Synthesis and studies of cis-Mo(CO)2(L–L′)2 and Mo(L–L′)3 complexes of 2-(phenylazo)pyridines (L–L′) and the crystal structures of Mo(CO)2(4-methyl-2-(phenylazo)pyridine)2 and Mo(4-methyl-2-(phenylazo)pyridine)3

The complexes cis-Mo(CO)2(X-2-(phenylazo)pyridine)2 (III) and Mo(X-2-(phenylazo)pyridine)3 (IV) (X=4-CH3O (a), 4-CH3 (b), H (c), 4-Cl (d), 5-Br (e), 5-CF3 (f), 6-CH3 (g)), cis-Mo(CO)2(2-(2-CH3-phenylazo)pyridine)2 (IIIh), and Mo(2-(2-CH3-phenylazo)pyridine)3 (IVh) have been synthesized and characterized by cyclic voltammetry, by visible and infrared spectroscopy, and by 1H, 13C, and 95Mo NMR spectroscopy. Correlations among these data and correlations of the data with the Hammett σ parameter within each series of complexes were investigated. Initially, correlations were found only for the Hammett σ parameter with the first oxidation potential and with the first reduction potential for both the type III and type IV complexes and with the sum of the carbonyl stretching frequencies for the type III complexes. However, combining 95Mo NMR linewidth and chemical shift data for this quadrupolar metal allowed separation of the nephelauxetic and spectrochemical effects and revealed a number of additional correlations. The X-ray crystal structures of cis-Mo(CO)2(4-CH3-2-(phenylazo)pyridine)2 (IIIb) and Mo(4-CH3-2-(phenylazo)pyridine)3 (IVb) also have been determined. In IIIb each CO is trans to a pyridyl nitrogen of a 2-(phenylazo)pyridine ligand. In IVb each pyridyl nitrogen is trans to an azo nitrogen, yielding the facial isomer of the complex.