Sphere, inner coordination

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. 

For elimination of intramolecular energy losses, we have synthesized ligands with high hydrophobisity - perfluoro-P-diketones R -CO-CH -CO-R, (R = CgF j or CgF R = phenyl or a-thienyl), that without second ligand eliminate completely water molecules from the inner coordination sphere. These ligands we have used in analysis at determination of Sm, Eu, Nd, Yb microamounts in high-purity lanthanide and yttrium oxides. 

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. 

For [Ni(taptacn)]2+, electronic spectra confirm that the inner coordination sphere remains intact in CH3CN or CH3NQ2 solution. In aqueous acidic media, however, ready dissociation... 

The water exchange rate is hardly affected by substituents which do not directly interfere in the inner coordination sphere. Different bisamide DTPA derivatives have similar exchange rates.28-30 Substituents on the carbon backbone of DTPA also have little influence on the water-exchange kinetics.31 38 39... 

The chain termination on variable-valence metals in the systems in which hydroperoxyl and hydroxyperoxyl radicals act as chain-propagating species is characterized by very high coefficients / 104-106. Both reactions may include several stages. If an aqueous solution of a copper salt, for example, sulfate, is used, the following mechanism involving the incorporation of H02 into the inner coordination sphere of the metal ion is possible ... 

In biological systems, as in all others, metal ions exist in an inner coordination sphere, an ordered array of ligands binding directly to the metal. Surrounding this is... 

Two types of electron transfer mechanisms are defined for transition metal species. Outer-sphere electron transfer occurs when the outer, or solvent, coordination spheres of the metal centers is involved in transferring electrons. No reorganization of the inner coordination sphere of either reactant takes place during electron transfer. A reaction example is depicted in equation 1.27 ... 

Inner-sphere electron transfers involve the inner coordination sphere of the metal complexes and usually take place through a bridging ligand. The classic example, typical of those studied and explained by H. Taube,12 is illustrated by Figure 1.11 s... 

Unlike the other alkaline earth and transition metal ions, essentially on account of its small ionic radius and consequent high electron density, Mg2+ tends to bind the smaller water molecules rather than bulkier ligands in the inner coordination sphere. Many Mg2+-binding sites in proteins have only 3, 4 or even less direct binding contacts to the protein, leaving several sites in the inner coordination sphere occupied by water, or in the phosphoryl transferases, by nucleoside di- or triphosphates. 

The Homogeneous Case. Margerum (1978) and Hering and Morel (1990) have elaborated on mechanisms and rates of metal complexation reactions in solution. In the Eigen mechanism, formation of an outer-sphere complex between a metal and a ligand is followed by a rate limiting loss of water from the inner coordination sphere of the metal, Thus, for a bivalent hexaaqua metal ion... 

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 ... 

Coordinative Environment. The coordinative environment of transition metal ions affects the thermodynamic driving force and reaction rate of ligand substitution and electron transfer reactions. FeIIIoH2+(aq) and hematite (a-Fe203) surface structures are shown in Figure 3 for the sake of comparison. Within the lattice of oxide/hydroxide minerals, the inner coordination spheres of metal centers are fully occupied by a regular array of O3- and/or 0H donor groups. At the mineral surface, however, one or more coordinative positions of each metal center are vacant (15). When oxide surfaces are introduced into aqueous solution, H2O and 0H molecules... 

We carried out some measurements some years ago in order to measure the transfer coefficient in DMF for this couple at a mercury electrode [Hush, N. S. Dyke, J. M. J. Electroanal. Interfac. Electrochem. 1974, 53, 253]. The deviation from one-half for the value so obtained was consistent with reasonable values for the free energy of activation of ligand exchange in the inner-coordination spheres. 

We believe that these large changes in rate constant are primarily attributable to restrictions imposed upon the inner-coordination sphere by the macrocyclic ligands. Presumably, the use of a suitable macrobicyclic ligand, such as you have used... 

Inner-sphere electron transfers involve the inner coordination sphere of the metal complexes and usually take place through a bridging ligand. The classic example, typical of those studied and explained by H. Taube, is illustrated by Figure 1.11 s reaction sequence adapted from reference 7. In this reaction sequence, production of [Cr(III)(Fl20)5Cl] " implies that electron transfer through the bridged intermediate from Cr(II) to Co(III) and CF transfer from Co to Cr are mutually interdependent acts. 

The extractabilities of metal-organic complexes depend on whether inner or outer sphere complexes are formed. Case 1, section 4.2.1, the extraction of ura-nyl nitrate by TBP, is a good example. The free uranyl ion is surrounded by water of hydration, forming U02(H20)f, which from nitric acid solutions can be crystallized out as the salt U02(H20)6 (N03), though it commonly is written U02(N03)2(H20)6. Thus, in solution as well as in the solid salt, the UOf is surrounded by 6 HjO in an inner coordination sphere. In the solid nitrate salt, the distance du.o(nitrate) between the closest oxygen atoms of the nitrate anions, (0)2N0, and the U-atom is longer than the corresponding distance, du-o(water), to the water molecules, OH2, i.e., du.o(nitrate) > 4u.o(water) thus the nitrate anions are in an outer coordination sphere. 

Migration experiments have shown that the hydrated cations not only carry with them the water in the inner coordination sphere, but also one or more shells of additional water molecules, for typical total values of 10-15. When the metal ion leaves the aqueous phase in the solvent extraction step, this ordered coordinated water returns to the bulk water structure, contributing an additional factor to consider in evaluating the thermodynamics of extraction. 

In the calculations of the energy of hydration of metal complexes in the inner coordination sphere, one must consider hydrogen bond formation between the first-shell water molecules and those in bulk water, which leads to chains of hydrogen-bonded water molecules. Such hydrogen-bonded chains of ethanol molecules attached to the central metal ion have been found as a result of DFT B3LYP calculations on ethanol adducts to nickel acetylacetonate, where the calculated energy of hydrogen bonds correlated well with experimental data [90]. 

All the Gd(III)-based contrast agents commercially available and those under development present one or more water molecules in their inner coordination sphere. The water molecule(s) is labile and the exchange from the coordination site in the complex and the bulk solvent represents the main source of the solvent relaxation enhancement. Therefore, the inner sphere longitudinal relaxivity is given by the following expression ... 

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