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Study Lies (study + ly)
Selected AbstractsA covariance-adaptive approach for regularized inversion in linear modelsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2007Christopher Kotsakis SUMMARY The optimal inversion of a linear model under the presence of additive random noise in the input data is a typical problem in many geodetic and geophysical applications. Various methods have been developed and applied for the solution of this problem, ranging from the classic principle of least-squares (LS) estimation to other more complex inversion techniques such as the Tikhonov,Philips regularization, truncated singular value decomposition, generalized ridge regression, numerical iterative methods (Landweber, conjugate gradient) and others. In this paper, a new type of optimal parameter estimator for the inversion of a linear model is presented. The proposed methodology is based on a linear transformation of the classic LS estimator and it satisfies two basic criteria. First, it provides a solution for the model parameters that is optimally fitted (in an average quadratic sense) to the classic LS parameter solution. Second, it complies with an external user-dependent constraint that specifies a priori the error covariance (CV) matrix of the estimated model parameters. The formulation of this constrained estimator offers a unified framework for the description of many regularization techniques that are systematically used in geodetic inverse problems, particularly for those methods that correspond to an eigenvalue filtering of the ill-conditioned normal matrix in the underlying linear model. Our study lies on the fact that it adds an alternative perspective on the statistical properties and the regularization mechanism of many inversion techniques commonly used in geodesy and geophysics, by interpreting them as a family of ,CV-adaptive' parameter estimators that obey a common optimal criterion and differ only on the pre-selected form of their error CV matrix under a fixed model design. [source] In search of well-started beginning science teachers: Insights from two first-year elementary teachersJOURNAL OF RESEARCH IN SCIENCE TEACHING, Issue 6 2010Lucy Avraamidou Abstract The purpose of this qualitative case study was to explore what aspects of two first-year elementary teachers' practices were most consistent with an inquiry-based approach, what PCK served as a mechanism for facilitating these practices, and what experiences have mediated the nature and development of these teachers' PCK. For each of the participants data included audio-recorded interviews, video-recorded classroom observations, lesson plans, and samples of student work. Data analysis illustrated that both participants engaged their students in question-driven investigations, the use of observational data, making connections between evidence and claims, and communicating those claims to others. Moreover, there was clear evidence in the findings of the study that a considerable degree of coherence existed between the two participants' knowledge on one hand and their instructional practices on the other hand. The participants perceived specific learning experiences during their programs as being critical to their development. The contribution of this study lies in the fact that it provides examples of well-started beginning elementary teachers implementing inquiry-based science in 2nd and 5th grade classrooms. Implications of the study include the need for the design of university-based courses and interventions by which teacher preparation and professional development programs support teachers in developing PCK for scientific inquiry and enacting instructional practices that are congruent with reform initiatives. © 2010 Wiley Periodicals, Inc. J Res Sci Teach 47:661,686, 2010 [source] GELLING BEHAVIOR OF RICE FLOUR DISPERSIONS AT DIFFERENT CONCENTRATIONS OF SOLIDS AND TIME OF HEATINGJOURNAL OF TEXTURE STUDIES, Issue 3 2008ALKA KAPRI ABSTRACT Rice flour dispersions, under suitable conditions of processing, can form a gel. The effect of concentration of solids (10,18%) and time (0,75 min) of processing on textural attributes, and viscoelasticity were investigated along