Crystal structures of some cubic hexafluorophosphates at ambient temperatures

Structures of some alkaline metals and silver(I) hexafluorophosphates MPF6, have been determined by X-ray single crystallography at ambient temperatures. Although all the salts exhibit a rock salt structure (Fm (3) over bar m), three types arise due to the orientational disorders of anions. In NaPF6, Na+ and octahedral PF6- form a linear P-F-Na array without a disorder. PF6- in AgPF6 shows a three-fold orientational disorder described as a rotation by 45 degrees around one of the three crystal axes starting from the original position found in NaPF6. Salts of the heavier alkaline metals are isostructural, showing a four-fold orientational disorder of PF6- described as a rotation by 60 degrees around one of the four diagonals of the crystal lattice from the original orientation in NaPF6. (C) 2000 Elsevier Science S.A. All rights reserved.