The structure of potassium difluorophosphate
Crystals of potassium difluorophosphate are orthorhombic, a= 8·039, b= 6·205, c= 7·635Å, Z= 4, space group Pnma. The structure was determined from the three-dimensional Patterson function using Mo-Kα scintillation-counter results, and refined by least-squares methods, oxygen and fluorine atoms being distinguished on the basis of bond distances and angles, and of electron counts. The final R is 0·038 for 448 observed reflexions.
The difluorophosphate anion has dimensions P–O = 1·470 ± 0·005 Å, P–F = 1·575 ± 0·005 Å, ∠FPF = 97·1°± 0·4°, ∠OPO = 122·4°± 0·4°(after correction for rotational oscillation effects), suggesting about 83% double-bond character for the P–O bond. The crystal structure is similar to that of barium sulphate; the K+ ion has fourteen oxygen and fluorine neighbours in the range 2·76–3·88 Å.