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The mol­ecules of ethyl 4-(5-amino-3-methyl-1H-pyrazol-1-yl)­benzoate, C13H15N3O2, are linked by two independent N—H...O hydrogen bonds into a chain of edge-fused and alternating R42(8) and R22(20) rings. A combination of N—H...N and N—H...O hydrogen bonds links the mol­ecules of methyl 4-(5-amino-3-tert-butyl-1H-pyrazol-1-yl)benzoate, C15H19N3O2, into sheets of alternating R22(20) and R66(32) rings. In 4-(5-amino-3-methyl-1H-pyrazol-1-yl)benzoic acid monohydrate, C11H11N3O2·H2O, the mol­ecular components are linked into a three-dimensional framework structure by a combination of five independent hydrogen bonds, two of O—H...N type and one each of O—H...O, N—H...O and N—H...N types.

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The bond distances in the title compound, C11H16N4, provide evidence for peripheral delocalization of [pi] electrons. The mol­ecules are linked by two independent N-H...N hydrogen bonds into a three-dimensional framework structure.

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The mol­ecules of 3-tert-butyl-5-[(4-methoxy­benz­yl)amino]-1-phenyl-1H-pyrazole, C21H25N3O, are linked into simple C(9) chains by a single C—H...N hydrogen bond. 5-[(Benzotriazol-1-ylmeth­yl)(4-methoxy­benz­yl)amino]-3-tert-butyl-1-phenyl-1H-pyrazole, C28H30N6O, crystallizes with Z′ = 2 in the space group P21/c. The mol­ecules are weakly linked into centrosymmetric tetra­molecular aggregates by a combination of C—H...N and C—H...O hydrogen bonds.

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The mol­ecules of ethyl 5-amino-1-(4-cyano­phen­yl)-1H-imidazole-4-carboxyl­ate, C13H12N4O2, are linked into a chain of alternating R22(10) and R44(34) rings by a combination of N-H...N and C-H...N hydrogen bonds. In ethyl 5-amino-1-(4-chloro­phen­yl)-1H-imidazole-4-carboxyl­ate, C12H12ClN3O2, where the ethyl group is disordered over two sets of sites, a combination of N-H...O, N-H...N, C-H...N and C-H...[pi](arene) hydrogen bonds links the mol­ecules into complex sheets. Two inter­molecular hydrogen bonds, one each of N-H...N and C-H...O types, link the mol­ecules of ethyl 5-amino-1-(2,6-difluoro­phen­yl)-1H-imidazole-4-carboxyl­ate, C12H11F2N3O2, into a continuous three-dimensional framework structure.

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Mol­ecules of methyl 4-[(5-methyl-1H-pyrazol-3-yl)amino]-3-nitro­benzoate, C12H12N4O4, (I), exhibit a polarized (charge-separated) structure in the nitro­aniline portion. The mol­ecules are linked into chains of edge-fused R22(16) and R22(22) rings by a combination of N-H...O(carbon­yl) and C-H...O(nitro) hydrogen bonds. Methyl 1-(5-methyl-1H-pyrazol-3-yl)-1H-benzimidazole-5-carboxyl­ate, C13H12N4O2, (II), which is readily formed from (I) by reduction followed by ring formation, crystallizes with Z' = 2 in the space group P\overline{1}. Each of the two independent mol­ecular types is linked into sheets of R44(28) rings by a combination of N-H...N and C-H...O(carbon­yl) hydrogen bonds.

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In 2,3-dimethoxy­benzaldehyde isonicotinoyl­hydrazone chloro­form monosolvate, C15H15N3O3·CHCl3, the hydrazone mol­ecules are linked by a combination of N—H...N and C—H...N hydrogen bonds into chains from which the chloro­form mol­ecules are pendent. 3,4,5-Trimethoxy­benzaldehyde isonicotinoyl­hydrazone forms two stoichiometric hydrates. In the monohydrate, C16H17N3O4·H2O, the components are linked into sheets by a combination of O—H...O, O—H...N and N—H...N hydrogen bonds, and in the dihydrate, C16H17N3O4·2H2O, a combination of O—H...O, O—H...N and N—H...O hydrogen bonds links the components into a three-dimensional framework structure.

