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1.  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
2.  2-(7,8-Diphenyl-1H-imidazo[4,5-f]quinoxalin-2-yl)phenol methanol disolvate 
The title compound, C27H18N4O·2CH4O, is a unsymmetrically substituted quinoxaline. An intra­molecular O—H⋯N hydrogen bond involving the hydr­oxy and imino groups generates an S(6) ring motif. Inter­molecular C—H⋯O and N—H⋯O hydrogen bonds form an R 2 1(7) ring motif involving a methanol O atom and two H atoms of the imidazole and benzene rings, respectively. The latter links neighbouring mol­ecules into one-dimensional extended chains along the a axis. The two benzene rings are inclined towards each other, as indicated by the dihedral angle of 52.13 (10)°. The phenol ring is almost coplanar with the basic quinoxaline unit, making a dihedral angle of 2.43 (6)°. The short distances between the centroids of the five- and six-membered rings prove the existence of π–π inter­actions [centroid–centroid distances = 3.5234 (9)–3.7885 (10) Å]. The crystal structure is stabilized by intra­molecular O—H⋯N, inter­molecular O—H⋯O, N—H⋯O and C—H⋯O (× 2) hydrogen bonds and weak inter­molecular C—H⋯π and π–π inter­actions.
doi:10.1107/S1600536808025269
PMCID: PMC2960492  PMID: 21201724
3.  Crystal structures of trans-di­chlorido­tetra­kis­[1-(2,6-diiso­propyl­phen­yl)-1H-imidazole-κN 3]iron(II), trans-di­bromido­tetra­kis­[1-(2,6-diiso­propyl­phen­yl)-1H-imidazole-κN 3]iron(II) and trans-di­bromido­tetra­kis­[1-(2,6-diiso­propyl­phen­yl)-1H-imidazole-κN 3]iron(II) diethyl ether disolvate1  
The title compounds are iron(II) dihalide complexes of the bulky arylimidazole ligand 1-(2,6-diisopropylphenyl)-1H-imidazole. The FeCl2 and FeBr2 complexes are isotypic, while the third compound, also an FeBr2 complex, crystallizes as a diethyl ether disolvate.
The title compounds, [FeCl2(C15H20N2)4], (I), [FeBr2(C15H20N2)4], (II), and [FeBr2(C15H20N2)4]·2C4H10O, (IIb), respectively, all have triclinic symmetry, with (I) and (II) being isotypic. The FeII atoms in each of the structures are located on an inversion center. They have octa­hedral FeX 2N4 (X = Cl and Br, respectively) coordination spheres with the FeII atom coordinated by two halide ions in a trans arrangement and by the tertiary N atom of four aryl­imidazole ligands [1-(2,6-diiso­propyl­phen­yl)-1H-imidazole] in the equatorial plane. In the two independent ligands, the benzene and imidazole rings are almost normal to one another, with dihedral angles of 88.19 (15) and 79.26 (14)° in (I), 87.0 (3) and 79.2 (3)° in (II), and 84.71 (11) and 80.58 (13)° in (IIb). The imidazole rings of the two independent ligand mol­ecules are inclined to one another by 70.04 (15), 69.3 (3) and 61.55 (12)° in (I), (II) and (IIb), respectively, while the benzene rings are inclined to one another by 82.83 (13), 83.0 (2) and 88.16 (12)°, respectively. The various dihedral angles involving (IIb) differ slightly from those in (I) and (II), probably due to the close proximity of the diethyl ether solvent mol­ecule. There are a number of C—H⋯halide hydrogen bonds in each mol­ecule involving the CH groups of the imidazole units. In the structures of compounds (I) and (II), mol­ecules are linked via pairs of C—H⋯halogen hydrogen bonds, forming chains along the a axis that enclose R 2 2(12) ring motifs. The chains are linked by C—H⋯π inter­actions, forming sheets parallel to (001). In the structure of compound (IIb), mol­ecules are linked via pairs of C—H⋯halogen hydrogen bonds, forming chains along the b axis, and the diethyl ether solvent mol­ecules are attached to the chains via C—H⋯O hydrogen bonds. The chains are linked by C—H⋯π inter­actions, forming sheets parallel to (001). In (I) and (II), the methyl groups of an isopropyl group are disordered over two positions [occupancy ratio = 0.727 (13):0.273 (13) and 0.5:0.5, respectively]. In (IIb), one of the ethyl groups of the diethyl ether solvent mol­ecule is disordered over two positions (occupancy ratio = 0.5:0.5).
