CO Bond Strength Research Articles

Negative-ion mass spectra of trinuclear carbonyl clusters

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.