Solid-State ⁶³Cu and ⁶⁵Cu NMR Spectroscopy of Inorganic and Organometallic Copper(I) Complexes

Solid-state ⁶³Cu and ⁶⁵Cu NMR experiments have been conducted on a series of inorganic and organometallic copper(I) complexes possessing a variety of spherically asymmetric two-, three-, and four-coordinate Cu coordination environments. Variations in structure and symmetry, and corresponding changes in the electric field gradient (EFG) tensors, yield ^63/65Cu quadrupolar coupling constants (C_Q) ranging from 22.0 to 71.0 MHz for spherically asymmetric Cu sites. These large quadrupolar interactions result in spectra featuring quadrupolar-dominated central transition patterns with breadths ranging from 760 kHz to 6.7 MHz. Accordingly, Hahn-echo and/or QCPMG pulse sequences were applied in a frequency-stepped manner to rapidly acquire high S/N powder patterns. Significant copper chemical shielding anisotropies (CSAs) are also observed in some cases, ranging from 1000 to 1500 ppm. ³¹P CP/MAS NMR spectra for complexes featuring ^63/65Cu-³¹P spin pairs exhibit residual dipolar coupling and are simulated to determine both the sign of C_Q and the EFG tensor orientations relative to the Cu−P bond axes. X-ray crystallographic data and theoretical (Hartree−Fock and density functional theory) calculations of ^63/65Cu EFG and CS tensors are utilized to examine the relationships between NMR interaction tensor parameters, the magnitudes and orientations of the principal components, and molecular structure and symmetry.