Alfons Grunenberg

Polymorphism in binary mixtures, as exemplified by nimodipine

Abstract The results of studies on nimodipine in the solid state demonstrate that the compound occurs in two polymorphic forms. Modification I melts at + 124°C and crystallizes as the racemic compound. Modification II (m.p. + 116°C) is a conglomerate. The two polymorphs have been characterized by means of differential scanning calorimetry, infrared, Raman, and 13C-NMR spectroscopy, X-ray powder diffractometry, X-ray structure analysis, pycnometry, and solubility measurements. The thermodynamic relationships are illustrated in a semi-schematic energy/temperature diagram, which gives information about the relative stability and physical properties of the two modifications. Modification II is the stable form between absolute zero and about + 90°C. The melting characteristics of the two polymorphs are illustrated by the phase diagram. Modification I is yellow. Modification II is almost white. The differences in colour are discussed with reference to the results of X-ray structure analyses and the UV-Vis spectra.