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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.  Absolute configuration of naturally occurring glabridin 
Glabridin is a species-specific biomarker from the roots Glycyrrhiza glabra L. (European licorice, Fabaceae). Stereochemical analysis, including circular dichroism, NMR data and an X-ray diffraction data set with Bijvoet differences, confirms that glabridin, purified from its natural source, is found only in a C3 R configuration.
The title compound {systematic name: 4-[(3R)-8,8-dimethyl-3,4-di­hydro-2H-pyrano[2,3-f]chromen-3-yl]benzene-1,3-diol, commonly named glabridin}, C20H20O4, is a species-specific biomarker from the roots Glycyrrhiza glabra L. (European licorice, Fabaceae). In the present study, this prenylated isoflavan has been purified from an enriched CHCl3 fraction of the extract of the root, using three steps of medium-pressure liquid chromatography (MPLC) by employing HW-40F, Sephadex LH-20 and LiChroCN as adsorbents. Pure glabridin was crystallized from an MeOH–H2O mixture (95:5 v/v) to yield colorless crystals containing one mol­ecule per asymmetric unit (Z′ = 1) in the space group P212121. Although the crystal structure has been reported before, the determination of the absolute configuration remained uncertain. Stereochemical analysis, including circular dichroism, NMR data and an X-ray diffraction data set with Bijvoet differences, confirms that glabridin, purified from its natural source, is found only in a C3 R configuration. These results can therefore be used as a reference for the assignment of the configuration and enantio­purity of any isolated or synthetic glabridin sample.
doi:10.1107/S0108270113018842
PMCID: PMC4028893  PMID: 24192160
crystal structure; absolute configuration; glabridin; natural compounds
3.  A fused [3.3.0]-neoglycoside lactone derived from glucuronic acid 
The crystal structure of bridged neoglycoside, 1-deoxy-1-[(methoxy)methylamino)]-2,5-di-O-triethylsilyl-β-d-glucofuranurono-γ-lactone revealed a 1 T 2-like conformation is preferred for the furanoid ring, while the γ-lactone system adopts an E 4 conformation. This structure supports the properties associated with the anomeric effect for furanosides.
The bridged next-generation aminoglycoside (neoglycoside), 1-deoxy-1-[(methoxy)methylamino)]-2,5-di-O-triethylsilyl-β-d-glucofuranurono-γ-lactone {systematic name: (3S,3aS,5R,6R,6aS)-5-[methoxy(methyl)amino]-3,6-bis[(triethylsilyl)oxy]-2,3,3a,5,6,6a-hexahydrofuro[3,2-b]furan-2-one}, C20H41NO6Si2, was synthesized in a one-pot manner from commercially available d-glucuronic acid. This structure supports the properties associated with the anomeric effect for furanosides and can be employed to provide insight into the mechanisms by which alkoxyamine-appended natural products derive their enhanced biological activity. To the best of our knowledge, this is the first published crystal structure of a bicyclic neoglycoside and is the first neoglycoside to be completely and unambiguously characterized.
doi:10.1107/S0108270113013723
PMCID: PMC3769141  PMID: 24005522
crystal structure; neoglycoside
4.  Determination of the electron density in methyl (±)-(1S,2S,3R)-2-methyl-1,3-di­phenyl­cyclo­propane­carboxyl­ate using refinements with X-ray scattering factors from wavefunction calculations of the whole mol­ecule 
The electron density in the title substituted cyclo­propane has been determined by refining single-crystal X-ray data using scattering factors derived from quantum mechanical calculations. Topological analysis of the electron densities in the three cyclo­propane C—C bonds was carried out and shows the effects of substitution on these C—C bonds.
