Synthesis, Structure, and Luminescence of a Binuclear Copper(I) Complex Based on 1,3-Diaza-5-Phosphacyclohexane

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We report syntheses of two new 1,3-diaza‑5‑phosphacyclohexanes bearing a pyridine-2-yl or pyridine-2-ylethyl substituent at the phosphorus atom and biphenyl groups at the nitrogen atoms. A binuclear copper(I) complex with iodide bridges is prepared on the basis of the ligand with a pyridine-2-ylethyl substituent at the phosphorus atom. Single crystal X-ray diffraction analysis reveals that the ligand in the crystalline state adopts an asymmetric heterocycle conformation with one biphenyl substituent occupying an axial position, thereby leading to pyramidalization of one of the endocyclic nitrogen atoms due to 1,3-syn-axial repulsion. Regardless of the reaction stoichiometry, the interaction of the N-biphenyl‑substituted ligand with CuI exclusively affords a centrosymmetric dimeric complex of composition Cu2I2L2 with a planar four‑membered Cu2I2 core, in which the ligand acts as a chelating P,N-donor. The resulting complex exhibits two-band luminescence in the solid state, with each band being selectively excitable owing to different excitation spectra. The long (microsecond) luminescence lifetimes indicate a triplet origin for both emission bands.