with sensory attributes. The textural attribute determined is gel strength, while viscoelasticity was determined in terms of mechanical spectra like storage modulus (G,), loss modulus (G,), complex viscosity (,*) and loss factor (tan ,) during a frequency sweep varying from 0.01 to 40 Hz at a constant stress of 25 Pa. Microstructural observation indicates the swelling of starch granules in the beginning of heating, while damaged granule and leached-out materials are visible at the end of the gelling process. Desirability function analysis has been applied to obtain a rice gel with acceptable textural attributes; a solid concentration of 15.2% and a heating time of 75 min can lead to the development of a gel with a satisfaction level of 0.6. PRACTICAL APPLICATIONS Rice flour gels in the form of hard-set gels, porridges and spreads are popular in several parts of the world particularly for feeding of infants and children. The application of the present study lies in understanding the role of major processing variables on the quality attributes and viscoelasticity of a product, characterization of cooked gels and for developing rice flour-based food gels. The findings may also be extended for the development of other cereal-based gels. [source] A multilevel model for the study of breastfeeding determinants in BrazilMATERNAL & CHILD NUTRITION, Issue 4 2010Daniela Wenzel Abstract The benefits of breastfeeding for the children's health have been highlighted in many studies. The innovative aspect of the present study lies in its use of a multilevel model, a technique that has rarely been applied to studies on breastfeeding. The data reported were collected from a larger study, the Family Budget Survey-Pesquisa de Orçamentos Familiares, carried out between 2002 and 2003 in Brazil that involved a sample of 48 470 households. A representative national sample of 1477 infants aged 0,6 months was used. The statistical analysis was performed using a multilevel model, with two levels grouped by region. In Brazil, breastfeeding prevalence was 58%. The factors that bore a negative influence on breastfeeding were over four residents living in the same household [odds ratio (OR) = 0.68, 90% confidence interval (CI) = 0.51,0.89] and mothers aged 30 years or more (OR = 0.68, 90% CI = 0.53,0.89). The factors that positively influenced breastfeeding were the following: higher socio-economic levels (OR = 1.37, 90% CI = 1.01,1.88), families with over two infants under 5 years (OR = 1.25, 90% CI = 1.00,1.58) and being a resident in rural areas (OR = 1.25, 90% CI = 1.00,1.58). Although majority of the mothers was aware of the value of maternal milk and breastfed their babies, the prevalence of breastfeeding remains lower than the rate advised by the World Health Organization, and the number of residents living in the same household along with mothers aged 30 years or older were both factors associated with early cessation of infant breastfeeding before 6 months. [source] Students' perceptions of relationships between some educational variables in the out-patient settingMEDICAL EDUCATION, Issue 8 2002D H J M Dolmans Background Medical education uses the cognitive apprenticeship model of student learning extensively. Students rotate among different hospitals and out- patient clinics where they are exposed to a range of professionally relevant contexts. Here they learn to think and act in different domains under the supervision of experts. Previous research has shown that these learning situations involve little teaching. Students see a narrow range of patient problems and feedback is limited. The aim of this study is to investigate relationships among some educational variables in the out-patient clinic. Method This paper provides a theoretical model that specifies the factors influencing the effectiveness of student rotations at out-patient clinics. The model makes distinctions between input variables, such as organizational quality, number of students contemporaneously involved and available space, and process variables, such as patient mix and supervision, and the output variable of the effectiveness of rotations in out-patient clinics. Results The model was tested against empirical data from evaluative surveys