Luminescence properties and optimized structural conformations of the S0, S1 and T1 states of a tetranuclear formamidinate complex based on AuI and AgI metal ions.

Abstract

N,N'-Bis(pyridin-4-yl)formamidine (4-pyfH) was reacted with AuI and AgI metal salts to form a novel tetranuclear complex, tetrakis[μ-N,N'-bis(pyridin-4-yl)formamidinato]digold(I)disilver(I), [Ag2Au2(C11H9N4)2] or [AuxAg4-x(4-pyf)4] (x = 0-4), 1, which is supported by its metallophilicity. Due to the potential permutation of the coordinated metal ions, six different canonical structures of 1 can be obtained. Complex 1 shows an emission at 501 nm upon excitation at 375 nm in the solid state and an emission at 438 nm upon excitation at 304 nm when dispersed in methanol. Time-dependent density functional theory (TD-DFT) calculations confirmed that these emissions can be ascribed to metal-to-ligand charge transfer (MLCT) processes. Moreover, the calculations of the optimized structural conformations of the S0 ground state, and the S1 and T1 excited states are discussed and suggest a distorted planar conformation for the tetranuclear Au2Ag2 complex.