Metoprolol Fumarate: Crystal Structure from Powder X-ray Diffraction Data and Comparison with the Tartrate and Succinate Salts

The metoprolol fumarate (MF) salt has been characterized by a combined use of powder X-ray diffraction (PXRD), variable temperature PXRD (VT-PXRD), and differential scanning calorimetry. Its molecular and crystal structure, as determined from PXRD data, has been thoroughly compared to those of the analogous tartrate (MT-o) and succinate (MS-m) salts. Moreover, Hirshfeld surface analysis and graph sets analysis have been performed to achieve insights into the intermolecular interactions. Despite their evident similarities at the molecular level, the three salts behave differently upon temperature variation: MF expands/contracts anisotropically (as MS-m), but the melt takes 3 days to recover the starting crystalline phase (as MT-o). A rationale for this behavior is provided based on their crystal arrangements.