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The title compound, C15H12N2O3, crystallizes with Z' = 2 in the space group P\overline{1} and the intra­molecular dimensions show evidence for a polarized mol­ecular-electronic structure. Each of the two independent types of mol­ecule forms its own hydrogen-bonded supra­molecular substructure, and these are entirely different from one another: one type of mol­ecule forms a chain of edge-fused rings, while the other type forms sheets.

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There are no direction-specific inter­actions between the mol­ecules of 3-(2-methoxy­benz­yl)-2-(2-methoxy­phen­yl)-1,3-thia­zolidin-4-one, C18H19NO3S, (I); the mol­ecules of 3-(4-nitro­benz­yl)-2-(4-nitro­phen­yl)-1,3-thia­zolidin-4-one, C16H13N3O5S, (II), are linked by four independent C—H...O hydrogen bonds into complex chains of fused rings. In 3-(4-methoxy­benz­yl)-2-(4-methoxy­phen­yl)-1,3-thia­zolidin-4-one, (III), isomeric with (I), the mol­ecules are linked into sheets by a combination of C—H...O and C—H...π(arene) hydrogen bonds, while in 3-(2-nitro­benz­yl)-2-(2-nitro­phen­yl)-1,3-thia­zolidin-4-one, (IV), isomeric with (II), the sheets are built from three independent C—H...O hydrogen bonds and one C—H...π(arene) hydrogen bond, and reinforced by an aromatic π–π stacking inter­action. In 3-(2-fluoro­benz­yl)-2-(2-fluoro­phen­yl)-1,3-thia­zolidin-4-one, C16H13F2NOS, (V), where the 2-aryl ring exhibits orientational disorder, the mol­ecules are linked into sheets by a combination of C—H...O and C—H...π(arene) hydrogen bonds, and the sheets are linked in pairs, forming bilayers, by an aromatic π–π stacking inter­action.

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In the title compound, C14H10N4O·H2O, the mol­ecular components are linked into a three-dimensional framework by three hydrogen bonds, one each of the O—H...O, O—H...N and N—H...O types, weakly augmented by two C—H...O hydrogen bonds.

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The structures of five metal complexes containing the 4-oxo-4H-pyran-2,6-dicarboxyl­ate dianion illustrate the remarkable coordinating versatility of this ligand and the great structural diversity of its complexes. In tetra­aqua­beryllium 4-oxo-4H-pyran-2,6-dicarboxyl­ate, [Be(H2O)4](C7H2O6), (I), the ions are linked by eight independent O—H...O hydrogen bonds to form a three-dimensional hydrogen-bonded framework structure. Each of the ions in hydrazinium(2+) diaqua­(4-oxo-4H-­pyran-2,6-dicarboxyl­ato)calcate, (N2H6)[Ca(C7H2O6)2(H2O)2], (II), lies on a twofold rotation axis in the space group P2/c; the anions form hydrogen-bonded sheets which are linked into a three-dimensional framework by the cations. In bis­(μ-4-oxo-4H-pyran-2,6-dicarboxyl­ato)bis­[tetraaquamanganese(II)] tetra­hydrate, [Mn2(C7H2O6)2(H2O)8]·4H2O, (III), the metal ions and the organic ligands form a cyclic centrosymmetric Mn2(C7H2O6)2 unit, and these units are linked into a complex three-dimensional framework structure containing 12 independent O—H...O hydrogen bonds. There are two independent CuII ions in tetra­aqua­(4-oxo-4H-pyran-2,6-dicarboxyl­ato)­copper(II), [Cu(C7H2O6)(H2O)4], (IV), and both lie on centres of inversion in the space group P\overline{1}; the metal ions and the organic ligands form a one-dimensional coordination polymer, and the polymer chains are linked into a three-dimensional framework containing eight independent O—H...O hydrogen bonds. Diaqua­(4-oxo-4H-pyran-2,6-dicarboxyl­ato)cadmium monohydrate, [Cd(C7H2O6)(H2O)2]·H2O, (V), forms a three-dimensional coordination polymer in which the organic ligand is coordinated to four different Cd sites, and this polymer is inter­woven with a complex three-dimensional framework built from O—H...O hydrogen bonds.

