Butane-1,4-diammonium bis(perchlorate).

The butane-1,4-diammonium cation of the title compound, C(4)H(14)N(2) (2+)·2ClO(4) (-), lies on a special position of site symmetry 2/m, whereas the perchlorate anion is located on a crystallographic mirror plane. An intricate three-dimensional hydrogen-bonding network exists in the crystal structure with each H atom of the ammonium group exhibiting bifurcated inter-actions to the perchlorate anion. Complex hydrogen-bonded ring and chain motifs are also evident, in particular a 50-membered ring with graph-set notation R(10) (10)(50) is identified.

Ethane-1,2-diammonium dibromide: a redetermination at 100†K.

In the redetermined [for the previous study, see Søtofte (1976 ▶). Acta Chem. Scand. Ser. A, 30, 309-311] crystal structure of the title compound, C(2)H(10)N(2) (2+)·2Br(-), the H atoms have been located and the hydrogen-bonding scheme is described. The ethane-1,2-diammonium cation lies over a crystallographic inversion centre and straddles a crystallographic mirror plane with the C and N atoms in special positions. In the crystal, the cations and anions are linked by N-H⋯Br and N-H⋯(Br,Br) hydrogen bonds, which generate various ring and chain motifs including an R(10) (5)(32) loop.

Penta-carbonyl-2κC-chlorido-1κCl-bis-[1(η)-cyclo-penta-dien-yl](µ-1-oxido-ethyl-ene-1:2κO:C)chromium(0)zirconium(IV).

The title compound, [CrZr(C(5)H(5))(2)(C(2)H(3)O)Cl(CO)(5)], consists of two metal centres, with a (penta-carbonyl-chromium)oxymethyl-carbene group coordinating as a monodentate ligand to the zirconocene chloride. π-Delocalization through the Zr-O-C=Cr unit is indicated by a short Zr-O distance [2.041 (3) Å] and a nearly linear Zr-O-C angle [170.5 (3)°]. Mol-ecules are aligned with their mol-ecular planes (through Zr, Cl, carbene and Cr) parallel to the ab plane. C-H⋯Cl inter-actions result in zigzag chains of mol-ecules propagating parallel to the b axis.

Hexane-1,6-diammonium dinitrate.

The hexane-1,6-diammonium cation of the title compound, C(6)H(18)N(2) (2+)·2NO(3) (-), lies across a crystallographic inversion centre and shows significant deviation from planarity in the hydro-carbon chain. This is evident from the torsion angle of -64.0°(2) along the N-C-C-C bond and thse torsion angle of -67.1°(2) along the C-C-C-C bonds. An intricate three-dimensional hydrogen-bonding network exists in the crystal structure, with each H atom on the ammonium group exhibiting bifurcated inter-actions to the nitrate anion. Complex hydrogen-bonded ring and chain motifs are also evident, in particular a 26-membered ring with graph-set notation R(4) (4)(26) is observed.

Hydrogen-bonding motifs and thermotropic polymorphism in redetermined halide salts of hexamethylenediamine.

The redetermined crystal structures of hexane-1,6-diammonium dichloride, C(6)H(18)N(2)(2+) x 2 Cl(-), (I), hexane-1,6-diammonium dibromide, C(6)H(18)N(2)(2+) x 2 Br(-), (II), and hexane-1,6-diammonium diiodide, C(6)H(18)N(2)(2+) x 2 I(-), (III), are described, focusing on their hydrogen-bonding motifs. The chloride and bromide salts are isomorphous, with both demonstrating a small deviation from planarity [173.89 (10) and 173.0 (2) degrees, respectively] in the central C-C-C-C torsion angle of the hydrocarbon backbone. The chloride and bromide salts also show marked similarities in their hydrogen-bonding interactions, with subtle differences evident in the hydrogen-bond lengths reported. Bifurcated interactions are exhibited between the N-donor atoms and the halide acceptors in the chloride and bromide salts. The iodide salt is very different in molecular structure, packing and intermolecular interactions. The hydrocarbon chain of the iodide straddles an inversion centre and the ammonium groups on the diammonium cation of the iodide salt are offset from the planar hydrocarbon backbone by a torsion angle of 69.6 (4) degrees. All three salts exhibit thermotropic polymorphism, as is evident from differential scanning calorimetry analysis and variable-temperature powder X-ray diffraction studies.

Penta-carbonyl-2κC-chlorido-1κCl-bis-[1(η)-cyclo-penta-dien-yl][µ(2)-oxido(meth-yl)methyl-ene-1:2κO:C]tungsten(0)zirconium(IV).

