SOLID-STATE NMR AND X-RAY-DIFFRACTION STUDIES OF THE GEOMETRY AND INTRAMOLECULAR DYNAMICS OF BIS(ORGANOTHIOPHOSPHORYL) DICHALCOGENIDES

Information stored in the Cambridge Crystallographic Data Centre shows that anti-anti conformation is common for bis(organothiophosphoryl) d ichalcogenides. In view of the 1-4 repulsion, the syn-syn conformation of the S-1=P-X-X-4-P=S (X = S and Se) backbone is unfavorable. Howeve r, in compounds with at least one phenyl group directly bonded to the phosphorus, such as bis[tert-butyl(phenyl)thiophosphinyl] disulfide (K nopik, P. et al. J. Chem. Sec., Dalton Trans. 1993, 2749), bis(dipheny lthiophosphinyl) disulfide (Gallacher, A. C. et al. Acta Crystallogr. 1993, C49, 1793) and bis[tert-butyl(phenyl)thiophosphinyl] diselenide (this work) there is the syn-syn geometry caused by the aromatic-aroma tic interactions. Bis[tert-butyl(phenyl)thiophosphinyl] diselenide is monoclinic, space group C2/c with a = 20.424(2) Angstrom, b = 9.373(1) Angstrom, c = 12.907(1) Angstrom, V = 2406.4(2) Angstrom(3), D-c = 1. 525 (2) g/cm(3), and Z = 4. Refinement using 2351 reflection for 118 v ariables gives R = 0.047. We have used high-resolution Se-77 MAS NMR t o study the structural properties of the compound. The principal eleme nts T-ii of the Se-77 effective dipolar/chemical shift tensor were cal culated from the intensities of the spinning sidebands. The values of the anisotropy and asymmetry parameters reflect the distortion of the environment of selenium. For a series of bis(organothiophosphoryl) dis elenides the T-33 tensor component gives the largest contribution to t he isotropic chemical shifts and the span parameter Omega reflects the strength of the diselenide bond. Molecular packing significantly infl uences the intramolecular dynamics of the aliphatic and aromatic group s. The C-13 dipolar dephasing experiment and line shape analysis of th e H-1-H-2 CP/MAS spectra of selectively H-2-labeled compounds show tha t the phenyl groups are static as a result of the aromatic-aromatic in teraction, while the tert-butyl groups are under a fast motional regim e, with C-3v jumps around the P-C and C-C bonds.