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1.  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.
PMCID: PMC4186174  PMID: 25309256
8-hy­droxy­quinoline; hydrogen bonds; polymorphism; crystal structure
2.  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
3.  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
4.  (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
5.  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
6.  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
7.  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
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).
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).
PMCID: PMC3772465  PMID: 24046608
10.  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
11.  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
12.  (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
13.  1,1′,2,2′-Tetra­methyl-3,3′-(p-phenyl­enedimethyl­ene)diimidazol-1-ium bis­(tetra­fluoridoborate) 
The title imidazolium-based ionic-liquid salt, C18H24N4 2+·2BF4 −, has the cation lying about a center of inversion. The five-membered imidazole ring is approximately perpendicular to the six-membered phenyl­ene ring [dihedral angle = 86.9 (1)°]. The tetra­fluoro­borate anion is disordered over two sites in a 0.722 (3):0.278 (3) ratio.
PMCID: PMC2977162  PMID: 21583531
14.  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.
PMCID: PMC2959632  PMID: 21580991
15.  1,1′,2,2′-Tetra­methyl-3,3′-(p-phenyl­enedimethyl­ene)diimidazol-1-ium bis­(hexa­fluoridophosphate) 
The title imidazolium-based ionic-liquid salt, C18H24N4 2+·2PF6 −, has the cation lying about a center of inversion. The five-membered imidazole ring is disordered over two positions (the methyl substituents are ordered). This imidazole ring is approximately perpendicular to the six-membered phenyl­ene ring [dihedral angle = 81.3 (8)° for one disorder component and 83.8 (8)° for the other; the two components are off-set by 2.7 (8)°]. The crystal is a non-merohedral twin with a twin component of 23%.
PMCID: PMC2977199  PMID: 21583532
16.  3,3′-(p-Phenyl­enedimethyl­ene)di-1H-imidazol-1-ium bis­(4-nitro­benzoate)–4-nitro­benzoic acid (1/2) 
The asymmetric unit of the title compound, C14H16N4 2+·2C7H4NO4 −·2C7H5NO4, comprises one-half of the 3,3′-(p-phenyl­enedimethyl­ene)di-1H-imidazol-1-ium dication, which lies on an inversion centre, one 4-nitro­benzoate anion and one 4-nitro­benzoic acid mol­ecule. In the crystal, the components are linked into a two-dimensional network parallel to (110) by O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds.
PMCID: PMC2979657  PMID: 21579549
17.  3,3′-Dibenzyl-1,1′-(2,4,6-trimethyl-m-phenyl­enedimethyl­ene)diimidazol-3-ium dibromide 
In the title molecular salt, C31H34N4 2+·2Br−, the central benzene ring makes dihedral angles of 80.47 (12) and 82.78 (12)° with the adjacent imidazole rings. The dihedral angle between the two terminal phenyl rings is 79.16 (13)°. In the crystal, the cations and anions are linked via C—H⋯Br hydrogen bonds, forming supra­molecular chains along the c axis.
PMCID: PMC3051991  PMID: 21522396
18.  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
19.  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
20.  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
21.  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.
PMCID: PMC3239035  PMID: 22199883
22.  10α-Hy­droxy-13-{[4-(4-meth­oxy­phen­yl)piperazin-1-yl]meth­yl}-4,9-dimethyl-3,8,15-trioxatetra­cyclo­[,4.07,9]penta­decan-14-one 
The title compound, C26H36N2O6, was synthesized from 9α-hy­droxy­parthenolide (9α-hy­droxy-4,8-dimethyl-12-methylen-3,14-dioxa-tricyclo­[,4]tetra­dec-7-en-13-one), which was isolated from the chloro­form extract of the aerial parts of Anvillea radiata. The mol­ecule is built up from fused five- and ten-membered rings with two additional ep­oxy ring systems and a meth­oxy­phenyl­piperazine group as a substituent. The ten-membered ring adopts an approximate chair–chair conformation, while the piperazine ring displays a chair conformation and the five-membered ring shows an envelope conformation with the C atom closest to the hy­droxy group forming the flap. The mol­ecular conformation is determined by an O—H⋯N hydrogen bond between the hy­droxy group and a piperazine N atom. The crystal structure is built up by weak C—H⋯O inter­actions.
PMCID: PMC3295488  PMID: 22412599
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)°.
PMCID: PMC3238907  PMID: 22199760
24.  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
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 (333034)