Evidence for Bidentate and Terdentate Coordination of the Ligand 2,2′:6′,2″-Terpyridine in Oxotechnetium(V) Complexes

Complexes formed by the ligand exchange reactions of [TcOCl4]− with the potentially terdentate nitrogen-donor ligand 2,2′:6′,2″-terpyridine (terpy) under different reaction conditions have been investigated. Both bidentate and terdentate coordination of terpy have been established in the complexes prepared. In dichloromethane as reaction medium the six-coordinate complex TcOCl3(terpy-N,N′) has been isolated, in which terpy acts as a bidentate ligand. The reaction of terpy with a twofold molar excess of [TcOCl4]− in boiling ethanol led to the formation of the cationic six-coordinate complex [TcOCI2(terpy-N,N′,N″)]+, which precipitated from solution as the pertechnetate salt. With terpy in excess to [TcOCI4]− the cationic dimeric complex μ-O[TcOCl(terpy-N,N′,N″)]2Cl2. was isolated in ethanol. The reaction of TcO− 4 with terpy in an ethanolic/HCl solution led to the precipitation of the neutral six-coordinate complex TcOCl3(terpy .HC1), which could also be prepared from [TcOCl4]−. These compounds were characterized by elemental analysis, vibrational, optical and proton nuclear magnetic resonance spectroscopy.