Equilibria in complexes of N-heterocycles. Part 50(1) The formation and properties in solution of the 1 : 1 adducts of Bis(2,2 '-bipyridine)platinum(II) and related ions with hydroxide

Equilibrium constants are given for addition (mol ratio 1:1) of hydroxide t o several palladium(II) and platinum(II) cations. [Pt(bpy)(2)](2+) (bpy: 2, 2 ' -bipyridine) and hydroxide ion form the well-known 1:1 adduct rapidly i n water; the rate is given at 25 degreesC by k = 1.6 x 10(2) mol(-1) dm(3) s(-1). The equilibrium constants for adding hydroxide to [Pt(bpy)(2)](2+) a nd to [Pt(3,3 '-[H-2](2)-bpy)(2)](2+) are the same, but differ considerably from those for [Pt([H-2](8)-bpy)(2)](2+) and for [Pt(6,6 '-[H-2](2)-bpy)(2 )](2+) with hydroxide. In this reaction, the infrared spectrum (1700-900 cm (-1)) of the cation initially [Pt(bpy)(2)](2+) in the aqueous solution show s distinct changes between pH = 7.0 and pH = 11.0, notably in the aromatic region, where the intensity of the band due to C=N at ca. 1600 cm(-1) is mu ch reduced. At pH = 7.0, the methyl groups in [Pt(5,5 ' -dmbpy)(2)](2+) (dm bpy: dimethyl-2,2 ' -bipyridine) or the 4,4 ' -isomer are equivalent in H-1 magnetic resonance but become inequivalent in the 1:1 adducts with hydroxi de. In the presence of (-)-methylbenzylamine, both [Pt(terpy)Cl]Cl (terpy: 2,2 ' ,2 " -terpyridine) and [Pt(bpy)(2)](2+) manifest a strong Pfeiffer ef fect, but not the 'exciton' coupling characteristic of cis-octahedral ions. These observations are interpreted in terms of addition of hydroxide to th e bipyridine ligands.