POLYMORPHISM IN BINARY-MIXTURES, AS EXEMPLIFIED BY NIMODIPINE

The results of studies on nimodipine in the solid state demonstrate that the compound occurs in two polymorphic forms. Modification I melts at + 124 degrees C and crystallizes as the racemic compound. Modification II(m.p. + 116 degrees C) is a conglomerate. The two polymorphs have been characterized by means of differential scanning calorimetry, infrared, Raman, and C-13-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 degrees 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.