LATTICE VIBRATION-SPECTRA .58. OD(OH) FREQUENCY VERSUS H-BOND DISTANCE CORRELATION DIAGRAMS - A CASE-STUDY FOR ISOMORPHIC MG(SO3)2.3H2O, MN(SO3)2.3H2O, FE(SO3)2.3H2O, CO(SO3)2.3H2O, NI(SO3)2.3H2O, ZN(SO3)2.3H2O

The uncloupled νOD band frequencies of matrix isolated HDO molecules in isostructural MSO3·3H2O (MMg, Mn, Fe, Co, Ni, Zn) have been assigned to the six different H positions in the structure by Raman single crystal techniques. The physical basis of this technique presented first in 1984 is described. The water molecules H2O I and II are extremely asymmetric, i.e. the most asymmetric known so far, forming a very strong and a mediate H-bond each. The bifurcated H-bonds of H2O III reveal a dynamic behaviour, as possibly common for bifurcated hydrogen bonds. The strength of the H-bonds present as well as the correlation between the OD(OH) band frequencies and the H⋯O hydrogen bond distances obtained from neutron diffraction studies are discussed in terms of the different acceptor strength (basicity) of the H-bond acceptor groups (SO2-3, H2O), the synergetic effect, and the repulsive forces at the respective lattice sites. The increase of the H-bond donor strength (acidity) of the water molecules owing to metal-oxygen interactions (MOH2) (synergetic effect) resembles that of the acid strengths of M(H2O)2+6 of the metal ions involved. © 1990.