Solid-State (63)Cu, (65)Cu, and (31)P NMR Spectroscopy of Photoluminescent Copper(I) Triazole Phosphine Complexes

The results of a solid-state (63/65)Cu and (31)P NMR investigation of several copper(I) complexes with functionalized 3-(2'-pyridyl)-1,2,4-triazole and phosphine ligands that have shown potential in the preparation of photoluminescent devices are reported. For each complex studied, distinct NMR parameters, with moderate (63)Cu nuclear quadrupolar coupling constant (CQ) values ranging from -17.2 to -23.7 MHz, are attributed to subtle variations in the distorted four-coordinate environments about the copper nuclei. The spans of the copper chemical shift (CS) tensors, δ11-δ33, for the mono- and bisphosphine complexes are also similar, ranging from 1000 to 1150 ppm, but that for a complex with a strained bidentate phosphine ligand is only 650 ppm. The effects of residual dipolar and indirect spin-spin coupling arising from the (63/65)Cu- (31)P spin pairs, observed in the solid-state (31)P NMR spectra of these complexes, yield information about the orientations of the copper electric field gradient (EFG) tensors relative to the Cu-P bond. Variable-temperature (31)P NMR measurements for [Cu(bptzH)(dppe)]ClO4 (bptzH = 5-tert-butyl-3-(2'-pyridyl)-1,2,4-triazole; dppe = 1,2-bis(diphenylphosphino)ethane), undertaken to investigate the cause of the broad unresolved spectra observed at room temperature, demonstrate that the broadening arises from partial self-decoupling of the (63/65)Cu nuclei, a consequence of rapid quadrupolar relaxation. Ab initio calculations of copper EFG and CS tensors were performed to probe relationships between NMR parameters and molecular structure. The analysis demonstrated that CQ((63/65)Cu) is negative for all complexes studied here and that the largest components of the EFG tensors are generally coincident with δ11.