Structural chemistry of alkaline metal hydrogen sulfates. A review of new structural data. Part I. Synthesis, metal and sulfur polyhedra

Hydrogen sulfates of alkaline metals (M:Li,Cs in particular) crystallize from solutions of the corresponding sulfates in sulfuric acid. A series of new metal hydrogen sulfates have been synthesized and crystallographically characterized recently. The present paper deals with general structural aspects of crystalline water-free alkaline metal hydrogen sulfates of the following compositions: M3[H(SO4)2), 2(HSO4), M2(HSO4)2(H2SO4), M(HSO4)(H2SO4), M(HSO4)(HSO4)(H2SO4)2, M[H(HSO4)2](H2SO4)2. In the general formula MXHNSO4 (with X+N=2), the value N defines the average number of hydrogen donor functions (OH groups) per SO4 tetrahedron. All crystal structures contain M+ ions co-ordinated by O atoms with coordination numbers ranging from 4 to 10 depending mainly on the metal radii. Counterparts consist of simple HSO4 tetrahedra (N=1) or their combination with an SO2-4 (N<1, [H(SO4)2]3-) or an H2SO4 molecule (N>1). The s-O bond lengths correlate with the additional structural functions of O atoms such as co-ordination by M atom(s), H-acceptor, or H-donor functions. The S-OH distances are generally 0.1 angstrom longer that the S-O distances. Both the S-O and the S-OH distances are slightly longer (by 0.02-0.03 angstrom) in HSO4- as compared to those in the H2SO4 unit. (authors). 40 refs., 5 figs., 4 tabs