doi:10.1107/S1600536814014056
PMCID: PMC4158527  PMID: 25249858
aryl­imidazole; iron(II); crystal structure
4.  Enrofloxacinium picrate 
There is one cation–anion pair in the asymmetric unit of the title compound [systematic name: 4-(3-carb­oxy-6-fluoro-4-oxo-1,4-dihydroquinolin-7-yl)-1-ethyl­piperazin-1-ium 2,4,6-tri­nitro­phenolate], C19H23FN3O3 +·C6H2N3O7 −. The six-membered piperazine group in the cation adopts a slightly distorted chair conformation and contains a protonated N atom. The dihedral angles between the mean planes of the cyclo­propyl and piperazine rings in the cation with the 10-atom ring system of the quinolone group are 48.1 (1) and 69.9 (5)°, respectively. The picrate anion inter­acts with the protonated N atom of an adjacent cation through a bifurcated N—H⋯O three-center hydrogen bond, forming an R 1 2(6) ring motif. Furthermore, there is an intra­molecular O—H⋯O hydrogen bond. The dihedral angle between the mean planes of the anion benzene and cation piperizine, quinoline and cyclo­propyl rings are 61.3 (6), 31.1 (4) and 70.4 (9)°, respectively. The mean planes of the two o-NO2 and single p-NO2 groups in the picrate anion are twisted by 6.7 (6), 38.3 (9) and 12.8 (7)° with respect to the mean plane of the benzene ring. Strong N—H⋯O and weak inter­molecular C—H⋯O hydrogen bonds in concert with weak π–π stacking inter­actions [centroid–centroid distances = 3.5785 (13), 3.7451 (12) and 3.6587 (13) Å] dominate the crystal packing.
doi:10.1107/S160053681100170X
PMCID: PMC3051675  PMID: 21523099
5.  5-Diethyl­amino-2-{[2-(2,4-dinitro­phen­yl)hydrazin-1-yl­idene]meth­yl}phenol 
In the title compound, C17H19N5O5, obtained from the condensation reaction of 4-diethyl­amino-2-hy­droxy­benzalde­hyde and 2,4-dinitro­phenyl­hydrazine, the two benzene rings are twisted by a dihedral angle of 1.75 (12)°. The nitro groups are slightly twisted with the respect to the benzene ring to which they are attached, making dihedral angles of 8.20 (15) and 5.78 (15)°. An intra­molecular O—H⋯N hydrogen bond occurs. In the crystal, mol­ecules are linked by pairs of inter­molecular N—H⋯O hydrogen bonds, forming dimers through R 2 2(12) rings. These dimers are further linked by C—H⋯O and C—H⋯π and weak slipped π–π inter­actions [centroid–centroid distance = 3.743 (2)Å]. One of the ethyl groups is disordered over two positions, with occupancy factors in the ratio 0.72:0.28.
doi:10.1107/S1600536810044983
PMCID: PMC3011673  PMID: 21589414
6.  5-Chloro-N-(4,5-dihydro-1H-imidazol-2-yl)-2,1,3-benzothia­diazol-4-amine (tizanidine) 
There are two independent mol­ecules (A and B) with similar conformations in the asymmetric unit of the title compound, C9H8ClN5S. The benzothia­diazole ring systems of both mol­ecules are essentially planar [maximum deviation = 0.021 (2) Å in mol­ecule A and 0.022 (1) Å in mol­ecule B] and make dihedral angles of 68.78 (9) and 54.39 (8)°, respectively, with the mean planes of their 4,5-dihydro-1H-imidazole rings. An intra­molecular N—H⋯Cl hydrogen bond occurs in mol­ecule B. In the crystal, both mol­ecules form centrosymmetric dimers through π-stacking of their benzothia­diazole rings, with inter­planar distances of 3.3174 (7) and 3.2943 (6) Å. These dimers are further linked via pairs of N—H⋯N hydrogen bonds with the dihydro­imidazole rings as the hydrogen-bonding donors and one of the benzothia­diazole N atoms as the acceptors, generating R 2 2(16) ring motifs. The A 2 and B 2 dimers in turn form additional N—H⋯N hydrogen bonds with the secondary amine as the H-atom donor and the dihydro­imidazole N atom as the acceptor. These R 2 2(8)-type inter­actions connect the A 2 and B 2 dimers with each other, forming infinite chains along [11].
