Synthesis and structural characterization of heteroleptic Cu(I) perchlorate complexes with diimines derived from pyridinyliminobenzoic acids

The synthesis and the study of molecular and electronic structure of three heteroleptic monovalent copper complexes with the general formula [Cu(L)(PPh3)2][ClO4], where L are 3-, 4-pyridinylimino and 3,5-dipyridinylimino substituted benzoic acid, respectively, are reported. The crystal structures of the complexes reveal coordination of the metal to the diimine site of the ligands. The tetrahedral environment of the metal is completed by the coordination of two triphenylphosphane molecules. The compounds with the mono-substituted ligands crystallize as dimers via hydrogen bonds between the carboxylic groups. The electronic absorption spectra are dominated by the intraligand bands while characteristic charge transfer transitions are observed in the region 360–500 nm. The complexes proved to be weak emitters both at room and at low temperature (77 K rigid matrix). This lack of photoluminescence cannot be attributed to the facile oxidation of the Cu(I) metal core as their cyclic voltammetry studies revealed E1/2 values higher than 1.0 V but to the flexibility of the coordination environment which undergoes reorganization upon oxidation.