The title compound, [ZrW(C(5)H(5))(2)(C(2)H(3)O)Cl(CO)(5)] or [W(CO)(5)C(CH(3))OZr(C(5)H(5))(2)Cl], consists of two metal centres, with a (tungsten penta-carbon-yl)oxymethyl-carbene group coordinating as a monodentate ligand to the chloridozirconocene. The two halves of the mol-ecule are related by a crystallographic mirror plane. Delocalization through the Zr-O-C=W unit is indicated by a short Zr-O distance and a nearly linear Zr-O-C angle.

Variable-temperature powder X-ray diffraction of aromatic carboxylic acid and carboxamide cocrystals.

The effect of temperature on the cocrystallization of benzoic acid (BA), pentafluorobenzoic acid (FBA), benzamide (BAm), and pentafluorobenzamide (FBAm) is examined in the solid state. BA and FBA formed a 1:1 complex 1 at ambient temperature by grinding with a mortar and pestle. Grinding FBA and BAm together resulted in partial conversion into the 1:1 adduct 2 at 28 degrees C and complete transformation into the product cocrystal at 78 degrees C. Further heating (80-100 degrees C) and then cooling to room temperature gave a different powder pattern from that of 2. BAm and FBAm hardly reacted at ambient temperature, but they afforded the 1:1 cocrystal 3 by melt cocrystallization at 110-115 degrees C. Both BA+FBAm (4) and BA+BAm (5) reacted to give new crystalline phases upon heating, but the structures of these products could not be determined owing to a lack of diffraction-quality single crystals. The stronger COOH and CONH2 hydrogen-bonding groups of FBA and FBAm yielded the equimolar cocrystal 6 at room temperature, and heating of these solids to 90-100 degrees C gave a new crystalline phase. The X-ray crystal structures of 1, 2, 3, and 6 are sustained by the acid-acid/amide-amide homosynthons or acid-amide heterosynthon, with additional stabilization from phenyl-perfluorophenyl stacking in 1 and 3. The temperature required for complete transformation into the cocrystal was monitored by in situ variable-temperature powder X-ray diffraction (VT-PXRD), and formation of the cocrystal was confirmed by matching the experimental peak profile with the simulated diffraction pattern. The reactivity of H-bonding groups and the temperature for cocrystallization are in good agreement with the donor and acceptor strengths of the COOH and CONH2 groups. It was necessary to determine the exact temperature range for quantitative cocrystallization in each case because excessive heating caused undesirable phase transitions.

Dichlorido(3,5-dimethyl-1H-pyrazole)[(3,5-dimethyl-1H-pyrazol-1-yl)(o-tol-yl)methanone]palladium(II).

In the title compound, [PdCl(2)(C(5)H(8)N(2))(C(12)H(12)N(2)O)], the Pd atom adopts a slightly distorted trans-PdCl(2)N(2) square-planar arrangement. The different Pd-N bond lengths can be related to the the electron-withdrawing effect of the o-toluoyl group on the substituted pyrazole ligand. The complex crystallizes as centrosymmetric hydrogen-bonded dimers through N-H⋯Cl linkages.

Conformational, concomitant polymorphs of 4,4-diphenyl-2,5-cyclohexadienone: conformation and lattice energy compensation in the kinetic and thermodynamic forms.

4,4-Diphenyl-2,5-cyclohexadienone (1) crystallized as four conformational polymorphs and a record number of 19 crystallographically independent molecules have been characterized by low-temperature X-ray diffraction: form A (P2(1), Z'=1), form B (P1, Z'=4), form C (P1, Z'=12), and form D (Pbca, Z'=2). We have now confirmed by variable-temperature powder X-ray diffraction that form A is the thermodynamic polymorph and B is the kinetic form of the enantiotropic system A-D. Differences in the packing of the molecules in these polymorphs result from different acidic C-H donors approaching the C=O acceptor in C-H...O chains and in synthons I-III, depending on the molecular conformation. The strength of the C-HO interaction in a particular structure correlates with the number of symmetry-independent conformations (Z') in that polymorph, that is, a short C-HO interaction leads to a high Z' value. Molecular conformation (Econf) and lattice energy (Ulatt) contributions compensate each other in crystal structures A, B, and D resulting in very similar total energies: Etotal of the stable form A=1.22 kcal mol(-1), the metastable form B=1.49 kcal mol(-1), and form D=1.98 kcal mol(-1). Disappeared polymorph C is postulated as a high-Z', high-energy precursor of kinetic form B. Thermodynamic form A matches with the third lowest energy frame based on the value of Ulatt determined in the crystal structure prediction (Cerius2, COMPASS) by full-body minimization. Re-ranking the calculated frames on consideration of both Econf (Spartan 04) and Ulatt energies gives a perfect match of frame #1 with stable structure A. Diphenylquinone 1 is an experimental benchmark used to validate accurate crystal structure energies of the kinetic and thermodynamic polymorphs separated by <0.3 kcal mol(-1) (approximately 1.3 kJ mol(-1)).