and showed a reasonable fit. The model offers suggestions for improving the learning environment of clinical rotations. Discussion The strength of this study lies in its process evaluation perspective which investigates interactions between intervening variables rather than the influence of particular variables in isolation from other variables. [source] Clindamycin hydrochloride monohydrate and its ethanol solvateACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2010Krishnan Ravikumar Clindamycin hydrochloride, an antibiotic of the lincomycin family, was crystallized as the monohydrate, namely (2S,4R)-2-(N -{(1S,2S)-2-chloro-1-[(3R,4S,5R,6R)-3,4,5-trihydroxy-6-(methylsulfanyl)perhydropyran-2-yl]propyl}aminocarbonyl)-4-propylpyrrolidinium chloride monohydrate, C18H34ClN2O5S+·Cl,·H2O, (I), and as the monohydrate ethanol solvate, C18H34ClN2O5S+·Cl,·H2O·C2H6O, (II). The conformation of the clindamycin molecule in both crystal structures is the same and is found to be similar to that in enzyme-bound clindamycin. The simultaneous presence of free chloride ions and water molecules in (I) and of additional ethanol molecules in (II) provides an interesting network of hydrogen bonds. The significance of this study lies in the interactions in these structures and the aggregations occurring via hydrogen bonds in the hydrated and solvated crystalline forms of the title compound. [source] 5-Amino-1-naphthol: two-dimensional sheets built up from R44(18) rings formed by O,H...N, N,H...O and ,,, interactionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2009Ewa Rozycka-Sokolowska The crystal structure of the title compound, C10H9NO, (I), contains intermolecular O,H...N and N,H...O hydrogen bonds which together form sheets parallel to the (001) plane containing rings with an unusual R44(18) motif. These rings are additionally stabilized by an intermolecular ,,, stacking interaction. The significance of this study lies in the comparison drawn between the molecular structure of (I) and those of related compounds (1,5-diaminonaphthalene, 8-amino-2-naphthol, 3-amino-2-naphthol and aniline), which shows a close similarity in the noncoplanar orientation of the amine group and the aromatic moiety. Comparison of the crystal structures of (I) and several of its simple analogues (1-naphthol, naphthalene-1,4-diol, naphthalene-1,5-diol and 4-chloro-1-naphthol) shows a close similarity in the packing of the molecules, which form ,-stacks along the shortest crystallographic axes with a substantial spatial overlap between adjacent molecules. [source] Lenalidomide, an antineoplastic drug, and its hemihydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009Krishnan Ravikumar The crystal structures of lenalidomide [systematic name: (RS)-3-(4-amino-1-oxoisoindolin-2-yl)piperidine-2,6-dione], C13H13N3O3, (I), an antineoplastic drug, and its hemihydrate, C13H13N3O3·0.5H2O, (II), have been determined by single-crystal X-ray diffraction analysis. The overall conformation of the molecule defined by the orientation of the two ring portions, viz. pyridinedione and isoindolinone, is twisted in both structures. The influence of the self-complementary pyridinedione ring is seen in the crystal packing of both structures through its involvement in forming hydrogen-bonded dimers, although alternate dione O atoms are utilized. An extensive series of N,H...O hydrogen bonds link the dimers into two-dimensional supramolecular arrays built up from infinite chains. The water molecule in (II) has a cohesive function, connecting three lenalidomide molecules by hydrogen bonds. The significance of this study lies in the analysis of the interactions in these structures and the aggregations occurring via hydrogen bonds in the hydrated and dehydrated crystalline forms of the title compound. [source] Lamotrigine, an antiepileptic drug, and its chloride and nitrate saltsACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2009Balasubramanian Sridhar In lamotrigine [systematic name: 6-(2,3-dichlorophenyl)-1,2,4-triazine-3,5-diamine], C9H7Cl2N5, (I), the asymmetric unit contains one lamotrigine base molecule. In lamotriginium chloride [systematic name: 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazin-2-ium chloride], C9H8Cl2N5+·Cl,, (II), the