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1.  Conformation and crystal structures of 1-amino­cyclo­hexa­neacetic acid (β3,3Ac6c) in N-protected derivatives1  
The gauche conformation of backbone torsion angles (ϕ, θ) for β3,-Ac6c-OH is observed in the N-protected derivatives of 1-amino­cyclo­hexa­neacetic acid.
N-Protected derivatives of 1-amino­cyclo­hexa­neacetic acid (β3,3-Ac6c), namely Valeroyl-β3,3-Ac6c-OH [2-(1-pentanamidocyclohexyl)acetic acid, C13H23NO3], (I), Fmoc-β3,3-Ac6c-OH [2-(1-{[(9H-fluoren-9-yloxy)carbonyl]amino}cyclohexyl)acetic acid, C23H25NO4], (II), and Pyr-β3,3-Ac6c-OH {2-[1-(pyrazine-2-amido)cyclohexyl]acetic acid, C13H17N3O3}, (III), were synthesized and their conformational properties were determined by X-ray diffraction analysis. The backbone torsion angles (ϕ, θ) for β3,3-Ac6c-OH are restricted to gauche conformations in all the derivatives, with a chair conformation of the cyclo­hexane ring. In the crystal structure of (I), the packing of mol­ecules shows both carb­oxy­lic acid R 2 2(8) O—H⋯O and centrosymmetric R 2 2(14) N—H⋯O hydrogen-bonding inter­actions, giving rise to chains along the c-axis direction. In (II), centrosymmetric carb­oxy­lic acid R 2 2(8) O—H⋯O dimers are extended through N—H⋯O hydrogen bonds and together with inter-ring π–π inter­actions between Fmoc groups [ring centroid distance = 3.786 (2) Å], generate a layered structure lying parallel to (010). In the case of compound (III), carb­oxy­lic acid O—H⋯Npyrazine hydrogen bonds give rise to zigzag ribbon structures extending along the c-axis direction.
doi:10.1107/S1600536814020777
PMCID: PMC4257263  PMID: 25484721
crystal structure; disubstituted-β-amino acids; π–π inter­action; hydrogen bonds; conformation
2.  Dimethyl 7-meth­oxy­tetra­cyclo­[6.4.0.02,4.03,7]dodeca-1(12),5,8,10-tetra­ene-3,4-dicarboxyl­ate 
The title compound, C17H16O5, is a previously unreported substituted semibulvalene cage compound (that is, a tricyclic hydro­carbon formed from one cyclo­propane and two cyclo­pentene rings which also has one double bond fused to a benzene ring). It has one meth­oxy substituent attached to the bridgehead C atom that links only the two cyclo­pentene rings and two methyl carboxyl­ate groups located on the C atom shared by all three non-benzene rings and that shared only between the cyclo­propane and the cyclo­pentene rings. The stereochemistry of the two enanti­omers (racemate) that assemble in each unit cell is RRRS and SSSR. In the crystal, mol­ecules are linked via C—H⋯O hydrogen bonds and C—H⋯π inter­actions, forming double-layered sheets lying perpendicular to the a axis.
doi:10.1107/S1600536812037233
PMCID: PMC3470198  PMID: 23125642
3.  Crystal structure of 8-[7,8-bis­(4-chloro­benzo­yl)-7H-cyclo­penta­[a]ace­naphthylen-9-yl]naphthalene-1-carb­oxy­lic acid 
The title compound packs with a three-dimensional supra­molecular architecture via O—H⋯O, C—H⋯O and C—H⋯Cl hydrogen bonds and through C—H⋯π inter­actions.
