The vibrational spectra of the copper(II) formates: I. Raman spectra of polycrystalline copper(II) formate tetrahydrate and the light blue modification of anhydrous copper(II) formate

Abstract

The infrared and Raman spectra of the light blue modification of anhydrous copper(II) formate, Cu(HCOO) 2, and copper(II) formate-d 2, Cu(DCOO) 2, are reported, as well as the Raman spectra of copper(II) formate tetrahydrate Cu(HCOO) 2 · 4H 2O and copper(II) formate tetrahydrate-d 8 Cu(HCOO) 2 · 4D 2O over a wide range of temperatures. In the latter two compounds, the fundamental formate modes, active in the Raman spectra, showed splittings when the phase transition temperature was traversed. These low-temperature Raman spectra were interpreted in terms of a P2 1 space group and prove that the phase transition not only involves an ordering in the orientation of the water molecules, but also displacements of the heavy atoms. Only a limited number of weak translational modes of the water molecules could be identified in the Raman spectra of the copper(II) formate tetrahydrate, and it is not possible therefore to determine exactly how ordering affects the Raman-active lattice modes of these molecules.