Crystal structure determination and ab initio molecular structure prediction for exo,exo-α-P4Se3(CN)2 , the first phosphorus selenide cyanide

Abstract

Bicyclic exo,exo-α-P ₄ Se ₃ (CN) ₂ 1 was made by reaction of α-P ₄ Se ₃ I ₂ with AgCN, and its crystal structure determined from X-ray data collected at 160 K. Molecular structures were predicted for exo,exo-α-P ₄ Se ₃ (CN) ₂ , exo,exo-α-P ₄ S ₃ (CN) ₂ and P ₂ Se ₅ 2 by restricted Hartree–Fock ab initio molecular-orbital calculations using STO-3G, 3-21G* and LanL2DZ(d) ECP basis sets, and for P ₂ Se ₅ additionally using Ahlrichs’ split-valence and triple-zeta valence basis sets. Comparisons with the crystal structure of exo,exo-α-P ₄ Se ₃ (CN) ₂ and with a previously published crystal structure of P ₂ Se ₅ showed that the 3-21G* basis sets gave sufficiently good predictions for most bond angles that the effects on them of intermolecular interactions in the crystals could be discussed.