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Central Atom (central + atom)
Selected AbstractsSandwich compounds with central hypercoordinate carbon, nitrogen, and oxygen: A quantum-chemical studyHETEROATOM CHEMISTRY, Issue 6 2006Ruslan M. Minyaev Ab initio (MP2(fu)/6-311+G**) and DFT (B3LYP/6-311+G**) calculations predict stable structures of sandwich compounds with the central carbon, nitrogen, and oxygen atoms surrounding lithium counterions between three-membered (BH)3 rings. The lithium counterions play a crucial role in the stabilization of these systems. The topological Bader analysis performed for these sandwich systems demonstrates that the central atom is linked to the ligands by nine-bond paths and, consequently, should be regarded as a nine-coordinated atom. Such a coordination number of carbon is the highest for all known main group organoelement compounds. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:464,474, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20268 [source] Poly(urethanes) containing silarylene and/or germarylene unitsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008C. A. Terraza Abstract A series of 10 poly(urethanes) were synthesized by solution polymerization from bis(chloroformates) and aromatic diamines, containing both silicon or germanium as central atom. So, the polymers prepared contain two silicon atoms or two germanium atoms exclusively or combinations of both. Me, Et, and Ph groups were bonded to the central atoms according to the nature of the monomers employed. Poly(urethanes) were characterized by FTIR, 1H, 13C, and 29Si NMR spectroscopy and the results agreed with the proposed structures. Additionally, intrinsic viscosity values were established in DMSO solutions and thermal analyses were developed. In all cases, thermostable oligomers were obtained, which showed a degradation process beginning at ,240,260°C. Polymers showed a thermal dependence with the nature of the heteroatom employed. Thus, in general, when germanium was used as central atom, the thermal stability was higher than the polymers containing silicon which agrees with the lower polarity and higher energy of the CGe bond in comparison with the CSi one. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008. [source] Oxygen Position, Octahedral Distortion, and Bond-Valence Parameter from Bond Lengths in Ti1,xSnxO2 (0 ,x, 1)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2000Toshiya Hirata Based on the virtual crystal approximation (or Vegard's law), the bond lengths of Ti1,xSnxO2 were deduced from those of TiO2 and SnO2, to allow the oxygen position and octahedral distortion to be determined as a function of x. The oxygen positional parameter (u) increased linearly when the Sn4+ cation (which has a larger ionic radius) was substituted for the Ti4+ cation, whereas the octahedral distortion exhibited a nonlinear decay with increasing x in Ti1,xSnxO2. At the same time, the bond-valence parameter, which relates bond valence to bond length, so that the central atom in the octahedron can retain a constant valence of +4.0, exhibited a correlation with u for Ti1,xSnxO2. The present results indicate that the different phonon/physical properties of TiO2 and SnO2 and/or their dependence on x in Ti1,xSnxO2 can be associated with different octahedral distortions. [source] Structural correlations for 1H, 13C and 15N NMR coordination shifts in Au(III), Pd(II) and Pt(II) chloride complexes with lutidines and collidineMAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2010Leszek Pazderski Abstract 1H, 13C and 15N NMR studies of gold(III), palladium(II) and platinum(II) chloride complexes with dimethylpyridines (lutidines: 2,3-lutidine, 2,3lut; 2,4-lutidine, 2,4lut; 3,5-lutidine, 3,5lut; 2,6-lutidine, 2,6lut) and 2,4,6-trimethylpyridine (2,4,6-collidine, 2,4,6col) having general formulae [AuLCl3], trans -[PdL2Cl2] and trans -/cis- [PtL2Cl2] were performed and the respective chemical shifts (,1H, ,13C, ,15N) reported. The deshielding of protons and carbons, as well as the shielding of nitrogens was observed. The 1H, 13C and 15N NMR coordination shifts (,1Hcoord, ,13Ccoord, ,15Ncoord; ,coord = ,complex , ,ligand) were discussed in relation to some structural features of the title complexes, such as the type of the central atom [Au(III), Pd(II), Pt(II)], geometry (trans - or cis -), metal-nitrogen bond lengths and the position of both methyl groups in the pyridine