Halogen...halogen contacts for the stabilization of a new polymorph of 9,10-dichloroanthracene

A new polymorph of 9,10-dichloroanthracene (9,10-DCA) namely as 'gama' form, was obtained. The crystal structure of the 'gama' polymorphic system showed an orthorhombic P212121 space group with a = 3.8957(2) Å, b = 15.9383(5) Å, c = 17.3107(7) Å, α = β = 'gama' = 90° , while the other polymorphs, α and β, crystallized in P21/a and P-1 ones, respectively. The intermolecular geometries of 'gama' form were analyzed showing that the crystalline self-assembly of this new polymorph of the 9,10-DCA is stabilized by nonclassical C-H...Cl hydrogen bonds, π-π stacking interactions, and mainly by Cl...Cl interactions. Structural parameters confirmed the halogen...halogen contacts correspond to the Type II geometry. Complementary, electronic structure calculations were performed in other to estimate the energetic contribution of the observed intermolecular interactions in the crystal packing of the new system. Density Functional Theory (DFT) considering empirical dispersion corrections (named as DFT-D) and MP2 correlated very well and showed energy values according to previously reported related compounds (e.g., the energy for the Cl...Cl is -5.37 and -3.25 kcal mol-1 for MP2/6-31+G** and B2PLYP-D/6-31+G**, respectively). On the other hand, and as expected, DFT using B3LYP as functional was not able to describe properly the studied intermolecular interactions. Moreover, it even predicts repulsive energies for most of the analyzed arrangements.UBACyT (W583)FonCyT (PICT 2010-2649)CONICET (PIP 112-201001-00125)CNPqCAPESFAPESP (09/08131-1