An NMR and relativistic DFT investigation of one-bond nuclear spin–spin coupling in solid triphenyl group-14 chlorides

Abstract

A solid-state nuclear magnetic resonance and zeroth-order regular approximation density functional theory, ZORA-DFT, study of one-bond nuclear spin–spin coupling between group-14 nuclei and quadrupolar ^35/37Cl nuclei in triphenyl group-14 chlorides, Ph₃XCl (X = C, Si, Ge, Sn and Pb), is presented. This represents the first combined experimental and theoretical systematic study of spin–spin coupling involving spin-pairs containing quadrupolar nuclei. Solid-state NMR spectra have been acquired for all compounds in which X has a spin-1/2 isotope—¹³C, ²⁹Si, ^[117/119]Sn and ²⁰⁷Pb—at applied magnetic fields of 4.70, 7.05 and 11.75 T. From simulations of these spectra, values describing the indirect spin–spin coupling tensor—the isotropic indirect spin–spin coupling constant, ¹J(X,^35/37Cl)_iso and the anisotropy of the J tensor, Δ¹J(X,^35/37Cl)—have been determined for all but the lead–chlorine spin-pair. To better compare the indirect spin–spin coupling parameters between spin-pairs, ¹J_iso and Δ¹J values were converted to their reduced coupling constants, ¹K_iso and Δ¹K. From experiment, the sign of ¹K_iso was found to be negative while the sign of Δ¹K is positive for all spin-pairs investigated. The magnitude of both ¹K_iso and Δ¹K was found to increase as one moves down group-14. Theoretical values of the magnitude and sign of ¹K_iso and Δ¹K were obtained from ZORA-DFT calculations and are in agreement with the available experimental data. From the calculations, the Fermi-contact mechanism was determined to provide the largest contribution to ¹K_iso for all spin-pairs while spin-dipolar and paramagnetic spin–orbit mechanisms make significant contributions to the anisotropy of K. The inclusion of relativistic effects was found to influence K(Sn,Cl) and K(Pb,Cl).