X-ray diffraction and molecular simulation study of the crystalline and liquid states of succinic anhydride.

The crystal structure of succinic anhydride was studied at five temperatures between 100 K and the melting point by single-crystal X-ray diffraction. The temperature dependence of molecular libration tensors was determined. Intermolecular interactions, in particular through unusually close molecule-molecule contacts, are discussed, with a detailed calculation of electrostatic energies. A method for the adaptation of existing crystal force fields to molecular dynamics has been developed; the adapted force field was used to study molecular motion and rotational diffusion with increasing temperature. Equilibration of the crystalline system becomes impossible at a temperature very close to the experimental melting temperature, where a sudden transition to the liquid state occurs, and a partial kinetic picture of the melting process is obtained. After validation of the force field against experimental crystal data, the state equation of the liquid was predicted. Enthalpies of sublimation, melting, and vaporization were calculated. The dynamics of a solution of succinic anhydride in a nonpolar solvent was simulated, for a discussion of the aggregation process leading to demixing and to crystal nucleation.