NEUTRON REFINEMENTS OF NACU2(H3O2)(SO4)2 AND RBCU2(H3O2)(SEO4)2 - VARIATION OF THE HYDROGEN-BOND SYSTEM IN THE NATROCHALCITE-TYPE SERIES

In the natrochalcite-type compounds NaCu2(H3O2)(SO4)2 and RbCu2(H3O2)( SeO4)2 the lengths of the two different hydrogen bridges vary widely: 2.44 angstrom and 2.70 angstrom in the Na-S member, and 2.60 angstrom and 3.03 angstrom in the Rb-Se member. Both structures were refined by single-crystal neutron diffraction methods. Least-squares refinements (harmonic vibrations for all atoms) resulted in a splitting of the H atom positions of the short bridges by 0.265(13) angstrom in the Na-S member, and by 0.472(6) angstrom in the Rb-Se member. In the two compo unds no clear evidence for an ordering of the split position of the H atom was found.