CRYSTAL-STRUCTURE, NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY AND INDIVIDUAL GAUGE FOR LOCALIZED ORBITALS (IGLO) CALCULATIONS OF C6H4P2S6, A NEW TETRATHIADIPHOSPHORINANE, AND COMPARISON WITH RELATED P-S COMPOUNDS

The reaction of 1,2-diphosphinobenzene with sulfur yielded a new constitution of a tetrathiadiphosphorinane ring: 4,6-(1,2-phenylene)-4,6-dithioxo-1,2,3,5,4 lambda(5),6 lambda(5)-tetrathiadiphosphorinane the crystal structure of which has been determined, orthorhombic, space group Pbca (no. 61), a = 12.846(4), b = 16.929(7), c = 11.178(6) Angstrom and Z = 8: The tetrathiadiphosphorinane ring has a chair structure with axial positions of the 1,2-phenylene carbons and equatorial positions of the terminal sulfur atoms. One molecule per unique volume is an independent structural unit. This is consistent with the fact that the solid-state P-31 cross-polarisation magic angle spinning (CP MAS) NMR spectra give two sets of slightly different principal values of the nuclear magnetic shielding tenser. A comparison with the crystal structure and the solid-state NMR data of trans-2,4-diphenyl-2,4-dithioxo-1,3,2 lambda(5),4 lambda(5)-dithiadiphosphetane and cis-2,4-(1,8-naphthalenediyl)-2,4-dithioxo-1,3,2 lambda(5),4 lambda(5)-dithiadiphosphetane shows that the nuclear shielding does not only depend on the molecular structure. Short intermolecular S ... S distances lead to deshielding effects on the P-31 nucleus. Results of individual gauge for localised orbitals (IGLO) calculations of the P-31 nuclear shielding of isolated molecules agree, nevertheless, satisfactorily with the experimental principal values and additionally allow the determination of the orientation of the principal axes in the molecular framework. The IGLO calculations indicate that the principal 3 axis for the most shielded principal value lies nearly parallel with the P=S bond.