2,2′:6′,2′′-Terpyridine switches from tridentate to monodentate coordination in a gold(iii) terpy complex upon reaction with sodium azide

Reaction of [AuCl(terpy-kappa(3)-N-1,N-1 ',N-1 '')]Cl-2 with an excess of sodium azide did not result in the expected exchange of the chlorido by an azido ligand to give [Au(N-3)(terpy-kappa(3)-N-1,N-1 ',N-1 '')](2+). Instead, X-ray structure analysis showed that the isolated product is [Au(N-3)(3)(terpy-kappa(1)-N-1)], in which the terpyridine ligand is in a very rare monodentate coordination mode. This is also the dominant species in solution, together with a minor amount of [Au(N-3)(2)(terpy-kappa(2)-N-1,N-1 ')](+). The stability of the tris(azido)gold(iii) moiety relative to other possible species was also confirmed by DFT calculations.