The mol­ecule of the title compound, C18H18O2, is a substituted cyclo­propane ring. The electron density in this mol­ecule has been determined by refining single-crystal X-ray data using scattering factors derived from quantum mechanical calculations. Topological analysis of the electron densities in the three cyclo­propane C—C bonds was carried out. The results show the effects of this substitution on these C—C bonds.
doi:10.1107/S0108270113017496
PMCID: PMC3732075  PMID: 23907888
crystal structure; electron density; molecular modelling
5.  Solid-state tautomeric structure and invariom refinement of a novel and potent HIV integrase inhibitor 
The conformation and tautomeric structure of (Z)-4-[5-(2,6-difluoro­benzyl)-1-(2-fluoro­benzyl)-2-oxo-1,2-dihydro­pyridin-3-yl]-4-hy­droxy-2-oxo-N-(2-oxopyrrolidin-1-yl)but-3-enamide, C27H22F3N3O5, in the solid state has been resolved by single-crystal X-ray crystallography. The electron distribution in the mol­ecule was evaluated by refinements with invarioms, aspherical scattering factors by the method of Dittrich et al. [Acta Cryst. (2005), A61, 314–320] that are based on the Hansen–Coppens multipole model [Hansen & Coppens (1978 ▶). Acta Cryst. A34, 909–921]. The β-diketo portion of the mol­ecule exists in the enol form. The enol –OH hydrogen forms a strong asymmetric hydrogen bond with the carbonyl O atom on the β-C atom of the chain. Weak intra­molecular hydrogen bonds exist between the weakly acidic α-CH hydrogen of the keto–enol group and the pyridinone carbonyl O atom, and also between the hydrazine N—H group and the carbonyl group in the β-position from the hydrazine N—H group. The electrostatic properties of the mol­ecule were derived from the mol­ecular charge density. The mol­ecule is in a lengthened conformation and the rings of the two benzyl groups are nearly orthogonal. Results from a high-field 1H and 13C NMR correlation spectroscopy study confirm that the same tautomer exists in solution as in the solid state.
doi:10.1107/S0108270113003806
PMCID: PMC3589111  PMID: 23459357
6.  The effect of hydrogen bonding on the conformations of 2-(1H-indol-3-yl)-2-oxoacetamide and 2-(1H-indol-3-yl)-N,N-dimethyl-2-oxoacetamide 
In the title compounds, C10H8N2O2, (I), and C12H12N2O2, (II), the two carbonyl groups are oriented with torsion angles of −149.3 (3) and −88.55 (15)°, respectively. The single-bond distances linking the two carbonyl groups are 1.528 (4) and 1.5298 (17) Å, respectively. In (I), the mol­ecules are linked by an elaborate system of N—H⋯O hydrogen bonds, which form adjacent R 2 2(8) and R 4 2(8) ring motifs to generate a ladder-like construct. Adjacent ladders are further linked by N—H⋯O hydrogen bonds to build a three-dimensional network. The hydrogen bonding in (II) is far simpler, consisting of helical chains of N—H⋯O-linked mol­ecules that follow the 21 screw of the b axis. It is the presence of an elaborate hydrogen-bonding system in the crystal structure of (I) that leads to the different torsion angle for the orientation of the two adjacent carbonyl groups from that in (II).
doi:10.1107/S0108270112038322
PMCID: PMC4028885  PMID: 23007543
7.  4,4′-(4,5-Dimethyl-1,2-phenyl­ene)bis­(2-methyl­but-3-yn-2-ol): structural variation in vicinal dialkynols 
The structure of the title compound, C18H22O2, contains two non-equivalent mol­ecules which differ primarily in the location of the –OH groups on opposite sides or on the same side of the mol­ecular plane. Inversion-symmetric pairs of mol­ecules form inter­molecular O—H⋯O hydrogen-bonded tetra­meric synthons that link non-equivalent mol­ecules into an approximately square double layer parallel to (02). Recently reported fluorinated analogues [Kane, Meyers, Yu, Gerken & Etzkorn (2011 ▶). Eur. J. Org. Chem. pp. 2969–2980] have significantly different structures of varying complexity that incorporate intra­molecular hydrogen bonding and suggest that further study of structure versus substituents in vicinal dialkynols could be fruitful.
