Structure determination of a new cocrystal of carbamazepine and DL-tartaric acid by synchrotron powder X-ray diffraction.

The crystal structure of a new cocrystal of carbamazepine (systematic name: 5H-dibenzo[b,f]azepine-5-carboxamide, CHNO) and DL-tartaric acid (CHO), obtained by liquid-assisted grinding, was solved by powder X-ray diffraction (PXRD). The high-resolution PXRD pattern of this new phase was recorded at room temperature thanks to synchrotron experiments at the European Synchrotron Radiation Facility (Grenoble, France). The starting structural model was generated by a Monte-Carlo simulated annealing method. The final structure was obtained through Rietveld refinement and an energy minimization simulation was used to estimate the H-atom positions. The stability of the proposed structure as a function of temperature was also assessed from molecular dynamics simulations. The symmetry is monoclinic (space group P2/c) and contains eight molecules per unit cell, namely, four DL-tartaric acid and four carbamazepine molecules.