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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.
doi:10.1107/S1600536808031334
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.
doi:10.1107/S160053681202274X
PMCID: PMC3379432  PMID: 22719630
3.  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
4.  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.
doi:10.1107/S1600536812019113
PMCID: PMC3379052  PMID: 22719273
5.  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.
doi:10.1107/S1600536811043182
PMCID: PMC3247454  PMID: 22220072
6.  (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.
doi:10.1107/S1600536809045474
PMCID: PMC2971990  PMID: 21578550
7.  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.
doi:10.1107/S1600536812016376
PMCID: PMC3344566  PMID: 22590328
8.  An orthorhombic polymorph of mulinic acid 
The title compound [systematic name: (3S,3aS,10bR)-3-isopropyl-5a,8-dimethyl-2,3,4,5,5a,6,7,10,10a,10b-deca­hydro-endo-epidioxy­cyclo­hepta­[e]indene-3a(1H)-carboxylic acid], C20H30O4, is a polymorphic form of a previously reported structure [Loyola et al. (1990 ▶). Tetra­hedron, 46, 5413–5420]. The newly found ortho­rhom­bic polymorph crystallizes in P212121 with two mol­ecules in the asymmetric unit. The mol­ecules are linked into discrete D(2) chains by simple O—H⋯O inter­actions. There are only slight variations in the mol­ecular geometry and supra­molecular organization in the crystal structures of the two polymorphs. The densities are 1.145 (monoclinic, P21) and 1.155 Mg m−3 (ortho­rhom­bic, P212121).
doi:10.1107/S1600536810000528
PMCID: PMC2979944  PMID: 21579761
9.  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).
doi:10.1107/S1600536813014700
PMCID: PMC3772465  PMID: 24046608
10.  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.
doi:10.1107/S1600536811041894
PMCID: PMC3247371  PMID: 22219989
11.  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.
doi:10.1107/S1600536810040262
PMCID: PMC3008970  PMID: 21589001
12.  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.
doi:10.1107/S1600536809002086
PMCID: PMC2968313  PMID: 21581963
13.  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.
doi:10.1107/S1600536810017113
PMCID: PMC2979426  PMID: 21579443
14.  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.
doi:10.1107/S1600536810033490
PMCID: PMC3007914  PMID: 21588775
15.  Bis[(m-phenyl­enedimethyl­ene)­diammonium] tetra­deca­borate 
The title compound 2C8H14N2 2+·[B14O20(OH)6]4−, contains diprotonated C8H14N2 2+ cations and centrosymmetric tetra­deca­borate anions. The crystal structure is stabilized by O—H⋯O and N—H⋯O hydrogen bonds.
doi:10.1107/S1600536808033333
PMCID: PMC2959632  PMID: 21580991
16.  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.
doi:10.1107/S1600536809046868
PMCID: PMC2971774  PMID: 21578791
17.  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.
doi:10.1107/S1600536811045983
PMCID: PMC3238873  PMID: 22199726
18.  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.
doi:10.1107/S0108270109033083
PMCID: PMC2816929  PMID: 19805886
19.  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].
doi:10.1107/S1600536811054626
PMCID: PMC3254567  PMID: 22259517
20.  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
21.  Crystal structure of the di-Mannich base 4,4′-di­chloro-3,3′,5,5′-tetra­methyl-2,2′-[imidazolidine-1,3-diylbis(methyl­ene)]diphenol 
In the title compound, the imidizadoline ring adopts an envelope conformation and the nitro­gen lone pairs are oriented in a syn disposition. The crystal packing is stabilized by C—H⋯O hydrogen-bonding inter­actions.
