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In methyl 4-(4-chloro­anilino)-3-nitro­benzoate, C14H11ClN2O4, (I), there is an intra­molecular N-H...O hydrogen bond and the intra­molecular distances provide evidence for electronic polarization of the o-quinonoid type. The mol­ecules are linked into sheets built from N-H...O, C-H...O and C-H...[pi](arene) hydrogen bonds, together with an aromatic [pi]-[pi] stacking inter­action. The mol­ecules of methyl 1-benzyl-2-(4-chloro­phenyl)-1H-benzimidazole-5-carboxyl­ate, C22H17ClN2O2, (II), are also linked into sheets, this time by a combination of C-H...[pi](arene) hydrogen bonds and aromatic [pi]-[pi] stacking inter­actions.

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In the mol­ecule of 4-(2-chloro­phenyl)­pyrrolo­[1,2-a]­quinoxa­line, C17H11ClN2, (I), the bond lengths are consistent with electron delocalization in the two outer rings of the fused tricyclic system, with a localized double bond in the central ring. The mol­ecules of (I) are linked into chains by a [pi]-[pi] stacking inter­action. In (4RS)-4-(1,3-benzo­dioxol-6-yl)-4,5-di­­hydro­pyrrolo­[1,2-a]­quinoxaline, C18H14N2O2, (II), the central ring of the fused tricyclic system adopts a conformation inter­mediate between screw-boat and half-chair forms. A combination of N-H...O and C-H...[pi](arene) hydrogen bonds links the mol­ecules of (II) into a sheet. Comparisons are made with related compounds.

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The mol­ecules of both methyl 4-[2-(4-chloro­benzo­yl)hydrazin­yl]-3-nitro­benzoate, C15H12ClN3O5, (I), and methyl 4-[2-(2-fluoro­benzo­yl)hydrazin­yl]-3-nitro­benzoate, C15H12FN3O5, (II), contain an intra­molecular N-H...O hydrogen bond, and both show electronic polarization in the nitrated aryl ring. In both compounds, mol­ecules are linked by a combination of N-H...O and C-H...O hydrogen bonds to form sheets, which are built from R43(18) rings in (I) and from R44(28) rings in (II). In each of methyl 3-phenyl-1,2,4-benzotriazine-6-carboxyl­ate, C15H11N3O2, (III), and methyl 3-(4-methyl­phen­yl)-1,2,4-benzotriazine-6-carboxyl­ate, C16H13N3O2, (IV), the benzotriazine unit shows naphthalene-type delocalization. There are no hydrogen bonds in the structures of compounds (III) and (IV), but in both compounds, the mol­ecules are linked into chains by [pi]-[pi] stacking inter­actions involving the benzotriazine units. The mechanism of chain formation is the same in both (III) and (IV), and the different orientations of the two chains can be related to the approximate relationship between the unit-cell metrics for (III) and (IV).

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In di­benzyl­ammonium hydrogen maleate [or di­benzyl­am­monium (2Z)-3-carb­oxy­prop-2-enoate], C14H16N+·C4H3O4-, (I), the anion contains a fairly short and nearly linear O-H...O hydrogen bond, with an O...·O distance of 2.4603 (16) Å, but with the H atom clearly offset from the mid-point of the O...O vector. The counter-ions in (I) are linked by two N-H...O hydrogen bonds to form C22(6) chains and these chains are weakly linked into sheets by a C-H...O hydrogen bond. Bis(di­benzyl­amino)­methane, C29H30N2, (II), crystallizes with two independent mol­ecules lying across twofold rotation axes in the space group C2/c, and the mol­ecules are conformationally chiral; there are no direction-specific inter­molecular inter­actions in the crystal structure of (II).
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