doi:10.1107/S1600536811008348
PMCID: PMC3100067  PMID: 21754121
7.  1-Piperonylpiperazinium 4-nitro­benzoate monohydrate 
In the title hydrated salt [systematic name: 1-(1,3-benzodioxol-5-ylmeth­yl)piperazin-1-ium 4-nitro­benzoate monohydrate], C12H17N2O2 +·C7H4NO4 −·H2O, the piperazinium ring of the cation adopts a slightly distorted chair conformation. The piperonyl and piperazine rings are rotated with respect to each other with an N—C—C—C torsion angle of 45.6 (2)°. In the anion, the nitro group is almost coplanar with the adjacent benzene ring, forming a dihedral angle of only 3.9 (4)°. In the crystal, the cations, anions and water mol­ecules are linked through N—H⋯O and O—H⋯O hydrogen bonds into chains along the a axis. In addition, weaker inter­molecular C—H⋯O inter­actions are also observed within the chains. The anions form centrosymmetric couples through π-stacking inter­actions, with an inter­centroid distance of 3.681 (4) Å between the benzene rings.
doi:10.1107/S160053681400261X
PMCID: PMC3998489  PMID: 24764985
8.  N-Cyclo­heptyl­idene-N′-(2,4-dinitro­phenyl)hydrazine 
The title compound, C13H16N4O4, is a new hydrazone. An intra­molecular N—H⋯O hydrogen bond generates a six-membered ring, producing an S(6) ring motif. The nitro groups in the ortho and para positions are almost coplanar with the benzene ring to which they are bound, making dihedral angles of 0.60 (11) and 3.18 (11)°, respectively. Pairs of inter­molecular C—H⋯O hydrogen bonds link neighbouring mol­ecules into inversion dimers with R 2 2(10) motifs. The crystal structure is further stabilized by inter­molecular π–π inter­actions, with a benzene centroid-to-centroid distance of 3.6601 (4) Å.
doi:10.1107/S1600536809002657
PMCID: PMC2968402  PMID: 21581978
9.  5-Diethyl­amino-2-[(E)-(4-methyl-3-nitro­phenyl)­imino­meth­yl]phenol: a redetermination 
The title compound, C18H21N3O3, is a potential bidentate Schiff base ligand. The whole mol­ecule is disordered with a refined site-occupancy ratio of 0.567 (4):0.433 (4) and not just one ethyl group as reported previously [Sarojini et al. (2007 ▶). Acta Cryst. E63, o4782–o4782]. Using the whole mol­ecule disorder, R values are much smaller than those published. An intra­molecular O—H⋯N hydrogen bond generates a six-membered ring, producing an S(6) ring motif. The dihedral angle between the mean plane of the two benzene rings (major component) is 9.0 (5)°. The crystal structure shows short C⋯C [3.189 (15)–3.298 (12) Å] and C⋯O [2.983 (5)–3.149 (13) Å] contacts. Inter­molecular C—H⋯O inter­actions link neighbouring mol­ecules into dimers with R 2 2(18) motifs. In the crystal structure, these dimers are linked together by inter­molecular C—H⋯O inter­actions into one-dimensional extended chains along the b axis. The crystal structure is further stabilized by inter­molecular π–π stacking inter­actions [centroid–centroid distances = 3.458 (8)–3.691 (6) Å].
