Complexes of 2,2'-bipyridyl and 1,10-phenanthroline with bivalent palladium and platinum having covalencies greater than four

Abstract

Conductimetric titrations of the perchlorates [Pd(chel)₂](ClO₄)₂ (chel = 2,2'-bipyridyl or 1,10-phenanthroline) with X^- ions (X = Cl, Br, I) in the solvents nitrobenzene and nitromethane give an end-point after the addition of one equivalent of halide ion, owing to the formation of the ions [Pd(chel)₂X]⁺. Another endpoint is obtained after the addition of a second equivalent of halide ion. Spectral evidence suggests that in nitrobenzene the compound [Pd(bipy)₂I₂] (bipy = 2,2'- bipyridyl) is formed. In nitromethane the second end-point is regarded as due to the reaction [Pd(chel)₂X]⁺ + X^- → [Pd(chel)X₂]+ chel. The compound [Pt(bipy)₂](ClO₄)₂ was prepared and titrated conductimetrically with halide ions in nitrobenzene and nitromethane. Only one end-point was obtained, indicating that the ions [Pt(bipy)₂X]⁺, unlike the corresponding palladium complexes, are stable in the presence of excess halide ion. It is assumed that in all these monohalogeno-complex ions the metal atom is sexicovalent, due to the coordination of one molecule of solvent. Evidence is presented for the occurrence of six-coordinated platinum(II) in the compounds [Pt(bipy)₂I(H₂O)]I.H₂O, [Pt(bipy)_zI(H₂O)](ClO₄)₂.H₂O, and [Pt(bipy)₂I₂].