The title compound, C40H22Cl2O4, was formed by a Michael–Aldol domino reaction sequence, which coupled acenaphthene­quinone with 4-chloro­aceto­phenone in the presence of KOH in methanol. The dihedral angles between the central cyclo­penta­[a]ace­naphthyl­ene fused-ring system (r.m.s. deviation = 0.066 Å) and the 4-chloro­benzoyl rings are 62.25 (10) and 70.19 (10)°. The dihedral angle between the central ring system and the naphthoic acid grouping is 62.46 (7)°. This twisting of the pendant rings facilitates the formation of an intra­molecular aromatic π–π stacking inter­action between the 4-chloro­benzoyl and naphthoic acid rings, with centroid–centroid distances of 3.4533 (16) and 3.5311 (16) Å, and a C—H⋯π inter­action between one of the H atoms of the central moiety and the 4-chloro­benzoyl ring with an H⋯π distance of 2.57 Å. In the crystal, carb­oxy­lic acid inversion dimers generate R 2 2(8) loops. The dimers are linked by weak C—H⋯O and C—H⋯Cl hydrogen bonds and C—H⋯π inter­actions, generating a three-dimensional architecture.
doi:10.1107/S2056989014026334
PMCID: PMC4331862
crystal structure; domino reaction; acenaphthene­quinone; 4-chloro­aceto­phenone; hydrogen bonding
4.  Benzene-1,2,4,5-tetra­carb­oxy­lic acid bis­(1,3,7-trimethyl-2,3,6,7-tetra­hydro-1H-purine-2,6-dione) 
The asymmetric unit of the title co-crystal, C10H6O8·2C8H10N4O2, comprises a centrosymmetric benzene-1,2,4,5-tetra­carb­oxy­lic acid (LH4) mol­ecule and a mol­ecule of caffeine in a general position. LH4 is nonplanar, with the dihedral angles between the ring and pendent carb­oxy­lic acid groups being 44.22 (7) and 49.74 (7)°. By contrast, the caffeine mol­ecule is planar (r.m.s. deviation = 0.040 Å). Supra­molecular layers parallel to (-1-10) are sustained by carb­oxy­lic acid O—H⋯O(carbon­yl) and O—H⋯N(imidazole) hydrogen bonds, as well as by meth­yl–carbonyl C—H⋯O inter­actions. These stack via π–π inter­actions between the benzene and imidazole rings [inter-centroid distance = 3.4503 (10) Å].
doi:10.1107/S1600536813022563
PMCID: PMC3884421  PMID: 24427071
5.  4-Meth­oxy­anilinium 2-carb­oxy-4,5-di­chloro­benzoate 
In the title salt C7H10NO+·C8H3Cl2O4 − the benzene rings of the cation and anion are essentially parallel [inter-ring dihedral angle 4.8 (2)°]. In the anion the carb­oxy­lic acid and carboxyl­ate groups make dihedral angles of 19.0 (2) and 79.5 (2)°, respectively, with the benzene ring. Aminium N—H⋯O, carb­oxy­lic acid O—H⋯O and weak aromatic C—H⋯O hydrogen-bonding associations with carboxyl O-atom acceptors together with cation–anion π–π ring inter­actions [minimum ring centroid separation = 3.734 (3) Å] give rise to a sheet structure lying parallel to (001).
doi:10.1107/S1600536813025014
PMCID: PMC3790412  PMID: 24098231
6.  4-(4-Nitro­benz­yl)pyridinium 3-carb­oxy-4-hy­droxy­benzene­sulfonate 
In the title salt, C12H11N2O2 +·C7H5O6S−, the dihedral angle between the benzene and pyridine rings in the 4-(4-nitro­benz­yl)pyridinium cation is 82.7 (2)°. Within the anion there is an intramolecular hydroxy-O—H⋯O(carboxylic acid) bond. In the crystal, the cation forms a single N+—H⋯Osulfonate hydrogen bond with the anion. These cation–anion pairs inter­act through duplex anion carb­oxy­lic acid O—H⋯Osulfonate hydrogen bonds, giving a centrosymmetric cyclic association [graph set R 2 2(16)]. The crystals studied were non-merohedrally twinned.
