Vibrational spectra of cobalt dihydrogen phosphate dihydrate, Co(H2PO4)2·2H2O

The infrared and Raman spectra of protiated and deuterated crystalline Co(H2PO4)2·2H2O are presented and discussed with respect to the internal vibrations of the H2PO4− ions, the OH stretching vibrations and the water librations. A detailed interpretation of the vibrational spectra is proposed on the basis of the isotopic and temperature shifts of the vibrational bands. The mutual exclusion rule is obeyed for all vibrations under consideration. Strong vibrational couplings are established between the PO4 stretching modes and POH bending modes, as well as between the PO4 bending modes and the water librations. The values of the correlation splittings A-B and g-u of the γ(OH) vibrations evidence the significant intra- and inter-chain interactions between the H2PO4− ions. The four O⋯O hydrogen bonds are discussed with respect to their strengths and the multi band behaviour of the OH stretching modes of the respective POH groups.