W0031: The Crystal Structures of Trimellitic Anhydride and Two of its Solvates

W0031

The Crystal Structures of Trimellitic Anhydride and Two of its Solvates. James A. Kaduk, Joseph T. Golab, Frank J.J. Leusen, Amoco Corporation, Naperville, IL 60566 USA

The crystal structure of trimellitic anhydride (TMA) has been solved using Monte Carlo simulated annealing techniques, and refined using synchrotron powder diffraction data. TMA crystallizes in the orthorhombic space group P2₁2₁2₁, with a = 21.70237(35), b = 5.36879(9), c = 6.86300(14) Å, V = 799.64(2) Å³ at 27, and Z = 4. The crystal structure consists of helical hydrogen-bonded chains parallel to b. Prominent in the structure are C-H[Sigma][Sigma][Sigma]O=C hydrogen bonds between aromatic hydrogens and the carbonyl groups of the anhydride. The structures of two solvates of TMA have been determined using single crystal techniques. TMA:dimethylformamide (TMA:DMF) crystallizes in the monoclinic space group P2₁/n, with a = 7.198(3), b = 8.065(3), c = 21.562(9) Å, = 97.29(3), V = 1241.5(9) Å³, and Z = 4. The structure consists of hydrogen-bonded planar TMA:DMF pairs, including a formamide-carboxyl C-H[Sigma][Sigma][Sigma]O=C hydrogen bond. 2TMA:toluene (2TMA:Tol) crystallizes in the monoclinic space group P2₁/n, with a = 7.037(9), b = 12.635(9), c = 12.91(2) Å, = 104.74(10), V = 1110(2) Å³, and Z =4. The structure contains centrosymmetric hydrogen-bonded TMA dimers; the packing of these dimers results in channels parallel to a, in which the toluene molecules are disordered across centers of symmetry. Both potential planar conformations of TMA are observed in these structures; TMA and 2TMA:Tol contain the Z conformation, while the E conformation is observed in TMA:DMF. Computational studies suggest that Z-TMA is 096 kJ mol^-1 lower in energy than E-TMA, and that the rotational energy barrier is 46 kJ mol^-1.