doi:10.1107/S1600536809001731
PMCID: PMC2968344  PMID: 21581950
10.  Diaqua­bis­(N,N-diethyl­nicotinamide-κN 1)bis­(4-ethyl­benzoato-κO)cobalt(II) 
The title CoII complex, [Co(C9H9O2)2(C10H14N2O)2(H2O)2], contains two 4-ethyl­benzoate (PEB), two monodentate diethyl­nicotinamide (DENA) ligands and two water mol­ecules. The four O atoms in the equatorial plane around the CoII ion form a slightly distorted square-planar arrangement, while the slightly distorted octa­hedral coordination is completed by the two N atoms of the DENA ligands in the axial positions. Intra­molecular O—H⋯O hydrogen bonds link the water mol­ecules to the carboxyl­ate groups. The dihedral angles between the carboxyl­ate groups and the adjacent benzene rings are 4.52 (18) and 4.56 (18)°, while the pyridine rings and the benzene rings are oriented at dihedral angles of 7.76 (10) and 5.67 (13)°. In the crystal, inter­molecular O—H⋯O hydrogen bonds link the mol­ecules into chains propagating along [010]. C—H⋯O inter­actions and a π–π contact between the pyridine rings [centroid–centroid distance = 3.476 (2) Å] are also observed.
doi:10.1107/S1600536811014188
PMCID: PMC3089307  PMID: 21754332
11.  Diaqua­bis­(N,N′-diethyl­nicotinamide-κN 1)bis­(4-ethyl­benzoato-κO)copper(II) 
The title CuII complex, [Cu(C9H9O2)2(C10H14N2O)2(H2O)2], contains two 4-ethyl­benzoate (PEB) ligands, two monodentate diethyl­nicotinamide (DENA) ligands and two water mol­ecules. The four O atoms in the equatorial plane around the CuII ion form a slightly distorted square-planar arrangement, while the distorted octa­hedral coordination is completed by the two N atoms of the DENA ligands in the axial positions. Intra­molecular O—H⋯O hydrogen bonds link the water mol­ecules to the carboxyl­ate groups. The dihedral angles between the carboxyl­ate groups and the adjacent benzene rings are 4.6 (3) and 3.7 (2)°, while the pyridine rings and the benzene rings are oriented at dihedral angles of 6.82 (11) and 3.63 (14)°. In the crystal, inter­molecular O—H⋯O hydrogen bonds link the mol­ecules into chains propagating along [010]. C—H⋯O inter­actions and a π–π contact between the pyridine rings [centroid–centroid distance = 3.469 (2) Å] are also observed.
doi:10.1107/S1600536811018666
PMCID: PMC3120545  PMID: 21754663
12.  5-[(3,5-Dichloro­anilino)meth­yl]-N-(3,5-dichloro­phen­yl)-6-methyl-2-phenyl­pyrimidin-4-amine 
In the title compound, C24H18Cl4N4, the pyrimidine ring makes dihedral angles of 19.1 (2), 4.1 (2) and 67.5 (2)°, respectively, with phenyl and two benzene rings, and the mol­ecular conformation is stabilized by an intra­molecular N—H⋯N hydrogen bond closing a six-membered ring with an S(6) motif. In the crystal, a pair of inter­molecular N—H⋯N hydrogen bonds connect two mol­ecules, forming inversion dimers with R 2 2(12) motifs. C—H⋯π inter­actions links the dimers into a chain running along the a-axis direction. There are also π–π stacking inter­actions [centroid–centroid distance = 3.666 (4) Å] between the benzene rings of adjacent chains.
doi:10.1107/S160053681204665X
PMCID: PMC3588999  PMID: 23476235
13.  2-Meth­oxy-6-(6-methyl-1H-benzimid­azol-2-yl)phenol 
In the title mol­ecule, C15H14N2O2, the substituted benzene ring forms a dihedral angle of 4.15 (1)° with the benzimidazole ring system. An intra­molecular O—H⋯N hydrogen bond generates an S(6) ring motif. In the solid state, mol­ecules are linked into chains along the [001] via inter­molecular bifurcated N—H⋯(O,O) hydrogen bonds, which generate R 1 2(5) ring motifs. The crystal packing is also consolidated by C—H⋯π inter­actions, and π–π stacking inter­actions between the imidazole and substituted benzene rings [centroid–centroid distance = 3.5746 (13) Å]. The methyl group attached to the benzimidazole ring system is disordered over two positions with occupancies of 0.587 (6) and 0.413 (6), suggesting 180° rotational disorder for the benzimidazole group.
