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1.  1,4-Bis[(2,6-dimethoxy­phen­yl)ethyn­yl]benzene 
The title compound, C26H22O4, is a derivative of 1,4-bis­(phenyl­ethyn­yl)benzene substituted by four meth­oxy groups at the terminal benzene rings. The asymmetric unit consists of two half-molecules; one centrosymmetric molecule is planar but the other is non-planar, with dihedral angles of 67.7 (1)° between the central benzene ring and the terminal benzene rings. In the crystal structure, mol­ecules form a zigzag mol­ecular network due to π–π [the inter­planar and centroid–centroid distances between the benzene rings are 3.50 (1) and 3.57 (1) Å, respectively] and C—H⋯π inter­actions (2.75 Å). Introduction of the four meth­oxy groups results in the supra­molecular architecture.
doi:10.1107/S1600536808013664
PMCID: PMC2961624  PMID: 21202588
2.  1,4-Bis[(3,5-dimethoxy­phen­yl)ethyn­yl]benzene 
The title compound, C26H22O4, is a derivative of 1,4-bis­(phenyl­ethyn­yl)benzene substituted by four meth­oxy groups on the terminal benzene rings. The mol­ecule is almost planar with an r.m.s. deviation of 0.266 Å. The dihedral angles between the two terminal benzene rings and the central benzene ring are 7.96 (6) and 13.32 (7)°. In the crystal structure, mol­ecules aggregate via C—H⋯O inter­actions, forming mol­ecular tapes along the a axis, which aggregate to form a herring-bone structure.
doi:10.1107/S160053680900155X
PMCID: PMC2968219  PMID: 21581947
3.  1-[(2,3,4,5,6-Penta­fluoro­phen­yl)ethyn­yl]ferrocene 
The mol­ecular structure of the title compound, [Fe(C5H5)(C13H4F5)], consists of a ferrocenyl group and a 2,3,4,5,6-penta­fluoro­benzene group linked through an ethyne spacer. The crystal packing is dominated by inter­molecular C—H⋯F hydrogen bonds, C—F⋯π inter­actions between the penta­fluoro­benzene groups [F⋯centroid distances = 3.882 (2) and 3.884 (2) Å] and π–π inter­actions between the penta­fluoro­benzene and cyclo­penta­dienyl rings [centroid–centroid distance = 3.741 (1) Å].
doi:10.1107/S1600536810026772
PMCID: PMC3007523  PMID: 21588152
4.  1-Ethyl-2-phenyl-3-[2-(tri­methyl­sil­yl)ethyn­yl]-1H-indole 
The title compound, C21H23NSi, was synthesized by Sonogashira-type reaction of 1-ethyl-3-iodo-2-phenyl-1H-indole with tri­methyl­silyl­acetyl­ene. The indole ring system is nearly planar [maximum atomic deviation = 0.0244 (15) Å] and is oriented at a dihedral angle of 51.48 (4)° with respect to the phenyl ring. The supramolecular aggregation is completed by weak C—H⋯π inter­actions of the methylene and phenyl groups with the benzene and pyrrole rings of the indole ring system. The methyl groups of the tri­methyl­silyl unit are equally disordered over two sets of sites.
doi:10.1107/S1600536813012671
PMCID: PMC3685072  PMID: 23795091
5.  5,15-Bis(3,5-di-tert-butyl­phen­yl)-10,20-bis­(phenyl­ethyn­yl)porphyrin 
In the centrosymmetric title compound, C64H62N4, the two phenyl­ethynyl groups lie at diagonal meso positions. The 24-membered porphyrin has in-plane distortion with respect to the mean plane of the macrocycle and two intra-ring bifurcated N—H⋯(N,N) hydrogen bonds occur. The dihedral angles between the phenyl rings in the phenyl­ethynyl group and the 3,5-bis­(tert-but­yl)phenyl group with respect to the mean plane of the porphyrin are 17.2 (2) and 59.2 (3)°. The tert-butyl groups are disordered over two sets of sites in a 0.661 (13):0.339 (13) ratio.
