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1,4-Dibromobenzene melts at a considerably higher temperature than the 1,2- and 1,3-isomers. This melting-point difference is consistent with the molecular symmetry, as described by Carnelley's rule, and with the frequency of Br...Br halogen bonds. The lowest melting point of 1,3-dibromobenzene correlates with its two symmetry-independent molecules, indicating their inability to pack closely. Single crystals of 1,2- and 1,3-dibromobenzene have been grown under isochoric conditions in a diamond-anvil cell and at isobaric conditions in a glass capillary. Their structures have been determined in situ by X-ray diffraction. At 295 K 1,2-dibromobenzene crystallizes at 0.2 GPa as orthorhombic, space group Pbca, Z′ = 1, and 1,3-dibromobenzene at 0.3 GPa as orthorhombic, space group P212121, Z′ = 2. The same crystal phases are formed at ambient pressure by freezing these liquids below 256.15 and 248.45 K, respectively. The third isomer, 1,4-dibromobenzene, is a solid at room temperature and crystallizes as monoclinic, space group P21/ a. Striking relations between the structures and melting points of the corresponding dibromobenzene and dichlorobenzene isomers have been discussed. [ABSTRACT FROM AUTHOR]

Two phase transitions in compressed benzimidazole polymorphsreveala remarkable interplay of the H-site in NH···N hydrogen-bondedaggregates and the crystal structure. The ambient-pressure polar polymorphα, space group Pna21, at p1= 0.26 GPa transforms into centrosymmetricphase β, space group Pccn, and above p2= 2.26 GPa into another centrosymmetric polymorphγ, space group Pbca. Single crystals of formsα, β, and γ have been in situgrownin isothermal and isochoric conditions in a diamond-anvil cell, andtheir structures were determined by X-ray diffraction. Both at p1and p2the H-bonddistance N···N increases in the higher-pressure phase.However, the H-atom always assumes the site for which the H···Ndistance in the homoconjugated NH···N bond is shorter. [ABSTRACT FROM AUTHOR]

Abstract: Intermolecular interactions and the role of fluorine substitution have been investigated for a halogenated-ethane anesthetic. 2-Bromo-2-chloro-1,1,1-trifluoroethane, BrClCHCF3 (Halothane), has been in situ pressure frozen in a diamond anvil cell and its structure determined by single-crystal X-ray diffraction at 1.85(5)GPa/296K. Crystal is triclinic, space group . In this racemic structure the enantiomorphic molecules are substitutionally disordered at the same general positions in that way that bromine and chlorine atoms occupy the same site at the 50:50 ratio. Despite the fact that only the Br and Cl atoms are disordered, the crystal packing is dominated by halogen⋯halogen and halogen⋯hydrogen interactions. This X-ray diffraction study provides structural explanation of considerably increased vapor pressure of Halothane compared to its hydrogenated analogue. [Copyright &y& Elsevier]

Reports on the third polymorph (MH3) of maleic hydrazide, studied by X-ray diffraction and shown to be monoclinic, space group P2[sub 1]/n. Finding that the polymorph MH3 is the prevailing form along with the rare triclinic polymorph MH1; Accommodation of the supramolecular conformations to the requirements of close pacing of the aggregates in crystal lattices.

The molecular structure of 1,2-di(3-hydroxymethylpyridinium)ethane dibromide ( 1 ) has been characterized by X-ray diffraction, B3LYP/6-311++G(d,p) calculations, FTIR, Raman and NMR spectra. The crystals are monoclinic, space group C2/c . 1,2-Di(3-hydroxymethylpyridinium)ethane dication and hydrogen-bonded bromide anions in crystals are located at the inversion center. The both CH 2 OH groups are engaged in two equal length hydrogen bonds with bromide anions. Two structures ( 2 ) and ( 3 ) were optimized at the B3LYP/6-311++G(d,p) level of theory. The optimized complex ( 2) resembles the crystal structure, while complex ( 3 ) is preferred energetically. The O⋯Br − hydrogen bonds distances are: 3.289(2) Å in crystals ( 1 ), but in the optimized structures ( 2 ) and ( 3 ) they are 3.303 Å and 3.461 Å, respectively. The investigated complex is additionally stabilized by the N + ⋯Br − electrostatic attractions. The potential energy distributions (PED) were used for the assignments of IR and Raman frequencies in the experimental and calculated spectra of the title compound. The FTIR spectrum of ( 1 ) is consistent with the X-ray results. Interpretation of the 1 H and 13 C NMR spectra in DMSO- d 6 has been based on 2D experiments. The calculated GIAO/B3LYP/6-311++G(d,p) magnetic shielding constants have been used to predict 1 H and 13 C chemical shifts for the optimized structures of ( 2 ) and ( 3 ). [ABSTRACT FROM AUTHOR]