doi:10.1107/S1600536813000093
PMCID: PMC3569266  PMID: 23424489
7.  2-Carb­oxy-6-(quinolin-1-ium-8-yl­oxy)benzoate 
In the zwitterionic title compound, C17H11NO5, the dihedral angle between the two aromatic rings is 76.90 (7)°. The dihedral angles between the carboxyl groups and the benzene ring are 64.02 (9) and 21.67 (9)°, the larger angle being associated with an intra­molecular N—H⋯Ocarbox­yl hydrogen bond, resulting from proton transfer from the carb­oxy­lic acid group to the quinoline N atom and giving an S(9) ring motif. In the crystal, mol­ecules are connected by O—H⋯O hydrogen bonds into chains extending along the b-axis direction. An overall two-dimensional network structure is formed through π–π inter­actions between the quinoline rings [minimum ring-centroid separation = 3.6068 (6) Å].
doi:10.1107/S1600536812013980
PMCID: PMC3344484  PMID: 22590246
8.  Crystal structures of the co-crystalline adduct 5-(4-bromo­phen­yl)-1,3,4-thia­diazol-2-amine–4-nitro­benzoic acid (1/1) and the salt 2-amino-5-(4-bromo­phen­yl)-1,3,4-thia­diazol-3-ium 2-carb­oxy-4,6-di­nitro­phenolate 
The hydrogen-bonded structures of both a (1:1) mol­ecular adduct and a salt of 5-(4-bromo­phen­yl)-1,3,4-thia­diazol-2-amine with 4-nitro­benzoic acid and 3,5-di­nitro­salicylic acid, respectively, have been determined.
The structures of the 1:1 co-crystalline adduct C8H6BrN3S·C7H5NO4, (I), and the salt C8H7BrN3S+·C7H3N2O7 −, (II), obtained from the inter­action of 5-(4-bromo­phen­yl)-1,3,4-thia­diazol-2-amine with 4-nitro­benzoic acid and 3,5-di­nitro­salicylic acid, respectively, have been determined. The primary inter-species association in both (I) and (II) is through duplex R 2 2(8) (N—H⋯O/O—H⋯O) or (N—H⋯O/N—H⋯O) hydrogen bonds, respectively, giving heterodimers. In (II), these are close to planar [the dihedral angles between the thia­diazole ring and the two phenyl rings are 2.1 (3) (intra) and 9.8 (2)° (inter)], while in (I) these angles are 22.11 (15) and 26.08 (18)°, respectively. In the crystal of (I), the heterodimers are extended into a chain along b through an amine N—H⋯Nthia­diazole hydrogen bond but in (II), a centrosymmetric cyclic hetero­tetra­mer structure is generated through N—H⋯O hydrogen bonds to phenol and nitro O-atom acceptors and features, together with the primary R 2 2(8) inter­action, conjoined R 4 6(12), R 2 1(6) and S(6) ring motifs. Also present in (I) are π–π inter­actions between thia­diazole rings [minimum ring-centroid separation = 3.4624 (16) Å], as well as short Br⋯Onitro inter­actions in both (I) and (II) [3.296 (3) and 3.104 (3) Å, respectively].
doi:10.1107/S1600536814021138
PMCID: PMC4257302  PMID: 25484726
5-substituted-2-amino-1,3,4-thia­diazo­les; 4-nitro­benzoic acid; 3,5-di­nitro­salicylic acid; proton transfer; mol­ecular adducts; co-crystals; hydrogen bonding; π–π inter­actions; crystal structure
9.  Acrinathrin: (S)-cyano­(3-phen­oxy­phenyl)methyl (Z)-(1R,3S)-2,2-dimethyl-3-{2-[2,2,2-trifluoro-1-(trifluoro­methyl)eth­oxy­carbon­yl]vin­yl}cyclo­propane-1-carboxyl­ate 
In the title compound, C26H21F6NO5, the dihedral angle between the cyclo­propane ring plane and the vinyl group plane is 79.3 (3)°. The dihedral angle between the benzene and phenyl ring planes in the phen­oxy­benzyl group is 82.7 (1)°. In the crystal structure, weak inter­molecular C—H⋯π inter­actions and C—H⋯F hydrogen bonds contribute to the stabilization of the packing.
