Phosphorus NMR and ab initio study of pentaphosphorus dichalcogenide halides

All twelve molecules P5SnSe2-nX (n=0-2, X=;Cl, Br or I) have been identifie d by P-31 NMR spectroscopy in mixtures in solution, obtained after thermal reactions of red phosphorus, chalcogens, and phosphorus trihalides. Ab init io geometries of eight of the molecules (X=Cl or Br) have been calculated, and deformations of the cages from C-s symmetry ascribed to non-bonded intr amolecular interactions. Gauge including atomic orbitals (GIAO) calculation , at an economical level, of changes in P-31 NMR shieldings on formal atom replacement, has been shown to be a practical method for assignment of NMR spectra and hence identification of these compounds. Approximate calculatio n of differences in P-31-P-31 coupling constants, using Natural Bond Orbita l analysis and McConnell's equation, provided supporting evidence.