Metal-water interactions and hydrogen bonding in dittmarite-type compounds M'MPO4.H2O(M'= K+, NH4+;: M = Mn2+, Co2+, Ni2+) -: Correlations of IR spectroscopic and structural data

The vibrational behavior of the uncoupled nu(OD) Modes and of the water librations in dittmarite-type compounds M ' M '' PO4 center dot H2O (M ' = K+, NH4+; M '' = Mn2+, Co2+, Ni2+) is analyzed in terms of the influence of two types of metal-water interactions (M+-H2O and M2+-H2O), the hydrogen bonding and the repulsion potential of the lattices. The M+-H2O interaction is found to be the main factor, which influences nu(OD.) The strong K+-H2O interaction weakens in a higher degree the intramolecular O-H bonds than the corresponding M2+-H2O interactions (M2+ = Mn, Co, Ni). As a result nu(OD) is shifted to lower wavenumbers in the potassium series than in ammonium one, irrespective of the synergetic effect of M2+, the hydrogen bond lengths and the repulsion potential of the lattices. The analysis of the spectroscopic data evidences for the dominating influence of the M2+-H2O interaction on the wagging mode. The blue shift of nu(wag) strictly follows the increasing synergetic effect of M2+, i.e. nu(M ') < nu(M '/Co) < nu(M '/N1), in all cases, irrespective of the strength of the M+-H2O interactions, the hydrogen bond lengths and the higher repulsion potential of the K-lattices. The rocking mode is insensitive to the replacement of the M2+ ions. Some relations between the spectroscopic and structural data are given. (c) 2005 Elsevier B.V. All rights reserved.