The title compound, C21H26Cl2N2O2, was prepared in a solvent-free microwave-assisted synthesis, and crystallizes in the ortho­rhom­bic space group Pna21. The imidazolidine ring adopts an envelope conformation and its mean plane is almost perpendicular to the two pendant aromatic rings [dihedral angles = 84.61 (9) and 86.54 (9)°]. The mol­ecular structure shows the presence of two intra­molecular O—H⋯N hydrogen bonds between the phenolic hy­droxy groups and imidazolidine N atoms. The two 3-chloro-6-hy­droxy-2,4-di­methyl­benzyl groups are located in a cis orientation with respect to the imidazolidine fragment. As a result, the lone pairs of electrons on the N atoms are presumed to be disposed in a syn conformation. This is therefore the first example of an exception to the ‘rabbit-ears’ effect in such 2,2′-[imidazolidine-1,3-diylbis(methyl­ene)]diphenol derivatives.
doi:10.1107/S2056989015002212
PMCID: PMC4350744  PMID: 25844196
crystal structure; imidazolidine; di-Mannich base; hydrogen bonding; syn conformation
22.  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.
doi:10.1107/S1600536809025215
PMCID: PMC2977511  PMID: 21583336
23.  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)°.
doi:10.1107/S1600536811047039
PMCID: PMC3238907  PMID: 22199760
24.  Investigations of new potential photo-acid generators: crystal structures of 2-[(E)-2-phenyl­ethen­yl]phenol (ortho­rhom­bic polymorph) and (2E)-3-(2-bromo­phen­yl)-2-phenyl­prop-2-enoic acid 
In the crystal of the ortho­rhom­bic polymorph of compound (I), the mol­ecules are linked into chains by O—H⋯π inter­actions. In compound (II), carb­oxy­lic acid inversion dimers are observed; the dimers are linked into chains by C—H⋯O hydrogen bonds.
The title compounds, C14H12O, (I), and C15H11BrO2, (II), were prepared and characterized as part of our studies of potential new photo-acid generators. In (I), which crystallizes in the ortho­rhom­bic space group Pca21, compared to P21/n for the previously known monoclinic polymorph [Cornella & Martin (2013 ▸). Org. Lett. 15, 6298–6301], the dihedral angle between the aromatic rings is 4.35 (6)° and the OH group is disordered over two sites in a 0.795 (3):0.205 (3) ratio. In the crystal of (I), mol­ecules are linked by O—H⋯π inter­actions involving both the major and minor –OH disorder components, generating [001] chains as part of the herringbone packing motif. The asymmetric unit of (II) contains two mol­ecules with similar conformations (weighted r.m.s. overlay fit = 0.183 Å). In the crystal of (II), both mol­ecules form carboxyl­ate inversion dimers linked by pairs of O—H⋯O hydrogen bonds, generating R 2 2(8) loops in each case. The dimers are linked by pairs of C—H⋯O hydrogen bonds to form [010] chains.
doi:10.1107/S2056989016002942
PMCID: PMC4778828  PMID: 27006818
crystal structure; stilbene; cinnamic acid; photo-acid generator; O—H⋯π inter­actions
25.  Crystal structure of benzene-1,3,5-tri­carb­oxy­lic acid–4-pyridone (1/3) 
A 5:1 mixture of 4-hy­droxy­pyridine with benzene 1,3,5-tri­carb­oxy­lic acid in methanol yields the title hydrogen-bonded framework compound. This compound crystallizes in the ortho­rhom­bic space group Pna21 and is a polymorph of the same stoichiometric species, reported in Cc.
Slow co-crystallization of a solution of benzene-1,3,5-tri­carb­oxy­lic acid with a large excess of 4-hy­droxy­pyridine produces an inter­penetrating, three-dimensional, hydrogen-bonded framework consisting of three 4-pyridone and one benzene-1,3,5-tri­carb­oxy­lic acid mol­ecules, C9H6O6·3C5H5NO. This structure represents an ortho­rhom­bic polymorph of the previously reported C-centered, monoclinic structure [Campos-Gaxiola et al. (2014 ▸). Acta Cryst. E70, o453–o454].
doi:10.1107/S2056989015017867
PMCID: PMC4644998  PMID: 26594492
crystal structure; hydrogen-bond framework; polymorph

Results 1-25 (410553)