Infrared and Raman Spectra of Na2Cu(SO4)2·2H2O and (CH3NH3)2M(II)(SO4)2·6H2O withM(II)=Cu, Zn, and Ni

Abstract

FTIR and Raman spectra of Na2Cu(SO4)2·2H2O and (CH3NH3)2M(II)(SO4)2·6H2O withM(II)=Cu, Zn, and Ni are recorded and analyzed. Bands are assigned on the basis of SO2−4, CH3NH+3, and H2O vibrations. The lifting of degeneracies ofν2,ν3, andν4modes and the appearance ofν1andν2modes in the IR spectra confirm the lowering of symmetry of the SO2−4ion fromTdtoC1in all of the title compounds. Bands obtained indicate that the distortion of the SO2−4ion in the four crystals are in the order, (CH3NH3)Cu(SO4)2·6H2O > (CH3NH3)2Ni(SO4)2·6H2O > (CH3NH3)2Zn(SO4)2·6H2O > Na2Cu(SO4)2·2H2O. The appearance of NH3stretching modes at wavenumbers lower than the values obtained for the free ion indicates the presence of hydrogen bonds between NH3and SO2−4groups. The appearance of multiple bands in the bending and rocking mode regions and the broad nature of stretching modes show the existence of at least two symmetrically inequivalent water molecules in Na2Cu(SO4)2·2H2O. The shifting of stretching modes to lower wavenumbers and bending modes to higher wavenumbers of water molecules confirms the existence of strong hydrogen bonds in the crystal which is in agreement with the X-ray data. Bands indicate the presence of strong hydrogen bonds involving water molecules in (CH3NH3)2Cu(SO4)2·6H2O and (CH3NH3)2Zn(SO4)2·6H2O and of lesser strength in (CH3NH3)2Ni(SO4)2· 6H2O.