doi:10.1107/S0108270112013169
PMCID: PMC3338315  PMID: 22476152
8.  Sulfapyridine (polymorph III), sulfapyridine dioxane solvate, sulfapyridine tetra­hydro­furan solvate and sulfapyri­dine piperi­dine solvate, all at 173 K 
The X-ray crystal structures of solvates of sulfapyridine have been determined to be conformational polymorphs. 4-Amino-N-(1,2-dihydro­pyridin-2-yl­idene)benzene­sulfonamide (polymorph III), C11H11N3O2S, (1), 4-amino-N-(1,2-dihydro­pyri­din-2-yl­idene)benzene­sulfonamide 1,3-dioxane monosolvate, C11H11N3O2S·C4H8O2, (2), and 4-amino-N-(1,2-dihydro­pyri­din-2-yl­idene)benzene­sulfonamide tetra­hydro­furan monosolvate, C11H11N3O2S·C4H8O, (3), crystallized as the imide form, while piperidin-1-ium 4-amino-N-(pyridin-2-yl)benzene­sul­fon­amidate, C5H12N+·C11H10N3O2S−, (4), crystallized as the piperidinium salt. The tetra­hydro­furan and dioxane solvent mol­ecules in their respective structures were disordered and were refined using a disorder model. Three-dimensional hydrogen-bonding networks exist in all structures between at least one sulfone O atom and the aniline N atom.
doi:10.1107/S0108270111041825
PMCID: PMC3229324  PMID: 22138921
9.  Co-crystals of 3-de­oxy-3-fluoro-α-d-glucopyran­ose and 3-de­oxy-3-fluoro-β-d-glucopyran­ose 
3-De­oxy-3-fluoro-d-glucopyran­ose crystallizes from acetone to give a unit cell containing two crystallographically independent mol­ecules. One of these mol­ecules (at site A) is structurally homogeneous and corresponds to 3-de­oxy-3-fluoro-β-d-glucopyran­ose, C6H11FO5, (I). The second mol­ecule (at site B) is structurally heterogeneous and corresponds to a mixture of (I) and 3-de­oxy-3-fluoro-α-d-glucopyran­ose, (II); treatment of the diffraction data using partial-occupancy oxygen at the anomeric center gave a high-quality packing model with an occupancy ratio of 0.84:0.16 for (II):(I) at site B. The mixture of α- and β-anomers at site B appears to be accommodated in the lattice because hydrogen-bonding partners are present to hydrogen bond to the anomeric OH group in either an axial or equatorial orientation. Cremer–Pople analysis of (I) and (II) shows the pyranosyl ring of (II) to be slightly more distorted than that of (I) [θ(I) = 3.85 (15)° and θ(II) = 6.35 (16)°], but the general direction of distortion is similar in both structures [ϕ(I) = 67 (2)° (B C1,C4) and ϕ(II) = 26.0 (15)° (C3 TB C1); B = boat conformation and TB = twist-boat conformation]. The exocyclic hy­droxy­methyl (–CH2OH) conformation is gg (gauche–gauche) (H5 anti to O6) in both (I) and (II). Structural comparisons of (I) and (II) to related unsubstituted, de­oxy and fluorine-substituted monosaccharides show that the gluco ring can assume a wide range of distorted chair structures in the crystalline state depending on ring substitution patterns.
doi:10.1107/S0108270110040096
PMCID: PMC3089378  PMID: 21051824
10.  4-De­oxy-4-fluoro-β-d-gluco­pyranose 
4-De­oxy-4-fluoro-β-d-glucopyran­ose, C6H11FO5, (I), crystallizes from water at room temperature in a slightly distorted 4 C 1 chair con­formation. The observed chair distortion differs from that observed in β-d-glucopyran­ose [Kouwijzer, van Eijck, Kooijman & Kroon (1995 ▶). Acta Cryst. B51, 209–220], (II), with the former skewed toward a B C3,O5 (boat) conformer and the latter toward an O5 TB C2 (twist–boat) conformer, based on Cremer–Pople analysis. The exocyclic hy­droxy­methyl group conformations in (I) and (II) are similar; in both cases, the O—C—C—O torsion angle is ∼−60° (gg con­former). Inter­molecular hydrogen bonding in the crystal structures of (I) and (II) is conserved in that identical patterns of donors and acceptors are observed for the exocyclic substituents and the ring O atom of each monosaccharide. Inspection of the crystal packing structures of (I) and (II) reveals an essentially identical packing configuration.
doi:10.1107/S0108270110034001
PMCID: PMC3089016  PMID: 20921614
11.  Tri-tert-butyl 3-oxo-4-oxa-1,8,11-tri­aza­spiro­[5.6]dodecane-1,8,11-tri­acetate 
The title compound, C26H45N3O8, is a bicyclic mol­ecule; the seven-membered diazepane ring has a twisted-chair conformation and the six-membered morpholine ring has a boat conformation.
doi:10.1107/S0108270109049361
PMCID: PMC2850304  PMID: 20354302
12.  Strontium tetra­fluoro­borate. Erratum 
Erratum to Acta Cryst. (2007), C63, i75–i76.
