N Atoms (n + atom)

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of N Atoms

  • amine n atom
  • imine n atom

  • Selected Abstracts

    Syntheses, Characterization, and Luminescent Properties of Monoethylzinc Complexes with Anilido,Imine Ligands

    Qing Su
    Abstract The syntheses of three anilido,imine ligands of the general formula ortho -C6H4(NHAr,)(CH=NAr, [Ar, = 7-(2,4-Me2)C9H4N, Ar, = 2,6-Me2C6H3 (2a); Ar, = 7-(2,4-Me2)C9H4N, Ar,= 2,6-Et2C6H3 (2b); Ar, = 7-(2,4-Me2)C9H4N, Ar,= 2,6- iPr2C6H3 (2c)] and four zinc(II) complexes of the general formula [ortho -C6H4(NHAr,)(CH=NAr,)]ZnEt [Ar, = 7-(2,4-Me2)C9H4N, Ar,= 2,6-Me2C6H3 (3a); Ar, = 7-(2,4-Me2)C9H4N, Ar,= 2,6-Et2C6H3 (3b); Ar, = 7-(2,4-Me2)C9H4N, Ar, = 2,6- iPr2C6H3 (3c); Ar, = 2,6-Me2C6H3, Ar, = 2,6- iPr2C6H3 (3d)] are described. The complexes were synthesized from the reaction of ZnEt2 with corresponding ligands 2 by alkane elimination. All compounds were characterized by elemental analysis and 1H and 13C NMR spectroscopy. The molecular structures of compounds 2a, 2b, 3b, and 3c were determined by single-crystal X-ray crystallography. The X-ray analysis reveals that complexes 3b and 3c exist in the dimeric form with the N atom in the quinolyl ring coordinating to the other Zn atom to make the Zn atoms four coordinate. Luminescent properties of ligands 2a,2d and complexes 3a,3d in both solution and the solid state were studied. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Dicopper(II) Complexes with the Enantiomers of a Bidentate Chiral Reduced Schiff Base: Inclusion of Chlorinated Solvents and Chiral Recognition of1,2-Dichloroethane Rotamers in the Crystal Lattice

    Vamsee Krishna Muppidi
    Abstract Bisphenoxo-bridged dicopper(II) complexes [Cu2Ln2Cl2] {1 (n = 1) and 2 (n = 2)} with the N,O-donor reduced Schiff bases N -(2-hydroxybenzyl)-(R)-,-methylbenzylamine (HL1) and N -(2-hydroxybenzyl)-(S)-,-methylbenzylamine (HL2) have been synthesised and characterised. In both 1 and 2, the bidentate chiral ligands coordinate the metal centres through the secondary amine N atom and the bridging phenolate O atom. The chloride ion occupies the fourth coordination site and completes a slightly distorted square-planar NO2Cl environment around each copper(II) centre. Magnetic susceptibility measurements in the solid state suggest a strong antiferromagnetic interaction between the metal centres in both complexes. Both 1 and 2 readily form 1:1 host-guest compounds with chlorinated solvents such as CH2Cl2, CHCl3 and Cl(CH2)2Cl. All the host-guest compounds crystallise in noncentrosymmetric space groups. 1·CH2Cl2 and 2·CH2Cl2 crystallise in the P21 space group while 1·CHCl3, 2·CHCl3, 1·Cl(CH2)2Cl and 2·Cl(CH2)2Cl crystallise in the P212121 space group. In these inclusion crystals, the C,H···Cl interactions between the guest and the host molecules are primarily responsible for enclatheration of the chloroalkane molecules. In the case of CH2Cl2, one of its Cl atoms acts as the acceptor. On the other hand, for CHCl3 and Cl(CH2)2Cl, the metal coordinated Cl atom of the host complex acts as the acceptor. The structures of 1·(P)-Cl(CH2)2Cl and 2·(M)-Cl(CH2)2Cl provide rare examples for chiral recognition of the right handed (P) and the left handed (M) gauche forms of Cl(CH2)2Cl in molecular assemblies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    Sodium Hydro(isothiocyanato)borates: Synthesis and Structures

