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.