The behaviour of the photochemically produced tungsten pentacarbonyl is investigated by laser flash photolysis and conventional ultraviolet/visible spectrophotometric methods. Rate constants for their reactions with 2- and 4-picoline and other pyridine derivatives are reported along with their proposed mechanisms. W(CO)5(L) complexes (L = pyridine, 2- or 4-phenylpyridine, or 2,2«dipyridylamine) are synthesised along with 3,6-bis(2-pyridyl)-l,4-dihydro-l,2,4,5-tetrazene derivatives of M(CO)6 (M = Cr, Mo, or W) These complexes are characterised by infrared, ultraviolet/visible, proton nuclear magnetic resonance spectroscopy, and by X-ray diffraction analysis Attempts to synthesise the W(CO)5(L) complexes (L = 2- aminomethylpyridine or bispicoylamine) were also reported The solvatochromie behaviour of these penta and tetra-carbonyl complexes was also investigated.