    Heinrich Nöth
    Abstract Sodium thiocyanate reacts in THF solution with 18-crown-6 to give the molecular compound Na(18-crown-6)(THF)NCS (3) with the N atom of the NCS anion oriented towards Na+. The same reaction with 15-crown-5 yields the ion pair Na(15-crown-5)NCS (4). In contrast, Na(NCS)(py)4, obtained by treating a solution of Na(H3BNCS) in THF with pyridine, yields Na(py)4(NCS) (5), which has a chain structure with hexacoordinate Na atoms coordinated to five N atoms and an S atom. Na(NCS) in THF adds 1 equiv. of BH3 to give Na(H3BNCS)·nTHF. Addition of 18-crown-6 to this solution yields crystals of the salt [Na(18-crown-6)(THF)2][H3BNCS] (1), as shown by X-ray crystallography. Both the cation and the anion show site disorder. However, when 15-crown-5 is used for complexation, the salt [Na(15-crown-5)(THF)][H3BNCS] (2) can be isolated. Its anion shows an almost linear B,N,C,S unit. Only a mixture of (catecholato)(isothiocyanato)borates results on treating Na(NCS) in THF with catecholborane. However, the borate Na[catB(NCS)2] is readily formed by adding Na(NCS) to B -(isothiocyanato)catecholborane. Single crystals of this compound were obtained as the salt [Na(18-crown-6)(THF)2][catB(NCS)2] (6). On the other hand, the reaction of Na(NCS) with 9-borabicyclo[3.3.1]nonane (9-BBN) in THF yields Na[(9-BBN)NCS)]·nTHF, and, on addition of 18-crown-6, the complex [Na(18-crown-6)(THF)2][(9-BBN)NCS] was isolated. Suitable crystals for X-ray structure determination were, however, only obtained by crystallization from tetrahydropyran. This solvate has the rather unusual structure [Na(18-crown-6)(thp)2][{(9-BBN)NCS}2Na(thp)4] (8). The sodiate anion has an Na atom coordinated by two S and four O atoms. DFT calculations support these experimental results: The (isothiocyanato)borates are more stable than the thiocyanato isomers. For the latter a bent structure of the B,S,C,N unit with a B,S,C bond angle of 105.7° is predicted. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    On the Way to Glycoprocessing Inhibitors , Synthesis of an Imidazolo-Nectrisine-Phosphono Acid Derivative: A Potential Glycosyltranferase Inhibitor

    Théophile Tschamber
    Abstract Assuming the transition state of glycosyltransferase inhibitors to be similar to those encountered with potent glycosidase inhibitors , i.e. a flattened conformation with a positively charged anomeric centre , we worked out a synthesis of the D - arabino -configured phosphonic acid target molecule 2 derived from an imidazolo-sugar. The key synthetic intermediate is the linear imidazolo L - xylo compound 10 which could be obtained, either from L - threo precursor 6 by a coupling reaction with imidazole derivative 5, or from L -sorbose. A multi-step and site specific iodination of 10 gave the mono-iodo- L - xylo derivative 14 which was cyclised to the D - arabino -configured bicyclic azasugar 15. Phosphorylation of the Grignard derivative of the latter, followed by mono-esterification with citronellol along with some protection-deprotection steps led to target molecule 2. The potential inhibitor 2 is supposed to be protonated at its most basic N atom by a carboxylic acid residue in the arabinosyl-transferase active site. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Escherichia coli cyclophilin B binds a highly distorted form of trans -prolyl peptide isomer

    FEBS JOURNAL, Issue 18 2004
    Michiko Konno
    Cyclophilins facilitate the peptidyl-prolyl isomerization of a trans -isomer to a cis -isomer in the refolding process of unfolded proteins to recover the natural folding state with cis -proline conformation. To date, only short peptides with a cis -form proline have been observed in complexes of human and Escherichia coli proteins of cyclophilin A, which is present in cytoplasm. The crystal structures analyzed in this study show two complexes in which peptides having a trans -form proline, i.e. succinyl-Ala- trans -Pro-Ala- p -nitroanilide and acetyl-Ala-Ala- trans -Pro-Ala-amidomethylcoumarin, are bound on a K163T mutant of Escherichia coli cyclophilin B, the preprotein of which has a signal sequence. Comparison with cis -form peptides bound to cyclophilin A reveals that in any case the proline ring is inserted into the hydrophobic pocket and a hydrogen bond between CO of Pro and N,2 of Arg is formed to fix the peptide. On the other hand, in the cis -isomer, the formation of two hydrogen bonds of NH and CO of Ala preceding Pro with the protein fixes the peptide, whereas in the trans -isomer formation of a hydrogen bond between CO preceding Ala-Pro and His47 N,2 via a mediating water molecule allows the large distortion in the orientation of Ala of Ala-Pro. Although loss of double bond character of the amide bond of Ala-Pro is essential to the isomerization pathway occurring by rotating around its bond, these peptides have forms impossible to undergo proton transfer from the guanidyl group of Arg to the prolyl N atom, which induces loss of double bond character. [source]

    Theoretical studies on four-membered ring compounds with NF2, ONO2, N3, and NO2 groups

    Xiao-Wei Fan
    Abstract Density functional theory (DFT) method has been employed to study the geometric and electronic structures of a series of four-membered ring compounds at the B3LYP/6-311G** and the B3P86/6-311G** levels. In the isodesmic reactions designed for the computation of heats of formation (HOFs), 3,3-dimethyl-oxetane, azetidine, and cyclobutane were chosen as reference compounds. The HOFs for N3 substituted derivations are larger than those of oxetane compounds with ONO2 and/or NF2 substituent groups. The HOFs for oxetane with ONO2 and/or NF2 substituent groups are negative, while the HOFs for N3 substituted derivations are positive. For azetidine compounds, the substituent groups within the azetidine ring affect the HOFs, which increase as the difluoroamino group being replaced by the nitro group. The magnitudes of intramolecular group interactions were predicted through the disproportionation energies. The strain energy (SE) for the title compounds has been calculated using homodesmotic reactions. For azetidine compounds, the NF2 group connecting N atom in the ring decrease the SE of title compounds. Thermal stability were evaluated via bond dissociation energies (BDE) at the UB3LYP/6-311G** level. For the oxetane compounds, the ONO2 bond is easier to break than that of the ring CC bond. For the azetidine and cyclobutane compounds, the homolysises of CNX2 and/or NNX2 (X = O, F) bonds are primary step for bond dissociation. Detonation properties of the title compounds were evaluated by using the Kamlet,Jacobs equation based on the calculated densities and HOFs. It is found that 1,1-dinitro-3,3-bis(difluoroamino)-cyclobutane, with predicted density of ca. 1.9 g/cm3, detonation velocity (D) over 9 km/s, and detonation pressure (P) of 41 GPa that are lager than those of TNAZ, is expected to be a novel candidate of high energy density materials (HEDMs). The detonation data of nitro-BDFAA and TNCB are also close to the requirements for HEDMs. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source]