In the paper by Bunič, Tavčar, Goreshnik & Žemva [Acta Cryst. (2007 ▶), C63, i75–i76], the structure reported as Sr(BF4)2 is actually that of Cd(BF4)2. The correct structure of Sr(BF4)2 is now reported.
doi:10.1107/S0108270109054286
PMCID: PMC2855578
13.  Ammine(2,2′-bipyridine-κ2 N,N′)silver(I) nitrate: a dimer formed by π–π stacking and ligand-unsupported Ag⋯Ag inter­actions 
Reaction of AgNO3 and 2,2′-bipyridine (bipy) under ultrasonic treatment gave the title compound, [Ag(C10H8N2)(NH3)]NO3. The crystal structure consists of dimers formed by two symmetry-related AgI–bipy monomers connected through intra-dimer π–π stacking and ligand-unsupported Ag⋯Ag inter­actions. A crystallographic C2 axis passes through the mid-point of and is perpendicular to the Ag⋯Agi(−x + 1, y, −z + ) axis. In addition, each AgI cation is coordinated by one chelating bipy ligand and one ammine ligand, giving a trigonal coordination environment capped by the symmetry-equivalent Ag atom. Mol­ecules are assembled by Ag⋯Ag, π–π, hydrogen-bond (N—H⋯O and C—H⋯O) and weak Ag⋯π inter­actions into a three-dimensional framework. Comparing the products synthesized under different mechanical treatments, we found that reaction conditions have a significant influence on the resulting structures. The luminescence properties of the title compound are also discussed.
doi:10.1107/S010827011000377X
PMCID: PMC2855567  PMID: 20203399
14.  p-Phenyl­enediamine and its dihydrate: two-dimensional isomorphism and mechanism of the dehydration process, and N—H⋯N and N—H⋯π inter­actions 
p-Phenyl­enediamine can be obtained as the dihydrate, C6H8N2·2H2O, (I), and in its anhydrous form, C6H8N2, (II). The asymmetric unit of (I) contains one half of the p-phenyl­ene­diamine mol­ecule lying about an inversion centre and two halves of water mol­ecules, one lying on a mirror plane and the other lying across a mirror plane. In (II), the asymmetric unit consists of one mol­ecule in a general position and two half mol­ecules located around inversion centres. In both structures, the p-phenyl­enediamine mol­ecules are arranged in layers stabilized by N—H⋯π inter­actions. The diamine layers in (I) are isostructural with half of the layers in (II). On dehydration, crystals of (I) transform to (II). Comparison of their crystal structures suggests the most plausible mechanism of the transformation process which requires, in addition to translational motion of the diamine mol­ecules, in-plane rotation of every fourth p-phenyl­enediamine mol­ecule by ca 60°. A search of the Cambridge Structural Database shows that the formation of hydrates by aromatic amines should be considered exceptional.
doi:10.1107/S010827011000541X
PMCID: PMC2855568  PMID: 20203409
15.  The new ternary phases of La3(Zn0.874Mg0.126)11 and Ce3(Zn0.863Mg0.137)11  
The La3(Zn0.874Mg0.126)11 and Ce3(Zn0.863Mg0.137)11 inter­metallic compounds are isostructural and crystallize in the ortho­rhom­bic La3Al11 structure type. Compared to the structure of La3Al11, in La3(Zn0.874Mg0.126)11, a significant decrease of 11.9% in the unit-cell b axis and and an increase in the other two directions, of 3.6% along a and 5.2% along c, are observed. Such an atypical deformation is caused by the closer packing of atoms in the unit cell due to atom shifts that reflect strengthening of metallic-type bonding.