asymmetric unit contains one lamotriginium cation and one chloride anion, while in lamotriginium nitrate, C9H8Cl2N5+·NO3,, (III), the asymmetric unit contains two crystallographically independent lamotriginium cations and two nitrate anions. In all three structures, N,H...N hydrogen bonds form an R22(8) dimer. In (I) and (II), hydrophilic layers are sandwiched between hydrophobic layers in the crystal packing. In all three structures, hydrogen bonds lead to the formation of a supramolecular hydrogen-bonded network. The significance of this study lies in its illustration of the differences between the supramolecular aggregation in the lamotrigine base and in its chloride and nitrate salts. [source] Supramolecular hydrogen-bonded networks in adeninediium hemioxalate chloride and adeninium semioxalate hemi(oxalic acid) monohydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009Balasubramanian Sridhar In 9H -adenine-1,7-diium hemioxalate chloride, C5H7N52+·0.5C2O42,·Cl,, (I), adenine is doubly protonated, while in 7H -adenin-1-ium semioxalate hemi(oxalic acid) monohydrate, C5H6N5+·C2HO4,·0.5C2H2O4·H2O, (II), adenine and one oxalate anion are both monoprotonated. In (I), the adeninium cation forms R22(8) and R12(5) hydrogen-bonding motifs with the centrosymmetric oxalate anion, while in (II), the cation forms R21(6) and R12(5) motifs with the centrosymmetric oxalic acid molecule and R12(5)and R22(9) motifs with the monoprotonated oxalate anion. Linear hydrogen-bonded trimers are observed in (I) and (II). In both structures, the hydrogen bonds lead to the formation of two-dimensional supramolecular hydrogen-bonded sheets in the crystal packing. The significance of this study lies in the analysis of the interactions occurring via hydrogen bonds and the diversity seen in the supramolecular hydrogen-bonded networks as a result of such interactions. [source] 4-Chloro-1-naphtholACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009Ewa Rozycka-Sokolowska Molecules of the title compound, C10H7ClO, (I), are connected by a single strong O,H...O hydrogen bond into a simple C(2) chain, which runs parallel to the c axis and is additionally stabilized by intermolecular ,,, stacking interactions. The significance of this study lies in the comparison drawn between the crystal structure of (I) and those of several of its simple analogues. This comparison shows a close similarity in the packing of the molecules that form ,-stacks along the shortest crystallographic axes. A substantial spatial overlap is observed between adjacent molecules in such a ,-stack, depending mainly on the kind of substituent. [source] Two- and three-dimensional hydrated coordination polymers of diaqualanthanum(3+) ions with 2-hydroxypropanedioate, oxalate and acetate anions as bridging ligandsACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009Rajesh Koner The title compounds, poly[[tetraaquadi-,-2-hydroxypropanedioato-,-oxalato-dilanthanum(III)] tetrahydrate], {[La2(C2O4)(C3H2O5)2(H2O)4]·4H2O}n, (I), and poly[[tetra-,-acetato-tetraaqua-,-oxalato-dilanthanum(III)] dihydrate], {[La2(C2O4)(C2H3O2)4(H2O)4]·2H2O}n, (II), represent crystalline hydrates of coordination polymers of diaqualanthanum(3+) ions with different combinations of bridging carboxylate ligands, viz. 2-hydroxypropanedioate and oxalate in a 2:2:1 ratio in (I), and acetate and oxalate in a 2:4:1 ratio in (II). While the acetate component was one of the reactants used, the other ligands were obtained in situ by aerial oxidation of the dihydroxyfumaric acid present in the reactions. The crystal structure of (I) consists of two-dimensional polymeric arrays with water molecules intercalated between and hydrogen bonded to the arrays. The oxalate components are located on inversion centres. The crystal structure of (II) reveals an open three-dimensional polymeric connectivity between the interacting components, with the solvent water molecules incorporated within the intralattice voids and hydrogen bonded to the polymeric framework. The LaIII ion and the noncoordinated water molecules are located on axes of twofold symmetry. The oxalate group is centred at the 222 symmetry site, the intersection of the three rotation axes. The coordination number