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1.  (m-Phenyl­enedimethyl­ene)diammonium dichloride 
The asymmetric unit of the title compound, C8H14N2 2+·2Cl−, contains one and a half of the dications and three chloride anions. The half molecule is completed by crystallographic twofold symmetry with two C atoms lying on the rotation axis. The two ammonium groups in each cation adopt a trans conformation with respect ot the benzene ring. The ammonium groups and chloride anions are involved in the formation of a three-dimensional N—H⋯Cl hydrogen-bonding network, which stabilizes the crystal packing.
PMCID: PMC2959707  PMID: 21580926
2.  3,3′-Dicyclo­pentyl-1,1′-(1,3-phenyl­enedimethyl­ene)dibenzimidazol-1-ium bis­(hexa­fluoro­phosphate) 
In the title compound, C32H36N4 2+·2PF6 −, the cation and the anions each have crystallographic twofold rotation symmetry. The benzimidazole ring is almost planar [r.m.s. deviation = 0.0161 (1) Å] and makes a dihedral angle of 5.77 (4)° with its symmetry-related component and a dihedral angle of 80.96 (5)° with the central benzene ring. The cyclo­pentyl ring adopts a half-chair conformation. In the crystal, mol­ecules are linked into a three-dimensional network through C—H⋯F hydrogen bonds. A C—H⋯π inter­action is also observed.
PMCID: PMC3379432  PMID: 22719630
3.  (m-Phenyl­enedimethyl­ene)bis­(triphenyl­phospho­nium) bis­[chlorido(penta­fluoro­phen­yl)aurate(I)] dichloro­methane disolvate 
The title compound, (C44H38P2)[AuCl(C6F5)]2·2CH2Cl2, crystallizes with a twofold rotation axis through the central benzene ring in the bis-phospho­nium dication. In the crystal, the dications and anions are ordered into columns running parallel to the c axis by contacts of the pro-ylidic CH2 groups with the Cl atom of one and an ortho-F atom of another anion. The space between the columns is occupied by CH2Cl2 solvent mol­ecules.
PMCID: PMC2971990  PMID: 21578550
4.  1,3-Bis(2-chloro­phen­yl)thio­urea: a monoclinic polymorph 
The title compound, C13H10Cl2N2S, represents a monoclinic polymorph of the previously reported ortho­rhom­bic form [Ramnathan et al. (1996 ▶). Acta Cryst. C52, 134–136]. The mol­ecule is twisted with the dihedral angle between the benzene rings being 55.37 (7)°. The N—H atoms are syn to each other, which contrasts their anti disposition in the ortho­rhom­bic form. In the crystal, mol­ecules assemble into zigzag chains along the c axis via N—H⋯S hydrogen bonds. Chains are connected into layers via C—H⋯Cl inter­actions, and these stack along the a axis.
PMCID: PMC3247371  PMID: 22219989
5.  A monoclinic polymorph of N-(3-chloro­phen­yl)benzamide 
The title compound, C13H10ClNO, (I), is a polymorph of the structure, (II), first reported by Gowda et al. [Acta Cryst. (2008), E64, o462]. In the original report, the compound crystallized in the ortho­rhom­bic space group Pbca (Z = 8), whereas the structure reported here is monoclinic P21/c (Z = 4). The principal difference between the two forms lies in the relative orientations of the phenyl and benzene rings [dihedral angle = 8.90 (13)° for (I) and 61.0 (1)° for (II)]. The inclination of the amide –CONH– units to the benzoyl ring is more similar [15.8 (7)° for (I) and 18.2 (2)° for (II)]. In both forms, the N—H bonds are anti to the 3-chloro substituents of the aniline rings. In the crystal, inter­molecular N—H⋯O hydrogen bonds form C(4) chains along c. These chains are bolstered by weak C—H⋯O inter­actions that generate R 2 1(6) and R 2 1(7) ring motifs.