doi:10.1107/S1600536811014760
PMCID: PMC3089073  PMID: 21754558
10.  Benzamidinium 2-meth­oxy­benzoate 
The title mol­ecular salt, C7H9N2 +.C8H7O3 −, was synthesized by reaction between benzamidine (benzene­carboximidamide) and 2-meth­oxy­benzoic acid. In the cation, the amidinium group has two similar C—N bonds [1.3070 (17) and 1.3145 (16) Å] and is almost coplanar with the benzene ring, making a dihedral angle of 5.34 (12)°. In the anion, the meth­oxy substituent forces the carboxyl­ate group to be twisted by 69.45 (6)° with respect to the plane of the aromatic fragment. In the crystal, the components are connected by two N+—H⋯O− (±)CAHB (charge-assisted hydrogen bonds), forming centrosymmetric ionic dimers with graph-set motif R 2 2(8). These ionic dimers are then joined in ribbons running along the b-axis direction by another R 4 2(8) motif involving the remaining N+—H⋯O− hydrogen bonds. Remarkably, at variance with the well known carb­oxy­lic dimer R 2 2(8) motif, the carboxyl­ate–amidinium pair is not planar, the dihedral angle between the planes defined by the CN2 + and CO2 − atoms being 18.57 (12)°.
doi:10.1107/S1600536813016395
PMCID: PMC3770387  PMID: 24046672
11.  rac-4-Carbamoylpiperidinium cis-2-car­boxy­cyclo­hexane-1-carboxyl­ate 
In the title racemic salt, C6H13N2O+·C8H11O4 −, formed from the reaction of cis-cyclo­hexane-1,2-dicarb­oxy­lic anhydride with isonipecotamide, the cations are linked into duplex chain substructures through both centrosymmetric cyclic head-to-head ‘amide motif’ hydrogen-bonding associations [graph set R 2 2(8)] and ‘side-by-side’ R 2 2(14) associations. The anions are incorporated into the chains through cyclic R 4 3(10) inter­actions involving amide and piperidinium N—H⋯Ocarbox­yl hydrogen bonds which, together with inter-anion carb­oxy­lic acid O—H⋯Ocarbox­yl hydrogen bonds, give a two-dimensional layered structure extending along (011).
doi:10.1107/S1600536812004710
PMCID: PMC3295451  PMID: 22412562
12.  Crystal structures and hydrogen bonding in the co-crystalline adducts of 3,5-di­nitro­benzoic acid with 4-amino­salicylic acid and 2-hy­droxy-3-(1H-indol-3-yl)propenoic acid 
The crystal structures of the co-crystal adducts of 3,5-di­nitro­benzoic acid with 4-amino­salicylic acid (a 2:2:0.4-hydrate) and with 2-hy­droxy-3-(1H-indol-3-yl)propenoic acid (a 1:1:1 d 6-DMSO solvate) show, respectively, polymeric and hexa­molecular hydrogen-bonded and π–π-bonded structures
The structures of the co-crystalline adducts of 3,5-di­nitro­benzoic acid (3,5-DNBA) with 4-amino­salicylic acid (PASA), the 1:1 partial hydrate, C7H4N2O6·C7H7NO3·0.2H2O, (I), and with 2-hy­droxy-3-(1H-indol-3-yl)propenoic acid (HIPA), the 1:1:1 d 6-dimethyl sulfoxide solvate, C7H4N2O6·C11H9NO3·C2D6OS, (II), are reported. The crystal substructure of (I) comprises two centrosymmetric hydrogen-bonded R 2 2(8) homodimers, one with 3,5-DNBA, the other with PASA, and an R 2 2(8) 3,5-DNBA–PASA heterodimer. In the crystal, inter-unit amine N—H⋯O and water O—H⋯O hydrogen bonds generate a three-dimensional supra­molecular structure. In (II), the asymmetric unit consists of the three constituent mol­ecules, which form an essentially planar cyclic hydrogen-bonded heterotrimer unit [graph set R 3 2(17)] through carboxyl, hy­droxy and amino groups. These units associate across a crystallographic inversion centre through the HIPA carb­oxy­lic acid group in an R 2 2(8) hydrogen-bonding association, giving a zero-dimensional structure lying parallel to (100). In both structures, π–π inter­actions are present [minimum ring-centroid separations = 3.6471 (18) Å in (I) and 3.5819 (10) Å in (II)].