of the LaIII ion in the two structures is 10. The significance of this study lies mainly in the characterization of two new coordination polymers, as well as in the confirmation that dihydroxyfumaric acid tends to rearrange to form smaller components in standard laboratory procedures, and should be considered a poor reagent for formulating hybrid coordination polymers with metal ions. [source] (2R,4S)-7-Bromo-2-phenyl-2,3,4,5-tetrahydro-1,4-epoxynaphtho[1,2- b]azepine, (2RS,4SR)-7-bromo-2-(4-chlorophenyl-2,3,4,5-tetrahydro-1,4-epoxynaphtho[1,2- b]azepine and (2RS,4SR)-2-(4-fluorophenyl)-2,3,4,5-tetrahydro-1,4-epoxynaphtho[1,2- b]azepine: hydrogen-bonded structures in two and three dimensionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009Alirio Palma (2R,4S)-7-Bromo-2-phenyl-2,3,4,5-tetrahydro-1,4-epoxynaphtho[1,2- b]azepine, C20H16BrNO, (I), exhibits evidence of a modest degree (ca 10%) of inversion twinning, while both (2RS,4SR)-7-bromo-2-(4-chlorophenyl)-2,3,4,5-tetrahydro-1,4-epoxynaphtho[1,2- b]azepine, C20H15BrClNO, (II), and (2RS,4SR)-2-(4-fluorophenyl)-2,3,4,5-tetrahydro-1,4-epoxynaphtho[1,2- b]azepine, C20H16FNO, (III), crystallize as genuine racemic mixtures. The molecules of (I) are linked into sheets by a combination of one C,H...O hydrogen bond and two C,H...,(arene) hydrogen bonds, while those of (II) are linked into sheets of ,-stacked hydrogen-bonded chains. A combination of one C,H...O hydrogen bond and four independent C,H...,(arene) hydrogen bonds links the molecules of (III) into a three-dimensional framework. The significance of this study lies in its finding, via comparison with the structures of some closely-related epoxybenzazepine analogues, of significant changes in crystal structures consequent upon small changes in the peripheral substituents. [source] Square-grid coordination networks of (5,10,15,20-tetra-4-pyridylporphyrinato)zinc(II) in its clathrate with two guest molecules of 1,2-dichlorobenzene: supramolecular isomerism of the porphyrin self-assemblyACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009Rajesh Koner The title compound, (5,10,15,20-tetra-4-pyridylporphyrinato)zinc(II) 1,2-dichlorobenzene disolvate, [Zn(C40H24N8)]·2C6H4Cl2, contains a clathrate-type structure. It is composed of two-dimensional square-grid coordination networks of the self-assembled porphyrin moiety, which are stacked one on top of the other in a parallel manner. The interporphyrin cavities of the overlapping networks combine into channel voids accommodated by the dichlorobenzene solvent. Molecules of the porphyrin complex are located on crystallographic inversion centres. The observed two-dimensional assembly mode of the porphyrin units represents a supramolecular isomer of the unique three-dimensional coordination frameworks of the same porphyrin building block observed earlier. The significance of this study lies in the discovery of an additional supramolecular isomer of the rarely observed structures of metalloporphyrins self-assembled directly into extended coordination polymers without the use of external ligand or metal ion auxiliaries. [source] 3-Oxoandrosta-4,6-dien-17,-yl 2-methyl-1H -imidazole-1-carboxylate and 3-oxo-5,-androst-17,-yl 2-methyl-1H -imidazole-1-carboxylate: C,H..., and ,,, intermolecular interactionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009Manuela Ramos Silva The title compounds, C24H30N2O3, (I), and C24H34N2O3, (II), both contain an androstane backbone and a 2-methylimidazole-1-carboxylate moiety at the 17-position. Compound (I) contains two symmetry-independent molecules (denoted 1 and 2), while compound (II) contains just one molecule in the asymmetric unit. The C,C,O,C torsion angle that reflects the twisting of the 2-methylimidazole-1-carboxylate moiety from the mean steroid plane is 143.1,(2)° for molecule 1 of (I), 73.1,(3)° for molecule 2 of (I) and 86.63,(17)° for (II). The significance of this study lies in its observation of significant differences in both molecular conformation and supramolecular aggregation between the molecules of the title compounds. The solid-state conformations compared with those obtained theoretically from ab initio methods for the isolated molecules show large differences, especially