PMCID: PMC3008970  PMID: 21589001
6.  An ortho­rhom­bic polymorph of 5-[(4-methyl­phen­yl)diazen­yl]salicylaldehyde 
The title compound, C14H12N2O2, is an ortho­rhom­bic polymorph of the previously reported monoclinic form [Bakir et al. (2005 ▶). Acta Cryst. E61, o1611–o1613]. The dihedral angle between the aromatic rings is 4.32 (13)°. The mol­ecular structures of the two polymorphs, including short intra­molecular O—H⋯O hydrogen bonds between the the hydr­oxy and keto groups, are quite similar but their crystal packings are distinct. Unlike the monoclinic form, in which centrosymmetrically related hydr­oxy and keto groups form {⋯H⋯O}2 synthons via weak O—H⋯O contacts, leading to dimeric aggregates, in the ortho­rhom­bic form, the hydrogen bonding between these groups leads to the formation of supra­molecular chains orientated along the a axis.
PMCID: PMC2971774  PMID: 21578791
7.  5,5′-[(1,4-Phenyl­enedimethyl­ene)bis­(sulfanedi­yl)]bis­(1-methyl-1H-1,2,3,4-tetra­zole) 
The title mol­ecule, C12H14N8S2, has point symmetry since it is situated on a crystallographic centre of symmetry. The 1-meth­yl/5-thio groups are in an anti­periplanar conformation. The dihedral angle between the benzene and tetra­zole rings is 84.33 (2)°. In the crystal, C—H⋯N hydrogen bonds link mol­ecules into ladder-like chains running along the b axis. There are also C—H⋯π inter­actions present in the crystal structure.
PMCID: PMC3247454  PMID: 22220072
8.  Second monoclinic polymorph of 4-[(1H-benzimidazol-1-yl)meth­yl]benzoic acid 
Recently, we reported the first monoclinic [Kuai & Cheng (2011). Acta Cryst., E67, o2787] and the ortho­rhom­bic polymorph [Kuai & Cheng (2011). Acta Cryst., E67, o3014] of the title compound, C15H12N2O2. Another monoclinic polymorph was obtained accidentally by the hydro­thermal reaction of the title compound with manganese chloride in the presence of potassium hydroxide at 413 K. The asymmetric unit consists of four independent mol­ecules. In the crystal, O—H⋯N hydrogen bonds link the independent mol­ecules into four separate chains parallel to the b axis.
PMCID: PMC3238873  PMID: 22199726
9.  3,3′-(p-Phenyl­enedimethyl­ene)di­imidazol-1-ium bis­(3-carb­oxy-4-hydroxy­benzene­sulfonate) dihydrate 
In the title compound, C14H16N4 2+·2C7H5O6S−·2H2O, the 3,3′-(p-phenyl­enedimethyl­ene)diimidazol-1-ium dication lies on a crystallographic inversion center. In the crystal structure, dications, anions and solvent water mol­ecules are linked via O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds, and C—H⋯π inter­actions, forming a three-dimensional network containing R 2 2(4), R 2 4(12), R 4 4(22), R 8 10(32) and R 12 14(66) ring motifs.
PMCID: PMC2968313  PMID: 21581963
10.  4,4′-Dimethyl-1,1′-(p-phenyl­enedimethyl­ene)dipyridinium bis­[7,7,8,8-tetra­cyano­quinodimethanide(1−)] 
In the title salt, C20H22N2 2+·2C12H4N4 −, the cations and anions stack along the b axis into segregated columns. In the cation, which has a crystallographically imposed centre of symmetry, the dihedral angle between the benzene and pyridine rings is 89.14 (4)°. Centrosymmetrically related anions form dimers by π–π stacking inter­actions, with centroid–centroid separations of 3.874 (4) Å. The crystal packing is stabilized by inter­columnar C—H⋯N hydrogen bonds.
PMCID: PMC2979426  PMID: 21579443
11.  1,1′,2,2′-Tetra­methyl-3,3′-(p-phenyl­enedimethyl­ene)diimidazol-1-ium bis­(trifluoro­methane­sulfonate) 
In the solid form of the title imidazolium-based ionic liquid salt, C18H24N4 2+·2CF3SO3 −, the complete cation is generated by a crystallographic inversion centre. The five-membered imidazole ring is approximately perpendicular to the six-membered phenyl­ene ring [dihedral angle = 85.11 (11)°]. In the crystal, the components are linked by C—H⋯O interactions.
