Carbon coordinated

D Bassohno-Klimas, RE Bniccolen. Application of a directed conformational search for generating 3-D coordinates for protein structures from a-carbon coordinates. Proteins 14 465-474, 1992. 

Infinite zigzag B chains with C strongly bonded to B eonstitute the basic building element of transition-metal carboborides (M -BC). The boron coordination is trigonal prismatic BM, whereas carbon coordination is a M -sBOh- However, with an increasing ratio of radii the B-chain elements are replaced by B pairs or... 

The idea (50, 5/) of dual coordination of CO implies the presence of two coordination centers in a Fischer-Tropsch catalyst system, i.e., a carbonyl carbon coordinating center, Ma, and a carbonyl oxygen coordinating center, M6 (14). It is this concept which has led at least two groups to examine transition metal carbonyl cluster compounds as homogeneous Fischer-Tropsch catalysts. 

Dicyanometalates Dicyanometalates of silver and gold are known. Abrahams et al. [44] have described a cobalt dicyanoaurate. In these compounds, gold ions are carbon coordinated and form linear structures. Cobalt ions are coordinated by four nitrogen atoms of the cyanide group. The unit cell has a hexagonal symmetry. 

The formal potentials of solid hexa-cyanometalates can also be correlated with the lattice constants, that is, with a parameter that depends mainly on the radii of the two metal ions forming the framework of the compounds. This theoretically derived dependence can be verified when the nitrogen coordinated metal ion and the inserting metal ions are kept constant and the carbon coordinated metal ions are varied, for example, when hexacyanoferrate, hexa-cyanocobaltate, hexacyanomanganate, and so on are compared [53, 55]. The equation... 

Presumably, these skeletal reorganization reactions start by coordination of a metal ion to an alkyne part in 78 to allow an alkene part to attack the resulting electrophilic alkyne carbon coordinated by the metal. However, the reaction mechanism remains yet to be clarified, and it is thought that each reaction mechanism differs depending on the metal used. 

As shown in Fig. 2.5, the cyclic voltammograms for Prussian blue attached to paraffin-impregnated graphite electrodes (PIGEs) in contact with aqueous electrolytes exhibit two well-defined one-electron couples. Prussian blue crystals possess a cubic structure, with carbon-coordinated Fe + ions and nitrogen-coordinated Fe + ions, in which potassium ions, and eventually some Fe + ions, are placed in the holes of the cubes as interstitial ions. The redox couple at more positive potentials can be described as a solid-state process involving the oxidation of Fe + ions. Charge conservation requires the parallel expulsion of K+ ions [77] ... 

The coordination environment of the two copper atoms is tetragonal pyramidal and the carbonate coordinates along the basal plane. In the molecule both the N4 coordinated Cu2+ ions are bridged by carbonate in a bidentate fashion (see E). The Cu Cu distances in the molecules D, and D2 are 4.303 and 4.548 A, respectively, and the phen ligands show strong stacking interaction in the crystal. 

In the binuclear complex, [(bpy)2(0H2)Zn(p2-C03)Zn(bpy)2] (N03)2-7H20 (F), the two N4-bound Znx and Zn2 ions are bridged by carbonate in monodentate and bidentate modes, the Znx being coordinated to one H20. Both the zinc ions are octahedrally coordinated with a relatively greater degree of distortion at Zn2 due to the chelating mode of the carbonate bridge. In these binuclear carbonate complexes of Zn(II) and Cu(II) an unexpected behavior, viz. Zn-0 distances < distances for carbonate coordination, was reported (341). 

In another recent study, Mao et al. (34k) have used the Cu11 complexes of 2,2 -bypridine and 1,10-phenanthroline to identify the different carbonate coordination modes which may be kinetically significant. Stopped-flow and T-jump techniques were used. The... 

Most of the organosilicon compounds contain bonds between the silicon and carbon atom. In the following paragraph the structural chemistry of the Si—C single bond is discussed, mostly in compounds with tetracoordinate silicon and tetracoordinate carbon atoms. The structural chemistry of the Si—C bond in compounds where the carbon coordination state is different, is also discussed. The Si—C bond is markedly polarized and the increase of the bond ionicity by attaching different substituents to either the silicon or the carbon atoms may affect its length. The electronic and steric effects are discussed later. 

PDB, containing the alpha-carbon coordinates of all loops plus those of the four neighboring residues, called "stem7 residues, on both ends of each loop. 

It is possible to describe the site preference of metals for nitrogen or carbon coordination in a Prussian blue analog in terms of ligand field stabilization energies Shriver, Shriver and Anderson, 1965). In application, even this simple treatment requires a number of estimates nevertheless, it affords reasonable agreement with experimentally determined structures and provides a framework for the systemization of Prussian blue type structures. One expectation from this approach is that if one of the two metal ions has more than six d electrons and the other has six or less, the latter will be carbon coordinated and the former nitrogen coordinated. 

Fe11 (nitrogen coordinated) Fe11 (carbon coordinated)... 

The typical olefinic carbon coordination shift to higher field is therefore negative. In the case of the i) -alkyl metal complexes (M-R) it is useful to compare the shifts with those of the corresponding hydrocarbon (H-R). 

NMR chemical shifts have been reported for a number of car-boranes (Table XVI). Using revised NMR chemical shift data, it was suggested that there is a relationship between the NMR chemical shift and the carbon coordination number 217). It is therefore feasible to use NMR chemical shifts to obtain structural information on carboranes. 

As with the low-field signal for the proton bonded to alkyne carbons coordinated to the metal, the 13C signals often prove a useful diagnostic tool. These 13 C signals also tend to be at low field, but the position of the signal may vary by several hundred ppm depending on the environment of the carbon atom. There are a number of important steric and electronic factors which have a major influence on the interaction between the alkyne carbons and the metal framework that prevent the maximum use of this data. 

Lappert developed the thermolysis of an electron-rich olefin in the presence of a transition metal complex as another way to synthesise these compounds [4], When, in 1975, Clarke and Taube published their findings on carbon coordinated purine transition metal complexes [5], transition metal NHC complexes with functionalised NHC made their debut in biochemistry. The chemistry of carbenes from natural products became firmly established following the discovery that the catalytic activity of thiamine (vitamin Bl) is based on the intermediate formation of a carbene derived from thiazole [6-9] (see Figure 1.2). 

A successful approach to reducing CO 1 the dual coordination of CO with a carbonyl carbon coordinating center M and a carbonyl oxygen coordinating center Mj followed by hydrogen transfer (27). 

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