Negative-ion mass spectra of trinuclear carbonyl clusters

Abstract

Negative-ion mass spectra at 70 eV of the clusters [Fe₃(CO)₁₂], [FeRu₂(CO)₁₂], [Ru₃(CO)₁₂], [Ru₂Os(CO)₁₂], [RuOs₂(CO)₁₂], and [Os₃(CO)₁₂] are reported. Negative molecular ions are absent, and the trinuclear gragments formed are due to the loss of CO groups mainly by dissociative electron-capture processes. A decreasing intensity of [M₃(CO)₁₁]^–, the base peak in the spectrum of [Os₃(CO)₁₂], is observed on passing from Os to Ru and to Fe. The ion [Ru₃(CO)₁₀]^– is the base peak in the spectrum of [Ru₃(CO)₁₂] and [Fe₃(CO)₉]^– in that of [Fe₃(CO)₁₂]. The same behaviour is observed in the mixed-metal carbonyls. This trend is explained by the different stability of the ionic species, which it is suggested is mainly related to the strength of the metal–metal bonds. The negative-ion mass spectra of [Ru₃(CO)₁₁(PEt₂Ph)] and [Os₃(CO)₁₁(PEt₂Ph)] indicate that both the M–CO bond strengths and the ionisation potentials of the metals do not play a major role. The negative-ion mass spectra of the compounds [Fe₃(CO)₉X₂](X = S, Se, or Te) follow a similar behaviour and exhibit [Fe₃(CO)₇X₂]^– as the base peak with a weak [Fe₃(CO)₈X₂]^– when X = Te.