doi:10.1107/S1600536809045954
PMCID: PMC2972159  PMID: 21578743
6.  A polymorph of 2,4-dinitro­phenyl­hydrazine 
The crystal structure of a previously unreported polymorph (form II) of 2,4-dinitro­phenyl­hydrazine (DNPH), C6H6N4O4, was determined at 90 K. The first polymorph (form I) is described in the monoclinic space group P21/c [Okabe et al. (1993 ▶). Acta Cryst. C49, 1678–1680; Wardell et al. (2006 ▶). Acta Cryst. C62, o318–320], whereas form II is in the monoclinic space group Cc. The mol­ecular structures in forms I and II are closely similar, with the nitro groups at the 2- and 4-positions being almost coplanar with the benzene ring [dihedral angles of 3.54 (1) and 3.38 (1)°, respectively in II]. However, their packing arrangements are completely different. Form I exhibits a herringbone packing motif, whereas form II displays a coplanar chain structure. Each chain in form II is connected to adjacent chains by the inter­molecular inter­action between hydrazine NH2 and 2-nitro groups, forming a sheet normal to (101). The sheet is stabilized by N—H⋯π inter­actions.
doi:10.1107/S1600536813004571
PMCID: PMC3588540  PMID: 23476598
7.  A series of N-(2-phenyl­ethyl)nitro­aniline derivatives as precursors for slow and sustained nitric oxide release agents 
A series of N-(2-phenyl­ethyl)nitro­aniline derivatives is presented, demonstrating that modest changes in the functional groups cause significant differences in mol­ecular conformation, inter­molecular inter­actions and packing.
2,4-Di­nitro-N-(2-phenyl­ethyl)aniline, C14H13N3O4, (I), crystallizes with one independent mol­ecule in the asymmetric unit. The adjacent amine and nitro groups form an intra­molecular N—H⋯O hydrogen bond. The anti conformation about the ethyl C—C bond leads to the phenyl and aniline rings being essentially parallel. Mol­ecules are linked into dimers by inter­molecular N—H⋯O hydrogen bonds, such that each amine H atom participates in a three-centre inter­action with two nitro O atoms. Though the dimers pack so that the arene rings of adjacent mol­ecules are parallel, the rings are staggered and π–π inter­actions do not appear to be favoured. 4,6-Di­nitro-N,N′-bis­(2-phenyl­ethyl)benzene-1,3-di­amine, C22H22N4O4, (II), differs from (I) in the presence of a second 2-phenyl­ethyl­amine group on the substituted ring. Compound (II) also crystallizes with one unique mol­ecule in the asymmetric unit. Both amine groups are involved in intra­molecular N—H⋯O hydrogen bonds with adjacent nitro groups. Although one ethyl group adopts an anti conformation as in (I), the other is gauche, with the result that the pendant phenyl rings are not parallel. The amine group that is part of the gauche conformation participates in a three-centre N—H⋯O hydrogen bond with the nitro group of a neighbouring mol­ecule, leading to dimers as in (I). The other amine H atom does not form any inter­molecular hydrogen bonds. The packing leads to separations of ca 3.4 Å of the parallel anti phenyl and amino­benzene rings. 2-Cyano-4-nitro-N-(2-phenyl­ethyl)aniline, C15H13N3O2, (III), differs from (I) only in having a cyano group in place of the 2-nitro group. The absence of the adjacent nitro group eliminates the intra­molecular N—H⋯O hydrogen bond. Mol­ecules of (III) adopt the same anti conformation about the ethyl group as in (I), but crystallize in the higher-symmetry monoclinic space group P21/n. The mol­ecules are linked into dimers via N—H⋯N amine–cyano hydrogen bonds, while the nitro groups are not involved in any N—H⋯O inter­actions. Owing to the different symmetry, the mol­ecules pack in a herringbone pattern with fewer face-to-face inter­actions between the rings. The closest such inter­actions are about 3.5 Å between rings that are largely slipped past one another. 4-Methyl­sulfonyl-2-nitro-N-(2-phenyl­ethyl)aniline, C15H16N2O4S, (IV), differs from (I) in having a methyl­sulfonyl group in place of the 4-nitro group. The intra­molecular N—H⋯O hydrogen bond is present as in (I). However, unlike (I), the conformation about the ethyl group is gauche, so the two arene rings are nearly per­pen­dicular rather than parallel. The packing is significantly different from the other three structures in that there are no inter­molecular hydrogen bonds involving the N—H groups. The mol­ecules are arranged in tetra­gonal columns running along the c axis, with the aniline rings mostly parallel and separated by ca 3.7 Å. Taken together, these structures demonstrate that modest changes in functional groups cause significant differences in mol­ecular conformation, inter­molecular inter­actions and packing.
