Hydrogen positions in KCo-, CsCo-, CsNi-, and CsCu-Tutton salt compounds determined by neutron powder diffraction

Complementary to single crystal X-ray diffraction, neutron powder diffraction has been used to localize the hydrogen positions in isotypic Tutton salt compounds M(2)(I)[M(II)(H(2)O)(6)](SO(4))(2) (M(I) = K, Cs and M(II) = Co, Ni, Cu) which crystallize in the monoclinic space group P2(1)/a. Different approaches have been tested using varying experimental conditions and refinement strategies: (1) time-of-flight and/or fixed wavelength angle-dispersive diffraction, (2) measurements on protonated and/or deuterated samples, (3) measurements at room and low temperatures, (4) refinements of crystallographic standard parameters of all atoms compared to refinements of H(D) parameters only with fixed non-hydrogen atom positions obtained from single crystal X-ray data. Estimated standard deviations, agreement indices and differences of atomic parameters obtained from the different experiments and refinements are summarized. The results are discussed with respect to the accuracy of the metal-water distances and the hydrogen bond system.