in the orientation of the methylimidazole substituent. [source] 4-Hydroxy-2-vinyl-2,3,4,5-tetrahydro-1-benzazepine and its 7-fluoro and 7-chloro analogues are isomorphous but not strictly isostructuralACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009Lina M. Acosta 4-Hydroxy-2-vinyl-2,3,4,5-tetrahydro-1-benzazepine, C12H15NO, (I), and its 7-fluoro and 7-chloro analogues, namely 7-fluoro-4-hydroxy-2-vinyl-2,3,4,5-tetrahydro-1-benzazepine, C12H14FNO, (II), and 7-chloro-4-hydroxy-2-vinyl-2,3,4,5-tetrahydro-1-benzazepine, C12H14ClNO, (III), are isomorphous, but with variations in the unit-cell dimensions which preclude in compound (III) one of the weaker intermolecular interactions found in compounds (I) and (II). Thus the compounds are not strictly isostructural in terms of the structurally significant intermolecular interactions, although the corresponding atomic coordinates are very similar. The azepine rings adopt chair conformations. The molecules are linked by a combination of N,H...O and O,H...N hydrogen bonds into chains of edge-fused R33(10) rings, which in compounds (I) and (II) are further linked into sheets by a single C,H...,(arene) hydrogen bond. The significance of this study lies in its observation of isomorphism in compounds (I),(III), and its observation of a sufficient variation in one of the cell dimensions effectively to alter the range of significant hydrogen bonds present in the crystal structures. [source] Different hydrogen-bonded structures in the isomeric solvates 2-amino-6-anilino-4-methoxy-5-[(E)-4-nitrobenzylideneamino]pyrimidine dimethyl sulfoxide solvate and 2-amino-6-[methyl(phenyl)amino]-5-[(E)-4-nitrobenzylideneamino]pyrimidin-4(3H)-one dimethyl sulfoxide solvateACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009Ricaurte Rodríguez The title solvates, (I) and (II), both C18H16N6O3·C2H6OS, are isomeric. The conformations adopted by the 6-substituent are significantly different, with the 6-aminophenyl unit remote from the nitrophenyl ring in methoxypyrimidine (I) but adjacent to it in pyrimidinone (II). Pairs of pyrimidine molecules in (I) are linked by N,H...N hydrogen bonds to form cyclic centrosymmetric dimers from which the dimethyl sulfoxide molecules are pendent, while in (II) a combination of three independent N,H...O hydrogen bonds links the components into a chain containing both R22(8) and R42(8) rings, in which the dimethyl sulfoxide component acts as a double acceptor of hydrogen bonds. The significance of this study lies in its observation of different conformations for the pyrimidine components in (I) and (II), and different hydrogen-bonded structures, apparently dominated by the different roles adopted by the dimethyl sulfoxide components. [source] Two-dimensional hydrogen-bonded networks in 1-(diaminomethylene)thiouron-1-ium nitrate and bis[1-(diaminomethylene)thiouron-1-ium] phosphonate monohydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009Jan Janczak Crystals of the title compounds, C2H7N4S+·NO3,, (I), and 2C2H7N4S+·HPO32,·H2O, (II), are built up from 1-(diaminomethylene)thiouron-1-ium cations and nitrate anions in (I), and from phosphonate anions and water molecules in (II). In both crystals, the cations and anions are linked together via N,H...O hydrogen bonds. The 1-(diaminomethylene)thiouron-1-ium cations exhibit a twisted conformation. Both arms of the cations are planar and are turned in opposite directions around the C,N bond involving the central N atom. Hydrogen-bonding interactions join oppositely charged units into layers in the nitrate salt and into double layers in the phosphonate monohydrate salt. In addition, the structures are stabilized by ,,, interactions between the delocalized , bonds of the cations. The significance of this study lies in the illustration of the differences between the supramolecular aggregations in the nitrate and phosphonate salts of a small organic molecule. The different geometries of the counter-ions and their different potential for hydrogen-bond formation results in markedly different hydrogen-bond arrangements. [source] Quinolin-6-ol at 100,KACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Anna Michta The title compound, C9H7NO, has two symmetry-independent molecules