    Theoretical evidence on O,N type smiles rearrangement mechanism: a computational study on the intramolecular cyclization of N -methyl-2-(2-chloropyridin-3-yloxy)-acetamide anion

    Hui Sun
    Abstract Smiles rearrangement (SR) falls under a broad category of organic synthesis for many important compounds. A complete understanding toward SR process appeals to the assistance of theoretical research. Herein, by performing quantum chemistry calculations, we give a theoretical evidence for the mechanism of a representative O,N type SR, the intramolecular cyclization of N -methyl-2-(2-chloropyridin-3-yloxy)acetamide anion. It is found that the SR to the ipso -position involves a two-step mechanism and is energetically more favorable than the direct nucleophilic attack by N atom on the ortho -position. The present result rationalizes well the experimentally observed ipso -SR product and provides a consistent picture of the O,N SR process. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    NMR and DFT investigations of the substituent and solvent effect on amino,imino tautomerism in acridin-9-amines substituted at the exocyclic nitrogen atom,

    Youssif Ebead
    Abstract The 1H and 13C NMR spectra of 9-(methoxyamino)acridine (1) and 9-hydrazinoacridine (2) show that these compounds exist principally in the imino tautomeric form in CDCl3, acetone- d6, CD3CN, DMSO- d6 and Py- d5, all solvents with different polarities and abilities to participate in specific interactions. The spectra of the other two compounds investigated,N -(2-chloroethyl)acridin-9-amine (3) and N -(5-methylpyridin-2-yl)acridin-9-amine (4),indicate that they coexist in the amino and imino forms. The amino tautomer of compound 3 predominates in CDCl3, CD3CN and Py- d5 and that of compound 4 in CDCl3 and Py- d5. On the other hand, the amino and imino forms of compound 3 coexist in acetone- d6 and probably DMSO- d6, whereas those of compound 4 coexist in acetone- d6 and DMSO- d6. The positions of the signals in the NMR spectra compare qualitatively with those predicted computationally at the GIAO/DFT level of theory. The equilibrium constants predicted by the DFT(PCM) method are in agreement with the results of NMR spectral analysis. In general, both the data predicted at the DFT level of theory and x-ray structural data show that the imino tautomers display a ,butterfly'-type geometry, whereas the amino forms are characterized by an almost flat acridine moiety. Electron-attracting substituents at the exocyclic N atom improve the stability of the imino form, and electron-withdrawing substituents do likewise for the amino form. The importance of tautomeric phenomena in the context of the ability of acridin-9-amines to participate in specific interactions is outlined in brief, as are the possible applications of these compounds as probes of environmental properties. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Influence of substituents on the kinetics of epoxy/aromatic diamine resin systems

    Heping Liu
    Abstract Eleven different epoxy/diamine systems, including tetraglycidyl-4,4,-diaminodiphenylmethane (TGDDM), triglycidyl p -aminophenol (TGAP), and diglycidyl ether of bisphenol A (DGEBA) with 4,4,-diaminodiphenylsulfone (DDS), diethyltoluenediamine (DETDA), dimethylthiotoluenediamine (DMTDA), and meta -phenylenediamine (m -PDA), were studied with near-infrared spectroscopy at different temperatures. The reactivities of the epoxies were determined and found to be in the following order when reacted with the same amine: DGEBA > TGAP > TGDDM. When the primary amine was reacted with the same epoxy, the order was DETDA > DDS > DMTDA; for the secondary amine, the order was DETDA > DMTDA > DDS. The relative reaction rates of the secondary amine to the primary amine were compared and discussed in terms of the structural differences and the corresponding substitution effect. It was concluded that the increase in the secondary amine reactivity of DETDA and DMTDA was caused by the deconjugation of the benzene-ring , electrons from the lone pair on the N atom. The overall order of the secondary amine relative reactivity was DMTDA > DETDA > DDS for the same epoxy and TGDDM > TGAP > DGEBA for the same amine. The m -PDA systems had no significant positive or negative substitution effects. Molecular orbital calculations were performed, and the results showed the most significant deconjugation effect in the secondary amine of DETDA. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3143,3156, 2004 [source]

    Verification of a distortion in the microstructure of GaN detected by EXAFS using ab initio density functional theory calculations

    Nicholas Dimakis
    X-ray absorption fine structure (XAFS) measurements on a series of epitaxially grown GaN samples have shown a distortion in the microstructure of GaN. More specifically the central N atom is 4-fold coordinated but the four Ga atoms are not equidistant. It has been shown that 2.9 to 3.5 of them (depending on the growth conditions) are found in the expected from XRD distance of 1.94 Å and the remaining are at a distance longer by approximately 15%. Second derivative calculation of the conformation energy using the Density Functional Theory (DFT) is used to investigate if the symmetric GaN cluster as given by XRD is the most energetically favorable configuration and if not which distorted structure corresponds to the most energetically favorable one. A very good agreement between DFT results and experimental XAFS spectra has been found. Generalization this technique to other dislocated clusters is also discussed. [source]

    Electron ionization mass spectra of phosphorus-containing heterocycles.