doi:10.1107/S0108270113025869
PMCID: PMC3818095  PMID: 24192194
crystal structure; N-(2-phenyl­ethyl)nitro­aniline derivatives; secondary amines; nitric oxide release agents
8.  4,4′-[Thio­phene-2,5-diylbis(ethyne-2,1-di­yl)]dibenzonitrile 
In the solid state, the title compound, C22H10N2S, forms centrosymmetric dimers by pairs of non-classical C—H⋯S hydrogen bonds linking approximately coplanar mol­ecules. The benzene ring involved in this inter­action makes a dihedral angle of only 7.21 (16)° with the thio­phene ring, while the other benzene ring is twisted somewhat out of the plane, with a dihedral angle of 39.58 (9)°. The hydrogen-bonded dimers stack on top of each other with an inter­planar spacing of 3.44 Å. C—H⋯N hydrogen bonds link together stacks that run in approximately perpendicular directions. Each mol­ecule thus inter­acts with 12 adjacent mol­ecules, five of them approaching closer than the sum of the van der Waals radii for the relevant atoms. Optimization of the inter-stack contacts contributes to the non-planarity of the mol­ecule.
doi:10.1107/S1600536808008106
PMCID: PMC2961030  PMID: 21202153
9.  4-(4-Bromo­phen­yl)-7,7-dimethyl-2-methyl­amino-3-nitro-7,8-di­hydro-4H-chromen-5(6H)-one including an unknown solvate 
In the title compound, C18H19BrN2O4, the chromene unit is not quite planar (r.m.s. deviation = 0.199 Å), with the methyl C atoms lying 0.027 (4) and 1.929 (4) Å from the mean plane of the chromene unit. The six-membered carbocyclic ring of the chromene moiety adopts an envelope conformation, with the dimethyl-substituted C atom as the flap. The methyl­amine and nitro groups are slightly twisted from the chromene moiety, with C—N—C—O and O—N—C—C torsion angles of 2.7 (4) and −0.4 (4)°, respectively. The dihedral angle between the mean plane of the chromene unit and the benzene ring is 85.61 (13)°. An intra­molecular N—H⋯O hydrogen bond generates an S(6) ring motif, which stabilizes the mol­ecular conformation. In the crystal, mol­ecules are linked via N—H⋯O hydrogen bonds, forming hexa­gonal rings lying parallel to the ab plane. A region of disordered electron density, most probably disordered ethanol solvent mol­ecules, occupying voids of ca 432 Å3 for an electron count of 158, was treated using the SQUEEZE routine in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155]. Their formula mass and unit-cell characteristics were not taken into account during refinement.
doi:10.1107/S1600536814007983
PMCID: PMC4011266  PMID: 24860381
10.  6-Chloro-2-phenyl-3-(2-phenyl­ethyn­yl)quinoxaline 
In the title compound, C22H13ClN2, the quinoxaline ring system is close to planar [maximum deviation = 0.061 (2) Å]. The phenyl ring at the 2-position and the phenyl ring of the phenyl­ethynyl substituent make dihedral angles of 49.32 (7) and 11.99 (7) °, respectively, with the quinoxaline mean plane. The two phenyl rings are inclined to one another by 61.27 (9)°. In the crystal, mol­ecules are linked by C—H⋯π and π–π inter­actions [centroid–centroid distances = 3.6210 (12) and 3.8091 (12) Å].
