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

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, P=O ⋯ P, of 2.88 and 3.14 Å.