doi:10.1107/S1600536809022478
PMCID: PMC2969490  PMID: 21582885
14.  Crystal structure of (E)-1-methyl-2-[2-(2-methoxphen­yl)ethen­yl]-4-nitro-1H-imidazole 
In the asymmetric unit of the title compound, C13H13N3O3, the 2-(2-methoxphen­yl)ethenyl unit is connected to the methyl-nitro­imidazole 1-methyl-4-nitro-1H-imidazole moiety. The mol­ecule is quasi-planar and the planes of the two rings form a dihedral angle of 0.92 (11)°. The crystal packing can be described as layers parallel to the (011) plane, stabilized by inter­molecular C—H⋯O hydrogen bonding, resulting in the formation of an infinite three-dimensional network linking these layers. Strong π–π stacking inter­actions are observed, viz. benzene–benzene, imidazole–imidazole and benzene–imidazole rings, with centroid–centroid distances of 3.528 (2), 3.457 (2) and 3.544 (2) Å, respectively. Intensity statistics indicated twinning by non-merohedry, with refined weighs of the twin components of 0.3687:0.6313.
doi:10.1107/S1600536814017206
PMCID: PMC4186069  PMID: 25309283
crystal structure; hydrogen bonding; π–π stacking inter­actions; nitro­imidazoles,
15.  (E)-1-[(2-Amino-5-nitro­phen­yl)iminio­meth­yl]naphthalen-2-olate 
The title Schiff base compound, C17H13N3O3, crystallizes in a zwitterionic form and exists in a trans configuration about the C=N bond. The mol­ecule is slightly twisted, the dihedral angle between the benzene ring and naphthalene ring system being 10.80 (9)°. The nitro group is twisted relative to the plane of the benzene ring [dihedral angle = 8.88 (12)°]. Bifurcated intra­molecular N—H⋯N and N—H⋯O hydrogen bonds formed between iminium groups and amine N atoms and naphthalen-2-olate O atoms generate S(5) and S(6) ring motifs, respectively. In the crystal, neighbouring zwitterions are linked through weak C—H⋯O inter­actions, giving rise to screw chains along [010]. Mol­ecules in these chains are linked to those of an adjacent chains through N—H⋯O hydrogen bonds and weak C—H⋯O inter­actions, forming sheets parallel to the ac plane. O⋯C [2.895 (3) Å] short contacts and π–π inter­actions [centroid–centroid distance = 3.8249 (19) Å] are also observed.
doi:10.1107/S1600536810014923
PMCID: PMC2979134  PMID: 21579252
16.  Diaqua­bis[4-(dimethyl­amino)benzoato](isonicotinamide)zinc(II) 
The mol­ecule of the title ZnII complex, [Zn(C9H10NO2)2(C6H6N2O)(H2O)2], contains two 4-(dimethyl­amino)benzoate (DMAB) ligands, one isonicotinamide (INA) ligand and two water mol­ecules; one of the DMAB ions acts as a bidentate ligand while the other and INA are monodentate ligands. The four O atoms in the equatorial plane around the Zn atom form a distorted square-planar arrangement, while the distorted octa­hedral coordination is completed by the N atom of the INA ligand and the O atom of the water mol­ecule in the axial positions. Intra­molecular C—H⋯O hydrogen bonding results in the formation of a six-membered ring adopting an envelope conformation. The dihedral angle between the carboxyl groups and the adjacent benzene rings are 4.87 (16) and 2.2 (2)°, while the two benzene rings are oriented at a dihedral angle of 65.13 (8)°. The dihedral angle between the benzene and pyridine rings are 11.47 (7) and 74.83 (8)°, respectively. In the crystal structure, inter­molecular O—H⋯O, O—H⋯N and N—H⋯O hydrogen bonds link the mol­ecules into a supra­molecular structure. π–π contacts between the pyridine and benzene rings and between the benzene rings [centroid–centroid distances = 3.695 (1) and 3.841 (1) Å, respectively] further stabilize the structure. Weak inter­molecular C—H⋯π inter­actions are also present.