    The 1,3,4,2-oxadiazaphosphinane 2-oxides differ not only in the relative configuration of the P atom (R* or S*), but also in many other ways such as the ring size, ring fusion, P substitution and bridgehead N atom whose effects on their fragmentations have been studied. Some fragmentations resembled those of 3,1,2-oxazaphosphinane 2-oxides and 1,3,2-diazaphosphinane-2-oxides, but new routes were also found, initiated by ionization at the bridgehead N atom. The relative abundances of the molecular ions and some fragment ions allowed the differentiation of cis-trans epimers. Compounds with n,=,2 and R,,N(CH2CH2Cl)2, and linearly or angularly isoquinoline-fused isomers in most cases, gave more numerous ions with lower relative abundances than the other compounds in this series. Only the isoquinoline derivatives provided fragments resulting from ionization of the aromatic part of the molecule. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Charge density and electrostatic potential analyses in paracetamol

    Nouzha Bouhmaida
    The electron density of monoclinic paracetamol was derived from high-resolution X-ray diffraction at 100,K. The Hansen,Coppens multipole model was used to refine the experimental electron density. The topologies of the electron density and the electrostatic potential were carefully analyzed. Numerical and analytical procedures were used to derive the charges integrated over the atomic basins. The highest charge magnitude (,1.2,e) was found for the N atom of the paracetamol molecule, which is in agreement with the observed nucleophilic attack occurring in the biological media. The electric field generated by the paracetamol molecule was used to calculate the atomic charges using the divergence theorem. This was simultaneously applied to estimate the total electrostatic force exerted on each atom of the molecule by using the Maxwell stress tensor. The interaction electrostatic energy of dimers of paracetamol in the crystal lattice was also estimated. [source]

    Hydrophobic `lock and key' recognition of N -4-nitrobenzoylamino acid by strychnine

    Zbigniew Ciunik
    During racemic resolution of N -4-nitrobenzoyl- dl -amino acids (alanine, serine and aspartic acid) by a fractional crystallization of strychninium salts, crystals of both diastereo­meric salts were grown, and the crystal structures of strychninium N -4-nitrobenzoyl- l -alaninate methanol disolvate (1a), strychninium N -4-nitrobenzoyl- d -alaninate dihydrate (1b), strychninium N -4-nitrobenzoyl- d -serinate dihydrate (2a), strychninium N -4-nitrobenzoyl- l -serinate methanol solvate hydrate (2b), strychninium hydrogen N -4-nitrobenzoyl- l -aspartate 3.75 hydrate (3a) and strychninium hydrogen N -4-nitrobenzoyl- d -aspartate 2.25 hydrate (3b) were determined. The strychninium cations form corrugated layers, which are separated by hydrogen-bonded anions and solvent molecules. Common features of the corrugated layers are deep hydrophobic grooves at their surfaces, which are occupied by the 4-nitro­benzoyl groups of suitable anions. The hydrophobic `lock and key' recognition of 4-nitrobenzoyl groups of amino acid derivatives in deep grooves of the strychnine self-assembly causes the resulting surface to have more hydrophilic properties, which are more appropriate for interactions in the hydrophilic environments from which strychninium salts were crystallized. In the crystal structure of (2a) and (3a), such hydrophobic `lock and key' recognition is responsible for the lack of N,H+,O, hydrogen bonds that are usually formed between the protonated tertiary amine N atom of the strychninium cation and the deprotonated carboxyl group of the resolved acid. In the crystal structure of (2a) and (3a), the protonated amine N atom is a donor of hydrogen bonds, while the hydroxyl group of the serine derivative and water molecules are their acceptors. In light of the hydrophobic recognition, chiral discrimination depends on the nature of the hydrogen-bond networks, which involve anions, solvent molecules and the protonated amine N atom of strychninium cations. [source]

    Green chemistry synthesis: 2-amino-3-[(E)-(2-pyridyl)methylideneamino]but-2-enedinitrile monohydrate and 5-cyano-2-(2-pyridyl)-1-(2-pyridylmethyl)-1H -imidazole-4-carboxamide

