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

<div><p>A new series of mononuclear copper(I) halide complexes possessing 5-<i>tert</i>-butyl-3-(pyrimidine-2-yl)-1<i>H</i>-1,2,4-triazole (bpmtzH) and PPh<sub>3</sub>, Cu(bpmtzH)(PPh<sub>3</sub>)X (X = I (<b>1</b>); Br (<b>2</b>); Cl (<b>3</b>)), have been synthesized and characterized. As revealed via X-ray crystallography, <b>1–3</b> show a chiral, distorted tetrahedral N<sub>2</sub>PX 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 CH<sub>2</sub>Cl<sub>2</sub> solutions of <b>1–3</b> at room temperature, ascribing to charge-transfer transitions with appreciable metal-to-ligand charge transfer (MLCT) character. Complexes <b>1–3</b> 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 <sup>3</sup>MLCT and <sup>3</sup>XLCT transitions, can be modulated via alteration of the halide bound to {Cu(bpmtzH)(PPh<sub>3</sub>)} motif.</p></div>