Acta Cryst. (2014). B70, 157-171 [ doi:10.1107/S2052520613034987 ]
Abstract: X-ray crystallographic and computational studies are reported for a series of boranthrenes, substituted with halogen atoms. The role of competitive hydrogen (O-HO, O-HF, C-HO) and halogen (ClCl, OBr, FF) bonding interactions on the molecular arrangement in the crystal structures is discussed. The structural analysis and calculations reveal that the O-HO hydrogen bond in the unsubstituted derivative 5,10-dihydroxy-5,10-dihydroboranthrene, C12H10B2O2, is of moderate strength (ca -20 kJ mol-1), but weaker than that in the related thiophene derivative 4,8-dihydro-4,8-dihydroxy-p-diborino[2,3-b:5,6-b]dithiophene, C8H6B2O2S2 (ca -40 kJ mol-1). This is due to shielding of the OH group by the H atoms in the -position of the boranthrene unit. Structural diversity derived from the flexibility of the O-HO hydrogen bond facilitates the occurrence of other competitive interactions. For instance, in the 1,6-difluoro derivative, C12H8B2F2O2, the crystal packing results from O-HF and FF interactions. In turn, the 1,6-dibromo derivative, C12H8B2Br2O2, is dominated by BrO halogen-bond interactions. In the most interesting case, the 1,6-dichloro derivative, C12H8B2Cl2O2, molecular disorder leads to the formation of two different supramolecular arrangements co-existing in the crystal lattice, one based on the ClCl and C-HO bonds, and the other stabilized by O-HO hydrogen bonds. Calculations performed with density-functional theory (DFT; CRYSTAL09) and PIXEL methodologies show that both lattices are characterized by similar energy values (ca -100 kJ mol-1). A mixed arrangement with random or short-range-ordered molecular orientations can also be expected.
Keywords: hydrogen bonding; halogen bonding; boranthrenes; energy calculations; X-ray structural analysis.
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