Gold-197 Mössbauer spectra and the bonding of some gold–gold and gold–platinum clusters

Abstract

The ¹⁹⁷Au Mössbauer parameters of the AuPt₃, Au₂Pt₂, and Au₂Pt₃ clusters [AuPt₃(µ-CO)₃L₄]⁺, [Au₂Pt₂L₄(CNR)₄]²⁺, [AuPt₃(µ-SO₂)₂(µ-Cl)L₄] and [Au₂Pt₃(µ-SO₂)₂(µ-Cl)L₄][L = P(C₆H₁₁)₃ or P(C₆H₄F-p)₃, R = xylyl] are consistent with the bonding schemes previously proposed, showing a diminution with increasing delocalisation of the bonding electrons and increase in the metal-metal bond lengths. Separate signals are resolved for the non-equivalent gold atoms in [Au₆{P(C₆H₁₁)Ph₂}₆]²⁺, the parameters and intensities of which correlate with the expected electron densities and observed connectivities of the gold atoms. The centred-crown cluster [Au₉L₈]³⁺[L = P(C₆H₄OMe-p)₃] gives slightly greater parameters than its icosahedral-fragment analogues, consistently with the observed shortening in Au–Au contacts. No separate signal is resolved for the central gold atom.