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C Interactions (c + interaction)
Selected AbstractsPyrazolate-Based Dinucleating Ligands in L2M2 Scaffolds: Effects of Bulky Substituents and Coligands on Structures and M···H,C InteractionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2004Jens C. Röder Abstract A series of nickel(II) and palladium(II) complexes [L2M2]2+ have been prepared and structurally characterized, where L is a pyrazolate ligand with bulky 2,6-dimethyl- or 2,6-di(isopropyl)anilinomethyl side arms. Coordinating counter anions such as chloride can bind to axial sites of the dinickel species in a solvent-dependent process, giving rise to five-coordinate high-spin metal ions. In the case of weakly coordinating anions, the metal ions are found in roughly square-planar environments, and the structures are governed by the tendency of the bulky aryl groups to avoid each other, which forces the methyl or isopropyl substituents in the aryl 2- and 6-positions to approach the metal ions from the axial directions. This leads to drastic low-field shifts of the respective 1H NMR signals, e.g. , = 7.86 ppm for the isopropyl ,CH which comes in close proximity to the low-spin nickel(II) center. The relevance of such low-field NMR resonances of protons close to the axial sites of d8 metal ions for possible three-center four-electron M···H,C hydrogen bonds involving the filled d orbital of the metal ion is discussed. In the present case, attractive M···H interactions are assumed to be of no major significance. This was corroborated by the structure of a further [L2Ni2]2+ type complex where the anilinomethyl side arms bear only a single 2-isopropyl group, which was found rotated away from the metal. Additional spectroscopic and electrochemical properties of the various complexes are reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] The C,C pair in the vicinity of a bcc Fe bulk vacancy: electronic structure and bondingPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2007S. Simonetti Abstract C,Fe and C,C interactions near a bcc Fe vacancy were analysed using DFT calculations. A cell containing 14 atoms was used to simulate the local environment of the Fe vacancy. Carbon atoms were positioned in their local energy minimum configurations. The most stable positions for the C atoms in the vacancy region were found at about 1.23 Å from the vacancy centre and near the first nearest-neighbour octahedral sites. Changes in the electronic structure of Fe atoms near a vacancy were analysed. Fe,Fe bonds surrounding the vacancy weaken their bond when the C atoms are present. This bond weakening is a consequence of C,Fe bond formation. The Fe,C interactions occur mainly via Fe 4s orbitals with a lesser participation of Fe 3p orbitals. There is an electron transfer to the C atoms from their Fe nearest neighbours. The C,C interaction was also analysed. For the C,C distance of 1.462 Å, there is a bonding between the C atoms. The C,C interaction is stronger than the C,Fe interactions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Sodiated ,-Diphosphonate Carbanions: Characterization of the Tetrameric Cubane and the Hexameric Ladder Complexes [{(iPrO)2P(O)}2CHNa]4 and [{(EtO)2P(O)}2CHNa]6EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2003Roger Nassar Abstract Reaction of the methylene diphosphonates [(RO)2P(O)]2CH2, where R = iPr or Et, with the metalating reagents NaH, nBuNa or the superbasic mixture tBuONa/nBuLi leads to monodeprotonation, and formation of the complexes [{(iPrO)2P(O)}2CHNa]4 (1) and [{(EtO)2P(O)}2CHNa]6 (2). Single-crystal X-ray diffraction studies revealed that 1 is tetrameric in the solid state, with a central Na4O4 cubane core. Each metal in 1 is rendered pentacoordinate by binding to three ,3 -O phosphoryl bridges within the cubane, a chelating phosphoryl unit, and also a single iPrO group. In contrast, the structure of 2 is hexameric, and is composed of an unusual six-rung Na6O6 ladder core. Three distinct sodium environments as well as ,1 -, ,2 - and ,3 -O phosphoryl units are present within the ladder framework. No Na,C interactions are present in either 1 or 2. All of the six-membered NaOPCPO chelate rings display localized P=O double bonds and partial multiple bonding on the P,C,P linkages (mean P,O: 1.49 Å, and mean P,C: 1.69 Å). Ab initio molecular orbital calculations (HF/6,31G*) on model complexes indicate that the hexameric arrangement found for 2 is thermodynamically more stable than the cubane structure of 1, in the absence of steric effects. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Photophysical Processes in ,Supramolecular Balls' Formed by Lanthanide Chloride with 2,2,-BipyridineHELVETICA CHIMICA ACTA, Issue 11 2009Abstract The europium complex [EuCl2(bpy)2(H2O)2]Cl,1.25,C2H6O,0.37,H2O, where bpy is 2,2,-bipyridine, was synthesized and investigated with the aim to relate its molecular geometry and crystal packing to the efficiency of energy-transfer processes. The presence of H-bonds between noncoordinated Cl, ions and coordinated H2O molecules leads to the formation of discrete trimers assembled by a number of CH,,,Cl and stacking interactions into ,supramolecular balls' which contain Cl, ions and solvate molecules (H2O and EtOH). The additional stabilization of the complex is due to intramolecular N,,,C interactions between two bpy ligands that causes some shortening of the EuN bonds. Deciphering the luminescence properties of the Eu complex was performed under consideration of both the composition of the inner coordination sphere and the peculiarities of the crystal packing. The influence of the latter and the bpy orientation on the energy of the ligand,Eu charge-transfer state (LMCT) was established, and an additional excited state induced by the , -stacking interaction (SICT) was identified. [source] The C,C pair in the vicinity of a bcc Fe bulk vacancy: electronic structure and bondingPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2007S. Simonetti Abstract C,Fe and C,C interactions near a bcc Fe vacancy