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The structure of the triclinic polymorph of acetone 2,4-dinitrophenylhydrazone, C9H10N4O4, has been redetermined from diffraction data collected at 120 (2) K; the mol­ecules are linked by C-H...O hydrogen bonds into centrosymmetric R22(10) dimers which are themselves linked into a chain by an aromatic [pi]-[pi] stacking inter­action. In the monoclinic polymorph, which crystallizes with Z' = 2 in the space group P21/n, one type of mol­ecule forms dimers exactly as in the triclinic polymorph, while the other forms C(6) chains.

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In ethyl N-[2-(hydroxy­acetyl)phenyl]carbamate, C11H13NO4, all of the non-H atoms lie on a mirror plane in the space group Pnma; the mol­ecules are linked into simple chains by a single C-H...O hydrogen bond. The mol­ecules of ethyl N-[2-(hydroxy­acetyl)-4-iodo­phenyl]carbamate, C11H12INO4, are linked into sheets by a combination of O-H...I and C-H...O hydrogen bonds and a dipolar I...O contact. Ethyl N-­[2-(hydroxy­acetyl)-4-methyl­phenyl]carbamate, C12H15NO4, crystallizes with Z' = 2 in the space group P\overline{1}; pairs of mol­ecules are weakly linked by an O-H...O hydrogen bond and these aggregates are linked into chains by two independent aromatic [pi]-[pi] stacking inter­actions.

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Both 6-(1H-indol-3-yl)-3-methyl-4-(4-methyl­phen­yl)-1-phen­yl-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile and 6-(1H-indol-3-yl)-3-methyl-4-(4-methoxy­phen­yl)-1-phenyl-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile crystallize from dimethyl­formamide solutions as stoichiometric 1:1 solvates, viz. C29H21N5·C3H7NO, (I), and C29H21N5O·C3H7NO, (II), respectively; however, 6-(1H-indol-3-yl)-3-methyl-1-phenyl-4-(3,4,5-trimethoxy­phen­yl)-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile, C31H25N5O3, (III), crystallizes in the unsolvated form. The heterocyclic components of (I) are linked by C—H...π(arene) hydrogen bonds to form cyclic centrosymmetric dimers, from which the solvent mol­ecules are pendent, linked by N—H...O hydrogen bonds. In (II), the heterocyclic components are linked by a combination of C—H...N and C—H...π(arene) hydrogen bonds into chains containing two types of centrosymmetric ring, and the pendent solvent mol­ecules are linked to these chains by N—H...O hydrogen bonds. Mol­ecules of (III) are linked into simple C(12) chains by an N—H...O hydrogen bond, and these chains are weakly linked into pairs by an aromatic π–π stacking inter­action.

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In the title compound, C13H10O4, prepared by the condensation reaction between phthalic anhydride and pentane-2,4-dione, one of the acetyl groups in the pentane-2,4-dione fragment is almost coplanar with the isobenzofuran ring system, while the other group is twisted out of this plane by almost 80°. The corresponding C-C and C-O distances in the two acetyl units are consistent with dipolar delocalization into the coplanar unit only. There is no supra­molecular aggregation of the mol­ecules, but a number of rather short inter­molecular contacts of C-H...O, O...O and O...C types occur.

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In the title compound (systematic name: N-anilino-4-nitro­benzamide), C13H11N3O3, the mol­ecules are linked into a complex three-dimensional framework structure by a combination of two-centre N-H...O and C-H...O hydrogen bonds and a three-centre N-H...(O,N) hydrogen bond.

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The mol­ecules of 2-cyano-4-iodo­acetanilide, C9H7IN2O, are linked by N-H...N and C-H...O hydrogen bonds into chains of alternating R22(12) and R22(14) rings.

