IR study of dibarium copper formate tetrahydrate

The infrared spectra of Ba2Cu(HCOO)(6) . 4H(2)O and its deuterated analogues have been recorded and the internal modes of the formate groups and water molecules are reported. Some of the internal formate modes (nu(4), nu(3) and nu(2)) reflect the existence of three crystallographically independent formate ions. The frequency separations between the asymmetric and symmetric C-O stretching modes is explained in terms of different C-O bond lengths within each formate group. The number and positions of the bands in the high-frequency region (4000-2300 cm(-1)) is evidence for the existence of two inequivalent water molecules. The librational modes of the water molecules are also discussed. (C) 1997 Elsevier Science B.V.