ring system. Copyright © 2010 John Wiley & Sons, Ltd. [source] Conjugated Macrocycles as Active Materials in Nonlinear Optical Processes: Optical Limiting Effect with Phthalocyanines and Related CompoundsTHE CHEMICAL RECORD, Issue 3 2002Michael Hanack Abstract An overview of the optical limiting (OL) processes in phthalocyanines and related compounds is presented, particularly a description of the synthesis and relevant optical properties of a series of axially substituted indium(III), titanium(IV), phthalo- and naphthalocyanines, and octaarylporphyrazines. Several techniques, such as transient absorption, Z-scan, and degenerate four-wave mixing, were used to assess the optical properties and OL performance of the investigated compounds. The versatility of the methods of organic synthesis leads to the achievement of effective systems in terms of OL performance through the appropriate combination and modulation of several structural components. The chemistry of the macrocycles here considered allows the variation of the different chemical features, such as the degree of electronic conjugation of the macrocycle and the nature of the ring substituents, the central atom, and the ligands attached to the central atom. © 2002 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 2: 129,148, 2002: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.10024 [source] Orientational disorder and phase transitions in crystals of (NH4)2NbOF5ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2008Anatoly A. Udovenko Ammonium oxopentafluoroniobate, (NH4)2NbOF5, was synthesized in a single-crystal form and the structures of its different phases were determined by X-ray diffraction at three temperatures: phase (I) at 297,K, phase (II) at 233,K and phase (III) at 198,K. The distorted [NbOF5]2, octahedra are of similar geometry in all three structures, with the central atom shifted towards the O atom. The structure of (I) is disordered, with three spatial orientations of the [NbOF5]2, octahedron related by a jump rotation around the pseudo-threefold local axis such that the disorder observed is of a dynamic nature. As the temperature decreases, the compound undergoes two phase transitions. The first is accompanied by full anionic ordering and partial ordering of the ammonium groups (phase II). The structure of (III) is completely ordered. The F and O atoms in the structures investigated were identified via the Nb,X (X = O and F) distances. The crystals of all three phases are twinned. [source] Synthesis, structure and muscarinic agonist activity of substituted N -(silatran-1-ylmethyl)acetamidesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2010Vera G. Pukhalskaya Abstract Substituted N -(silatran-1-ylmethyl)acetamides, N -methyl- N -[1-(3,,7,,10,-trimethylsilatran-1-yl)methyl]acetamide (2a) and N -(2-hydroxyethyl)- N -[1-(3,,7,,10,-trimethylsilatran-1-yl)methyl]acetamide (2b) were prepared by the reactions of triisopropanolamine with N -methyl- N -(trimethoxysilylmethyl)acetamide (1a) and 2,2-dimethoxy-4-acetyl-1-oxa-4-aza-2-silacyclohexane (1b), respectively. According to X-ray data, the structures of the silatrane moieties are superpositions of unsymmetrical and symmetrical stereoisomers. The O , Si coordination between the central atom and exocyclic substituent is absent in both compounds. Silatranes 2a and 2b are partial muscarinic agonists which demonstrate submaximal effect and mimic the effect of acetylcholine by binding directly to cholinoreceptors of the ileal smooth muscle. Copyright © 2009 John Wiley & Sons, Ltd. [source] Synthesis and Characterisation of Coordination Polymers of CuII and ZnII with 1,3-Bis(1,2,3,4-tetrazol-2-yl)propane , Rotational Freedom of the Donor Group Favours Structural DiversificationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2004Robert Bronisz Abstract The novel bidentate ligand 1,3-bis(1,2,3,4-tetrazol-2-yl)propane (pbtz), which possesses a flexible spacer, was synthesised in order to investigate the influence of the flexibility of ligand molecules on the architecture of coordination polymers. For that purpose the reactions between pbtz and M(ClO4)2·6H2O salts (M = CuII and ZnII) were performed. The complexes [{Cu(pbtz)3}(ClO4)2], and [{Zn(pbtz)3}(ClO4)2·2EtOH], were characterised by IR and UV/Vis spectroscopy and their crystal structures were determined by single-crystal X-ray diffraction measurements. In both compounds the pbtz ligand molecules act as