Formation of some transition metal oxide cluster anions and reactivity towards methanol in the gas phase

Negative cluster ions of transition metal oxides ([M(x)O(y)](-); M = Mn, Fe, Co, Ni, Cu) have been generated by laser desorption ionisation from metal oxide pellets and studied using Fourier transform ion cyclotron resonance mass spectrometry. For the same metal, the stoichiometrically different oxides yield similar collections of anions, with small differences in the ion intensity distributions. The most intense transition metal anions were isolated and their reactivity towards methanol was investigated. The [MO(2)](-), [M(2)O(3)](-) and [M(2)O(4)](-) anions react exothermically with methanol leading to [MO(2)H(2)](-), [M(2)O(3)H(2)](-) and [M(2)O(4)H(2)](-) as primary products, respectively. The [MO(3)](-) anions are unreactive towards methanol. The rate constants determined for the various reactions suggest that the [MO(2)](-) and [M(2)O(3)](-) anions react more efficiently with methanol than the [M(2)O(4)](-) cluster anions. The reaction efficiences decrease when the metal varies from manganese to copper indicating that the number of electrons in the d shell of the metal atom appears to be an important factor on reactivity. (Int J Mass Spectrom 185/186/187 (1999) 825-835) (C) 1999 Elsevier Science B.V.