doi:10.1107/S1600536814019898
PMCID: PMC4257166  PMID: 25484647
co-crystal structures; carb­oxy­lic acid mol­ecular adducts; 3,5-di­nitro­benzoic acid; 4-amino­salicylic acid; 2-hy­droxy-3-(1H-indol-3-yl)propenoic acid; hydrogen bonding; homodimers; heterodimers; π–π inter­actions.
13.  rac-cis-Cyclo­hexane-1,2-dicarb­oxy­lic acid–isoquinoline (1/1) 
In the crystal structure of the title mol­ecular adduct, C9H7N·C8H12O4, the two species are ­linked through a carb­oxy­lic acid–isoquinoline O—H⋯N hydrogen bond. These mol­ecular pairs then inter-associate through the second acid group of the cis-cyclo­hexane-1,2-dicarb­oxy­lic acid molecules, forming a classic centrosymmetric cyclic head-to-head carb­oxy­lic acid–carboxyl O—H⋯O hydrogen-bonding association [graph-set R 2 2(8)], giving a zero-dimensional (cluster) structure, consisting of two of each species.
doi:10.1107/S1600536811030613
PMCID: PMC3200759  PMID: 22058919
14.  rac-2-Amino­pyridinium cis-2-carb­oxy­cyclo­hexane-1-carboxyl­ate 
In the structure of the title compound, C5H7N2 +·C8H11O4 −, the cis anions associate through head-to-tail carb­oxy­lic acid–carboxyl O—H⋯O hydrogen bonds [graph set C(7)], forming chains which extend along c and are inter­linked through the carboxyl groups, forming cyclic R 2 2(8) associations with the pyridinium and an amine H-atom donor of the cation. Further amine–carboxyl N—H⋯O inter­actions form enlarged centrosymmetric rings [graph set R 4 4(18)] and extensions down b, giving a three-dimensional structure.
doi:10.1107/S1600536811025256
PMCID: PMC3212294  PMID: 22090951
15.  4-[(4-Methyl­benzene­sulfonamido)­meth­yl]cyclo­hexa­necarb­oxy­lic acid 
The title compound, C15H21NO4S, crystallized with two independent mol­ecules in the asymmetric unit in which the dihedral angles between the mean planes of the benzene and cyclo­hexane rings are 78.3 (2) and 67.6 (2)°. The substituents of the cyclo­hexyl rings are in equatorial orientations. In the crystal, both mol­ecules form R 2 2(6) carb­oxy­lic acid inversion dimers via pairs of O—H⋯O hydrogen bonds. Further N—H⋯O and C—H⋯O inter­actions generate a three-dimensional network.
doi:10.1107/S1600536811020083
PMCID: PMC3151904  PMID: 21836976
16.  Crystal structures and hydrogen bonding in the proton-transfer salts of nicotine with 3,5-di­nitro­salicylic acid and 5-sulfosalicylic acid 
The crystal structures of the 1:1 salts of nicotine with 3,5-di­nitro­salicylic acid and with 5-sulfosalicylic acid both show polymeric hydrogen-bonded and π–π-bonded structures but these differ in that in the first example, cations and anions form separate cation chains or anion columns which are unassociated through formal hydrogen bonds while in the second, hydrogen-bonded cation–anion chains are found.
