Nitrogen-oxygen bond length/stretching frequency relationships in C-nitroso compounds and their coordination complexes

The mode of coordination of monomeric C-nitroso compds. to metals is discussed. In contrast to previous studies it is proposed that an understanding of the ν(N-O)/r(N-O) and r(C-N)/r(N-O) relationships in the noncoordinated nitroso compds. is of primary importance for assessment of the coordination mode. Both ν(N-O)/r(N-O) and r(C-N)/r(N-O) have linear interrelationships in C-nitroso compds. and the coordination compds. of RNO have the same ν(N-O)/r(N-O) relationship as the noncoordinated monomers. Previous correlations of Δν(N-O) with coordination mode are therefore correlations of r(N-O) with coordination mode. σ-N and σ-O complexes of arom. RNO conform to the same r(C-N)/r(N-O) equation (within a very small error) as the noncoordinated monomers. The extent of deviation from the r(C-N)/r(N-O) relationship for complexes of aliph. RNO is of a similar order of magnitude to that which occurs when C-nitroso monomers form the trans dimer. The coordination mode of aliph. RNO is, with one exception, σ-N. Nitrosobenzene has a variety of coordination modes to transition metals but does not display σ-O coordination. p-Nitrosodimethylaniline undergoes σ-O coordination to d10 metals.