Infrared spectra of unannealed and of annealed Cu4(OH)6(NO3)2

Abstract

The infrared spectra over the range 4000–150 cm−1 of Cu4(OH)6(NO3)2 along with site group and factor group analysis are reported for the first time. The observed absorption frequencies associated with OH and NO3 modes show distinct individual spectral features in the unannealed and annealed Cu4(OH)6(NO3)2. Three distinct types of OH groups involving different degrees of H-bonding are evident. The multiple frequencies involving Cu—O—H bending modes further reflect the varying degrees of H-bonding and OH coupling in Cu(OH)4O2 and Cu(OH)5O entities paralleling their behavior in Cu4(OH)6SO4. The NO3 internal optic modes' activities, fundamentals along with overtones and combination bands, illustrate distinct interaction effects (OH and Cu) with respect to specific modes relative to halo-nitrates with same site symmetry. The presence of CuO in the sample after the anneal effected a striking change in ν3. The Cu—O, O—Cu—O, and OH torsional mode frequencies show consistent behavior with Cu4(OH)6SO4.