doi:10.1107/S1600536809017620
PMCID: PMC2969605  PMID: 21583016
17.  4-Amino­pyridinium 4-nitro­benzoate 4-nitro­benzoic acid 
The asymmetric unit of the title compound, C5H7N2 +·C7H4NO4 −·C7H5NO4, consists of an amino­pyridinium cation, a 4-nitro­benzoate anion and a neutral 4-nitro­benzoic acid mol­ecule. The pyridine ring forms dihedral angles of 64.70 (5)° and 70.37 (5)°, respectively, with the benzene rings of 4-nitro­benzoic acid and 4-nitro­benzoate. In the crystal structure, the cations, anions and the neutral 4-nitro­benzoic acid mol­ecules are linked by O—H⋯O and N—H⋯O hydrogen bonds, forming a two-dimensional network parallel to (001). Adjacent networks are cross-linked via C—H⋯O hydrogen bonds and π–π stacking inter­actions [centroid–centroid distances 3.6339 (6) and 3.6566 (6) Å].
doi:10.1107/S1600536808027761
PMCID: PMC2959422  PMID: 21201092
18.  N-[(2,6-Di­ethyl­phen­yl)carbamo­thio­yl]-2,2-di­phenyl­acetamide 
In the title compound, C25H26N2OS, the diethyl-substituted benzene ring forms dihedral angles of 67.38 (9) and 55.32 (9)° with the terminal benzene rings. The mol­ecule adopts a trans–cis conformation with respect to the orientations of the di­phenyl­methane and 1,3-di­ethyl­benzene groups with respect to the S atom across the C—N bonds. This conformation is stabilized by an intra­molecular N—H⋯O hydrogen bond, which generates an S(6) ring. In the crystal, pairs of N—H⋯S hydrogen bonds link the mol­ecules into inversion dimers, forming R 2 2(6) loops. The dimer linkage is reinforced by a pair of C—H⋯S hydrogen bonds, which generate R 2 2(8) loops. Weak C—H⋯π and π–π [centroid–centroid seperation = 3.8821 (10) Å] inter­actions also occur in the crystal structure.
doi:10.1107/S1600536813013354
PMCID: PMC3685105  PMID: 23795124
19.  Crystal structures of 1,4-di­aza­bicyclo­[2.2.2]octan-1-ium 4-nitro­benzoate dihydrate and 1,4-di­aza­bicyclo­[2.2.2]octane-1,4-diium bis­(4-nitro­benzoate): the influence of solvent upon the stoichiometry of the formed salt 
Solvent-dependent outcomes are noted in co-crystallization experiments between DABCO and 4-nitrobenzoic acid with mono- and diprotonated forms of DABCO are isolated.
The 1:1 co-crystallization of 1,4-di­aza­bicyclo­[2.2.2]octane (DABCO) with 4-nitro­benzoic acid in ethanol–water (3/1) gave the salt dihydrate C6H13N2 +·C7H4NO4 −·2H2O, (1), whereas from methanol, the salt C6H14N2 2+·2C7H4NO4 −, (2), was isolated. In (1), the cation and anion are linked by a strong N—H⋯O hydrogen bond, and the carboxyl­ate anion is close to planar [dihedral angle between terminal residues = 6.83 (9)°]. In (2), a three-ion aggregate is assembled by two N—H⋯O hydrogen bonds, and the carboxyl­ate anions are again close to planar [dihedral angles between terminal residues = 1.7 (3) and 5.9 (3)°]. Through the inter­vention of solvent water mol­ecules, which self-assemble into helical supra­molecular chains along the b axis, the three-dimensional architecture in (1) is stabilized by water–DABCO O—H⋯N and water–carboxyl­ate O—H⋯O hydrogen bonds, with additional stability afforded by C—H⋯O inter­actions. The global crystal structure comprises alternating layers of water mol­ecules and ion pairs stacked along the c axis. In the crystal of (2), the three-ion aggregates are assembled into a three-dimensional architecture by a large number of methyl­ene–carboxyl­ate/nitro C—H⋯O inter­actions as well as π–π contacts between inversion-related benzene rings [inter-centroid distances = 3.5644 (16) and 3.6527 (16) Å]. The cations and anions assemble into alternating layers along the c axis.