    Muhammad Altaf
    The title compounds, C10H9N5O·H2O (L1·H2O) and C16H12N6O (L2), were synthesized by solvent-free aldol condensation at room temperature. L1, prepared by grinding picolinaldehyde with 2,3-diamino-3-isocyanoacrylonitrile in a 1:1 molar ratio, crystallized as a monohydrate. L2 was prepared by grinding picolinaldehyde with 2,3-diamino-3-isocyanoacrylonitrile in a 2:1 molar ratio. By varying the conditions of crystallization it was possible to obtain two polymorphs, viz. L2-I and L2-II; both crystallized in the monoclinic space group P21/c. They differ in the orientation of one pyridine ring with respect to the plane of the imidazole ring. In L2-I, this ring is oriented towards and above the imidazole ring, while in L2-II it is rotated away from and below the imidazole ring. In all three molecules, there is a short intramolecular N,H...N contact inherent to the planarity of the systems. In L1·H2O, this involves an amino H atom and the C=N N atom, while in L2 it involves an amino H atom and an imidazole N atom. In the crystal structure of L1·H2O, there are N,H...O and O,H...O intermolecular hydrogen bonds which link the molecules to form two-dimensional networks which stack along [001]. These networks are further linked via intermolecular N,H...N(cyano) hydrogen bonds to form an extended three-dimensional network. In the crystal structure of L2-I, symmetry-related molecules are linked via N,H...N hydrogen bonds, leading to the formation of dimers centred about inversion centres. These dimers are further linked via N,H...O hydrogen bonds involving the amide group, also centred about inversion centres, to form a one-dimensional arrangement propagating in [100]. In the crystal structure of L2-II, the presence of intermolecular N,H...O hydrogen bonds involving the amide group results in the formation of dimers centred about inversion centres. These are linked via N,H...N hydrogen bonds involving the second amide H atom and the cyano N atom, to form two-dimensional networks in the bc plane. In L2-I and L2-II, C,H..., and ,,, interactions are also present. [source]

    Z and E isomers of butenedioic acid with 2-amino-1,3-thiazole: 2-amino-1,3-thiazolium hydrogen maleate and 2-amino-1,3-thiazolium hydrogen fumarate

    Jain John
    Maleic acid and fumaric acid, the Z and E isomers of butenedioic acid, form 1:1 adducts with 2-amino-1,3-thiazole, namely 2-amino-1,3-thiazolium hydrogen maleate (2ATHM), C3H5N2S+·C4H3O4,, and 2-amino-1,3-thiazolium hydrogen fumarate (2ATHF), C3H5N2S+·C4H3O4,, respectively. In both compounds, protonation of the ring N atom of the 2-amino-1,3-thiazole and deprotonation of one of the carboxyl groups are observed. The asymmetric unit of 2ATHF contains three independent ion pairs. The hydrogen maleate ion of 2ATHM shows a short intramolecular O,H...O hydrogen bond with an O...O distance of 2.4663,(19),Å. An extensive hydrogen-bonded network is observed in both compounds, involving N,H...O and O,H...O hydrogen bonds. 2ATHM forms two-dimensional sheets parallel to the ab plane, extending as independent parallel sheets along the c axis, whereas 2ATHF forms two-dimensional zigzag layers parallel to the bc plane, extending as independent parallel layers along the a axis. [source]

    Ethyl 3-[1-(5,5-dimethyl-2-oxo-1,3,2-dioxaphosphorin-2-yl)propan-2-ylidene]carbazate: a combined X-ray and density functional theory (DFT) study

    Youssef Arfaoui
    In the title compound, C11H21N2O5P, one of the two carbazate N atoms is involved in the C=N double bond and the H atom of the second N atom is engaged in an intramolecular hydrogen bond with an O atom from the dimethylphosphorin-2-yl group, which is in an uncommon cis position with respect to the carbamate group. The cohesion of the crystal structure is also reinforced by weak intermolecular hydrogen bonds. Density functional theory (DFT) calculations at the B3LYP/6-311++g(2d,2p) level revealed the lowest energy structure to have a Z configuration at the C=N bond, which is consistent with the configuration found in the X-ray crystal structure, as well as a less stable E counterpart which lies 2.0,kcal,mol,1 higher in potential energy. Correlations between the experimental and computational studies are discussed. [source]


    Norman Lu
    As part of a homologous series of novel polyfluorinated bipyridyl (bpy) ligands, the title compound, C16H14F6N2O2, contains the smallest fluorinated group, viz. CF3. The molecule resides on a crystallographic inversion centre at the mid-point of the pyridine Cipso,Cipso bond. Therefore, the bpy skeleton lies in an anti conformation to avoid repulsion between the two pyridyl N atoms. Weak intramolecular C,H...N and C,H...O interactions are observed, similar to those in related polyfluorinated bpy,metal complexes. A ,,, interaction is observed between the bpy rings of adjacent molecules and this is probably a primary driving force in crystallization. Weak intermolecular C,H...N hydrogen bonding is present between one of the CF3CH2, methylene H atoms and a pyridyl N atom related by translation along the [010] direction, in addition to weak benzyl-type C,H...F interactions to atoms of the terminal CF3 group. It is of note that the O,CH2CF3 bond is almost perpendicular to the bpy plane. [source]

    Supramolecular association in proton-transfer adducts containing benzamidinium cations.


