Synthesis and characterization of emissive mononuclear Cu(I) complexes with 5-tert-butyl-3-(pyrimidine-2-yl)-1H-1,2,4-triazole

A new series of mononuclear copper(I) halide complexes possessing 5-tert-butyl-3-(pyrimidine-2-yl)-1H-1,2,4-triazole (bpmtzH) and PPh₃, Cu(bpmtzH)(PPh₃)X (X = I (1); Br (2); Cl (3)), have been synthesized and characterized. As revealed via X-ray crystallography, 1–3 show a chiral, distorted tetrahedral N₂PX arrangement, in which bpmtzH is a neutral bidentate chelating ligand using the 4-N of the 1,2,4-triazolyl ring and one N donor from the 2-pyrimidyl ring, consistent with the computational results. A comparatively weak low-energy absorption tail is observed between 320 and 450 nm for CH₂Cl₂ solutions of 1–3 at room temperature, ascribing to charge-transfer transitions with appreciable metal-to-ligand charge transfer (MLCT) character. Complexes 1–3 in the solid state have good luminescence at ambient temperature, although they are non-emissive in solution. The solid-state emission, most likely originating from both ³MLCT and ³XLCT transitions, can be modulated via alteration of the halide bound to {Cu(bpmtzH)(PPh₃)} motif.