Phosphorus NMR and ab initio study of pentaphosphorus dichalcogenide halides

Abstract

All twelve molecules P₅S_nSe_2 − nX (n = 0–2, X = Cl, Br or I) have been identified by ³¹P NMR spectroscopy in mixtures in solution, obtained after thermal reactions of red phosphorus, chalcogens, and phosphorus trihalides. Ab initio 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 intramolecular interactions. Gauge including atomic orbitals (GIAO) calculation, at an economical level, of changes in ³¹P 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 calculation of differences in ³¹P–³¹P coupling constants, using Natural Bond Orbital analysis and McConnell’s equation, provided supporting evidence.