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rac-2-Isopropyl-3-(2-nitro­benz­yl)-1,3-thia­diazo­lin-4-one, C13H16N2O3S, is a rare example of a racemate crystallizing in the space group P212121, with one mol­ecule each of S and R configurations, whose conformations are almost mirror images, within the asymmetric unit. The mol­ecules of S configuration are linked by two C-H...O hydrogen bonds into a three-dimensional framework, and the mol­ecules of R configuration are linked by two further C-H...O hydrogen bonds into a different type of three-dimensional framework; the two frameworks are linked by a fifth C-H...O hydrogen bond.

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Tetra­aqua­(18-crown-6)cerium(III) hexa­cyano­ferrate(III) di­hydrate, [Ce(C12H24O6)(H2O)4][Fe(CN)6]·2H2O, and tetra­aqua­(18-crown-6)neodymium(III) hexa­cyano­ferrate(III) dihydrate, [Nd(C12H24O6)(H2O)4][Fe(CN)6]·2H2O, are iso­morphous and isostructural in the C2/c space group, where the cations, which contain ten-coordinate lanthanoid centres, lie across twofold rotation axes and the anions lie across inversion centres. In these compounds, an extensive series of O—H...O and O—H...N hydrogen bonds links the components into a continuous three-dimensional framework. Triaqua­(18-crown-6)lanthanoid(III) hexa­cyano­ferrate(III) di­hydrate, [Ln(C12H24O6)(H2O)3][Fe(CN)6]·2H2O, where Ln = Sm, Eu, Gd or Tb, are all isomorphous and isostructural in the P\overline{1} space group, as are triaqua­(18-crown-6)gadolinium(III) hexa­cyano­chromate(III) dihydrate, [Gd(C12H24O6)(H2O)3][Cr(CN)6]·2H2O, and triaqua­(18-crown-6)gadolinium(III) hexa­cyano­cobaltate(III) dihydrate, [Gd(C12H24O6)(H2O)3][Co(CN)6]·2H2O. In these compounds, there are two independent anions, both lying across inversion centres, and the lanthanoid centres exhibit nine-coordination; in the crystal structures, an extensive series of hydrogen bonds links the components into a three-dimensional framework.

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In both 2,5-dimethyl-6,7-dihydro­benzo[h]pyrazolo[1,5-a]­quinazoline, C16H15N3, (I), and 2-tert-butyl-5-methyl-6,7-dihydro­benzo[h]pyrazolo[1,5-a]quinazoline, C19H21N3, (II), which crystallizes with Z' = 2 in the space group P\overline{1}, the non-aromatic carbocyclic rings adopt screw-boat conformations. The mol­ecules of (I) are linked into chains of rings by a combination of C-H...N and C-H...[pi](arene) hydrogen bonds, while in (II) there are no hydrogen bonds of any kind.

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The mol­ecules of methyl 3-(2-nitro­phenyl­hydrazono)­butan­oate, C11H13N3O4, (I), and methyl 3-(2,4-dinitro­phenyl­hydrazono)butanoate, C11H12N4O6, (II), both prepared from methyl 3-oxobutanoate and the corresponding nitro­phenyl­hydrazine, exhibit polarized mol­ecular electronic structures; in each of (I) and (II), the mol­ecules are linked into chains by a single C-H...O hydrogen bond. The mol­ecules of 5-hydroxy-3-methyl-1-phenyl-1H-pyrazole, C10H10N2O, (III), prepared by the reaction of methyl 3-oxobutanoate and phenyl­hydrazine, are linked into chains by a single O-H...N hydrogen bond. The reaction between methyl 3-oxobutanoate and 3-nitro­phenyl­hydrazine yields 5-hydr­oxy-3-methyl-1-(3-nitro­phen­yl)-1H-pyrazole, (IV), which when crystallized from acetone yields 4-isopropyl­idene-3-methyl-1-(3-nitro­phen­yl)-1H-pyrazol-5(4H)-one, C13H13N3O3, (V).

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In the title compound, C10H19NO6, both rings adopt almost perfect chair conformations and their mutual orientation is influenced by an intra­molecular O—H...N hydrogen bond. The mol­ecules are linked by three independent O—H...O hydrogen bonds into sheets containing equal numbers of R22(10) and R44(24) rings.