doi:10.1107/S1600536814011532
PMCID: PMC4120614  PMID: 25161500
crystal structure; amine; carb­oxy­lic acid; co-crystallization; salt formation
20.  Crystal structures of N-(pyridin-2-ylmeth­yl)pyrazine-2-carboxamide (monoclinic polymorph) and N-(pyridin-4-ylmeth­yl)pyrazine-2-carboxamide1  
The title molecules, HL1 and HL2, differ in their conformation with the pyridine ring being inclined to the pyrazine ring by 61.34 (6) and 84.33 (12)°, respectively. The crystal packing is also slightly different, with molecules of HL1 linked by pairs of N—H⋯N hydrogen bonds, forming inversion dimers, while for HL2 molecules are linked by N—H⋯N and C—H⋯N hydrogen bonds, forming chains along [010].
The title compounds, C11H10N4O (HL1) and C11H10N4O (HL2), are pyridine 2-ylmethyl and 4-ylmethyl derivatives, respectively, of pyrazine-2-carboxamide. HL1 was measured at 153 K and crystallized in the monoclinic space group P21/c with Z = 4. There has been a report of the same structure measured at room temperature but assumed to crystallize in the triclinic space group P-1 with Z = 4 [Sasan et al. (2008 ▶). Monatsh. Chem. 139, 773–780]. In HL1, the pyridine ring is inclined to the pyrazine ring by 61.34 (6)°, while in HL2 this dihedral angle is 84.33 (12)°. In both mol­ecules, there is a short N—H⋯N inter­action involving the pyrazine carboxamide unit. In the crystal of HL1, mol­ecules are linked by N—H⋯N hydrogen bonds, forming inversion dimers with an R 2 2(10) ring motif. The dimers are linked via bifurcated-acceptor C—H⋯O hydrogen bonds, forming sheets lying parallel to (102). The sheets are linked via C—H⋯N hydrogen bonds, forming a three-dimensional structure. In the crystal of HL2, mol­ecules are linked by N—H⋯N and C—H⋯N hydrogen bonds to form chains propagating along [010]. The chains are linked via C—H⋯O hydrogen bonds, forming sheets lying parallel to (100). Within the sheets there are π–π inter­actions involving neighbouring pyrazine rings [inter-centroid distance = 3.711 (15) Å]. Adjacent sheets are linked via parallel slipped π–π inter­actions involving inversion-related pyridine rings [inter-centroid distance = 3.6395 (17) Å], forming a three-dimensional structure.
doi:10.1107/S1600536814009519
PMCID: PMC4120586  PMID: 25161497
crystal structure; pyrazine; pyridine; carboxamide
21.  N-(4-Methyl-2-nitro­phen­yl)succinamic acid 
In the title compound, C11H12N2O5, the conformation of the N—H bond in the amide segment is syn to the ortho-nitro group in the benzene ring. The amide C=O and the carboxyl C=O of the acid segment are syn to each other and both are anti to the H atoms on the adjacent –CH2 groups. Furthermore, the C=O and O—H bonds of the acid group are in syn positions with respect to each other. The dihedral angle between the benzene ring and the amide group is 36.1 (1)°. The amide H atom shows bifurcated intra­molecular hydrogen bonding with an O atom of the ortho-nitro group and an inter­molecular hydrogen bond with the carbonyl O atom of another mol­ecule. In the crystal, the N—H⋯O(C) hydrogen bonds generate a chain running along the [100] direction. Inversion dimers are formed via a pair of O—H⋯O(C) interactions, that form an eight-membered hydrogen-bonded ring involving the carboxyl group.
