The first examples of 2,2′:6′,2″-terpyridine as a fluxional bidentate ligand

2,2′:6′,2″-Terpyridine (terpy) forms octahedral complexes fac-[ReBr(CO)3(terpy)], cis-[W(CO)4(terpy)] and fac-[PtClMe3(terpy)] in which the ligand oscillates between equivalent bidentate forms by a mechanism involving a ‘tick-tock’ twist of the metal moiety through an angle equal to the N–M–N angle of the octahedral centre and involving a seven-coordinate metal intermediate.