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

Abstract

The infrared spectra over the range 4000–150 cm −1 of Cu 4 (OH) 6 (NO 3 ) 2 along with site group and factor group analysis are reported for the first time. The observed absorption frequencies associated with OH and NO 3 modes show distinct individual spectral features in the unannealed and annealed Cu 4 (OH) 6 (NO 3 ) 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) 4 O 2 and Cu(OH) 5 O entities paralleling their behavior in Cu 4 (OH) 6 SO 4 . The NO 3 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 ν 3 . The Cu—O, O—Cu—O, and OH torsional mode frequencies show consistent behavior with Cu 4 (OH) 6 SO 4 .