    Four organic salts, namely benzamidinidium orotate (2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylate) hemihydrate, C7H9N2+·C5H3N2O4,·0.5H2O (BenzamH+·Or,), (I), benzamidinium isoorotate (2,4-dioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate) trihydrate, C7H9N2+·C5H3N2O4,·3H2O (BenzamH+·Isor,), (II), benzamidinium diliturate (5-nitro-2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-olate) dihydrate, C7H9N2+·C4H2N3O5,·2H2O (BenzamH+·Dil,), (III), and benzamidinium 5-nitrouracilate (5-nitro-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-ide), C7H9N2+·C4H2N3O4, (BenzamH+·Nit,), (IV), have been synthesized by a reaction between benzamidine (benzenecarboximidamide or Benzam) and the appropriate carboxylic acid. Proton transfer occurs to the benzamidine imino N atom. In all four acid,base adducts, the asymmetric unit consists of one tautomeric aminooxo anion (Or,, Isor,, Dil, and Nit,) and one monoprotonated benzamidinium cation (BenzamH+), plus one-half (which lies across a twofold axis), three and two solvent water molecules in (I), (II) and (III), respectively. Due to the presence of protonated benzamidine, these acid,base complexes form supramolecular synthons characterized by N+,H...O, and N+,H...N, (±)-charge-assisted hydrogen bonds (CAHB). [source]

    A third polymorph of 4-(2,6-difluorophenyl)-1,2,3,5-dithiadiazolyl

    Elisabeth M. Fatila
    The crystal structure of a third polymorphic form of the known 4-(2,6-difluorophenyl)-1,2,3,5-dithiadiazolyl radical, C7H3F2N2S2, is reported. This new polymorph represents a unique crystal-packing motif never before observed for 1,2,3,5-dithiadiazolyl (DTDA) radicals. In the two known polymorphic forms of the title compound, all of the molecules form cis -cofacial dimers, such that two molecules are ,-stacked with like atoms one on top of the other, a common arrangement for DTDA species. By contrast, the third polymorph, reported herein, contains two crystallographically unique molecules organized such that only 50% are dimerized, while the other 50% remain monomeric radicals. The dimerized molecules are arranged in the trans -antarafacial mode. This less common dimer motif for DTDA species is characterized by ,,, interactions between the S atoms [S...S = 3.208,(1),Å at 110,K], such that the two molecules of the dimer are related by a centre of inversion. The most remarkable aspect of this third polymorph is that the DTDA dimers are co-packed with monomers. The monomeric radicals are arranged in one-dimensional chains directed by close lateral intermolecular contacts between the two S atoms of one DTDA heterocycle and an N atom of a neighbouring coplanar DTDA heterocycle [S...N = 2.857,(2) and 3.147,(2),Å at 110,K]. [source]

    Copper(II) chloride and bromide complexes with 2-methyl-2H -tetrazol-5-amine: an X-ray powder diffraction study

    Ludmila S. Ivashkevich
    The complex catena -poly[[dibromidocopper(II)]-bis(,-2-methyl-2H -tetrazol-5-amine)-,2N4:N5;,2N5:N4], [CuBr2(C2H5N5)2]n, (I), and the isotypic chloride complex catena -poly[[dichloridocopper(II)]-bis(,-2-methyl-2H -tetrazol-5-amine)-,2N4:N5;,2N5:N4], [CuCl2(C2H5N5)2]n, (II), were investigated by X-ray powder diffraction at room temperature. The crystal structure of (I) was solved by direct methods, while the Rietveld refinement of (II) started from the atomic coordinates of (I). In both structures, the Cu atoms lie on inversion centres, adopting a distorted octahedral coordination of two halogen atoms, two tetrazole N atoms and two 5-amine group N atoms. Rather long Cu,Namine bonds allow consideration of the amine group as semi-coordinated. The compounds are one-dimensional coordination polymers, formed as a result of 2-methyl-2H -tetrazol-5-amine ligands bridging via a tetrazole N atom and the amine N atom. In the polymeric chains, adjacent Cu atoms are connected by two such bridges. [source]

    Pentacoordination versus tetracoordination in silicon derivatives of an O,N,O,-tridentate ligand

    Uwe Böhme
    Bis[2-(2-hydroxy-3-methoxybenzylideneamino)phenolato-,O]dimethylsilicon, C30H30N2O6Si, (II), was isolated from the reaction of 2-(2-hydroxy-3-methoxybenzylideneamino)phenol, (I), with dichlorodimethylsilane at 339,K. It consists of two ligand molecules and the Me2Si unit forming a dialkoxydimethylsilane with a tetracoordinate Si atom. [2-(3-Methoxy-2-oxidobenzylideneamino)phenolato-,3O,N,O,]dimethylsilicon, C16H17NO3Si, (III), was isolated from the same reaction conducted at 263,K. In this complex, the dianion of (I) is coordinated via two O atoms and an azomethine N atom to the pentacoordinate Si atom. According to quantum chemical calculations, (II) is the thermodynamically stable product and (III) is the kinetically favoured product. [source]

    Poly[,8 -4,4,-bipyridine-2,2,,6,6,-tetracarboxylato-dilead(II)]

    Su-Ping Zhou
    The PbII cation in the title compound, [Pb2(C14H4N2O8)]n, is seven-coordinated by one N atom and six O atoms from four 4,4,-bipyridine-2,2,,6,6,-tetracarboxylate (BPTCA4,) ligands. The geometric centre of the BPTCA4, anion lies on an inversion centre. Each pyridine-2,6-dicarboxylate moiety of the BPTCA4, ligand links four PbII cations via its pyridyl N atom and two carboxylate groups to form two-dimensional sheets. The centrosymmetric BPTCA4, ligand then acts as a linker between the sheets, which results in a three-dimensional metal,organic framework. [source]

