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Coordination Schemes (coordination + scheme)

Distribution by Scientific Domains

Chemistry	80%

Selected Abstracts

An Atropo-Stereogenic Diphosphane Ligand with a Proximal Cationic Charge: Specific Catalytic Properties of a Palladium Complex Thereof

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2008
Nathalie Debono
Abstract A class of cationic diphosphane ligands combining phosphane and amidiniophosphane moieties is illustrated on the N -methyl,N -naphthylbenzimidazolium framework. The palladium(II) complex thereof is described and compared to the corresponding complex of the analogous neutral diphosphane. Contrary to first-level expectations, the N2C,P and N2CP,Pd bonds in the cationic diphosphane complex are not longer than those occurring in its neutral counterpart. In the cationic ligand, the proximal positive charge is indeed conjugated to one phosphanyl group, and the coordination scheme is tentatively interpreted by resonance of the phosphane,metal dative bond (+N2C,P:,[Pd]) with a carbene,phosphenium dative bond (N2C:,[+P:,Pd]). Despite this peculiar structural feature, the electronic , donation (vs. , acceptation) towards the palladium centre remains lowered in the cationic ligand. This specific property can be a priori valuable in a catalytic process where oxidative addition is not the limiting step. It is indeed shown that although the neutral complex is more active in Suzuki coupling reactions, the cationic complex is more active in Sonogashira-type coupling reactions involving predissociated halide substrates, namely an acyl chloride. These likely atropo-chiral ligands deserve to be resolved for application in asymmetric catalysis.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Structures of the B1 domain of protein L from Peptostreptococcus magnus with a tyrosine to tryptophan substitution

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2001
Jason W. O'Neill
The three-dimensional structure of a tryptophan-containing variant of the IgG-binding B1 domain of protein L has been solved in two crystal forms to 1.7 and 1.8,Å resolution. In one of the crystal forms, the entire N-terminal histidine-tag region was immobilized through the coordination of zinc ions and its structural conformation along with the zinc coordination scheme were determined. However, the ordering of the histidine tag by zinc does not affect the overall structure of the rest of the protein. Structural comparisons of the tryptophan-containing variant with an NMR-derived wild-type structure, which contains a tyrosine at position 47, reveals a common fold, although the overall backbone root-mean-square difference is 1.5,Å. The Y47W substitution only caused local rearrangement of several side chains, the most prominent of which is the rotation of the Tyr34 side chain, resulting in a 6,Å displacement of its hydroxyl group. A small methyl-sized cavity bounded by ,-strands 1, 2 and 4 and the ,-helix was found in the structures of the Y47W-substituted protein L B1 domain. This cavity may be created as the result of subsequent side-chain rearrangements caused by the Y47W substitution. These high-resolution structures of the tryptophan-containing variant provide a reference frame for the analysis of thermodynamic and kinetic data derived from a series of mutational studies of the protein L B1 domain. [source]

Rally racing: knowledge and learning requirements for a winning team

KNOWLEDGE AND PROCESS MANAGEMENT: THE JOURNAL OF CORPORATE TRANSFORMATION, Issue 2 2001
Rafael Andreu
In this paper we discuss how a winning rally racing team was developed from scratch in Seat Sport, the racing division within Seat, one of Volkswagen's divisions, which decided to enter the World Rally Cup in 1995. The discussion focuses on how different types of knowledge were literally ,grown up' from practically nothing to a winning team. We start by describing the knowledge requirements stemming from the goal of developing a World Rally Cup winning team. Defining them in the form of success factors, we classify them from different standpoints (explicit versus implicit, individual versus collective, mental models, coordination schemes, etc.). Next, we show how these different knowledge requirements were acquired and developed at Seat Sport. Finally, we derive the actual learning processes that were present at Seat Sport and relate them to the different kinds of needs and requirements. Copyright © 2001 John Wiley & Sons, Ltd. [source]

A novel In3O16 fragment in Cs3In3(PO4)4

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010
Igor V. Zatovsky
The double phosphate Cs3In3(PO4)4, prepared by a flux technique, features a fragment of composition In3O16 formed by three corner-sharing InO6 polyhedra. The central In atom resides on a twofold rotation axis, while the other two In atoms are on general positions. The O atoms in this fragment also belong to PO4 tetrahedra, which link the structure into an overall three-dimensional anionic In,O,P network that is penetrated by tunnels running along c. Two independent Cs+ cations reside inside the tunnels, one of which sits on a centre of inversion. In general, the organization of the framework is similar to that of K3In3(PO4)4, which also contains an In3O16 fragment. However, in the latter case the unit consists of one InO7 polyhedron and one InO6 polyhedron sharing an edge, with a third InO6 octahedron connected via a shared corner. Calculations of the Voronoi,Dirichlet polyhedra of the alkali metals give coordination schemes for Cs of [9+2] and [8+4] ( symmetry), and for K of [8+1], [7+2] and [7+2]. This structural analysis shows that the coordination requirements of the alkali metals residing inside the tunnels cause the difference in the In3O16 geometry. [source]

The triple pyrophosphate Cs3CaFe(P2O7)2

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2010
Nataliya Yu.
The complex phosphate tricaesium calcium iron bis(diphosphate), Cs3CaFe(P2O7)2, has been prepared by the flux method. Isolated [FeO5] and [CaO6] polyhedra are linked by two types of P2O7 groups into a three-dimensional framework. The latter is penetrated by hexagonal channels along the a axis where three Cs atoms are located. Calculations of caesium Voronoi,Dirichlet polyhedra give coordination schemes for the three Cs atoms as [8,+,3], [9,+,1] and [9,+,4]. The structure includes features of both two- and three-dimensional frameworks of caesium double pyrophosphates. [source]