doi:10.1107/S1600536812020776
PMCID: PMC3379328  PMID: 22719526
11.  trans-Bis[1,2-bis­(diphenyl­phosphan­yl)ethane]­chlorido(ethyn­yl)ruthenium(II) 
The mol­ecular structure of the title compound, trans-[Cu(C2H)Cl(C26H24P2)2], consists of an RuII cation, located on an inversion centre, in an octa­hedral environment defined by two chelating phosphines, one acetyl­ide and one chloride ligand. The –C CH and the chlorine ligands are disordered over two equivalent positions (0.5 occupancy each). The coordination geometry is distorted octa­hedral, with the –C CH fragment and the Cl ligand in trans positions. The four P atoms occupy the equatorial plane of the octa­hedron and the chloride and acetyl­ide ligands the axial positions.
doi:10.1107/S1600536812044558
PMCID: PMC3588712  PMID: 23468677
12.  1,4-Dimeth­oxy-2,5-bis­{2-[4-(trifluoro­meth­yl)phen­yl]ethyn­yl}benzene 
The asymmetric unit of the title compound, C26H16F6O2, contains one half of the mol­ecule situated on an inversion centre. In the rod-like mol­ecule, the two terminal benzene rings form a dihedral angle of 71.9 (1)° with the central benzene ring. The trifluoro­methyl group is rotationally disordered over two orientations in a 0.53 (1):0.47 (1) ratio. The crystal packing exhibits no classical inter­molecular inter­actions.
doi:10.1107/S160053681102099X
PMCID: PMC3151946  PMID: 21837009
13.  1,3-Dicyclo­hexyl­imidazolidine-2,4,5-trione: a second polymorph 
The title compound, C15H22N2O3, was obtained as a by-product of oxidative cleavage of 1,3-dicyclo­hexyl-(3-oxo-2,3-dihydro­benzofuran-2-yl)imidazolidine-2,4-dione. Herein, we report the crystal structure of a second polymorph, which was obtained by crystallization from an ethanol solution at 253 K, instead of slow evaporation of the same solvent at room temperature. While the first polymorph [Talhi et al. (2011). Acta Cryst. E67, o3243] crystallized in the non-centrosymmetric space group P212121, this second polymorph crystallizes in the centrosymmetric space group P21/n. Compared to the first polymorph, in the crystal no C=O⋯C=O inter­actions were found (C⋯O inter­molecular distance longer than 3.15 Å) and instead, close packing of individual mol­ecular units is mediated by C—H⋯π and weak C—H⋯O inter­actions.
doi:10.1107/S1600536812043619
PMCID: PMC3515314  PMID: 23284534
14.  Redetermination of loperamide monohydrate 
The structure of the title compound {systematic name: 4-[4-(4-chloro­phen­yl)-4-hy­droxy­piperidin-1-yl]-N,N-dimethyl-2,2-di­phenyl­butanamide monohydrate}, C29H33ClN2O2·H2O, has been redetermined at 170 (2) K. The redetermination is of significantly higher precision than the previous structure determination at room temperature and includes the H-atom coordinates that were not included in the previous report [Germain et al. (1977 ▶). Acta Cryst. B33, 942–944]. It consists of a piperidin-1-yl ring in a distorted chair conformation, with the N,N-dimethyl-α,α-diphenyl­butyramide and the 4-chloro­phenyl and hy­droxy groups bonded in para positions and an external water mol­ecule within the asymmetric unit. The dihedral angles between the mean plane of the piperidine ring and the 4-chloro­phenyl and two benzene rings are 83.4 (5), 76.4 (2) and 85.9 (2)°, respectively. The two benzene rings are inclined to one another by 50.8 (6)°. In the crystal, mol­ecules are linked by O—H⋯O and O—H⋯N hydrogen bonds and weak C—H⋯O intermolecular interactions, forming an infinite two-dimensional network along [110].