The structures of the 1:1 anhydrous salts of nicotine (NIC) with 3,5-di­nitro­salicylic acid (DNSA) and 5-sulfosalicylic acid (5-SSA), namely (1R,2S)-1-methyl-2-(pyridin-3-yl)-1H-pyrrolidin-1-ium 2-carb­oxy-4,6-di­nitro­phenolate, C10H15N2 +·C7H3N2O7 −, (I), and (1R,2S)-1-methyl-2-(pyridin-3-yl)-1H-pyrrolidin-1-ium 3-carb­oxy-4-hy­droxy­benzene­sulfonate, C10H15N2 +·C7H5O6S−, (II), are reported. The asymmetric units of both (I) and (II) comprise two independent nicotinium cations (C and D) and either two DNSA or two 5-SSA anions (A and B), respectively. One of the DNSA anions shows a 25% rotational disorder in the benzene ring system. In the crystal of (I), inter-unit pyrrolidinium N—H⋯Npyridine hydrogen bonds generate zigzag NIC cation chains which extend along a, while the DNSA anions are not involved in any formal inter-species hydrogen bonding but instead form π–π-associated stacks which are parallel to the NIC cation chains along a [ring-centroid separation = 3.857 (2) Å]. Weak C—H⋯O inter­actions between chain substructures give an overall three-dimensional structure. In the crystal of (II), A and B anions form independent zigzag chains with C and D cations, respectively, through carb­oxy­lic acid O—H⋯Npyridine hydrogen bonds. These chains, which extend along b, are pseudocentrosymmetrically related and give π–π inter­actions between the benzene rings of anions A and B and the pyridine rings of the NIC cations C and D, respectively [ring centroid separations = 3.6422 (19) and 3.7117 (19) Å]. Also present are weak C—H⋯O hydrogen-bonding inter­actions between the chains, giving an overall three-dimensional structure.
doi:10.1107/S1600536814023253
PMCID: PMC4257264  PMID: 25484766
crystal structure; nicotine; proton-transfer salts; 3,5-di­nitro­salicylic acid; 5-sulfosalicylic acid; hydrogen-bonding; π–π inter­actions
17.  3-Acet­oxy-2-naphthoic acid 
In the title compound, C13H10O4, an analog of acetyl­salicylic acid, the naphthalene unit is twisted slightly due to ortho disubstitution [dihedral angle between conjugated rings system in the naphthalene unit = 2.0 (2)°]. The mean planes of the carb­oxy­lic and ester groups are almost coplanar and perpendicular, respectively, to the mean plane of the conjugated aromatic system, making dihedral angles of 8.9 (3) and 89.3 (1)°. In the crystal, mol­ecules are paired through their carb­oxy­lic groups by the typical centrosymmetric O—H⋯O inter­actions with R 2 2(8) hydrogen-bond motifs. In addition, several weak C—H⋯O inter­molecular contacts are also observed. Finally, the mol­ecules are stacked along crystallographic [100] and [010] directions.
doi:10.1107/S1600536810040365
PMCID: PMC3009309  PMID: 21589033
18.  The co-crystal N,N′-bis­[(pyridin-1-ium-2-yl)meth­yl]ethane­dithio­amide bis­(2,6-di­nitro­benzoate)–2,6-di­nitro­benzoic acid (1/4) 
The asymmetric unit of title co-crystal, C14H16N4S2 2+·2C7H3N2O6 −·4C7H4N2O6, comprises a centrosymmetric dipyridinium dication, a 2,6-di­nitro­benzoate anion and two independent 2,6-di­nitro­benzoic acid mol­ecules. The pyridin­ium rings are each approximately perpendicular to the central di­thio­amide unit [dihedral angle = 80.67 (12)°]. The carboxyl­ate/carb­oxy­lic acid groups are approximately perpendicular to the benzene ring to which they are attached [dihedral angles = 78.85 (16), 81.46 (19) and 71.28 (15)°]. By contrast, the major twist exhibited by a nitro group is manifested in a dihedral angle of 32.66 (17)°. The most prominent feature of the crystal packing is linear supra­molecular chains along [1-10], featuring O—H⋯O(carboxyl­ate) and pyridinium-N—H⋯O hydrogen bonds. These are consolidated into a three-dimensional architecture by thio­amide–nitro N—H⋯O, C—H⋯O and π–π [inter-centroid distance = 3.524 (2) Å] inter­actions. One of the nitro O atoms was refined over two sites; the major site was 0.65 (7) occupied.