in the asymmetric unit, which have different conformations of the hydroxy group with respect to the quinoline ring. One of the molecules adopts a cis conformation, while the other shows a trans conformation. Each type of independent molecule links into a separate infinite O,H...N hydrogen-bonded chain with the graph-set notation C(7). These chains are perpendicular in the unit cell, one extended in the a -axis direction and the other in the b -axis direction. There is also a weak C,H...O hydrogen bond with graph-set notation D(2), which runs in the c -axis direction and joins the two separate O,H...N chains. The significance of this study lies in the comparison drawn between the experimental and calculated data of the crystal structure of the title compound and the data of several other derivatives possessing the hydroxy group or the quinoline ring. The correlation between the IR spectrum of this compound and the hydrogen-bond energy is also discussed. [source] Probing the supramolecular interaction synthons of 1-benzofuran-2,3-dicarboxylic acid in its monoanionic formACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2009Rajesh Koner 1-Benzofuran-2,3-dicarboxylic acid (C10H6O5) is a dicarboxylic acid ligand which can readily engage in organometallic complexes with various metal ions. This ligand is characterized by an intramolecular hydrogen bond between the two carboxyl residues, and, as a monoanionic species, readily forms supramolecular adducts with different organic and inorganic cations. These are a 1:1 adduct with the dimethylammonium cation, namely dimethylammonium 3-carboxy-1-benzofuran-2-carboxylate, C2H8N+·C10H5O5,, (I), a 2:1 complex with Cu2+ ions in which four neutral imidazole molecules also coordinate the metal atom, namely bis(3-carboxy-1-benzofuran-2-carboxylato-,O3)tetrakis(1H -imidazole-,N3)copper(II), [Cu(C10H5O5)2(C3H4N2)4], (II), and a 4:1 adduct with [La(H2O)7]3+ ions, namely heptaaquabis(3-carboxy-1-benzofuran-2-carboxylato-,O3)lanthanum 3-carboxy-1-benzofuran-2-carboxylate 1-benzofuran-2,3-dicarboxylic acid solvate tetrahydrate, [La(C10H5O5)2(H2O)7](C10H5O5)·C10H6O5·4H2O, (III). In the crystal structure, complex (II) resides on inversion centres, while complex (III) resides on axes of twofold rotation. The crystal packing in all three structures reveals ,,, stacking interactions between the planar aromatic benzofuran residues, as well as hydrogen bonding between the components. The significance of this study lies in the first crystallographic characterization of the title framework, which consistently exhibits the presence of an intramolecular hydrogen bond and a consequent monoanionic-only nature. It shows further that the anion can coordinate readily to metal cations as a ligand, as well as acting as a monovalent counter-ion. Finally, the aromaticity of the flat benzofuran residue provides an additional supramolecular synthon that directs and facilitates the crystal packing of compounds (I),(III). [source] 2-Amino-4-chloro-5-formyl-6-[methyl(2-methylphenyl)amino]pyrimidine and 2-amino-4-chloro-5-formyl-6-[(2-methoxyphenyl)methylamino]pyrimidine are isostructural and form hydrogen-bonded sheets of R22(8) and R66(32) ringsACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2009Jorge Trilleras 2-Amino-4-chloro-5-formyl-6-[methyl(2-methylphenyl)amino]pyrimidine, C13H13ClN4O, (I), and 2-amino-4-chloro-5-formyl-6-[(2-methoxyphenyl)methylamino]pyrimidine, C13H13ClN4O2, (II), are isostructural and essentially isomorphous. Although the pyrimidine rings in each compound are planar, the ring-substituent atoms show significant displacements from this plane, and the bond distances provide evidence for polarization of the electronic structures. In each compound, a combination of N,H...N and N,H...O hydrogen bonds links the molecules into sheets built from centrosymmetric R22(8) and R66(32) rings. The significance of this study lies in its observation of the isostructural nature of (I) and (II), and in the comparison of their crystal and molecular structures with those of analogous compounds. [source] Four 2-amino-6-aryl-4-methoxy-11H -pyrimido[4,5- b][1,4]benzodiazepines: similar molecular structures but different crystal structuresACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2008Ricaurte