SYNTHESIS, STRUCTURE AND THERMAL-BEHAVIOR OF 2-VALENT METAL HYDROGEN SULFATES

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.