Correlations between 31P Chemical Shift Anisotropy and Molecular Structure in Polycrystalline O,O‘-Dialkyldithiophosphate Zinc(II) and Nickel(II) Complexes: 31P CP/MAS NMR and Ab Initio Quantum Mechanical Calculation Studies

Abstract

Different potassium salts and zinc(II) and nickel(II) O,O'-dialkyldithiophosphate complexes were studied by solid-state 31P CP/MAS and static NMR and ab initio quantum mechanical calculations. Spectra were obtained at different spinning frequencies, and the intensities of the spinning sidebands were used to estimate the chemical shift anisotropy parameters. Useful correlations between the shapes of the 31P chemical shift tensor and the type of ligand were found: terminal ligands have negative values of the skew kappa, while bridging and ionic ligands have positive values for this parameter. The experimental results were compared with known X-ray diffraction structures for some of these complexes as well as with ab initio quantum mechanical calculations, and a useful correlation between the delta22 component of the 31P chemical shift tensor and the S-P-S bond angle in the O,O'-dialkyldithiophoshate zinc(II) and nickel(II) complexes was found: delta22 increases more than 50 ppm with the increase of S-P-S bond angle from ca. 100 degrees to 120 degrees , while the other two principal values of the tensor, delta11 and delta33, are almost conserved. This eventually leads to the change in sign for kappa in the bridging type of ligand, which generally has a larger S-P-S bond angle than the terminally bound O,O'-dialkyldithiophosphate group forming chelating four-membered P(ss)Me heterocycles.