PMCID: PMC3007914  PMID: 21588775
12.  A novel monoclinic phase of impurity-doped CaGa2S4 as a phosphor with high emission intensity 
In the solid-state synthesis of impurity-doped CaGa2S4, calcium tetra­thio­digallate(III), a novel phosphor material (denominated as the X-phase), with monoclinic symmetry in the space group P21/a, has been discovered. Its emission intensity is higher than that of the known ortho­rhom­bic polymorph of CaGa2S4 crystallizing in the space group Fddd. The asymmetric unit of the monoclinic phase consists of two Ca, four Ga and eight S sites. Each of the Ca and Ga atoms is surrounded by seven and four sulfide ions, respectively, thereby sharing each of the sulfur sites with the nearest neighbours. In contrast, the corresponding sites in the ortho­rhom­bic phase are surrounded by eight and four S atoms, respectively. The photoluminescence peaks from Mn2+ and Ce3+ in the doped X-phase, both of which are supposed to replace Ca2+ ions, have been observed to shift towards the high energy side in comparison with those in the ortho­rhom­bic phase. This suggests that the crystal field around the Mn2+ and Ce3+ ions in the X-phase is weaker than that in the ortho­rhom­bic phase.
PMCID: PMC3379052  PMID: 22719273
13.  Pseudomerohedrally twinned monoclinic structure of unfolded ‘free’ nona­ctin: comparative analysis of its large conformational change upon encapsulation of alkali metal ions 
The title compound, C40H64O12, crystallizes in a pseudo­merohedrally twinned primitive monoclinic cell with similar contributions of the two twin components. There are two symmetry-independent half-mol­ecules of nona­ctin in the asymmetric unit. Each mol­ecule has a pseudo-S 4 symmetry and resides on a crystallographic twofold axis; the axes pass through the mol­ecular center of mass and are perpendicular to the plane of the macrocycle. The literature description of the room-temperature structure of nona­ctin as an order–disorder structure in an ortho­rhom­bic unit cell is corrected. We report a low-temperature high-precision ordered structure of ‘free’ nona­ctin that allowed for the first time precise determination of its bond distances and angles. It possesses an unfolded and more planar geometry than its complexes with encapsulated Na+, K+, Cs+, Ca2+ or NH4 + cations that exhibit more isometric overall conformations.
PMCID: PMC2816929  PMID: 19805886
14.  An ortho­rhom­bic polymorph of pyrazino­[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile 
The title compound, C16H6N6, is a polymorph of the previously reported structure [Kozlov & Goldberg (2008 ▶). Acta Cryst. C64, o498–o501]. Unlike the previously reported monoclinic polymorph (space group P21/c, Z = 8), the title compound reveals ortho­rhom­bic symmetry (space group Pnma, Z = 4). The mol­ecule shows crystallographic mirror symmetry, while the previously reported structure exhibits two independent mol­ecules per asymmetric unit. In the title compound, adjacent mol­ecules are essentially parallel along the c axis and tend to be vertical along the b axis with dihedral angles of 72.02 (6)°. However, in the reported polymorph, the entire crystal structure shows an anti­parallel arrangement of adjacent columns related by inversion centers and the two independent mol­ecules are nearly parallel with a dihedral angle of 2.48 (6)°.
PMCID: PMC3238907  PMID: 22199760
15.  Chlorido{4-chloro-2-[(2-morpholinoeth­yl)imino­meth­yl]phenolato-κ3 N,N′,O}copper(II) 
The CuII atom in the title compound, [Cu(C13H16ClN2O2)Cl], exists in a distorted square-planar coordination environment as the deprotonated Schiff base chelates to the CuII atom through three atom sites. In the crystal structure, adjacent mol­ecules are linked by a Cu⋯Cl [3.011 (1) Å] bridge, generating a linear chain running along the b axis of the ortho­rhom­bic unit cell.
