New Acyclic Neutral Phosphorus Sulfides and Sulfide Oxides

A great number of binary neutral phosphorus sulfides was discovered and investigated. However all stable representatives of this family of compounds adopt a polycyclic structure in contrast to their lighter homologues, the nitrogen oxides. Acyclic representatives can be stabilized by adduct formation with a nitrogen base. The bis(pyridine) adduct py(2)P(2)S(5) of the unstable acyclic phosphorus sulfide P2S5 is readily obtained stirring P4S10 in pyridine at ambient temperature. X-ray diffraction studies on single crystals of py(2)P(2)S(5)0.5 py (1b) show a N2O5 like structure for the P2S5 framework. The long P-N distances of 1.86 angstrom indicate only weak coordination of the pyridine molecules to phosphorus. Single crystal X-ray diffraction studies on py(2)P(2)S(4.34)O(0.66) (2) reveal the presence of py(2)P(2)S(4)O (3) together with py(2)P(2)S(5) in the crystal. Compound 3 contains the mixed phosphorus oxide sulfide molecule P2S4O stabilized as bis(pyridine) adduct. It is readily obtained from pyP(2)S(5) by oxidation with KMnO4 in pyridine. The oxygen atom occupies the bridging position between the two phosphorus atoms. Quantum chemical calculations at the MPW1PW91 level of theory as well as DTA/TG thermal analyses confirm the weak coordination of the pyridine molecules in py(2)P(2)S(5), py(2)P(2)S(4)O, and py(2)P(2)S(7) to phosphorus.