Rodríguez 2-Amino-4-methoxy-6-phenyl-11H -pyrimido[4,5- b][1,4]benzodiazepine, C18H15N5O, (I), and its 6-(2-fluorophenyl)-, 6-(3-nitrophenyl)- and 6-(4-methoxyphenyl)- analogues, viz. C18H14FN5O, (II), C18H14N6O3, (III), and C19H17N5O2, (IV), respectively, all adopt molecular conformations which are almost identical, containing boat-shaped seven-membered rings. In each structure, paired N,H...N hydrogen bonds link the molecules into centrosymmetric dimers. In each of (I),(III), the dimers are further linked, forming a different three-dimensional framework in each case, while in compound (IV) the dimers are linked into sheets. The significance of this study lies in the observation of different crystal structures in four compounds whose molecular structures are very similar. [source] Hydrogen-bonding interactions in (3,4-dimethoxyphenyl)acetic acid monohydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2008Barbara Hachu The crystal structure of the title compound, C10H12O4·H2O, consists of (3,4-dimethoxyphenyl)acetic acid and water molecules linked by O,H...O hydrogen bonds to form cyclic structures with graph-set motifs R12(5) and R44(12). These hydrogen-bond patterns result in a three-dimensional network with graph-set motifs R44(20) and R44(22), and the formation of larger macrocycles, respectively. The C,C bond lengths and the endocyclic angles of the benzene ring show a noticeable asymmetry, which is connected with the charge-transfer interaction of the carboxyl or methoxy groups and the benzene ring. The title compound is one of the simple carboxylic acid systems that form hydrates. Thus, the significance of this study lies in the analysis of the interactions in this structure and the aggregations occurring via hydrogen bonds in two crystalline forms of (3,4-dimethoxyphenyl)acetic acid, namely the present hydrate and the anhydrous form [Chopra, Choudhury & Guru Row (2003). Acta Cryst. E59, o433,o434]. The correlation between the IR spectrum of this compound and its structural data are also discussed. [source] Low-temperature study of 3-acetylindole at 110,KACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2008Barbara Hachu The title compound, C10H9NO, contains an acetyl group that is nearly coplanar with the indole ring system, with an angle between the planes of the heterocyclic ring and the acetyl group of 1.75,(17)°. The planes of the benzene and pyrrole rings in the indole system make a dihedral angle of 2.05,(11)°. Each molecule in the unit cell is linked through N,H...O hydrogen bonds to two other molecules, forming hydrogen-bonded chains in the [101] direction with graph set C(6). The significance of this study lies in the analysis of the interactions occurring via hydrogen bonds in this structure, as well as in the comparison drawn between the molecular structure of the title compound and those of several other indole derivatives possessing a 3-carbonyl group. The correlation between the IR spectrum of this compound and the structural data is also discussed. [source] Hydrogen bonding in the bromide salts of 4-aminobenzoic acid and 4-aminoacetophenoneACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2008Dominik Cin In the title compounds, 4-carboxyanilinium bromide, C7H8NO2+·Br,, (I), and 4-acetylanilinium bromide, C8H10NO+·Br,, (II), each asymmetric unit contains a discrete cation with a protonated amino group and a halide anion. Both crystal structures are characterized by two-dimensional hydrogen-bonded networks. The ions in (I) are connected via N,H...Br, N,H...O and O,H...Br hydrogen bonds, with three characteristic graph-set motifs, viz. C(8), C21(4) and R32(8). The centrosymmetric hydrogen-bonded R22(8) dimer motif characteristic of carboxylic acids is absent. The ions in (II) are connected via N,H...Br and N,H...O hydrogen bonds, with two characteristic graph-set motifs, viz. C(8) and R42(8). The significance of this study lies in its illustration of the differences between the supramolecular aggregations in two similar compounds. The presence of the methyl group in (II) at the site corresponding to the hydroxyl group in (I) results in a significantly different hydrogen-bonding arrangement. [source] | ||||||||||||||||