doi:10.1107/S1600536812007258
PMCID: PMC3297880  PMID: 22412683
22.  3-Benzyl-4-ethyl-1H-1,2,4-triazole-5(4H)-thione 
The title compound, C11H13N3S, exists in the 5-thioxo tautomeric form. The benzene ring exhibits disorder with a refined ratio of 0.77 (2):0.23 (2) for components A and B with a common bridgehead C atom. The 1,2,4-triazole ring is essentially planar, with a maximum deviation of 0.002 (3) Å for the benzyl-substituted C atom, and forms dihedral angles of 88.94 (18) and 86.56 (49)° with the benzene rings of components A and B, respectively. The angle between the plane of the ethyl chain and the mean plane of 1,2,4-triazole ring is 88.55 (15)° and this conformation is stabilized by an intra­molecular C—H⋯S contact. In the crystal, pairs of N—H⋯S hydrogen bonds link mol­ecules into inversion dimers. π–π inter­actions are observed between the triazole and benzene rings, with centroid–centroid separations of 3.547 (4) and 3.544 (12) Å for components A and B, and slippages of 0.49 (6) and 0.58 (15) Å, respectively.
doi:10.1107/S1600536812051276
PMCID: PMC3569223  PMID: 23424446
23.  2-(1H-Benzimidazol-2-yl)phenol 
The title mol­ecule, C13H10N2O, is essentially planar, the maximum deviation from the plane of the non-H atoms being 0.016 (2) Å. The imidazole ring makes a dihedral angle of 0.37 (13)° with the attached benzene ring. An intra­molecular O—H⋯N hydrogen bond generates an S(6) ring motif. In the crystal, mol­ecules are linked through N—H⋯O hydrogen bonds, forming chains propagating in [001]. The crystal packing also features four π–π stacking inter­actions involving the imidazole ring, fused benzene ring and attached benzene ring system [centroid–centroid distances = 3.6106 (17), 3.6108 (17), 3.6666 (17) and 3.6668 (17) Å].
doi:10.1107/S1600536814001366
PMCID: PMC3998336  PMID: 24764897
24.  [3-(5-Nitro-2-fur­yl)-1-phenyl-1H-pyrazol-4-yl](phen­yl)methanone 
In the title pyrazole compound, C20H13N3O4, an intra­molecular C—H⋯O hydrogen bond generates a seven-membered ring, producing an S(7) ring motif. The essentially planar furan and pyrazole rings [maximum deviations of 0.002 (1) and 0.007 (1) Å, respectively] are coplanar with each other, forming a dihedral angle of 3.06 (10)°. The pyrazole ring forms dihedral angles of 8.51 (9) and 56.81 (9)° with the two benzene rings. The nitro group is coplanar with the attached furan ring, as indicated by the dihedral angle of 2.5 (3)°. In the crystal packing, inter­molecular C—H⋯O hydrogen bonds link adjacent mol­ecules into two-mol­ecule-wide chains along the a axis. The crystal packing is further stabilized by weak inter­molecular C—H⋯π and π–π inter­actions [centroid–centroid distance = 3.4441 (10) Å].
doi:10.1107/S1600536810015199
PMCID: PMC2979013  PMID: 21579253
25.  5-[(4-Fluoro­anilino)meth­yl]-6-methyl-N-(4-methyl­phen­yl)-2-phenyl­pyrimidin-4-amine 
In the title compound, C25H23FN4, the pyrimidine ring makes dihedral angles of 11.3 (2), 24.5 (2) and 70.1 (2)° with the phenyl and two benzene rings, and the mol­ecular conformation is stabilized by an intra­molecular N—H⋯N hydrogen bond with an S(6) ring motif. In the crystal, a pair of weak C—H⋯F hydrogen bonds link two mol­ecules into an inversion dimer with an R 2 2(16) motif. In the dimer, there is also an inter­molecular π–π stacking inter­action [centroid–centroid distance = 3.708 (4) Å] between the fluorinated benzene rings. The dimers are further linked by a C—H⋯π inter­action, so forming a column along the c axis.
doi:10.1107/S160053681203783X
PMCID: PMC3470299  PMID: 23125712

Results 1-25 (499792)