    Poly[bis(,4 -benzene-1,2-dicarboxylato)di-,3 -isonicotinato-dilanthanum(III)]

    Guo-Ming Wang
    In the title compound, [La2(C8H4O4)2(C6H4NO2)2]n, there are two crystallographically independent La centres, both nine-coordinated in tricapped trigonal prismatic coordination geometries by eight carboxylate O atoms and one pyridyl N atom. The La centres are linked by the carboxylate groups of isonicotinate (IN,) and benzene-1,2-dicarboxylate (BDC2,) ligands to form La,carboxylate chains, which are further expanded into a three-dimensional framework with nanometre-sized channels by La,N bonds. In the construction of the resultant architecture, in tricapped trigonal prismatic coordination geometries by eight carboxylate O atoms and one pyridyl N atom, while the BDC ligands link to four different cations each, displaying penta- and heptadentate chelating,bridging modes, respectively. [source]

    2,3-Dihydro-1,3-benzothiazol-2-iminium monohydrogen sulfate and 2-iminio-2,3-dihydro-1,3-benzothiazole-6-sulfonate: a combined structural and theoretical study

    Rafal Kruszynski
    The 2-aminobenzothiazole sulfonation intermediate 2,3-dihydro-1,3-benzothiazol-2-iminium monohydrogen sulfate, C7H7N2S+·HSO4,, (I), and the final product 2-iminio-2,3-dihydro-1,3-benzothiazole-6-sulfonate, C7H6N2O3S2, (II), both have the endocyclic N atom protonated; compound (I) exists as an ion pair and (II) forms a zwitterion. Intermolecular N,H...O and O,H...O hydrogen bonds are seen in both structures, with bonding energy (calculated on the basis of density functional theory) ranging from 1.06 to 14.15,kcal,mol,1. Hydrogen bonding in (I) and (II) creates DDDD and C(8)C(9)C(9) first-level graph sets, respectively. Face-to-face stacking interactions are observed in both (I) and (II), but they are extremely weak. [source]

    rac -5-Diphenylacetyl-2,2,4-trimethyl-2,3,4,5-tetrahydro-1,5-benzothiazepine and rac -5-formyl-2,2,4-trimethyl-2,3,4,5-tetrahydro-1,5-benzothiazepine

    Thanikasalam Kanagasabapathy
    rac -5-Diphenylacetyl-2,2,4-trimethyl-2,3,4,5-tetrahydro-1,5-benzothiazepine, C26H27NOS, (I), and rac -5-formyl-2,2,4-trimethyl-2,3,4,5-tetrahydro-1,5-benzothiazepine, C13H17NOS, (II), are both characterized by a planar configuration around the heterocyclic N atom. In contrast with the chair conformation of the parent benzothiazepine, which has no substituents at the heterocyclic N atom, the seven-membered ring adopts a boat conformation in (I) and a conformation intermediate between boat and twist-boat in (II). The molecules lack a symmetry plane, indicating distortions from the perfect boat or twist-boat conformations. The supramolecular architectures are significantly different, depending in (I) on C,H...O interactions and intermolecular S...S contacts, and in (II) on a single aromatic ,,, stacking interaction. [source]

    Two novel silver(I) coordination polymers: poly[(,2 -2-aminopyrimidine-,2N1:N3)bis(,3 -thiocyanato-,3S:S:S)disilver(I)] and poly[(2-amino-4,6-dimethylpyrimidine-,N)(,3 -thiocyanato-,3N:S:S)silver(I)]

    Geng-Geng Luo
    2-Aminopyrimidine (L1) and 2-amino-4,6-dimethylpyrimidine (L2) have been used to create the two novel title complexes, [Ag2(NCS)2(C4H5N3)]n, (I), and [Ag(NCS)(C6H9N3)]n, (II). The structures of complexes (I) and (II) are mainly directed by the steric properties of the ligands. In (I), the L1 ligand is bisected by a twofold rotation axis running through the amine N atom and opposite C atoms of the pyrimidine ring. The thiocyanate anion adopts the rare ,3 -,3S coordination mode to link three tetrahedrally coordinated AgI ions into a two-dimensional honeycomb-like 63 net. The L1 ligands further extend the two-dimensional sheet to form a three-dimensional framework by bridging AgI ions in adjacent layers. In (II), with three formula units in the asymmetric unit, the L2 ligand bonds to a single AgI ion in a monodentate fashion, while the thiocyanate anions adopt a ,3 -,1N,,2S coordination mode to link the AgL2 subunits to form two-dimensional sheets. These layers are linked by N,H...N hydrogen bonds between the noncoordinated amino H atoms and both thiocyanate and pyrimidine N atoms. [source]

    Hydrogen-bonded structures of the isomeric compounds of quinoline with 2-chloro-5-nitrobenzoic acid, 3-chloro-2-nitrobenzoic acid, 4-chloro-2-nitrobenzoic acid and 5-chloro-2-nitrobenzoic acid

