Electron-deficient bonding at pentacoordinate nitrogen

IT has been demonstrated recently that pentacoordinate and hexacoordinate carbon atoms can be prepared in complexes containing two-coordinate gold(I) species^1-3. This unusual environment for carbon can be ascribed to the tendency of gold(I) to form clusters with short intramolecular contacts between the metal atoms^4,5; the effect, termed 'aurophilicity', suggests the possibility of forming polyaurated species with the metal atoms clustering about a central element. Here we report that nitrogen, as well as carbon, can demonstrate unusually high coordination when included as the central atom in such complexes. We have prepared an aurated dication in which the nitrogen exhibits fivefold coordination. In keeping with theoretical predictions, we anticipate that it may prove possible to synthesize similar compounds containing other central elements, such as boron.