doi:10.1107/S1600536812003091
PMCID: PMC3275278  PMID: 22347134
15.  catena-Poly[[di­chlorido­mercury(II)]-μ-1,4-bis­[2-(pyridin-4-yl)ethyn­yl]benzene-κ2 N:N′] 
In the polymeric title compound, [HgCl2(C20H12N2)]n, the HgII atom is located on a twofold rotation axis and the benzene ring of the bidentate bridging 1,4-bis­[2-(pyridin-4-yl)ethyn­yl]benzene (L) ligand is located about a twofold rotation axis. The HgII atom is coordinated by two N atoms of two different L ligands and by two chloride ions in a distorted tetra­hedral geometry. The dihedral angle between the coordinating pyridine and the benzene ring is 12.8 (2)°. The result of the bridging is the formation of a zigzag chain running parallel to [102]. The chains pack with no specific inter­molecular inter­actions between them.
doi:10.1107/S1600536814010228
PMCID: PMC4051079  PMID: 24940198
16.  Crystal structure of (E)-N′-(4-chloro­benzyl­idene)-4-methyl­benzene­sulfono­hydrazide: a hexa­gonal polymorph 
The title compound, C14H13ClN2O2S, crystallized in the enanti­omorphic defining hexa­gonal space group P61 [Flack parameter = −0.02 (7)]. The partially hydrated form of the same compound, crystallizing in the triclinic space group P-1, has been reported previously [Kia et al. (2009b). Acta Cryst. E65, o1119], as has the crystal structure of the bromo derivative, also crystallizing in the space group P-1 [Kia et al. (2009a). Acta Cryst. E65, o821]. The title mol­ecule is non-planar with the planes of the benzene rings being inclined to one another by 76.62 (13)°, and has an E conformation about the C=N bond. In the crystal, mol­ecules are linked via N—H⋯O hydrogen bonds forming 61 helical chains running along [001]. The chains are linked via C—H⋯O hydrogen bonds, C—H⋯π inter­actions and short Cl⋯O [3.015 (3) Å] inter­actions, forming a three-dimensional structure.
doi:10.1107/S1600536814023721
PMCID: PMC4257446  PMID: 25553026
crystal structure; hydrazones; sulfono­hydrazide; Schiff base; helical chains; hydrogen bonding.
17.  Crystal structure of 8-hy­droxy­quinoline: a new monoclinic polymorph 
In an attempt to grow 8-hy­droxy­quinoline–acetamino­phen co-crystals from equimolar amounts of conformers in a chloro­form–ethanol solvent mixture at room temperature, the title compound, C9H7NO, was obtained. The mol­ecule is planar, with the hy­droxy H atom forming an intra­molecular O—H⋯N hydrogen bond. In the crystal, mol­ecules form centrosymmetric dimers via two O—H⋯N hydrogen bonds. Thus, the hy­droxy H atoms are involved in bifurcated O—H⋯N hydrogen bonds, leading to the formation of a central planar four-membered N2H2 ring. The dimers are bound by inter­molecular π–π stacking [the shortest C⋯C distance is 3.2997 (17) Å] and C—H⋯π inter­actions into a three-dimensional framework. The crystal grown represents a new monoclinic polymorph in the space group P21/n. The mol­ecular structure of the present monoclinic polymorph is very similar to that of the ortho­rhom­bic polymorph (space group Fdd2) studied previously [Roychowdhury et al. (1978 ▶). Acta Cryst. B34, 1047–1048; Banerjee & Saha (1986 ▶). Acta Cryst. C42, 1408–1411]. The structures of the two polymorphs are distinguished by the different geometries of the hydrogen-bonded dimers, which in the crystal of the ortho­rhom­bic polymorph possess twofold axis symmetry, with the central N2H2 ring adopting a butterfly conformation.
