The Os (III) complexes [OsIII (tpy)(bpy)(py)] 3+ and [OsIII (bpy) 3] 3+(bpy: 2, 2′-bipyridine, py: pyridine, tpy: 2, 2′, 2′′-terpyridine) are unstable toward self-reduction in alkaline solution. Product analysis performed by using UV-Vis spectroscopy, cyclic voltammetry, HPLC and GC show that ca. 90% of the reduced product that appears is the unmodified polypyridyl complex of Os (II),[OsII (tpy)(bpy)(py)] 2+ or [OsII (bpy) 3] 2+. The remaining 10 ...