Inner-sphere solvent molecules

Molecular hydration in solution is described not only by the inner-sphere water molecules (first and second coordination spheres, see Section II.A.l) but also by solvent water molecules freely diffusing up to a distance of closest approach to the metal ion, d. The latter molecules are responsible for the so-called outer-sphere relaxation (83,84), which must be added to the paramagnetic enhancement of the solvent relaxation rates due to inner-sphere protons to obtain the total relaxation rate enhancement,... 

Mn (0.97, 0.81) Co (0.72) Mg (0.86), and Al (0.58). The solvent exchange rates (Kex S 1) for inner-sphere water molecules in metal ions are Al(10°) Mg (105) Co (105 5), and Mn(106 7) [21].The order of increasing rate constants in acidic solution is, Al Ligand exchange rates take on special importance for Al because they are slow and the system may not be at equilibrium. Mg, Mn, and Co have around 105 faster exchange rate over Al. These differential characteristics of the metals play a crucial role in metal-DNA interactions. 

The optimal conditions for the complexation were found. The luminescence of Tb " in (L ) complex was established to observed in a range of pH 2,0-11,0 with maximum at 7,0-7,5. The Tb (III) luminescence in complex with (L ) aslo depends on amount of reagents, solvent nature, amount of surfactants and trioctylphosphinoxide (TOPO). It was shown that introduction into the system Tb-L the 3-fold excess sodium dodecylsulfate (SDS) increases the luminescence intensity by 40 times and introduction into the system Tb-L the 3-fold excess TOPO increases the luminescence intensity by 25 times by the order value connecting with the crowding out of water molecules from the inner sphere of complexes. 

Where solvent exchange controls the formation kinetics, substitution of a ligand for a solvent molecule in a solvated metal ion has commonly been considered to reflect the two-step process illustrated by [7.1]. A mechanism of this type has been termed a dissociative interchange or 7d process. Initially, complexation involves rapid formation of an outer-sphere complex (of ion-ion or ion-dipole nature) which is characterized by the equilibrium constant Kos. In some cases, the value of Kos may be determined experimentally alternatively, it may be estimated from first principles (Margerum, Cayley, Weatherburn Pagenkopf, 1978). The second step is then the conversion of the outer-sphere complex to an inner-sphere one, the formation of which is controlled by the natural rate of solvent exchange on the metal. Solvent exchange may be defined in terms of its characteristic first-order rate constant, kex, whose value varies widely from one metal to the next. 

The analogy between electron-transfer via addition/elimination (Eq. 2b,c) or abstraction/elimination (Eq. 2a, c) and classical solvolysis involving closed-shell molecules (nonradicals) is seen by comparing Scheme 1 with Scheme 3, in which XY, the precursor of the ions X and Y , is formally derived from the two radicals X and Y". Analogous to Scheme 1, on the way to the ionic products that result from the interaction between X and Y there are two possibilities if XY denotes a transition state, the reaction (Eq. 3a, a ) is a case of outer-sphere electron transfer. If, however, a covalent bond is formed between X and Y, the path (Eq. 3b, b ) is an example of inner- sphere electron transfer. Obviously, part b of the scheme describes the classical area of S l solvolysis reactions (assuming either X or Y to be equal to C) [9, 10]. If a second reaction partner for C (other than the solvent) is allowed for (the (partial) ions then represent transition states), then Eq. 3b also covers Sn2 reactions. If looked upon from the point of view of radical-radical reactivity, Eqs. 3a and b show well-known reactions radical disproportionation in Eq. 3a,a and combination in Eq. 3b. 

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