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

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.