Structures of Fluoroarsenates KAsF6n (OH) n , n = 0, 1, 2: Application of the Heavy-Atom Method for Modulated Structures

Abstract

Structures of KAsF6−n (OH) n , n = 0, 1, 2, have been determined from single-crystal X-ray diffraction data. Potassium hexafluoroarsenate, KAsF6, has a standard structure, potassium hydroxopentafluoroarsenate, KAsF5(OH), has a superstructure, and potassium dihydroxotetrafluoroarsenate, KAsF4(OH)2, has an incommensurate modulated structure. The superstructure has been solved both in the supercell by standard methods and in the basic cell as a commensurate modulated structure, giving the same results in both cases. The heavy-atom method for modulated structures has been developed and applied to identify a good starting point for the refinement of strongly modulated KAsF4(OH)2. Moreover, the influence of hydrogen bonding on a regular disturbance of simple translation symmetry of the structure is discussed.