N4,N4, connectors bridging the central atoms, and the 2-substituted tetrazole rings coordinate in a monodentate fashion to the central atoms forming M(tetrazole)6 cores. [{Cu(pbtz)3}(ClO4)2], was isolated as a 1D coordination polymer. The copper(II) ions are triply bridged by ligand molecules, leading to the formation of infinite 1D chains. A highly unusual manner of bridging, with the tethering of two neighbouring central atoms by the same kind of ligand molecules, although possessing different conformations, is observed. In [{Zn(pbtz)3}(ClO4)2·2EtOH], the six-coordinate zinc(II) ions, which are bridged by single ligand molecules, serve as topological nodes, leading to the formation of a 3D ,-polonium-type network. The crystal structure of the ZnII complex contains only one such net solvated by ethanol molecules. A conformational analysis of the ligand molecules in both compounds demonstrates that the flexibility of the pbtz and the ability of the tetrazole rings in particular to adopt various, relative orientations is responsible for the diversity of the architectures of the obtained complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Poly(urethanes) containing silarylene and/or germarylene unitsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008C. A. Terraza Abstract A series of 10 poly(urethanes) were synthesized by solution polymerization from bis(chloroformates) and aromatic diamines, containing both silicon or germanium as central atom. So, the polymers prepared contain two silicon atoms or two germanium atoms exclusively or combinations of both. Me, Et, and Ph groups were bonded to the central atoms according to the nature of the monomers employed. Poly(urethanes) were characterized by FTIR, 1H, 13C, and 29Si NMR spectroscopy and the results agreed with the proposed structures. Additionally, intrinsic viscosity values were established in DMSO solutions and thermal analyses were developed. In all cases, thermostable oligomers were obtained, which showed a degradation process beginning at ,240,260°C. Polymers showed a thermal dependence with the nature of the heteroatom employed. Thus, in general, when germanium was used as central atom, the thermal stability was higher than the polymers containing silicon which agrees with the lower polarity and higher energy of the CGe bond in comparison with the CSi one. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008. [source] RbBa2(N3)5: a new ternary azideACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2006Grigori V. Vajenine Rubidium dibarium pentaazide, RbBa2(N3)5, was prepared from an aqueous solution of the binary azides at room temperature. It crystallizes in the monoclinic system (space group P2/n). Two central atoms of azide groups occupy the 2c () and 2b () positions, another azide group lies completely on a twofold axis (2f), while Rb atoms are situated in 2e (2) positions. The crystal structure of RbBa2(N3)5 can be regarded as a distorted AlB2 -type arrangement of the metal atoms, with the azide groups occupying the voids between the cations. This results in coordination numbers of 8 (Rb) and 10 (Ba). The N,N distances are in the range 1.169,(8),1.190,(5),Å, typical for the azide group. [source] Bis(tetraethylammonium) hydrogensulfate dihydrogenphosphate at 292 and 150,KACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2003Jan Fábry The title compound, 2C8H20N+·HSO4,·H2PO4,, was crystallized in a desiccator over P4O10 from a water solution of stoichiometric amounts of tetraethylammonium hydroxide and sulfuric and phosphoric acids. The compound is deliquescent. The structure contains two symmetry-independent cations in nearly the same conformation, as well as two symmetry-independent anions, the central atoms of which are equally occupied by P and S. The anions are interconnected by short O,O hydrogen bonds into one-dimensional chains. The distances and angles between some of the methyl or methylene groups and anionic O atoms indicate the presence of C,H,O hydrogen bonds. The structure was determined from data at 292,(2) and 150,(2) K. These room- and low-temperature structures are virtually the same, with the exception of the localization of the H atoms that participate in the symmetry-restricted O,O hydrogen bonds. A differential scanning calorimetry experiment indicated no phase transition below the temperature at which the compound started to decompose (353,K), down to 93,K. [source] | |||||||||||||