The new ternary inter­metallic title compounds, namely trilanthanum undeca­(zinc/magnesium), La3(Zn0.874Mg0.126)11, (I), and tricerium undeca­(zinc/magnesium), Ce3(Zn0.863Mg0.137)11, (II), are isostructural and crystallize in the ortho­rhom­bic La3Al11 structure type. These three phases belong to the same structural family, the representative members of which may be derived from the tetra­gonal BaAl4 structure type by a combination of inter­nal deformation and multiple substitution. Compared to the structure of La3Al11, in (I), a significant decrease of 11.9% in the unit-cell b axis and an increase in the other two directions, of 3.6% along a and 5.2% along c, are observed. Such an atypical deformation is caused by the closer packing of atoms in the unit cell due to atom shifts that reflect strengthening of metallic-type bonding. This structural change is also manifested in a significant difference in the coordination around the smaller atoms at the 8l Wyckoff position (site symmetry m). The Al atom in La3Al11 is in a tricapped trigonal prismatic environment (coordination number 9), while the Zn atoms in (I) and (II) are situated in a tetra­gonal anti­prism with two added atoms (coordination number 10).
doi:10.1107/S0108270110002556
PMCID: PMC2855569  PMID: 20203390
16.  (E)-N-{[6-Chloro-4-(4-chloro­phen­yl)-3-methyl-1-phenyl-1H-pyrazolo[3,4-b]pyridin-5-yl]methyl­ene}benzene-1,2-diamine: a three-dimensional framework structure built from only two hydrogen bonds 
The mol­ecules of the title compound, C26H19Cl2N5, are conformationally chiral, with none of the aryl groups coplanar with the pyrazolo[3,4-b]pyridine core of the mol­ecule. A single unique N—H⋯N hydrogen bond links the mol­ecules into two symmetry-related sets of C(11) chains running parallel to the [011] and [01] directions, respectively, and these two sets of chains are linked into a continuous three-dimensional framework structure by a single unique C—H⋯N hydrogen bond which forms a chain parallel to the [100] direction.
doi:10.1107/S0108270110004026
PMCID: PMC2855570  PMID: 20203411
17.  Two solid phases of pyrimidin-1-ium hydrogen chloranilate monohydrate determined at 225 and 120 K 
The crystal structures of two solid phases of the title compound, C4H5N2 +·C6HCl2O4 −·H2O, have been determined at 225 and 120 K. In the high-temperature phase, stable above 198 K, the transition temperature of which has been determined by 35Cl nuclear quadrupole resonance and differential thermal analysis measurements, the three components are held together by O—H⋯O, N⋯H⋯O, C—H⋯O and C—H⋯Cl hydrogen bonds, forming a centrosymmetric 2+2+2 aggregate. In the N⋯H⋯O hydrogen bond formed between the pyrimidin-1-ium cation and the water mol­ecule, the H atom is disordered over two positions, resulting in two states, viz. pyrimidin-1-ium–water and pyrimidine–oxonium. In the low-temperature phase, the title compound crystallizes in the same monoclinic space group and has a similar mol­ecular packing, but the 2+2+2 aggregate loses the centrosymmetry, resulting in a doubling of the unit cell and two crystallographically independent mol­ecules for each component in the asymmetric unit. The H atom in one N⋯H⋯O hydrogen bond between the pyrimidin-1-ium cation and the water mol­ecule is disordered, while the H atom in the other hydrogen bond is found to be ordered at the N-atom site with a long N—H distance [1.10 (3) Å].
doi:10.1107/S010827011000363X
PMCID: PMC2855571  PMID: 20203406
18.  La2Pb(SiS4)2  
The title structure is occupationally disordered on the La and Pb sites. A large gap was found around the coordination polyhedra, which makes the compound a prospective material in crystal engineering.
Crystals of La2Pb(SiS4)2, dilanthanum(III) lead(II) bis­[tetra­sulfido­sili­cate(IV)], were obtained from the La–Pb–Si–S system and structurally characterized using X-ray single-crystal diffraction. The La and Pb atoms are coordinated in bicapped trigonal prisms of S atoms, with the Si atoms in tetra­hedra. An occupational disorder of the La and Pb centres was refined for one position in the structure. The bicapped trigonal prisms and tetra­hedra share edges. A gap located 2.629 (1) Å from the sulfide anions was found around the coordination polyhedra, which makes La2Pb(SiS4)2 a prospective material in crystal engineering. The Si and one S atom lie on a threefold axis.
