IR characteristics of hydrotalcite-like compounds

The infrared spectra of well characterized hydrotalcite-like compounds with M2+/M3+= 2/1 and M2+/M3+=3/1 chemical ratios indicate that octahedral cation ordering is only present for the 2/1 composition. For M2+/M3+ ratios greater than 2/1, the octahedral sheets are disordered although local cation order can be present through cation segregation. The order-disorder characteristics of these compounds can be explained by the total cation charge around any hydroxyl which cannot exceed seven units nor be lower than six. In addition, the infrared spectra suggest that the interlayer anions are symmetrically perturbed, the electrostatic interaction being greater for the 2/1 compositions.