Magnetic properties in terms of localized quantities. XII. Normal- and hypervalent sulfur compounds

Abstract

Magnetic susceptibility and NMR chemical shift tensors are calculated for a number of sulfur containing compounds by means of the IGLO method (IGLO stands for individual gauge for localized molecular orbitals). The molecules investigated are H2S, the normal- and hypervalent sulfur fluorides SF2, SF4, SF3SF, and SF6, the triatomics OCS, SCS, OSO, NSF, NSCl, and SCl2, further NSF3, F2SO2, FSSF, SSF2, the thionyl compounds OSX2, X=CH3, F, Cl, the three-membered ring systems C2H4X, X=S, SO, SO2, and thiophene, C4H4S. With the provision that basis sets including at least two sets of polarization functions for the second row atoms are used, we obtain a rather satisfactory agreement between theory and experiment. Effects of antisymmetry are so large in NSF and NSCl that the anisotropies Δσ of their 33S, 35Cl, and 19F NMR shifts, calculated from the unsymmetric tensors differ from those obtained from the corresponding symmetrized eigenvalue problem by up to 100 ppm. Although a number of the molecules studied cannot be described entirely by localized MOs, MO contributions to magnetic properties provide valuable insight when discussing the orientation of the principal shielding axis systems, and when comparing iso-(valence)electronic molecules. Though iso-valencelectronic with ozone, SO2 shows a much smaller paramagnetic deviation from experimental data than the former, thus indicating that correlation effects, though important, are somewhat less essential for molecules containing second row elements.