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Dimeric Units (dimeric + unit)
Selected AbstractsChemInform Abstract: First-Principles Electronic Structure Calculations of Ba5Si2N6 with Anomalous Si2N6 Dimeric Units.CHEMINFORM, Issue 34 2001C. M. Fang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] [CuII4] Clusters From the Self-Assembly of Two Imidazolidinyl 2-Phenolate-Bridged [CuII2] Units: The Role of the Chloride BridgeEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2007Alok Ranjan Paital Abstract A new family of tetracopper clusters [Cu4(,4 -X)L2]ClO4·nH2O (1a,c) [X = Cl, Br, I; n = 12, 2, 2; H3L = 2-(2,-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine] have been synthesised and characterised. The X-ray crystal structure of 1a reveals that the template action of the spherical Cl, anion (,4 -Cl,), which features a unique rectangular planar bridging mode, is responsible for the self-assembly of two [Cu2L]+ units in complex 1a. In this family of complexes the spherical halides serve as templates to assemble the dimeric unit into tetrameric complexes, which gives an insight into the role of the halide bridge in tetranuclear complex formation. The capacity of this bridge to mediate magnetic coupling has been examined by bulk magnetic measurements for complex 1a. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Chemistry, Urease Inhibition, and Phytotoxic Studies of Binuclear Vanadium(IV) ComplexesCHEMISTRY & BIODIVERSITY, Issue 1 2007Rifat Ara Abstract Vanadium plays an important role in biological systems and exhibits a variety of bioactivities. In an effort to uncover the chemistry and biochemistry of vanadium with nitrogen- and oxygen-containing ligands, we report herein the synthesis and spectroscopic characterization of vanadium(IV) complexes with hydrazide ligands. Substituents on these ligands exhibit systematic variations of electronic and steric factors. Elemental and spectral data indicate the presence of a dimeric unit with two vanadium(IV) ions coordinated with two hydrazide ligands along with two H2O molecules. The stability studies of these complexes over time in coordinating solvent, DMSO, indicates binding of the solvent molecules to give [V2O2L2(H2O)2(DMSO)2]2+ (L=hydrazide ligand) and then conversion of it to a monomeric intermediate species, [VOL(DMSO)3]1+. Hydrazide ligands are inactive against urease, whereas vanadium(IV) complexes of these ligands show significant inhibitory potential against this enzyme and are found to be non-competitive inhibitors. These complexes also show low phytotoxicity indicating their usefulness for soil ureases. Structure,activity relationship studies indicate that the steric and/or electronic effects that may change the geometry of the complexes play an important role in their inhibitory potential and phytotoxicity. [source] Synthesis, Characterization, and Electrochemical Properties of Dinuclear Complexes Assembled from Asymmetric CoIII Bis(dioximates) and Boronic AcidsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2005Renata Dreos Abstract Bis(methylphenylglyoximate)cobalt(III) complexes exist both as cis and trans isomers due to the asymmetry of the equatorial ligand, and, when the axial ligands are different, the trans isomer is chiral. The reaction of racemic trans -[CH3Co(mpgH)2py] (1) with either 3- or 4-pyridylboronic acid affords dimeric units arranged on a crystallographic symmetry center such that the pyridyl nitrogen of one moiety coordinates to the Co atom of the symmetry-related unit. In principle, three structurally different dimeric species (two homodimers and one heterodimer) can be obtained. Time-resolved 1H NMR spectra of a 1:1 mixture of racemic 1 and either 3- or 4-pyridylboronic acid in CDCl3/CD3OD show that the reaction does not converge toward a unique species in solution. Nevertheless, X-ray structures show that the heterochiral dimers are the only products that crystallize from the reaction mixture. The nature of the dioximate side groups does not affect the geometry of the dimeric arrangements assembled by 4-pyridylboronic acid ("molecular box"). On the contrary, the geometry of the species assembled by 3-pyridylboronic acid varies from the "molecular parallelogram" obtained from the bis(dimethylglyoximates) to the highly squeezed "molecular box" obtained from bis(methylphenylglyoximates). Cyclic voltammetry studies show that the metal centers in the dimeric species do not interact with each other and undergo a simultaneous redox process. However, depending on the geometry of the systems, the redox process involves a single four-electron reduction for 3 and 5 or two consecutive two-electron reduction steps for 4 and 6. