 17.251(1), c = 12.245(1) Angstrom; beta = 95.50 (1)degrees. The Pt-O distance is 1.999(5) Angstrom, and the hydroxo group f orms strong hydrogen bonds with the molecule of water of crystallization.