Mono- and di-nuclear complexes of molybdenum carbonyl derivatives with pyridine-2-carbaldehyde azine and phosphines: syntheses, structure, spectroscopic and electrochemical characterisation and solvatochromic effects

Complexes containing phosphorus-donor ligands, [Mo(CO)3(PPh3)(pa)](pa = pyridine-2-carbaldehyde azine), [Mo2(CO)6(PPh3)2(µ-pa)], [Mo2(CO)7(PPh3)(µ-pa)] and [Mo2(CO)6(µ-dppe)(µ-pa)][dppe = 1,2-bis(diphenylphosphino)ethane], have been characterised by infrared and electronic spectroscopy, cyclic voltammetry and for the [Mo2(CO)6(µ-dppe)(µ-pa)] complex a single crystal X-ray structure. All of the complexes show strong solvatochromism which has been analysed both by using the empirical parameter E*MLCT and by using McRae's equation. The results are compared with those of their parent complexes [Mo(CO)4(pa)] and [Mo2(CO)8(µ-pa)], and with the results of extended-Hückel calculations with charge iteration.