Molybdenum and tungsten complexes of biquinoline.: Crystal structure of W(CO)4(2,2′-biquinoline)

M(CO)(6) (M = Mo and W) reacts with 2,2'-biquinoline (biq) to yield tetracarbonyl derivatives M(CO)(4)(biq). Crystals suitable for X-ray structure determination of W(CO)(4)(biq) were isolated from benzene solution. The u.v.-vis. spectra of the complexes exhibited visible transitions due to metal-to-ligand charge-transfers. Electrochemical investigation of the complexes showed some irreversible, reversible and quasi-reversible redox reactions due to tautomeric interconversions through electron transfer. The thermal properties of the complexes were also investigated using the thermogravimetric technique.