doi:10.1107/S0108270110000247
PMCID: PMC2855572  PMID: 20203388
19.  Hydrogen-bonding patterns in two aroylthio­carbamates and two aroylimidothio­carbonates 
In O-ethyl N-benzoyl­thio­carbamate, C10H11NO2S, the mol­ecules are linked into sheets by a combination of two-centre N—H⋯O and C—H⋯S hydrogen bonds and a three-centre C—H⋯(O,S) hydrogen bond. A combination of two-centre N—H⋯O and C—H⋯O hydrogen bonds links the mol­ecules of O-ethyl N-(4-methyl­benzoyl)thio­carbamate, C11H13NO2S, into chains of rings, which are linked into sheets by an aromatic π–π stacking inter­action. In O,S-diethyl N-(4-methyl­benzoyl)imidothio­carbonate, C13H17NO2S, pairs of mol­ecules are linked into centrosymmetric dimers by pairs of symmetry-related C—H⋯π(arene) hydrogen bonds, while the mol­ecules of O,S-diethyl N-(4-chloro­benzoyl)imidothio­carbonate, C12H14ClNO2S, are linked by a single C—H⋯O hydrogen bond into simple chains, pairs of which are linked by an aromatic π–π stacking inter­action to form a ladder-type structure.
doi:10.1107/S0108270110005032
PMCID: PMC2855573  PMID: 20203412
20.  Strong asymmetric hydrogen bonding in 2-(oxamoylamino)ethyl­ammonium oxamate–oxamic acid (1/1) 
The title compound, C4H10N3O2 +·C2H2NO3 −·C2H3NO3, con­tains at least 11 distinct hydrogen-bond inter­actions showing a great variety of bond strengths. The shortest and strongest hydrogen bond [O⋯O = 2.5004 (12) Å] is found between the uncharged oxamic acid molecule and the oxamate mono­anion. The grouping formed by such a strong hydrogen bond can thus be considered as a hydrogen bis­(oxamate) monoanion. It lacks crystallographic symmetry and the two oxamate groups have different conformations, showing an asymmetric hydrogen-bond inter­action. Significantly, the asymmetry allows us to draw a direct comparison of site basicity for the two inequivalent carboxyl­ate O atoms in the planar oxamate anion. The constituent mol­ecular ions of (I) form ribbons, where all amide and carboxyl­ate groups are coplanar. Graph-set analysis of the hydrogen-bonded net­works reveals the R 2 2(10) and R 2 2(9) homodromic nets as important structure-directing motifs, which appear to be a common feature of many oxamate-containing compounds.
doi:10.1107/S0108270110004233
PMCID: PMC2855574  PMID: 20203413
21.  The solid solution (Fe0.81Al0.19)(H2PO4)3 with a strong hydrogen bond 
A sample of synthetic (Fe0.81Al0.19)(H2PO4)3 was prepared by hydro­thermal methods in order to determine the crystal structure. The compound is a new monoclinic variety (γ-form) and the structure is based on a two-dimensional framework of distorted corner-sharing MO6 (M = Fe, Al) polyhedra sharing corners with PO4 tetra­hedra.
Single crystals of the solid solution iron aluminium tris(dihydrogenphosphate), (Fe0.81Al0.19)(H2PO4)3, have been pre­pared under hydro­thermal conditions. The compound is a new monoclinic variety (γ-form) of iron aluminium phosphate (Fe,Al)(H2PO4)3. The structure is based on a two-dimensional framework of distorted corner-sharing MO6 (M = Fe, Al) polyhedra sharing corners with PO4 tetra­hedra. Strong hydrogen bonds between the OH groups of the H2PO4 tetra­hedra and the O atoms help to consolidate the crystal structure.
doi:10.1107/S0108270110001344
PMCID: PMC2855575  PMID: 20203392
22.  Ba2Gd2(Si4O13): a silicate with finite Si4O13 chains 
Ba2Gd2(Si4O13) contains finite Si4O13 chains and Gd2O12 dimers. It is a representative of a rare class of silicates containing Si4O13 chains.
