Water coordination complexes

Direct interaction of water molecules at the metal center can lead to a water-soluble complex. As will be shown, addition of organic moieties to such water-coordinated complexes affords more labile water molecules. This in turn leads to potential active sites for substrate binding in the corresponding catalysts. 

Earlandite structure, 849 Electrical conductivity metal complexes, 133 tetracyanoplatinates anion-deficient salts, 136 Electrical properties metal complexes, 133-154 Electrocatalysis, 28 Electrochemical cells, 1 Electrochemistry, 1-33 hydrogen or oxygen production from water coordination complex catalysts, 532 mineral processing, 831 reduction, 831 Electrodeposi (ion of metals, 1-15 mineral processing difficulty, 831 Electrodes clay modified, 23 ferrocene modified, 20 nation coated, 15 polymers on, 16 polyvinylferrocene coated, 19 poly(4-vinylpyridine) coated, 17 redox centres, 17 Prussian blue modified, 21 surface modified, 15-31 Electrolysis... 

Other Coordination Complexes. Because carbonate and bicarbonate are commonly found under environmental conditions in water, and because carbonate complexes Pu readily in most oxidation states, Pu carbonato complexes have been studied extensively. The reduction potentials vs the standard hydrogen electrode of Pu(VI)/(V) shifts from 0.916 to 0.33 V and the Pu(IV)/(III) potential shifts from 1.48 to -0.50 V in 1 Tf carbonate. These shifts indicate strong carbonate complexation. Electrochemistry, reaction kinetics, and spectroscopy of plutonium carbonates in solution have been reviewed (113). The solubiUty of Pu(IV) in aqueous carbonate solutions has been measured, and the stabiUty constants of hydroxycarbonato complexes have been calculated (Fig. 6b) (90). 

The mother liquor is separated from the product and returned to the tower. Copper(II) oxychloride is iasoluble ia water, but dissolves readily ia mineral acids or warm acetic acid. The product dissolves ia ammonia and alkah cyanide solution upon the formation of coordination complexes. 

Like Ag, Au also readily forms linear 2-coordinate complexes such as [AuX2] (X = Cl, Br, I) " and also the technologically important [Au(CN)2] . But it is much more susceptible to oxidation and to disproportionation into Au and Au which renders all its binary compounds, except AuCN, unstable to water. It is also more clearly a class b or soft metal with a preference for the heavier donor atoms P, As and S. Stable, linear complexes are obtained when tertiary phosphines reduce Au in ethanol. 

The only reports of directed synthesis of coordination complexes in ionic liquids are from oxo-exchange chemistry. Exposure of chloroaluminate ionic liquids to water results in the formation of a variety of aluminium oxo- and hydroxo-contain-ing species [4]. Dissolution of metals more oxophilic than aluminium will generate metal oxohalide species. FFussey et al. have used phosgene (COCI2) to deoxochlori-nate [NbOa5] - (Scheme 6.1-1) [5]. 

Ligands bite at one or more points. Chelants bite at two or more points, so all ligands are not necessarily chelants. Chelants forming water-soluble complexes with metal ions are called sequestrants (but not all sequestrants are chelants). The most commonly employed BW chelant, ethylenediaminetetraacetic acid (EDTA) produces coordination complexes with four points of attachment and is termed a tetraden-tate ligand. 

Reactions of the hydrido(hydroxo) complex 2 with several substrates were examined (Scheme 6-14) [6]. The reactions are fairly complicated and several different types of reachons are observed depending on the substrate. Methyl acrylate and small Lewis bases such as CO, P(OMe)3, BuNC coordinate to the five-coordinated complex 2 affording the corresponding six-coordinate complexes. In reactions with the unsaturated bonds in dimethylacetylenedicarboxylate, carbon dioxide, phenylisocyanate indications for the addition across the O-H bond but not across the Os-OH bond were obtained. In reactions with olefins such as methyl vinyl ketone or allyl alcohol, elimination of a water molecule was observed to afford a hydrido metalla-cyclic compound or a hydrido (ethyl) complex. No OH insertion product was obtained. 

Fig. 12 (A) The d(CGCGAATTCGCG)2 duplex with a narrow groove and a sodium ion coordinated at the ApT step. (I) The DNA is shown in stick representation and the ion in space-filling size. Left view is directly into the central minor groove. Right view left view rotated 90° counterclockwise and tilted 30° to show the ion in the minor groove. (II) The base pair views are of the central ApT step. Top view is down the helix axis, bottom view is directly into the minor groove. (B) The DNA duplex with a phosphate-oxygen pair-sodium ion interaction and a water molecule coordinated at the ApT step. (II) Views as in Fig. 12A for the phosphate-ion-water-base complex at the AT site. Reproduced with permission from Ref. (42). Copyright 2000, American Chemical Society.

A template synthesis employing Ni(OAc)2, 2,5-dihydroxy-2,5-dimethyl-1,4-dithiane, and 3,3 -iminobis(propylamine) gave the water-soluble five-coordinate complex [Ni(495)], the crystal structure of which shows trigonal bipyramidal coordination of Ni11 with the central amine and terminal thiolates in plane and the two imino nitrogens in axial positions. Solvatochromism of the complex is interpreted in terms of S" H bonding, which may be of relevance to the catalytic cycle in hydrogenases.1341... 

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