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In methyl 4-(5-amino-3-phenyl-1H-pyrazol-1-yl)-3-nitro­benzo­ate, C17H14N4O4, the molecules are linked into complex sheets by a combination of N-H...N, N-H...O and C-H...O hydrogen bonds. In the isomeric methyl 3-nitro-4-[(5-phenyl-1H-pyrazol-3-yl)amino]­benzo­ate, mol­ecules exhibit a polarized mol­ecular-electronic structure and are linked into chains of edge-fused rings by a combination of N-H...O and C-H...O hydrogen bonds.

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The title compounds, namely 6-meth­oxy-3,3-dimethyl-3H-benzo[f]chromene, C16H16O2, (III), and racemic 3-bromo-2,2,6,6-tetra­methyl-3,4-dihydro-2H,6H-1,5-dioxatriphenyl­ene, C20H21BrO2, (IV), were both synthesized in one-step regioselective Wittig reactions from substituted 1,2-naphthoquinones. The new ring in both compounds adopts a screw-boat conformation. A single π–π stacking inter­action links the mol­ecules of (III) into centrosymmetric dimeric aggregates, and a single C—H...π(arene) hydrogen bond links the mol­ecules of (IV) into centrosymmetric dimers.

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The title compound, C30H26ClN3, crystallizes with Z' = 3 in the P\overline{1} space group. The three independent mol­ecules have very similar, although not identical, conformations, with almost perfect screw-boat forms adopted by the non-aromatic carbocyclic rings. Four independent C-H...[pi](arene) hydrogen bonds link the mol­ecules into centrosymmetric six-component aggregates.

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In the title compound, C8H12N+·C4H3O4, there is a short and almost linear but asymmetric O—H...O hydrogen bond in the anion. The ions are linked into C22(6) chains by two short and nearly linear N—H...O hydrogen bonds and the chains are further weakly linked into sheets by a single C—H...O hydrogen bond.

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The title compound [systematic name: 6-amino-5-formyl-1,3-dimethylpyrimidine-2,4(1H,3H)-dione monohydrate], C7H9N3O3·H2O, has been reexamined at 120 K. The improved precision of the intra­molecular dimensions provides evidence for a polarized mol­ecular–electronic structure, and the mol­ecular components are linked by one N—H...O and two O—H...O hydrogen bonds into two inter­woven three-dimensional frameworks, which are weakly linked by the longer component of a three-centre N—H...(O)2 hydrogen bond.

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The mol­ecules of 2-amino-4,6-bis­[N-methyl-N-(4-methyl­phenyl)amino]pyrimidine-5-carbaldehyde, C21H23N5O, (I), and 2-amino-4-(indolin-1-yl)-6-methoxy­pyrimidine-5-carbaldehyde, C14H14N4O2, (II), which crystallizes with Z' = 2 in the space group P\overline{1}, exhibit polarized electronic structures. Mol­ecules of (I) are linked by a combination of N-H...O, C-H...O and C-H...[pi](arene) hydrogen bonds into a three-dimensional framework structure, while those of (II) are linked into sheets by a combination of two N-H...O hydrogen bonds and one N-H...[pi](arene) hydrogen bond.

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The mol­ecular dimensions of both 2-amino-6-(N-methyl­anilino)pyrimidin-4(3H)-one, C11H12N4O, (I), and 2-amino-6-(N-methyl­anilino)-5-nitro­pyrimidin-4(3H)-one, C11H11N5O3, (II), are consistent with considerable polarization of the mol­ecular-electronic structures. The mol­ecules of (I) are linked into a three-dimensional framework by a combination of one N-H...N hydrogen bond, two independent N-H...O hydrogen bonds and one C-H...[pi](arene) hydrogen bond. The mol­ecules of (II) are linked into ribbons containing three types of edge-fused ring by the combination of two independent three-centre N-H...(O)2 hydrogen bonds.

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In the title compound, C23H24N4O3, the pyrimidine ring adopts an almost perfect boat conformation, and the bond distances provide evidence for some polarization of the mol­ecular-electronic structure. Two independent N-H...O hydrogen bonds link the mol­ecules into chains of edge-fused R24(8) and R22(20) rings.
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