The title compound, dibarium digadolinium(III) tetra­silicate, crystallized from a molybdate-based flux. It represents a new structure type and contains finite zigzag-shaped C 2-symmetric Si4O13 chains and Gd2O12 dimers built of edge-sharing GdO7 polyhedra. The [9+1]-coordinated Ba atoms are located in voids in the atomic arrangement. All atoms are in general positions except for one O atom, which lies on a twofold axis. The structure is compared with those of the few other known tetra­silicates.
doi:10.1107/S0108270110002842
PMCID: PMC2855576  PMID: 20203391
23.  A synchrotron radiation study of the one-dimensional complex of sodium with (1S)-N-carboxyl­ato-1-(9-deaza­adenin-9-yl)-1,4-dide­oxy-1,4-imino-d-ribitol, a member of the ’immucillin’ family 
The sodium salt of [immucillin-A–CO2H]− (Imm-A), namely catena-poly[[[triaqua­disodium(I)](μ-aqua)[μ-(1S)-N-car­box­yl­ato-1-(9-deaza­adenin-9-yl)-1,4-dide­oxy-1,4-imino-d-ribi­tol][triaqua­disodium(I)][μ-(1S)-N-carboxyl­ato-1-(9-deaza­aden­in-9-yl)-1,4-dide­oxy-1,4-imino-d-ribitol]] tetra­hydrate], {[Na2(C12H13N4O6)2(H2O)7]·4H2O}n, (I), forms a polymeric chain via Na+—O inter­actions involving the carboxyl­ate and keto O atoms of two independent Imm-A mol­ecules. Extensive N,O—H⋯O hydrogen bonding utilizing all water H atoms, including four waters of crystallization, provides crystal packing. The structural definition of this novel compound was made possible through the use of synchrotron radiation utilizing a minute fragment (volume ∼2.4 × 10−5 mm−3) on a beamline optimized for protein data collection. A summary of intra-ring conformations for immucillin structures indicates considerable flexibility while retaining similar intra-ring orientations.
doi:10.1107/S0108270110002738
PMCID: PMC2855577  PMID: 20203397
24.  The ansa-zirconocene [bis­(η5-cyclo­penta­dien­yl)phenyl­phosphine]­dichloridozirconium(IV) 
In the title compound, [Zr(C16H13P)Cl2], the geometry at the metal atom is distorted tetra­hedral; the Cl—Zr—Cl angle is 101.490 (16)° and the cyclo­penta­dienyl (Cp) centroids subtend an angle of 122.63 (3)° at the Zr atom. The P atom lies 0.474 (3) and 0.496 (3) Å out of the planes of the Cp rings. The C—P—C angle of 91.42 (7)° reflects the pincer effect of the two Cp rings. Three C—H⋯Cl, one C—H⋯P, one C—H⋯π and one Cl⋯P inter­action link the mol­ecules to form thick layers parallel to the bc plane.
doi:10.1107/S0108270110004531
PMCID: PMC2855579  PMID: 20203402
25.  Hydrogen-bonded network structures in dipyridinium, bis­(2-methyl­pyridinium), bis­(3-methyl­pyridinium) and bis­(4-methyl­pyridinium) dioxidobis(oxydiacetato)uranate(VI) 
Four complexes containing the [UO2(oda)2]2− anion (oda is oxy­diacetate) are reported, namely dipyridinium dioxidobis(oxydiacetato)uranate(VI), (C5H6N)2[U(C4H4O5)2O2], (I), bis(2-methyl­pyridinium) dioxidobis(oxydiacetato)uranate(VI), (C8H8N)2[U(C4H4O5)2O2], (II), bis­(3-methyl­pyridinium) di­oxido­bis(oxydiacetato)uranate(VI), (C8H8N)2[U(C4H4O5)2O2], (III), and bis­(4-methyl­pyridinium) dioxidobis(oxydiacetato)uranate(VI), (C8H8N)2[U(C4H4O5)2O2], (IV). The anions are achiral and are located on a mirror plane in (I) and on inversion centres in (II)–(IV). The four complexes are assembled into three-dimensional structures via N—H⋯O and C—H⋯O inter­actions. Compounds (III) and (IV) are isomorphous; the [UO2(oda)2]2− anions form a porous matrix which is nearly identical in the two structures, and the cations are located in channels formed in this matrix. Compounds (I) and (II) are very different from (III) and (IV): (I) forms a layered structure, while (II) forms ribbons.
doi:10.1107/S0108270109053839
PMCID: PMC2855580  PMID: 20203398

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