PMCID: PMC2977511  PMID: 21583336
16.  5-[(1R,2R,4R)-2-Meth­oxy-1,7,7-tri­methylbi­cyclo­[2.2.1]hept-2-yl]-1H-tetra­zole 
The title compound, C12H20N4O, undergoes a phase transition on cooling. The room-temperature structure is tetra­gonal (P43212, Z′ = 1), with the meth­oxy­bornyl group being extremely disordered. Below 213 K the structure is ortho­rhom­bic (P212121, Z′ = 2), with ordered mol­ecules. The two independent mol­ecules (A and B) have very similar conformations; significant differences only occur for the torsion angles about the Cborn­yl—Ctetra­zole bonds. The independent mol­ecules are approximately related by the pseudo-symmetry relation: xB = −1/4 + yA, yB = 3/4 - xA and zB = 1/4 + zA. In the crystal, mol­ecules are connected by N—H⋯N hydrogen bonds between the tetra­zole groups, forming a pseudo-43 helix parallel to the c-axis direction. The crystal studied was a merohedral twin with a refined twin fraction value of 0.231 (2).
PMCID: PMC3772465  PMID: 24046608
17.  An ortho­rhom­bic polymorph of 1-[(ferrocen­yl)(hydr­oxy)meth­yl]-1,2-dicarba-closo-dodecaborane 
An ortho­rhom­bic polymorph of the title compound, [Fe(C5H5)(C8H17B10O)] or C13H22B10FeO, is described here in addition to the known monoclinic polymorph [Crundwell et al. (1999 ▶). Acta Cryst. C55, IUC9900087]. The asymmetric unit contains four independent mol­ecules with Ccage–Ccage distances of 1.636 (16)–1.700 (16) Å, and with the methyl­hydr­oxy groups disordered over two positions in each mol­ecule [occupancy ratios 0.80 (2):0.20 (2), 0.59 (3):0.41 (3), 0.60 (2):0.40 (2) and 0.793 (17):0.207 (17)].
PMCID: PMC2980021  PMID: 21579923
18.  5-(Prop-2-yn-1-yl)-5H-dibenzo[b,f]azepine: ortho­rhom­bic polymorph 
In the title ortho­rhom­bic polymorph (space group Iba2), C17H13N, the dihedral angle between the benzene rings is 55.99 (10)° and the azepine ring adopts a boat conformation. In the crystal, mol­ecules are linked by C—H⋯π contacts. The previously-reported polymorph [Yousuf et al. (2012 ▶). Acta Cryst. E68, o1101] crystallizes in the monoclinic system (space group P21/c) with two mol­ecules in the asymmetric unit.
PMCID: PMC3588308  PMID: 23476404
19.  A monoclinic polymorph of (1E,5E)-1,5-bis­(2-hy­droxy­benzyl­idene)thio­carbono­hydrazide 
The title compound, C15H14N4O2S, is a derivative of thio­ureadihydrazide. In contrast to the previously reported polymorph (ortho­rhom­bic, space group Pbca, Z = 8), the current study revealed monoclinic symmetry (space group P21/n, Z = 4). The mol­ecule shows non-crystallographic C 2 as well as approximate C s symmetry. Intra­molecular bifurcated O—H⋯(N,S) hydrogen bonds, are present. In the crystal, inter­molecular N—H⋯S hydrogen bonds and C—H⋯π contacts connect the mol­ecules into undulating chains along the b axis. The shortest centroid–centroid distance between two aromatic systems is 4.5285 (12) Å.
PMCID: PMC3213636  PMID: 22091213
20.  A monoclinic polymorph of di-μ-oxido-bis­({2-[2-(methyl­amino)ethyl­imino­methyl]phenolato-κ3 N,N′,O}oxidovanadium(V)) 
A new monoclinic polymorph of the title compound, [V2(C10H13N2O)2O4], which is a centrosymmetric dimer, crystallizes in space group P21/c, whereas the previously known polymorph crystallizes in the ortho­rhom­bic space group Pbca [Mokry & Carrano (1993 ▶). Inorg. Chem. 32, 6119–6121]. Each VV atom is six-coordinated by one oxide group, two N atoms and one O atom from the Schiff base ligand, and by two additional bridging O atoms. The two methyl­ene groups are each disordered over two sites, with occupancy factors of 0.776 (14) and 0.224 (14). In the crystal structure, there are C—H⋯O hydrogen bonds and C—H⋯π inter­actions between the dimers.