doi:10.1107/S1600536814016110
PMCID: PMC4186174  PMID: 25309256
8-hy­droxy­quinoline; hydrogen bonds; polymorphism; crystal structure
18.  A second tricilinc polymorph of 6,6′-dieth­oxy-2,2′-[propane-1,2-diylbis(nitrilo­methyl­idyne)]diphenol 
The title Schiff base compound, C21H26N2O4, is a second triclinic polymorph of a previously reported room-temperature structure [Jia (2009 ▶). Acta Cryst. E65, o646]. Strong intra­molecular O—H⋯N hydrogen bonds generate S(6) ring motifs. Inter­molecular C—H⋯O inter­actions link neighbouring mol­ecules into dimers with an R 2 2(16) ring motif. The mean planes of the two benzene rings are almost perpendicular to each other, making a dihedral angle of 88.24 (5)°. An inter­esting feature of the crystal structure is the intermolecular short C⋯O [3.1878 (13) Å] contact which is shorter than the sum of the van der Waals radii of the relevant atoms. The crystal structure is further stabilized by inter­molecular C—H⋯π and π–π inter­actions [centroid–centroid distance = 3.7414 (6) Å]. The structure has a stereogenic centre but the space group is centrosymmetric, so the mol­ecule exists as a racemate.
doi:10.1107/S1600536809008137
PMCID: PMC2968989  PMID: 21582458
19.  N-(3-Nitro­phen­yl)maleamic acid 
In the title compound, C10H8N2O5, the mol­ecule is slightly distorted from planarity. The mol­ecular structure is stabilized by two intra­molecular hydrogen bonds. The first is a short O—H⋯O hydrogen bond (H⋯O distance = 1.57 Å) within the maleamic acid unit and the second is a C—H⋯O hydrogen bond (H⋯O distance = 2.24 Å) which connects the amide group with the benzene ring. The nitro group is twisted by 6.2 (2)° out of the plane of the benzene ring. The crystal structure manifests a variety of hydrogen bonding. The packing is dominated by a strong inter­molecular N—H⋯O inter­action which links the mol­ecules into chains running along the b axis. The chains within a plane are further assembled by three additional types of inter­molecular C—H⋯O hydrogen bonds to form a sheet parallel to the (01) plane.
doi:10.1107/S1600536810022245
PMCID: PMC3007040  PMID: 21587897
20.  [8-(Diphenyl­phosphan­yl)naphthyl-κ2 C 1,P](phenyl­ethyn­yl)tris­(trimethyl­phosphane-κP)iron(II) 
The title compound, [Fe(C8H5)(C22H16P)(C3H9P)3], was synthesized by the addition of phenyl­ethine to a solution of the parent methyl iron complex Fe(CH3){P(C6H5)2(C10H6)}(PMe3)3 at 213 K, accompanied by evolution of methane. The coordination around the iron center can be described as slightly distorted octa­hedral [Fe—P 2.2485 (12)–2.2902 (12) Å; Fe—C 1.918 (5), 2.015 (4) Å], with a meridional arrangement of the trimethyl­phosphine ligands and the introduced terminal alkinyl-ligand trans to the P(Ph)2-anchoring group.
doi:10.1107/S1600536808041421
PMCID: PMC2967909  PMID: 21581538
21.  Benzene-1,3,5-triol at 105 K 
The structure of the title compound, C6H6O3, has been redetermined at low temperature [room-temperature structure: Maartmann-Moe (1965 ▶). Acta Cryst. 19, 155–157]. The mol­ecule is planar with approximate D 3h point symmetry, yet it crystallizes in the chiral ortho­rhom­bic space group P212121 with a three-dimensional hydrogen-bonding network containing infinite O—H⋯O—H⋯O—H chains.
doi:10.1107/S1600536808030638
PMCID: PMC2959261  PMID: 21201217
22.  Bis[(4-methyl­phen­yl)ethyn­yl] telluride 
The tellurium atom in the title bis-ethynyl telluride, Te(C9H7)2 or C18H14Te, is located on a crystallographic twofold axis, the C—Te—C angle being 92.23 (15)°. The dihedral angle between the rings is 87.27 (7)°. In the crystal structure, mol­ecules are connected in chains parallel to the b axis and mediated by C—H⋯π inter­actions.
