Nitrosyl complexes bent bonds

Method (i) is a route commonly utilized in monometal nitrosyl complexes. The nitrosyl ligand may function as (formally) a three-electrop donor (NO+) with a linear bonding mode, or as (formally) a one-electron donor (NO ) with a bent (—120°) M-N-0 arrangement. Conversion of the M-NO system to a M-NO system has two effects. First, it increases the metal oxidation state by two second, it generates a vacant coordination site. The dinitrosyl cluster Os3(CO)8(NO)2, which has... 

This chapter describes the synthesis of transition metal nitrosyl complexes with particular reference to routes that involve common reagents (e.g., NO and NOBF4). Methods for their characterization by spectroscopic and structural techniques are critically reviewed. The application of NMR for distinguishing among linear, bent, and bridging nitrosyls are emphasized. The bonding in metal nitrosyl complexes is reviewed from a molecular orbital and valence-bond point of view. Finally, the reactions of transition metal nitrosyl complexes are discussed. 

The first accurately documented example of a distinctly bent M-N-0 linkage in a metal nitrosyl complex was presented in 1968. Ibers showed that the cation [IrCl(CO)NO(PPh3)2] (Figure 2) possessed a square pyramidal structure with a metal-nitrosyl bond angle of 124°. Subsequently other species exhibiting similar structural properties have been reported. It has now become clear that there are essentially two distinct orientations in which nitric oxide may be complexed. In one case the ligand is coordinated linearly and in the other it is bent (angle approximately 120°) for structural data available on linear and bent nitrosyls see Tables 1 and 2 respectively. 

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