THE MOLECULAR COMPOSITION OF SOLIDIFIED PHOSPHORUS-SULFUR MELTS AND THE CRYSTAL-STRUCTURE OF BETA-P4S6

Phosphorus sulfur melts were annealed for one week at 673 K and then quenched in ice water. The solids were dissolved in CS2 and the concentrations of phosphorus sulfides were determined by P-31 NMR spectroscopy. Samples containing between 44 and 70 mol% sulfur dissolved completely in CS2. Between 0 and 42 mol% remains an insoluble residue of red phosphorus. Above 72 mol% it consisted of sulfur chains linked by phosphorus atoms. The solutions contained mainly the congruently melting compounds P4S3, P4S7, and P4S10 having maximum concentrations at their stoichiometric compositions. Other compounds P4Sn (n = 4-9) which decompose on heating, according to the phase diagram, were also found in surprisingly high concentrations. One of these was beta-P4S6 which crystallizes in the monoclinic space group P2(1)/c with the lattice parameters a = 702.4(2), b = 1205.6(2), c = 1148.9(6) pm and beta = 103.4(2)degrees. Reaction of white phosphorus with sulfur was also investigated. In contrast to the results of previous authors, who described the system P-4-S-g below 373 K as eutectic, we found that the elements reacted below this temperature.