doi:10.1107/S1600536810006264
PMCID: PMC2983524  PMID: 21580428
23.  2,4-Bis(4-eth­oxy­phen­yl)-1-methyl-3-aza­bicyclo­[3.3.1]nonan-9-one 
In the title compound, C25H30NO3, a crystallographic mirror plane bis­ects the mol­ecule. Although it is a positional isomer of 2,4-bis(4-eth­oxy­phen­yl)-7-methyl-3-aza­bicyclo­[3.3.1]non­an-9-one [C25H31NO3, M r = 393.51; Park et al. (2012c ▶). Acta Cryst. E68, o779–780], its mol­ecular weight is 392.50 due to the 50:50 ratio of the methyl group at bridgehead C atoms. However, the title compound exists in the same twin-chair conformation as its 7-methyl isomer. Also, the 4-eth­oxy­phenyl groups are equatorially oriented on the bicycle as in its isomer. In the title compound, the cyclo­hexanone ring deviates from an ideal chair (total puckering amplitude Q T = 0.5390 Å) and the piperidone ring is closer to an ideal chair (Q T = 0.6064 Å). These Q T values are very similar to those of its isomer. Even though a center of symmetry passes through the 7-methyl analog, the benzene rings are oriented 26.11 (3)° with respect to each other, whereas the orientation is 53.10 (3)° for the title compound. The title compound exhibits inter­molecular N—H⋯O inter­actions [H⋯A = 2.25 (2) Å, versus 2.26 (2) Å for the analog].
doi:10.1107/S1600536812039840
PMCID: PMC3470358  PMID: 23125771
24.  A new polymorph of 2,6-dimeth­oxy­benzoic acid 
A new crystalline form of 2,6-dimeth­oxy­benzoic acid, C9H10O4, crystallizing in a tetra­gonal unit cell has been identified during screening for co-crystals. The asymmetric unit comprises a non-planar independent mol­ecule with a synplanar conformation of the carb­oxy group. The sterically bulky o-meth­oxy substituents force the carb­oxy group to be twisted away from the plane of the benzene ring by 65.72 (15)°. The carb­oxy group is disordered over two sites about the C—C bond [as indicated by the almost equal C—O distances of 1.254 (3) and 1.250 (3) Å], the occupancies of the disordered carboxym H atoms being 0.53 (5) and 0.47 (5). In the known ortho­rhom­bic form reported by Swaminathan et al. [Acta Cryst. (1976), B32, 1897–1900], due to the anti­planar conformation adopted by the OH group, the mol­ecular components are associated in the crystal in chains stabilized by linear O—H⋯O hydrogen bonds. However, in the new tetra­gonal polymorph, mol­ecules form dimeric units via pairs of O—H⋯O hydrogen bonds between the carb­oxy groups.
doi:10.1107/S1600536811049075
PMCID: PMC3239035  PMID: 22199883
25.  4-Nitro-N-(3-nitro­phen­yl)benzamide 
The title compound, C13H9N3O5, prepared as a solid derivative of 3-nitro­analine via reaction with 4-nitro­benzoyl chloride, crystallizes in a chiral space group. The mol­ecule is non-planar with a dihedral angle of 26.1 (1)° between the two benzene rings. Both nitro groups are twisted slightly out of the plane of their corresponding benzene rings, making dihedral angles of 10.7 (4) and 13.5 (4)°. The mol­ecules are stacked along the a axis with benzene ring centroid–centroid distances of 3.8878 (6) Å. In the crystal, inter­molecular benzene C—H⋯O inter­actions involving one nitro group and the carbonyl group link the mol­ecules, forming chains along [001]. An additional set of aromatic C—H⋯O inter­actions with the second nitro group form chains along [101], connecting adjacent chains to create layers perpendicular to the b axis.
doi:10.1107/S1600536811038062
PMCID: PMC3201324  PMID: 22065512

Results 1-25 (555935)