The structure of PO(OPF2)3 in the gaseous and crystalline phases

Abstract

The structure of P′O′(OPF₂)₃ has been determined in the gas and solid phases by electron diffraction and X-ray crystallography respectively. The compound was found to undergo an irreversible, topotactic phase change at ca. 77 K and, accordingly, the single-crystal structure for the lower-temperature form was determined. X-Ray powder diffraction was used to study both solid forms and investigate the transition between them. The principal parameters (r_a) found in the gas phase were r(P′O′) 1.401(10), r(P′–O) 1.590(9), r(O–P) 1.576(25), r(P–F) 1.581 (10)Å, and O–P′–O 102.8(7), O–P–F 98.3(6), and F–P–F 96.4(14)°. The conformations in the two phases are considerably different. Overall, a general flattening of the molecule is observed on going to the crystalline phase, due to an increase in the O–P′–O angle and changes in the P′–O–P–F dihedral angles. There was also a lengthening of r(P′O′) by about 0.08 Å to 1.478(9)Å, which may be associated with short intermolecular contacts, PO ⋯ P, of 2.88 and 3.14 Å.