Stepwise ligand dissociation and multiple changes in oxidation state in the fast atom bombardment mass spectra of cyanometalate complexes of transition metals

Abstract

Both positive- and negative-ion fast atom bombardment (f.a.b.) mass spectra of cyanometalate complexes (metal = Fe, Cr, Mn, Ni, Mo, or W in various oxidation states) show considerable fragmentation, especially when the counter ion is an alkali metal. Analysis of the spectra reveals the existence of several families of ions from each complex, each family being characterised by the number of cations associated with the complex ion. Each family of ions give long sequences of peaks which indicate the sequential loss of neutral CN and possibly (CN)₂ fragments, a conclusion confirmed by searching for the precursors of a given daughter ion. As each CN fragments is lost, the oxidation state of the metal decreases by one, leading eventually to very low oxidation states and co-ordination numbers. These sequential processes have implications for the mechanism of f.a.b., which is viewed as a gas-phase rather than a matrix process.