CRYSTAL-STRUCTURE DETERMINATION AND AB-INITIO MOLECULAR-STRUCTURE PREDICTION FOR EXO,EXO-ALPHA-P4SE3(CN)(2), THE FIRST PHOSPHORUS SELENIDE CYANIDE

Bicyclic exo,exo-alpha-P4Se3(CN), 1 was made by reaction of alpha-P4Se 3I2 with AgCN, and its crystal structure determined from X-ray data co llected at 160 K. Molecular structures were predicted fdr exo;exo-alph a-P4Se3(CN)(2), exo,exo-alpha-P4S3(CN)(2) and P2Se5 2 by restricted Ha rtree-Fock ab initio molecular-orbital calculations using STO-3G, 3-21 G and LanL2DZ(d) ECP basis sets, and for P2Se5 additionally using Ahl richs' split-valence and triple-zeta valence basis sets. Comparisons w ith the crystal structure of exo,exo-alpha-P4Se3(CN)(2) and with a pre viously published crystal structure of P2Se5 showed that the 3-21G ba sis sets gave sufficiently good predictions for most bond angles that the effects on them of intermolecular interactions in the crystals cou ld be discussed.