E. Kemnitz et al., SYNTHESIS, STRUCTURE AND THERMAL-BEHAVIOR OF 2-VALENT METAL HYDROGEN SULFATES, European journal of solid state and inorganic chemistry, 30(6), 1993, pp. 629-644
Hydrogen sulfates of two-valent metals (Mg,Ca,Sr,Ba,Cd,Zn) crystallize
from solutions of the corresponding sulfates in sulfuric acid dependi
ng on the temperature and the concentration of the acid. Three differe
nt compound classes are formed: Hydrogen sulfate dihydrogen sulfates,
M(HSO4)2(H2SO4)2, hydrogen sulfates, M(HSO4)2, and hydrogen sulfate mo
nohydrates, M(HSO4)2.H2O. There exist six different types of structure
s of these compounds. If the ionic radius of the M2+ cation is small (
< 100pm), isolated MO6 octahedra are formed which are connected over S
O3(OH) tetrahedra forming layer structures or three-dimensionally arra
nged structures. These structures can also he described as closest pac
kings of SO3(OH) and SO2(OH)2 tetrahedra. A part of the octahedral hol
es in this closest packing is occupied by M2+ ions. In the case of lar
ger M2+ cations (Ca2+, Sr2+, Ba2+) MO8 or MO9 polyhedra are formed whi
ch are connected over common edges forming infinite chains. The hydrog
en bonding system between SO3(OH) and SO2(OH)2 tetrahedra can be arran
ged as an ordinary chain, as a branched chain or in form of infinite n
ets. The absolute length of the S-O and S-OH bonds depends on the type
of the tetrahedron they belong to SO3(OH) or SO2(OH)2! as well as on
the peculiarities of the oxygen coordination.