Crystal and molecular structure of nonamethylcyclotetraphosphonitrilium pentacarbonyliodochromate(0)

Abstract

Crystals of the title compound are triclinic, a= 14·632(21), b= 10·364(10), c= 10·765(9)Å, α= 89·65(9), β= 106·98(13), γ= 63·72(7)°, Z= 2, space group P. The structure was determined from diffractometer data by Patterson and electron-density maps, and was refined by full-matrix least-squares methods to R 0·053 for 2112 observed reflexions. The anion has approximate C_4v symmetry. Mean Cr–C bond lengths cis to I are 1·893 Å and the trans Cr–C bond length is 1·859 Å. Mean C–O is 1·135, and the Cr–I 2·790 Å. The phosphonitrilic ring has an unusual distorted tub conformation, probably as a result of steric requirements. Bond length inequalities in the phosphonitrilic ring are discussed and compared with the P–N bond lengths in the [N₄P₄Me₈H⁺]ion.