Carbamazepine polymorphs: Theoretical and experimental vibrational spectroscopy studies

This paper provides a detailed overview on vibrational spectroscopy studies on polymorphic forms of carbamazepine based on literature data followed by new experimental and theoretical results. Raman, FT-MIR and, for the first time, FT-FIR spectra of carbamazepine were measured and interpreted by means of the B3LYP/6-311++G** theoretical calculations combined with the potential energy distribution (PED) analysis. Theoretical spectra of single molecule and dimer were similar in the frequency range of aromatic rings vibrations, whereas bands representing motion of carboxamide group were shifted. Relatively good agreement was found between experimental and theoretical spectra. The PED analysis of the theoretical modes enabled a detailed assignment of most of the experimental bands. Marker bands were identified for carbamazepine polymorphic forms I, III and IV on the basis of Raman and IR measurements. FT-FIR and FT-MIR analyses were much more discriminative than Raman spectra in terms of polymorphs differentiation.