The coordination- and photochemistry of copper(i) complexes: variation of N^N ligands from imidazole to tetrazole

Abstract

The prediction of coordination modes is of high importance when structure–property relationships are discussed. Herein, the coordination chemistry of copper(I) with pyridine-amines with a varying number of coordinating N-atoms, namely pyridine-benzimidazole, -triazole and -tetrazole, or their deprotonated analogues, and different phosphines was systematically studied and the photoluminescence properties of all synthesized complexes examined and related to DFT data. Each complex was characterized by single-crystal X-ray analysis and elemental analysis, and a set of prediction rules derived for the coordination chemistry of copper(I) with these ligands. A mononuclear cationic coordination motif was found for PPh₃ or DPEPhos with all N^N ligands, which exhibits blue to green luminescence of MLCT character d(Cu) → π*(pyridine-amine ligand) with quantum yields up to 46%. With the deprotonated N^N ligands, mononuclear neutral complexes were only expected with DPEPhos. The emission's nature of this complex type is strongly dependent on the electronic effects of the N^N ligand and was characterized as (ML + IL)CT transition. In contrast to the high quantum yields up to 78% for the tetrazolate complexes (as reported before), the triazolate and imidazolate based complexes show much lower emission efficiencies below 10%. Besides the mononuclear copper(I) complexes, cluster-type complexes were obtained, which show moderate luminescence in the blue to green region of the visible spectrum (469–505 nm).