Journal of the American Chemical Society, Vol.129, No.43, 13049-13065, 2007
Solid-state Cu-63 and Cu-65 NMR spectroscopy of inorganic and organometallic copper(I) complexes
Solid-state Cu-63 and Cu-65 NMR experiments have been conducted on a series of inorganic and organometallic copper(l) complexes possessing a variety of spherically asymmetric two-, three-, and fourcoordinate Cu coordination environments. Variations in structure and symmetry, and corresponding changes in the electric field gradient (EFG) tensors, yield Cu-63/65 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 SIN powder patterns. Significant copper chemical shielding anisotropies (CSAs) are also observed in some cases, ranging from 1000 to 1500 ppm. (31)p CP/MAS NMR spectra for complexes featuring (CU)-C-63/65-P-31 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 Cu-63/65 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.