Mononuclear carbonyls Metal/metallic nitrosyls

Few successful reactions are known by which an organometallic nitrosyl product has been formed from the condensation of mononuclear metal nitrosyl complexes. The unique cluster (Tj -C5H5)3Mn3(NO)4 (39), which contains the only i3-NO known (7) (40), is prepared using photochemical or thermal (41) decarbonylation of (Tj -C5H5)2Mn2(CO)2(NO)2 [Eq. (25)]. The use of the redox condensation of a nitrosyl carbonylmetallate with a neutral metal carbonyl cluster to produce a nitrosyl cluster has... 

This suggests that simple carbonyls are invariably spin-paired complexes (p. 134). These metals have even atomic numbers, those with Z odd do not form simple carbonyls. In the carbonyl nitrosyls and carbonyl hydrides which are mononuclear, a metal atom with an odd atomic number can similarly complete its d shell. Thus in Co(CO)aNO and Co(CO)4H, the —NO group and —COH group can be considered to contribute the single electron necessary to complete the 3d shell of the metal atom. The three CO molecules and the isoelectronic NO or COH are co-ordinated tetrahedrally, as are the four CO molecules in Ni(CO)4. 

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