were analysed using DFT calculations. A cell containing 14 atoms was used to simulate the local environment of the Fe vacancy. Carbon atoms were positioned in their local energy minimum configurations. The most stable positions for the C atoms in the vacancy region were found at about 1.23 Å from the vacancy centre and near the first nearest-neighbour octahedral sites. Changes in the electronic structure of Fe atoms near a vacancy were analysed. Fe,Fe bonds surrounding the vacancy weaken their bond when the C atoms are present. This bond weakening is a consequence of C,Fe bond formation. The Fe,C interactions occur mainly via Fe 4s orbitals with a lesser participation of Fe 3p orbitals. There is an electron transfer to the C atoms from their Fe nearest neighbours. The C,C interaction was also analysed. For the C,C distance of 1.462 Å, there is a bonding between the C atoms. The C,C interaction is stronger than the C,Fe interactions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Bond catastrophes in rhodium complexes: experimental charge-density studies of [Rh(C7H8)(PtBu3)Cl] and [Rh(C7H8)(PCy3)Cl]ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2010Hazel A. Sparkes Rhodium complexes have potential uses in both catalysis and promoting the cleavage of C,C bonds. In order to further our understanding of these species and their potential applications, it is vital to obtain insight into the bonding within the species, particularly the Rh,C interactions, and to this end experimental charge-density studies have been undertaken on the title complexes. High-resolution single-crystal datasets to sin,,/, = 1.06,Å,1 were obtained at 100,K and analysed using Bader's `Atoms in Molecules' (AIM) approach. The results of the studies have provided unique insights into the bonding involving rhodium and highlight the importance of undertaking such investigations for transition metal compounds. [source] 2-{[(3-Fluorophenyl)amino]methylidene}-3-oxobutanenitrile and 5-{[(3-fluorophenyl)amino]methylidene}-2,2-dimethyl-1,3-dioxane-4,6-dione: X-ray and DFT studiesACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2010Vratislav Langer In the crystal structures of the title compounds, C11H9FN2O, (I), and C13H12FNO4, (II), the molecules are joined pairwise via different hydrogen bonds and the constituent pairs are crosslinked by weak C,H...O hydrogen bonds. The basic structural motif in (I), which is partially disordered, comprises pairs of molecules arranged in an antiparallel fashion which enables C,H...N[triple-bond]C interactions. The pairs of molecules are crosslinked by two weak C,H...O hydrogen bonds. The constituent pair in (II) is formed by intramolecular bifurcated C,H...O/O, and combined inter- and intramolecular N,H...O hydrogen bonds. In both structures, F atoms form weak C,F...H,C interactions with the H atoms of the two neighbouring methyl groups, the H...F separations being 2.59/2.80 and 2.63/2.71,Å in (I) and (II), respectively. The bond orders in the molecules, estimated using the natural bond orbitals (NBO) formalism, correlate with the changes in bond lengths. Deviations from the ideal molecular geometry are explained by the concept of non-equivalent hybrid orbitals. The existence of possible conformers of (I) and (II) is analysed by molecular calculations at the B3LYP/6,31+G** level of theory. [source] 1-Deoxy-1-(4-fluorophenyl)-,- d -ribofuranose, its hemihydrate, and 1-deoxy-1-(2,4-difluorophenyl)-,- d -ribofuranose: structural evidence for intermolecular C,H,F,C interactionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2000Jan W. Bats The structures of 1-deoxy-1-(4-fluorophenyl)-,- d -ribofuranose in two crystal forms, (Ia) and (Ib) (C11H13FO4), 1-deoxy-1-(4-fluorophenyl)-,- d -ribofuranose hemihydrate, (Ic) (C11H13FO4·0.5H2O) and 1-deoxy-1-(2,4-difluorophenyl)-,- d -ribofuranose, (II) (C11H12F2O4), show two-dimensional networks of intermolecular hydrogen bonds between the hydroxyl groups. Weak intermolecular C,H,F,C and C,H,,arene interactions complete the packing in the third dimension. The ribofuranose ring has a conformation intermediate between a C1,- exo,C2,- endo twist and a C2,- endo envelope for (Ia) and (Ic), a conformation intermediate between a C2,- endo,C3,- exo twist and a C2,- endo envelope for (Ib) and an unsymmetrical C2,- exo,C3,- endo twist conformation for (II). [source] Mitochondria-targeted disruptors and inhibitors of cytochrome c/cardiolipin peroxidase complexes: A new strategy in anti-apoptotic drug discoveryMOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue 1 2009Valerian E. Kagan Abstract Thre critical role of mitochondria in programmed cell death leads to the design of mitochondriotropic agents as a strategy in regulating apoptosis. For anticancer therapy, stimulation of proapoptotic mitochondrial events in tumor cells and their suppression in surrounding normal cells represents a promising paradigm for new therapies. Different approaches targeting regulation of components of mitochondrial antioxidant system such as Mn-SOD demonstrated significant antitumor efficiency, particularly in combination therapy. This review is focused on a newly discovered early stage of mitochondria-dependent apoptosis , oxidative lipid signaling involving a mitochondria-specific phospholipid cardiolipin (CL). Cytochrome c (cyt c) acts as a CL-specific peroxidase very early in apoptosis. At this stage, the hostile events are still secluded within the mitochondria and do not reach the cytosolic targets. CL oxidation process is required for the release of pro-apoptotic factors into the cytosol. Manipulation of cyt c interactions with CL, inhibition of peroxidase activity, and prevention of CL peroxidation are prime targets for the discovery of anti-apoptotic drugs acting before the "point-of-no-return" in the fulfillment of the cell death program. Therefore, mitochondria-targeted disruptors and inhibitors of cyt c/CL peroxidase complexes and suppression of CL peroxidation represent new strategies in anti-apoptotic drug discovery. [source] | ||||||||||