doi:10.1107/S1600536813023490
PMCID: PMC3790379  PMID: 24098201
19.  Glycinium 3-carb­oxy-4-hy­droxy­benzene­sulfonate 
In the anion of the title salt, C2H6NO2 +·C7H5O6S−, the dihedral angle between the carb­oxy­lic acid group and the benzene ring is 5.02 (12)°. In the crystal, the anions are linked into inversion dimers through pairs of O—H⋯O hydrogen bonds between the carb­oxy­lic acid groups and sulfonate O atoms. A pair of C—H⋯O inter­actions is also observed within each dimer. The anion dimers and the cations are linked into a three-dimensional network by N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds.
doi:10.1107/S1600536814004590
PMCID: PMC3998566  PMID: 24826117
20.  Benzene-1,3,5-tri­carb­oxy­lic acid–pyridinium-2-olate (1/3) 
The asymmetric unit of the title compound, C9H6O6·3C5H5NO, contains one benzene-1,3,5-tri­carb­oxy­lic acid mol­ecule (BTA) and three pyridin-2-ol mol­ecules each present in the zwitterion form. In the crystal, these entities are linked through O—H⋯O− and N+—H⋯O− hydrogen bonds, forming sheets parallel to (10-1). These layers contain macrocyclic rings of composition [BTA]2[pyol]6 and with graph-set notation R 6 8(44), which are stacked along c through π–π inter­actions [inter-centroid distances = 3.536 (2)–3.948 (3) Å]. They are inter­connected by N+—H⋯O− hydrogen-bonded chains of pyridin-2-ol mol­ecules running parallel to c, forming a three-dimensional network. There are also C—H⋯O hydrogen bonds present which reinforce the three-dimensional structure.
doi:10.1107/S1600536814005534
PMCID: PMC3998530  PMID: 24826154
21.  Crystal structure of (E)-4-{2-[4-(all­yloxy)phen­yl]diazen­yl}benzoic acid 
The title compound has an E conformation about the azo­benzene linkage and the benzene rings are almost coplanar to one another [dihedral angle = 1.36 (7)°]. In the crystal, a combination of O—H⋯O and C—H⋯O hydrogen bonds and C—H⋯π inter­actions leads to the formation of slabs parallel to (001).
The title compound, C16H14N2O3, has an E conformation about the azo­benzene [—N=N– = 1.2481 (16) Å] linkage. The benzene rings are almost coplanar [dihedral angle = 1.36 (7)°]. The O atoms of the carb­oxy­lic acid group are disordered over two sets of sites and were refined with an occupancy ratio of 0.5:0.5. The two disordered components of the carb­oxy­lic acid group make dihedral angles of 1.5 (14) and 3.8 (12)° with the benzene ring to which they are attached. In the crystal, mol­ecules are linked via pairs of O—H⋯O hydrogen bonds, forming inversion dimers. The dimers are connected via C—H⋯O hydrogen bonds, forming ribbons lying parallel to [120]. These ribbons are linked via C—H⋯π inter­actions, forming slabs parallel to (001).
