Ethyl 4-hydr­oxy-2,6-diphenyl-5-(phenyl­sulfan­yl)pyridine-3-carboxyl­ate and ethyl 2,6-bis­(4-fluoro­phen­yl)-4-hydr­oxy-5-(4-methyl­phenyl­sulfan­yl)pyridine-3-carboxyl­ate: supra­molecular aggregation through C—H...O, C—H...F and C—H...π inter­actions

The title polysubstituted pyridines, ethyl 4-hydroxy-2,6-diphenyl-5-(phenylsulfanyl)pyridine-3-carboxylate, C₂₆H₂₁NO₃S, (I), and ethyl 2,6-bis(4-fluorophenyl)-4-hydroxy-5-(4-methylphenylsulfanyl)pyridine-3-carboxylate, C₂₇H₂₁F₂NO₃S, (II), adopt nearly planar structures. The crystal structure of (I) is stabilized by inter­molecular C—H...O and C—H...π inter­actions. The C—H...O hydrogen bonds generate rings of motifs R₂²(14) and R₂²(20). The crystal structure of (II) is stabilized by inter­molecular C—H...F and C—H...π inter­actions. The C—H...F bond generates a linear chain of motif C(14). In addition, in (I) and (II), intra­molecular O—H...O inter­actions generating a graph-set motif S(6) are found. No significant aryl–aryl or π–π inter­actions exist in these structures.

Lamellar aggregation and hydrogen-bonding motifs in 3-(amino­carbon­yl)­pyridinium perchlorate and hydrogen oxalate

In the title compounds, C₆H₇N₂O⁺·ClO₄⁻, (I), and C₆H₇N₂O⁺·C₂HO₄⁻, (II), the carboxamide plane is twisted from the plane of the protonated pyridine ring. Lamellar or sheet-like structural features are observed through N—H...O and O—H...O hydrogen-bonded motifs of cations and anions in (I) and (II), respectively. These sheets are aggregated through C(4) and C(5) chain motifs in (I) and (II), respectively. R₁²(4) ring motifs in (I) and R₁²(5) motifs in (II) are formed via pyridine–anion bifurcated N—H...O inter­actions. In (II), carboxamide groups form N—H...O dimers around the inversion centres of the unit cell, with R₂²(8) ring motifs. A 2₁ screw-related helical or ribbon-like structure along the b axis is formed in (II) through carboxamide and pyridinium N—H...O hydrogen bonds with the oxalate anions.

Hydrogen-bonding features in the 1:2 adduct of 4-amino­benzoic acid and L-proline

The title adduct, 4-amino­benzoic acid–L-proline–water (1/2/1), C₇H₇NO₂·2C₅H₉NO₂·H₂O, contains two independent proline chains with a C(5) motif, each of the head-to-tail type and each held together by N—H...O hydrogen bonds, propagated parallel to the b and c axes of the unit cell. Thus, the proline residues aggregate parallel to the ac plane. 4-Amino­benzoic acid (PABA) residues are arranged on both sides of the proline aggregate and are connected through water O atoms, which act as acceptors for PABA and as hydrogen-bond donors to the amino acids. The characteristic features of PABA, viz. twisting of the carboxyl plane from the aromatic ring and the formation of a head-to-tail chain motif [C(8)] along the b axis, are observed. A distinct feature of the structure is that no proton transfer occurs between proline and PABA.

(R)-3,5-Bis[(E)-benzyl­idene]-1-(1-phen­yl­ethyl)piperidin-4-one, 3,5-bis­[(E)-4-chloro­benzyl­idene]-1-[(R)-1-phenyl­ethyl]piperidin-4-one and 3,5-bis­[(E)-2-chloro­benzyl­idene]-1-[(R)-1-phenyl­ethyl]piperidin-4-one

Polysubstituted piperidones, viz. the title compounds, C₂₇H₂₅NO, (I), C₂₇H₂₃Cl₂NO, (II), and C₂₇H₂₃Cl₂NO, (III), adopt sofa conformations. The mol­ecular packing in (I) and (II) is a result of van der Waals inter­actions, whereas in (III), a C—H...O inter­action is also found.

4-Carboxy­anilinium (2R,3R)-tartrate and a redetermination of the α-polymorph of 4-amino­benzoic acid

In the title compounds, 4-carboxy­anilinium (2R,3R)-tartrate, C₇H₈NO₂⁺·C₄H₅O₆⁻, (I), and 4-amino­benzoic acid, C₇H₇NO₂, (II), the carboxyl planes of the 4-carboxy­anilinium cations/4-amino­benzoic acid are twisted from the aromatic plane. In (I), the characteristic head-to-tail inter­actions are observed through the tartrate anions, forming two C₂²(7) chain motifs propagating parallel to the a and c axes of the unit cell. Also, the tartrate anions are connected through two primary C₁¹(6) and C₁¹(7) chain motifs, leading to a secondary R₄⁴(22) ring motif. In (II), head-to-tail inter­action is seen through a discrete D₁¹(2) motif and carboxyl group dimerization is observed through centrosymmetrically related R₂²(8) motifs around the inversion centres of the unit cell. The crystal structures of both compounds are stabilized by intricate three-dimensional hydrogen-bonding networks. Alternate hydro­phobic and hydro­philic layers are observed in (I) as a result of a column-like arrangement of the anions and the aromatic rings of the cations.

1′-Methylcyclooctane-1-spiro-3′-pyrrolidine-2′-spiro-3′′-indoline-2,2′′-dione and 1,1′-dimethylpiper­idine-3-spiro-3′-pyrrolidine-2′-spiro-3′′-indoline-2′′,4-dione

In both title compounds, C₁₉H₂₄N₂O₂, (I), and C₁₇H₂₁N₃O₂, (II), respectively, there are two mol­ecules in the asymmetric unit and the pyrrolidine rings adopt envelope conformations. The conformations of the cyclo­octane [in (I)] and 1-methyl­piperidone [in (II)] rings are boat–chair and chair, respectively. The indolin-2-one group is almost perpendicular to the pyrrolidine ring. Inter­molecular C—H...O, N—H...O and N—H...N inter­actions provide stability to the structures.