Electron spin resonance studies of HPt(CN) 2–4 and Pt(CN) 2–3 formed by irradiation of K2Pt(CN)4 in solvents

Abstract

Exposure of dilute solutions of K₂Pt(CN)₄ in aqueous and methanolic solvents to ⁶⁰Co γ-rays resulted in electron addition to give the Pt(CN)^3–₄ anion, followed by protonation, to give HPt(CN)^2–₄. This species has a remarkably large proton hyperfine splitting of ca. 175 G which is the largest proton coupling ever detected for a transition-metal complex. In aqueous-acid glasses this species was formed directly, probably by hydrogen-atom addition. Hyperfine coupling to ¹⁹⁵Pt was also detected, the estimated spin densities showing that the SOMO is the σ^* Pt—H orbital, with little delocalisation onto the other ligands. Computer simulation of the e.s.r. spectra for the hydrido complex formed by the irradiation of a methanol solution has explained an unusual extra splitting. The possibility that the species is H—Pt(CN)^–₃ rather than H—Pt(CN)^2–₄ is considered, but the latter formulation is preferred. The other major species detected in methanolic glasses, but not in acidic glasses, is thought to be Pt(CN)^2–₃ rather than Pt(CN)^3–₄, primarily because the form of the g- and ¹⁹⁵Pt-tensor components suggest a ⋯d¹_z² configuration rather than the ⋯d¹_x²–y² configuration expected for the square-planar Pt(CN)^3–₄ structure.