    Kazuma Gotoh
    The structures of four isomeric compounds, all C7H4ClNO4·C9H7N, of quinoline with chloro- and nitro-substituted benzoic acid, namely, 2-chloro-5-nitrobenzoic acid,quinoline (1/1), (I), 3-chloro-2-nitrobenzoic acid,quinoline (1/1), (II), 4-chloro-2-nitrobenzoic acid,quinoline (1/1), (III), and 5-chloro-2-nitrobenzoic acid,quinoline (1/1), (IV), have been determined at 185,K. In each compound, a short hydrogen bond is observed between the pyridine N atom and a carboxyl O atom. The N...O distances are 2.6476,(13), 2.5610,(13), 2.5569,(12) and 2.5429,(12),Å for (I), (II), (III) and (IV), respectively. Although in (I) the H atom in the hydrogen bond is located at the O site, in (II), (III) and (IV) the H atom is disordered in the hydrogen bond over two positions with (N site):(O site) occupancies of 0.39,(3):0.61,(3), 0.47,(3):0.53,(3) and 0.65,(3):0.35,(3), respectively. [source]

    (Acetato-,O)aqua(1H -imidazole-,N3)(picolinato-,2N,O)copper(II) 0.87-hydrate: a Z,> 1 structure

    Anne-Christine Chamayou
    The crystal structure of the title compound, [Cu(C6H4NO2)(C2H3O2)(C3H4N2)(H2O)]·0.87H2O, has a square-pyramidal-coordinated CuII centre (the imidazole is trans to the picolinate N atom, the acetate is trans to the picolinate ,CO2 group and the aqua ligand is in a Jahn,Teller-elongated apical position) and has two symmetry-independent molecules in the unit cell (Z, = 2), which are connected through complementary imidazole,picolinate N,H...O hydrogen bonding. The two partially occupied solvent water molecules are each disordered over two positions. The disordered solvent water molecules, together with pseudosymmetry elements, support the notion that a crystal structure with multiple identical chemical formula units in the structural asymmetric unit (Z, > 1) can represent a crystal `on the way', that is, a kinetic intermediate form which has not yet reached its thermodynamic minimum. Neighbouring molecules form ,,, stacks between their imidazole and picolinate N-heterocycles, with centroid,centroid distances in the range 3.582,(2),3.764,(2),Å. [source]

    A structural systematic study of four isomers of difluoro- N -(3-pyridyl)benzamide

    Joyce McMahon
    The four isomers 2,4-, (I), 2,5-, (II), 3,4-, (III), and 3,5-difluoro- N -(3-pyridyl)benzamide, (IV), all with formula C12H8F2N2O, display molecular similarity, with interplanar angles between the C6/C5N rings ranging from 2.94,(11)° in (IV) to 4.48,(18)° in (I), although the amide group is twisted from either plane by 18.0,(2),27.3,(3)°. Compounds (I) and (II) are isostructural but are not isomorphous. Intermolecular N,H...O=C interactions form one-dimensional C(4) chains along [010]. The only other significant interaction is C,H...F. The pyridyl (py) N atom does not participate in hydrogen bonding; the closest H...Npy contact is 2.71,Å in (I) and 2.69,Å in (II). Packing of pairs of one-dimensional chains in a herring-bone fashion occurs via,-stacking interactions. Compounds (III) and (IV) are essentially isomorphous (their a and b unit-cell lengths differ by 9%, due mainly to 3,4-F2 and 3,5-F2 substitution patterns in the arene ring) and are quasi-isostructural. In (III), benzene rotational disorder is present, with the meta F atom occupying both 3- and 5-F positions with site occupancies of 0.809,(4) and 0.191,(4), respectively. The N,H...Npy intermolecular interactions dominate as C(5) chains in tandem with C,H...Npy interactions. C,H...O=C interactions form R22(8) rings about inversion centres, and there are ,,, stacks about inversion centres, all combining to form a three-dimensional network. By contrast, (IV) has no strong hydrogen bonds; the N,H...Npy interaction is 0.3,Å longer than in (III). The carbonyl O atom participates only in weak interactions and is surrounded in a square-pyramidal contact geometry with two intramolecular and three intermolecular C,H...O=C interactions. Compounds (III) and (IV) are interesting examples of two isomers with similar unit-cell parameters and gross packing but which display quite different intermolecular interactions at the primary level due to subtle packing differences at the atom/group/ring level arising from differences in the peripheral ring-substitution patterns. [source]

    The neutral cluster amminehexa-,2 -chlorido-,4 -oxido-tris(1,4,6-triazabicyclo[3.3.0]oct-4-ene)tetracopper(II)

    Gina M. Chiarella
    The title compound, [Cu4Cl6O(C5H9N3)3(NH3)], is a neutral conformationally chiral cluster which crystallizes under the conditions described in this paper as a racemic conglomerate. It contains four CuII atoms in a tetrahedral coordination with a central O atom lying on a crystallographic threefold axis. Six chloride anions bridge the four CuII atoms. Three CuII atoms are bound by an N atom of a monodentate 1,4,6-triazabicyclo[3.3.0]oct-4-ene (Htbo) ligand and the remaining CuII atom is bound by a terminal ammine ligand. The geometry at each copper center is trigonal bipyramidal, produced by the bound N atom of Htbo or ammonia, the O atom in the axial position, and three chloride ions in the equatorial plane. The chloride anions form an octahedron about the oxygen center. The copper,ammonia bond lies along the crystallographic threefold axis, along which the molecules are packed in a polar head-to-tail fashion. [source]