Solid-State ¹¹⁵In and ³¹P NMR Studies of Triarylphosphine Indium Trihalide Adducts

Solid-state 115In and 31P NMR spectroscopy, relativistic density functional theory (DFT) calculations, and single-crystal X-ray diffraction were used to investigate a series of triarylphosphine indium(III) trihalide adducts, X3In(PR3) and X3In(PR3)2 (X = Cl, Br or I; PR3 = triarylphosphine ligand). The electric field gradient tensors at indium as well as the indium and phosphorus magnetic shielding tensors and the direct and indirect 115In−31P spin−spin coupling were characterized; for complexes possessing a C3 symmetry axis, the anisotropy in the indirect spin−spin coupling, ΔJ(115In,31P), was also determined. The 115In quadrupolar coupling constants, CQ(115In), range from ±1.25 ± 0.10 to −166.0 ± 2.0 MHz. For any given phosphine ligand, the indium nuclei are most shielded for X = I and least shielded for X = Cl, a trend also observed for other group-13 nuclei in M(III) complexes. This experimental trend, attributed to spin−orbit effects of the halogen ligands, is reproduced by the DFT calculations. The spans of the indium magnetic shielding tensors for these complexes, δ11 − δ33, range from 40 ± 7 to 710 ± 60 ppm; those determined for phosphorus range from 28 ± 1.5 to 50 ± 3 ppm. Values of 1J(115In,31P) range from 550 ± 20 to 2500 ± 20 Hz. For any given halide, the 1J(115In,31P) values generally increase with increasing basicity of the PR3 ligand. Calculated values of 1J(115In,31P) and ΔJ(115In,31P) duplicate experimental trends and indicate that both the Fermi-contact and spin−dipolar Fermi-contact mechanisms make important contributions to the 1J(115In,31P) tensors.