doi:10.1107/S1600536814023745
PMCID: PMC4257410  PMID: 25552976
crystal structure; azo­benzene; benzoic acid; liquid crystal; nematic phase
22.  2-Amino­benzoic acid–4-[2-(pyridin-4-yl)eth­yl]pyridine (2/1) 
The asymmetric unit of the title co-crystal, C12H12N2·2C7H7NO2, comprises a centrosymmetric 4-[2-(pyridin-4-yl)eth­yl]pyridine mol­ecule and a 2-amino­benzoic acid mol­ecule in a general position. The acid has a small twist between the carb­oxy­lic acid residue and the ring [dihedral angle = 7.13 (6)°] despite the presence of an intra­molecular N—H⋯O(carbon­yl) hydrogen bond. Three-mol­ecule aggregates are formed via O—H⋯N(pyrid­yl) hydrogen bonds, and these are connected into supra­molecular layers in the bc plane by N—H⋯O(carbon­yl) hydrogen bonds and π–π inter­actions between pyridine and benzene rings [inter-centroid distance = 3.6332 (9) Å]. Layers are connected along the a axis by weak π–π inter­actions between benzene rings [3.9577 (10) Å].
doi:10.1107/S1600536813027128
PMCID: PMC3884291  PMID: 24454067
23.  3-[(E)-2-Chloro-3,3,3-trifluoro­prop-1-en-1-yl]-N-(2-chloro­phen­yl)-2,2-dimethyl­cyclo­propane-1-carboxamide 
In the title compound, C15H14Cl2F3NO, synthesized by the reaction of 3-[(E)-2-chloro-3,3,3-trifluoro­prop-1-en­yl]-2,2-dimethyl­cyclo­propane­carb­oxy­lic acid and 2-chloro­aniline, the aromatic ring makes a dihedral angle of 76.7 (3)° with the plane of the cyclo­propane ring. In the crystal, inter­molecular N—H⋯O hydrogen bonds link the mol­ecules into chains running along the b axis.
doi:10.1107/S1600536810050634
PMCID: PMC3050387  PMID: 21522772
24.  4-Cyclo­propyl-1-(6′-de­oxy-1′,2′-O-iso­propyl­idene-α-d-gluco­furanos­yl)-1H-1,2,3-triazole 
In the title compound, C14H21N3O5, the tetra­hydro­furan ring adopts an envelope conformation with the C atom bearing the substituent as the flap. The penta­furan­ose ring adopts a twisted conformation about the C—C bond fusing the rings. The dihedral angle between these rings (all atoms), which are cis fused, is 72.89 (14)°. The cyclo­propane ring is disordered over two orientations in a 0.576 (5):0.424 (5) ratio; the dihedral angles subtended to the triazole ring are 53.3 (11) and 46.6 (9)°, respectively. In the crystal, the mol­ecules are linked by O—H⋯N and O—H⋯O hydrogen bonds, generating (001) sheets. A weak C—H⋯O inter­action also occurs.
doi:10.1107/S1600536813021351
PMCID: PMC3884407  PMID: 24427028
25.  Crystal structure of (±)-(4RS,5RS,7SR)-4-[(1RS,2RS,3RS,6RS)-3-benzo­yloxy-2-(2-hy­droxy­ethyl)-6-meth­oxy­meth­oxy-2-methyl­cyclo­hex­yl]-8,10,10-trimethyl-2-oxo-1,3-dioxa­spiro­[4.5]dec-8-en-7-yl benzoate benzene monosolvate 
In the title compound, the ring conformations of the tricycles are in an envelope, a half-chair and a chair. In the crystal, inter­molecular O—H⋯O and C—H⋯O hydrogen bonds and C—H⋯π inter­actions link the mol­ecules into a three-dimensional architecture.
In the title compound, C36H44O10·C6H6, the dioxolane ring adopts an envelope conformation with the C atom bonded to the H atom as the flap, while the cyclo­hexene and cyclo­hexane rings are in half-chair and chair conformations, respectively. In the crystal, a pair of O—H⋯O hydrogen bonds with an R 2 2(26) graph-set motif connect the benzoate mol­ecules into an inversion dimer. The dimers are linked by a weak C—H⋯O inter­action into a tape structure along [01-1]. The benzene mol­ecule links the tapes through C—H⋯O and C—H⋯π inter­actions, forming a sheet parallel to (100).
doi:10.1107/S2056989014026048
PMCID: PMC4331859
crystal structure; hydrogen bonds; taxane skeleton; paclitaxel

Results 1-25 (570424)