Unusually short unsupported Au(III)⋯Au(III) aurophilic contacts in emissive lanthanide tetracyanoaurate(III) complexes.

A series of [Au(CN) 4 ] - salts with lanthanide 2,2'-bipyridine dioxide cations features Au(III) aurophilic interactions between [Au(CN) 4 ] - groups, with Au⋯Au distances of 3.3603(4) Å and 3.4354(4) Å that are shorter than any previously reported. Computations predict the interactions to be weakly attractive; packing effects appear to also contribute to the close contacts. The materials are emissive: there is no Au(III)-based luminescence, but for Ln = Eu the PLQY of 29% is surprisingly high compared to related analogues.