PMCID: PMC2959960  PMID: 21581160
21.  Tetra­gonal polymorph of 5,5-dichloro­barbituric acid 
The tetra­gonal polymorph of 5,5-dichloro­barbituric acid (m.p. 478 K), C4H2Cl2N2O3, forms an N—H⋯O hydrogen-bonded tape structure along [001]. Two tapes related by a twofold rotation axis are associated via Cl⋯O contacts [3.201 (1) Å], and four such chain pairs are arranged around a fourfold roto-inversion axis. The crystal structures of the monoclinic and ortho­rhom­bic polymorphs have been reported previously [Gelbrich et al. (2011 ▶). CrystEngComm, 13, 5502–5509].
PMCID: PMC3254567  PMID: 22259517
22.  A new polymorph of N-phenyl­phthalimide 
During an attempt to prepare a cocrystal of N-phenyl­phthalimide, C14H9NO2, with N-(2,3,4,5,6-penta­fluoro­phen­yl)phthalimide, a new ortho­rhom­bic polymorph of the first component was obtained. This new form has Z′ = 0.5 and the mol­ecule is located around a twofold axis, whereas in the previously reported polymorph (space group Pbca), the mol­ecule has no crystallographically imposed symmetry. Pairs of C—H⋯O inter­actions between inversion-related phthalimide units arrange mol­ecules into tapes that are further assembled into (010) layers via stacking inter­actions between phthalimide fragments [inter­planar distance = 3.37 (5) Å].
PMCID: PMC2968531  PMID: 21582305
23.  A monoclinic polymorph of (R,R)-4,4′-dibromo-2,2′-[cyclo­hexane-1,2-diylbis(nitrilo­methanylyl­idene)]diphenol 
The title compound, C20H20Br2N2O2, a tetra­dentate Schiff base, is the enanti­omerically pure R,R-diastereomer of four possible stereoisomers. The mol­ecular structure reveals two strong intra­molecular O—H⋯N hydrogen bonds between the hy­droxy O atom and the imino N atom, which each generate S(6) rings. In the crystal, mol­ecules are stacked in columns along the a axis; when viewed down the b axis, successive columns are stacked in the opposite direction. The structure reported herein is the monoclinic polymorph of the previously reported ortho­rhom­bic form [Yi & Hu (2009 ▶). Acta Cryst. E65, o2643], in which the complete mol­ecule is generated by a crystallographic twofold axis.
PMCID: PMC3344566  PMID: 22590328
24.  A second ortho­rhom­bic polymorph of 2-(pyridin-4-ylmeth­oxy)phenol 
The crystal structure of the title compound, C12H11NO2, represents a new ortho­rhom­bic polymorph II of the previously reported ortho­rhom­bic form I [Zhang et al. (2009 ▶) Acta Cryst. E65, o3160]. In polymorph II, the six-membered rings form a dihedral angle of 13.8 (1)° [71.6 (1)° in I], and O—H⋯N hydrogen bonds link mol­ecules into chains along [100], whereas the crystal structure of I features hydrogen-bonded centrosymmetric dimers.
PMCID: PMC3344498  PMID: 22590260
25.  A monoclinic polymorph of 1-(4-chloro­phen­yl)-3-(4-methoxy­phen­yl)prop-2-en-1-one 
The crystal structure of the title compound, C16H13ClO2 (II), (space group P21/c,) is a polymorph of the structure, (I), reported by Harrison, Yathirajan, Sarojini, Narayana & Indira [Acta Cryst. (2006), E62, o1647–o1649] in the ortho­rhom­bic space group Pna21. The dihedral angle between the mean planes of the 4-chloro- and 4-meth­oxy-substituted benzene rings is 52.9 (1)° in (II) compared to 21.82 (6)° for polymorph (I). The dihedral angles between the mean planes of the prop-2-en-1-one group and those of the 4-chloro­phenyl and 4-methoxy­phenyl rings are 23.3 (3) and 33.7 (1)°, respectively. in (II). The corresponding values are 17.7 (1) and 6.0 (3)°, respectively, in polymorph (I). In the crystal, weak C—H⋯π inter­actions are observed.
PMCID: PMC2979778  PMID: 21579708

Results 1-25 (201166)