Solids modeled by ab initio crystal field methods. Part 19. Structure of yellow and light yellow form of dimethyl 3,6-dichloro-2, 5-dihydroxyterephthalate

Dimethyl 3,6-dichloro-2,5-dihydroxyterephthalate is known for its color pol ymorphism in the solid state. For the yellow and light yellow form of this compound the geometry has been optimized using a supermolecule (SM) model. A cluster including the central molecule and the 14 nearest neighboring mol ecules was described by an ab initio Hartree-Fock wave function. This clust er was surrounded by other molecules represented by point charges placed at the atomic positions. The radius of the complete model was approximately 2 0 Angstrom. The geometry of dimethyl 3,6-dichloro-2,5-dihydroxyterephthalat e in the solid state has been compared to the optimized geometry of an isol ated molecule in order to identify the crystal field effects. The structura l differences between both polymorphic forms are well described using the S M model, The influence of the intermolecular interactions on the electron d istribution of the individual molecules has been studied using the cluster deformation electron density distribution. (C) 2001 Elsevier Science B.V. A ll rights reserved.