BICYCLIC IODO-TETRACHALCOGENA-TRIPHOSPHA- HEPTANES

The compounds P3Se4-nSnI (n = 0, 1, 2) have been identified by P-31 nm r spectroscopy. They were prepared by a direct thermal reaction of red phosphorus, sulfur, selenium and iodine in the stoichiometric ratio. These iodides could be converted into corresponding bromides and chlor ides by substitution reactions. All molecules show a diselenium bridge in which, in contrast to the other selenium positions, selenium could not be replaced by sulfur. Similar effects were observed for the dise lenium bridges of P2Se5. Systematic changes of the chemical shifts and coupling constants are caused by alterations in the molecular geometr y, either by replacement of selenium by sulfur, or of iodine by more e lectronegative ligands. An intramolecular exchange reaction is observe d for all molecules.