Negative ion mass spectra of Os3(CO)12X2 and Os3(CO)10X2 complexes (X = Br,I)

The negative-ion mass spectra at 70 eV of the compounds Os₃(CO)₁₂X₂ and Os₃(CO)₁₀X₂ (X =Br, I) are reported. Negative molecular ions are absent and only Os₃-containing fragments due to the loss of carbonyl groups are observed. [M  CO]^? is the base peak in the spectrum of Os₃(CO)₁₀I₂ and has a very high abundance in that of Os₃(CO)₁₀Br₂, whereas it is very weak in the spectra of Os₃(CO)₁₂X₂, where [M  3 CO]^? is the base peak. This change in the ionic intensities is related to the closed and open structure of the Os₃ unit in Os₃(CO)₁₀X₂ and Os₃(CO)₁₂X₂ respectively.