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Intermolecular , -dimer of oxoverdazyl radicals with long-distance multicenter (2e/8c) bonding via nitrogen atomsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2010Sergiy V. Rosokha Abstract The 1,5-dimethyl-6-oxoverdazyl radical's solid-state structure shows distinct , -dimeric units with close interplanar separations (3.10,Å) between the head-over-tail cofacial moieties and several interatomic contacts shorter than the sums of the van der Waals radii. Evaluations of the frontier orbitals of monomeric oxoverdazyl and its , -dimer reveal that interaction of the radical SOMOs (concentrated on the nitrogen atoms) leads to the formation of the supramolecular orbital involving four equivalent bonding (N,N) segments between two oxoverdazyl moieties. As such, this , -dimer represents a rare example of nitrogen-based multicenter (2e/8c) long-distance bonding and emphasizes the universal character of this phenomenon in organic (ion-) radical systems. Copyright © 2009 John Wiley & Sons, Ltd. [source] 4-(2-Hydroxyphenyl)-2-phenyl-2,3-dihydro-1H -1,5-benzodiazepine and the 2-(2,3-dimethoxyphenyl)-, 2-(3,4-dimethoxyphenyl)- and 2-(2,5-dimethoxyphenyl)-substituted derivativesACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2007Carlos A. Escobar The 1,5-benzodiazepine ring system exhibits a puckered boat-like conformation for all four title compounds [4-(2-hydroxyphenyl)-2-phenyl-2,3-dihydro-1H -1,5-benzodiazepine, C21H18N2O, (I), 2-(2,3-dimethoxyphenyl)-4-(2-hydroxyphenyl)-2,3-dihydro-1H -1,5-benzodiazepine, C23H22N2O3, (II), 2-(3,4-dimethoxyphenyl)-4-(2-hydroxyphenyl)-2,3-dihydro-1H -1,5-benzodiazepine, C23H22N2O3, (III), and 2-(2,5-dimethoxyphenyl)-4-(2-hydroxyphenyl)-2,3-dihydro-1H -1,5-benzodiazepine, C23H22N2O3, (IV)]. The stereochemical correlation of the two C6 aromatic groups with respect to the benzodiazepine ring system is pseudo-equatorial,equatorial for compounds (I) (the phenyl group), (II) (the 2,3-dimethoxyphenyl group) and (III) (the 3,4-dimethoxyphenyl group), while for (IV) (the 2,5-dimethoxyphenyl group) the system is pseudo-axial,equatorial. An intramolecular hydrogen bond between the hydroxyl OH group and a benzodiazepine N atom is present for all four compounds and defines a six-membered ring, whose geometry is constant across the series. Although the molecular structures are similar, the supramolecular packing is different; compounds (I) and (IV) form chains, while (II) forms dimeric units and (III) displays a layered structure. The packing seems to depend on at least two factors: (i) the nature of the atoms defining the hydrogen bond and (ii) the number of intermolecular interactions of the types O,H...O, N,H...O, N,H...,(arene) or C,H...,(arene). [source] Oligomerization of BenM, a LysR-type transcriptional regulator: structural basis for the aggregation of proteins in this familyACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 5 2007Sandra Haddad LysR-type transcriptional regulators comprise the largest family of homologous regulatory DNA-binding proteins in bacteria. A problematic challenge in the crystallization of LysR-type regulators stems from the insolubility and precipitation difficulties encountered with high concentrations of the full-length versions of these proteins. A general oligomerization scheme is proposed for this protein family based on the structures of the effector-binding domain of BenM in two different space groups, P4322 and C2221. These structures used the same oligomerization scheme of dimer,dimer interactions as another LysR-type regulator, CbnR, the full-length structure of which is available [Muraoka et al. (2003), J. Mol. Biol.328, 555,566]. Evaluation of packing relationships and surface features suggests that BenM can form infinite oligomeric arrays in crystals through these dimer,dimer interactions. By extrapolation to the liquid phase, such dimer,dimer interactions may contribute to the significant difficulty in crystallizing full-length members of this family. The oligomerization of dimeric units to form biologically important tetramers appears to leave unsatisfied oligomerization sites. Under conditions that favor association, such as neutral pH and concentrations appropriate for crystallization, higher order oligomerization could cause solubility problems with purified proteins. A detailed model by which BenM and other LysR-type transcriptional regulators may form these arrays is proposed. [source] | ||||||||||