Some comparisons among ring compounds of phosphorus and arsenic

Abstract

Numerous comparisons among various structural features in compounds containing 4-and 5-membered phosphorus rings and 5-and 6-membered arsenic rings are made. The molecular structure of (PCF3) 4 indicates that the torsion angle about P-P bonds tends to be different from 0 °, a conclusion confirmed by the results on the other molecules. The observed conformations of (PCFa) 5 and (AsCHa) ~ are very similar, and apparently result mainly from intra-, rather than inter-, molecular forces. The stable form of these five-membered rings is intermediate between symmetry m and 2. The P-C-F bond angles in (PCF3) 4 and (PCFz) 5 are explainable in terms of repulsion between non-bonded atoms. The stable orientation about P-C single bonds is the staggered one. The observed irregularities in the torsion angles about the As-C bonds in the (AsC6Hs) G molecule may be ascribed to efficient molecular packing in the crystal. Some interesting but as yet unexplained differences exist among bond distances and bond angles in arsenic ring compounds.

Tetra-tert-butylcyclotetraphosphane, [PC(CH3)3]4

“…Table 1 gives positional parameters and Table 2 gives intramolecular bond distances and angles not involving hydrogen, and selected torsion angles. * tetramers, pentamers, and hexamers, of CF 3 and/or phenyl substituents) (Donohue, 1962). The average P-C bond distance of 1.884 (8) A is equal to the value found in both the PCF 3 tetramer and pentamer, another somewhat surprising fact in view of the large difference in the group electronegativities of the trifluoromethyl and the tert-butyl groups.…”

“…The crystal structures of four cyclopolyphosphane molecules have been reported: the tetramer (PCF3) 4 (Palenik & Donohue, 1962), pentamers (PCF3) 5 (Spencer & Lipscomb, 1961, 1962 and (PPh) 5 (Daly, 1964) and the hexamer (PPh) 6 (Daly, 1965(Daly, , 1966. The present paper reports the structure of [PC(CH3)3] 4 which was determined in order to study the effects of the bulky tert-butyl groups on the phosphorus ring conformation and, through comparison with (PCF3)4, to evaluate the effect of substituent-group electronegativity on the structure of the tetramer ring.…”

An investigation of the ring size of cyclopolyphosphines

“…The steric factors that govern the ring sizes in the cyclopolyphosphines also appear to govern the ring sizes in cyclopolyarsines. 30 All known cyclopolyphosphines and cyclopolyarsines with the same substituent consist of the same ring size, with the single exception being the lack of evidence for the existence of a five-membered phenyl-substituted arsenic ring.…”

1179. The crystal and molecular structure of phosphobenzene A, (PC6H5)5

“…14 This plane passes through P4 and the mid-point of the Pl-P2 bond. In an equilateral pentagon, if 41 be the angle at P1 then 4 4 is related to 41 (= 4 2 ) by the equation15 sin (44/2) = 4-cos41.…”