Coordination in complexes

The principle of hard and soft acids and bases and the problem of competitive coordination in complex compounds. A, D. Garnovskii, D. A. Osipov and S. B. Bulgarevich, Russ. Chem. Rev. (Engl. Transl), 1972, 41, 341-359 (441). 

In II and III the Hg coordination is different from that shown (2 or 3 coordination) in complexes of Hg(I) with N-donor ligands (see 8.2.4.2.3). In II, three of the four pyridine-l-oxide molecules bridge adjacent Hg-Hg units, giving the Hg atom a coordination number of 4 or 5, whereas in III there are 4-coordinated Hg atoms. Attempts to prepare analogous complexes with Ph3AsO lead to disproportionation products . 

The present volume is a non-thematic issue and includes seven contributions. The first chapter byAndreja Bakac presents a detailed account of the activation of dioxygen by transition metal complexes and the important role of atom transfer and free radical chemistry in aqueous solution. The second contribution comes from Jose Olabe, an expert in the field of pentacyanoferrate complexes, in which he describes the redox reactivity of coordinated ligands in such complexes. The third chapter deals with the activation of carbon dioxide and carbonato complexes as models for carbonic anhydrase, and comes from Anadi Dash and collaborators. This is followed by a contribution from Sasha Ryabov on the transition metal chemistry of glucose oxidase, horseradish peroxidase and related enzymes. In chapter five Alexandra Masarwa and Dan Meyerstein present a detailed report on the properties of transition metal complexes containing metal-carbon bonds in aqueous solution. Ivana Ivanovic and Katarina Andjelkovic describe the importance of hepta-coordination in complexes of 3d transition metals in the subsequent contribution. The final chapter by Sally Brooker and co-workers is devoted to the application of lanthanide complexes as luminescent biolabels, an exciting new area of development. 

Fig. 4. Curve of rotation of trares-diazene coordinated in complex 1(N2H2) using the BP86/RI (left) and B3LYP (right) methods (TZVP basis set). The zero point of rotational energy is fixed arbitrarily. Note that the hydrogen atoms are not aligned with the S-Fe-S axes since they always point into the direction of the sulfurs lone pairs.

Applications of NMR spectroscopy to structural, thermodynamic, and dynamic processes have been described. A brief discussion of the types of problems appropriate for study by this technique has been included. H and 13C NMR spectroscopy has been applied to define the ligand coordination in complexes. These experiments, combined with 170-labeling experiments, allowed deduction of the coordination number of the vanadium atom. Integration of NMR spectra allowed measurement of the formation constants and equilibrium constants. 2D 13C and 51V EXSY experiments were used in a qualitative and quantitative manner to examine intra- and intermolecular dynamic processes, of which several examples are discussed. The interpretation of the rate matrix and its relationship to the chemical processes under examination were also described. 2D EXSY spectroscopy has great potential as a tool with which to probe mechanisms in complex reactions however, such uses often requires estimation of errors. The major source of error in 2D 51V EXSY NMR studies on a two- and four-site vanadate system were found to be baseline distortion and the errors were estimated. Our results suggest... 

It is evident that the geometries of these 7-coordinated complexes are very much dependent on the constraints due to the shapes of the polydentate ligands. A more extreme example is the pentagonal bipyramidal coordination in complexes formed by the pentadentate ligand L, such as the cations in the salts [FeL(NCS)2]C104, (where the NCS groups occupy the apical positions with Fe—N, 2-01 A as compared... 

A. Ma, A. R. Diimer (2005) Automatic Method for Identifying Reaction Coordinates in Complex Systems. J. Phys. Chem. B 109, p. 6769... 

The transition element cations, which comprise Schwarzenbach s class C, have 0 to 10 subshell electrons in the M shell (first series) or N shell (second series), etc. Examination of Table 3.5 shows that the class C cations are generally considered either hard or borderline hard-soft acids. These cations have partially filled 3d subshells either in the ground state or when ionized (Table 3.6). Moving across the periodic chart from Sc to Cu, protons are added to the nucleus and electrons to the unfilled inner 3d subshell. Attraction of these inner electrons to the nucleus leads to an overall decrease in cation radii (Table 3.7). The divalent ions are generally sixfold, coordinated in complexes. is an exception and, because of its small size and unique electronic configuration, tends... 

The copper(I) ion is characterised by tetrahedral coordination in complexes, and this plays a key role in the assembly of rotaxanes, catenanes and knots. 

Fritz and Hausen present a five-stage procedure model for the analysis, tailored improvement, development, and testing of a solution for a specific supply network. The paper shows results from the application of the procedure model to the agri-food production network. The emphasis in the model is on customized electronic supply chain management, to improve efficiency and coordination in complex supply networks. Several efficiency improvements can be realized by a tailored and embedded supply chain management platform. Empirical evidence was collected by laboratory experiments and from expert evaluations. Complexity could be reduced, process efficiency improved, and change efforts could be reduced. 

Supply networks with small and medium sized enterprises are complex in many industry sectors and, as a consequence, often inefficient. This paper has taken the complex supply chain situation in the agri-food sector as example for complex supply chains in general. The agri-food sector is an example for an industry sector with complex supply chains due to its market structure, with a majority of SMEs, the specifics of the agri-food products, and the transaction processes. Electronic supply chain management is an option to improve efficiency and coordination in complex supply chains. Prerequisite for the realization of improvements with electronic supply chain functionalities in complex markets is the appropriate development and embeddedment of the solution according to the supply chain scenario. 

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