Complex coordination sphere

Direct Photolysis of Surface-Located Inner Coordination Sphere Complexes. In the presence of a strong metal binding ligand, the underlying central metal ion in the surface layer of a metal oxide can exchange its structural OH" ions for the ligand. Thus, the association of citrate with an iron oxyhydroxide surface may be represented ... 

The binding of complex anions of transition metals such as the hexacyanides M(CN)6m yields second-coordination-sphere complexes, supercomplexes, [3.13a] and affects markedly their electrochemical [3.21, 3.22] and photochemical [3.23] properties. 

Sellmann, D. (1995) Chemistry of N2H2 and other nitrogen hybrids related to N2 fixation in the coordination sphere complexes, in Tichonovich, I. A., Provorov, N. A., Romanov, V. I., and Newton, W. E. (eds.), Nitrogen Fixation Fundamentals and Applications, Kluwer Academic Publishers, Dodrecht, pp. 123-128. 

Relative to carbon, silicon has a much smaller tendency to form compounds of coordination number less than four, such as silenes, silanones or silicenium ions, but a pronounced capacity for the enlargement of the coordination sphere. Complex formation by silicon tetrafluoride was first observed1 early in the nineteenth century, when Gay-Lussac and Davy reported the formation of the adduct SiF4 2NH3. A hexacoordinate cationic complex, Si(acac)3 HCI2 was described by Dilthey2 in 1903, and represented a new structural type for the element. 

Table 25-5 Some Ligands and Coordination Spheres (complexes)...

Divalent molybdenum compounds occur in mononuclear, dinuclear, and hexanuclear forms. Selected examples are shown in Figure 6. The mononuclear compounds are mostiy in the realm of organometaUic chemistry (30—32). Seven-coordinate complexes are common and include MoX2(CO)2(PR3)2, where X = Cl, Br, and I, and R = alkyl MoCl2(P(CH3)3)4, heptakis(isonitrile) complexes of the form Mo(CNR) 2 (Fig. 6d), and their chloro-substituted derivatives, eg, Mo(CNR)3CR. The latter undergo reductive coupling to form C—C bonds in the molybdenum coordination sphere (33). 

Molybdenum(0) also forms a variety of dinitrogen complexes (41), especially when there are phosphine ligands in the molybdenum coordination sphere (see Fig. 7c). This type of complex has been extensively studied because the coordinated dinitrogen is reduced to ammonia upon acidification. 

The complexes on surface of chelate-functionalized silica often include ligands available in solution in the coordination sphere. Use of a chromophore reagent as a ligand leads to the formation of colored mixed ligand complexes (MLC). The phenomena can be used as a basis for developing test-systems for visual determination of microquantities of inorganic cations in water. 

It is well known, that in aqueous solutions the water molecules, which are in the inner coordination sphere of the complex, quench the lanthanide (Ln) luminescence in result of vibrations of the OH-groups (OH-oscillators). The use of D O instead of H O, the freezing of solution as well as the introduction of a second ligand to obtain a mixed-ligand complex leads to either partial or complete elimination of the H O influence. The same effect may be achieved by water molecules replacement from the inner and outer coordination sphere at the addition of organic solvents or when the molecule of Ln complex is introduced into the micelle of the surfactant. 

It has been established, that both DN and Ibp form complex compounds with ions Eu(III), Sm(III), Tb(III) and Dy(III), possessing luminescent properties. The most intensive luminescence is observed for complex compounds with ion Tb(III). It has been shown, that complexation has place in low acidic and neutral water solutions at pH 6,4-7,0. From the data of luminescence intensity for the complex the ratio of component Tb Fig was established equal to 1 2 by the continuous variations method. Presence at a solution of organic bases 2,2 -bipyridil, (Bipy) and 1,10-phenanthroline (Phen) causes the analytical signal amplification up to 250 (75) times as a result of the Bipy (Phen) inclusion in inner coordination sphere and formation of different ligands complexes with component ratio Tb Fig Bipy (Phen) = 1 2 1. 

Titanium tetrachloride and tin tetrachloride can form complexes that are related in character to both those formed by metal ions and those formed by neutral Lewis acids. Complexation can occur with an increase in the coordination number at the Lewis acid or with displacement of a chloride from the metal coordination sphere. 

Certain metal cations are capable of electrophilic attack on alkenes. Addition is completed when a nucleophile adds to the alkene-cation complex. The nucleophile may be the solvent or a ligand from the metal ion s coordination sphere. 

There are two general routes to complexes. The first involves direct addition of molecular Ht either to an unoccupied coordination site in a 16-electron complex (as above) or by displacement of a ligand such as CO, Cl, H2O in the coordination sphere of an 18-electron complex in this latter case ultraviolet irradiation may be required to assist in the... 

The facile route for introduction of the phosphole ring into the coordination sphere of the chromium vinylcarbene complex is via [4 - - 2] intramolecular... 

A remarkable transformation of [(> -Ph2BpZ2)Mo(CO)2(i -pentadienyl)] (90OM1862) is the transformation with phosphines or phosphites of this 16-valence-electron species into 18-electron complexes hydrolysis leads to profound changes in the coordination sphere yielding 60. 

Transition metal catalysis in liquid/liquid biphasic systems principally requires sufficient solubility and immobilization of the catalysts in the IL phase relative to the extraction phase. Solubilization of metal ions in ILs can be separated into processes, involving the dissolution of simple metal salts (often through coordination with anions from the ionic liquid) and the dissolution of metal coordination complexes, in which the metal coordination sphere remains intact. 

For the silica gel (Figure 3A), the solution was removed slightly less effectively, and more Cs was left (ca. 0.0020 atoms/A2). The spectral behavior is quite similar to that of boehmite, except that there is a peak due to surface Cs coordinated by only water molecules and not in contact with the surface oxygens (so-called outer sphere complexes)at 30% RH. Complete dynamical averaging among sites at frequencies greater than ca. 10 kHz occurs at 70% RH and greater. 

Fluorine ions form the first coordination sphere around the tantalum ion, which is the central atom of the complex. Potassium ions form the second coordination sphere, which significantly affects the geometry and force field of the first coordination sphere. The melting of K2TaF7 leads to the dissociation of the compound into ions, as follows ... 

The appearance of the seventh ligand (Xn ) predominantly in the first coordination sphere of the complex or outside of the complex depends on the polarization potential of the alkali metal cation, M+, and on the polarity of the seventh anion, Xn". Increased polarity of the anion favors its entering into the first coordination sphere of the complex ion. 

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