Substitution reactions of [W(CO) 5 (THF)] with the azo-functionalized monopyridyl and dipyridyl ligands, namely, 4-phenylazopyridine L 1 and 4,4'-azopyridine L 2 , readily afford two tungsten carbonyl complexes [W(CO) 5 (NC 5 H 4 N N C 6 H 5 )] (1) and [(CO) 5 W(μ-NC 5 H 4 N N C 5 H 4 N)W(CO) 5 ] (2) in good yields. Ligation of L 1 and L 2 with the activated triosmium carbonyl cluster [Os 3 (CO) 1 0 (NCMe) 2 ] by ortho-metallation reaction provides [Os 3 (μ-H)(CO) 1 0 (μ-NC 5 H 3 N N C 6 H 5 )] (3) and the linking cluster [Os 3 (μ-H)(CO) 1 0 (μ-NC 5 H 3 N N C 5 H 3 N)Os 3 (μ-H)(CO) 1 0 ] (4) in satisfactory yields. All of the complexes have been fully characterized by IR, 1 H-NMR, UV-vis spectroscopies, fast atom bombardment (FAB) mass spectrometry and electrochemical measurements. The solid-state molecular structures of 1-4 have been ascertained by single-crystal X-ray diffraction methods. The structures of 1 and 3 involve the coordination of L 1 to one {W(CO) 5 } and {Os 3 (CO) 1 0 } moieties, respectively. In the case of 2 and 4, two identical metal cores are linked together by the bridging ligand L 2 . Spectroscopic investigations revealed that the metal-to-ligand charge transfer (MLCT) transitions of 1 and 2 demonstrate strong solvent dependency, displaying a large negative solvatochromism in a wide range of organic solvents.