SYNTHESIS, CRYSTAL-STRUCTURE, AND PROPERTIES OF TETRAAMINOPHOSPHONIUM IODIDE[P(NH2)(4)]I

The title compound has been prepared starting from phosphorothionic triamide SP(NH2)(3) by methylation of the sulfur atom and subsequent ammonolysis reaction in dry acetonitrile and dichloromethane, respectively, both at room temperature. Suitable single crystals are obtained from an acetonitrile solution in a temperature gradient between 70 degrees C and room temperature. The crystal structure of [P(NH2)(4)]I has been determined by single crystal X-ray methods (P4/n b m; a = 842.6(2), c = 486.7(2) pm, Z = 2). In the solid [P(NH2)(4)](+)- and I(-)ions are found with significant N-H...I-hydrogen bonding interactions between anions and cations (H...I: 276.4 pm). The P-N-bond length in the cation (160.7(2) pm) represents the shortest P-NH2 bond distance reported to date indicating a significant electrostatic strengthening. The condensation behaviour of [P(NH2)(4)]I in solution and in the solid has been investigated.