Effect of the Methanol Molecule on the Stabilization of C sub(18)H sub(18)O sub(4) Crystal: Combined Theoretical and Structural Investigation

The ability of the chalcone, C sub(18)H sub(18)O sub(4), to form solvates was theoretically and experimentally investigated. The unit cell with Z' > 1, composed of two independent chalcone molecules ( alpha and beta ), shows the formation of a stable molecular complex which is related with the presence of methanol in this crystal lattice. Aiming to understand the process of crystal lattice stabilization, a combination of techniques was used, including X-ray diffraction (XRD), computational molecular modeling, and an ab initio molecular dynamic. The results show that alpha and beta molecules are sterically barred from forming a direct hydrogen bond with one other. In addition, the presence of the methanol molecule stabilizes the crystal structure by a bifurcated O-H...O interaction acting as a bridge between them. The theoretical thermodynamic parameter and the rigid potential energy surface scan describe the role of methanol in the energy stabilization of the crystal. The absence of the methanol compound in the asymmetric unit destabilizes the crystalline structure, making the formation process of the asymmetric unit nonspontaneous. The energy difference between alpha and beta molecules is around 0.80 kcal.mol super(-1), indicating that both are stable and equally possible in the crystal lattice. The analysis of the energy profile of the C14-O2...H1-O3 and O2-H1...O3-C17 torsion angles in the crystal packing shows that the alpha and beta molecules are confined in the stable potential region, in agreement with the two conformers in the asymmetric unit. The Molecular Electrostatic Potential (MEP) shows that the methanol has no steric effects, which prevents small motion around the torsion angles.