Preparation and molecular structure of a new isomer of P4S3I2: 3,5-di-iodo-2,6,7-trithia-1,3,4,5-tetraphosphabicyclo[2,2,1]heptane

Abstract

Addition of iodine to P₄S₃ in solution yields a new isomer of the di-iodo-compound, β-P₄S₃I₂. The i.r., Raman, and mass spectra of both isomers are reported. A single-crystal X-ray diffraction study shows that β-P₄S₃I₂ is isostructural with P₄Se₃I₂; the crystals are orthorhombic, space group Pnma, a= 9·45, b= 16·33, c= 6·67 Å, Z= 4. The molecular structure is derived from that of P₄S₃ by the addition of a molecule of iodine across a P–P bond. On melting, β-P₄S₃I₂ undergoes a rapid skeletal rearrangement to give the stable isomer, α-P₄S₃I₂.