Infrared spectroscopic study of mixed copper-cobalt and copper-nickel formate dihydrates (cation distribution in mixed crystals)

The infrared (IR) spectra of Co(HCOO)(2). 2H(2)O, Ni(HCOO)(2). 2H(2)O and CuxCo(Ni)(1-x)(HCOO)(2). 2H(2)O mixed crystals (0 < x less than or equal to 0.5) have been recorded and the internal modes of the formate groups and the water molecules are discussed. The analysis of the spectra of the mixed crystals reveals that when copper ions replace cobalt and nickel ions in Co(HCOO). 2H(2)O and Ni(HCOO)(2). 2H(2)O, the Cu2+ ions are localized at the two available positions. However, the occupancy degree of the Me(1) and Me(2) sites by the different cations needs X-ray diffraction (XRD) studies of the single crystals. The new crystal phase Co0.17Cu0.83(HCOO)(2). 2H(2)O obtained from the Co(HCOO)(2). 2H(2)O-Cu(HCOO)(2). 2H(2)O-H2O system at 50 degreesC crystallizes in the monoclinic system with lattice parameters: a = 12.329(4); b = 7.241(2), c = 8.707(5) Angstrom and beta = 103.13(3)degrees (SG probably P2(1)/c). The number of the bands corresponding to the uncoupled OD vibrations and the water librations shows that probably more than two water molecules are expected to exist in the structure. Furthermore, it is assumed that the water molecules bonded to the copper ions form stronger hydrogen bonds (stronger Cu-OH2 interaction) than those bonded to the cobalt ions. (C) 2001 Elsevier Science B.V. All rights reserved.