Transition metal complexes solvates

The solvated sulfenamides [Li2( BuNSC6H4Me-4)2(THF)n] (n = 2,4) have dimeric structures with a central Li2N2 ring. The coordination mode is determined by the extent of solvation of the Li" ions monosolvation allows for rj -N,S coordination whereas disolvation restricts the coordination mode to // -M Variable temperature NMR studies indicated that a dynamic exchange between these two structural types occurs in THF solution (Scheme 10.10). The dihapto coordination mode is observed exclusively in transition-metal complexes and the... 

The most significant class of inorganic supports, which is used for the direct ion exchange of positively charged transition-metal complexes, are smectite clays. Pin-navaia has introduced the use of these swelling, layered silicate clays for catalysis. Other clays include montmorillonite, bentonite, and laponite. As shown by Pinna-vaia, cationic transition-metal complexes can be readily exchanged (intercalated) into the solvated interlayers of these silicates (Eq. (1)) [117] ... 

For compounds that are usually not available in larger amounts or are expensive, e.g., many transition metal complexes, the static approach was applied as well (Fig. 14). Here, the cell is loaded with a known amount of the solute and SCCO2 of known density [124]. This technique is convenient, because it allows for in situ analysis, and the solvatation equilibrium is obtained easily. 

At present, the correlation contains one transition metal complex, Cu(Hfacac)2. The results on this complex are very interesting and somewhat unusual for a transition metal system in that enthalpies have been obtained in a poorly solvating solvent with nonionic donors (52), instead of the t5 ical stability constant study on a metal cation in some highly polar solvent. Data from this latter type of investigation have many practical uses, but are impossible to interpret and understand. The transition metal ion complex we have studied can be incorporated into the E and C scheme using the same base parameters that are used to correlate the enthalpies of formation of all the other Lewis acid-base adducts in the scheme. 

Since these cationic, weakly solvated transition metal complexes are reactive towards atmospheric moisture, all manipulations should be performed using standard inert atmosphere techniques. 

Solvated transition metal cations containing weakly bonded organic ligands are potentially useful as intermediates in preparative coordination chemistry. The coordinated solvent molecules provide solubility of the compounds in various organic solvents, and they can be replaced readily by other ligands with better donor properties.1, 2 The preparation of mononuclear transition metal complexes with weakly bonded anions has been described previously3 and preparative applications of such complexes have been reviewed.4... 

Since the a- and n forms of a transition metal complex would be expected to differ only slightly in such physical properties as ligation and solvation and lattice energies, the predominance of one form or the other must be primarily due to the nature of the metal-ligand bonding. There are three alternate explanations of the proclivity to cr-v or n-cr rearrangement in terms of bonding. These are summarized as follows. 

The determination of the charge distribution in a molecule, needed here for the latter term, (Ges), has been a considerable problem in force field calculations, especially for transition metal compounds (see Sections 3.2.6 and 3.3.6). Most promising but not yet fully tested for transition metal complexes are semi-empiri-cal quantum-mechanical methods[ 103,1041. Future studies might show whether a combination of approximate methods for the computation of charge distributions and solvation will lead to a reliable approximation of solvation parameters of coordination compounds. 

Thirdly, it will be important to gain more direct information on the stability of outer-sphere precursor states, especially with regard to the limitations of simple electrostatic models (Sect. 4.2). One possible approach is to evaluate Kp for stable reactants by means of differential capacitance and/or surface tension measurements. Little double-layer compositional data have been obtained so far for species, such as multicharged transition-metal complexes, organometallics, and simple aromatic molecules that act as outer-sphere reactants. The development of theoretical double-layer models that account for solvation differences in the bulk and interfacial environments would also be of importance in this regard. 

Although superoxide ion reacts with reduced transition metal complexes (Fe , Mn Co Fe (EDTA), Fe (TPP)) bi62 to give oxidized products, for simple solvated cations the reaction sequence is a Tewis acid catalyzed disproportionation (equation 155) with subsequent Fenton... 

Photoredox Reactions Photolysis of Transition Metal Complexes 743 Solvated Electron... 

Many reviews of this area are available and no attempt will be made to be comprehensive here. Instead the focus will be on the relationship between photochemistry and photophysics with emphasis on the use of directly measured kinetic data (lifetimes and quantum yields) to draw mechanistic interpretations. The photochemical discussion will be limited to substitution, especially solvation, reactions. The effect of solvent motion will be explicitly treated. Reactions of a few hexacoordinated transition metal complexes will be used to illustrate the important ideas. 

Several methods have been applied to determine the solvent power of ionic liquids determined by solvation polarity and nucleophilicity (donor power). A common approach for determining the solvent polarity and setting up an empirical scale is to evaluate the UV-Vis spectra of optical probes such as solvatochromic dyes or transition metal complexes in the solvents under investigation [53], The absorption or emission bands of the probe show a strong shift in their optical spectra according to the polarity of the solvent in which they are dissolved [54-57],... 

R395 S. Kaizaki, Roles of Solvation in Variability of Ligand Field and Stereochemistry for Transition Metal Complexes as Revealed by UV-Vis, CD and/or Paramagnetic NMR Spectroscopy , Trends Inorg. Chem., 1999, 6, 105... 

This 2m(QM/MM) term is usually critical in solvation problems, because one of the points of interest is precisely how the quantum mechanical properties of the solute are modified by the presence of the solvent. In the case of a transition metal complex, this term would account mainly for the electronic effects of the ligand substituents on the metal center. A common way to introduce the g /QM/ MM) term is to put electrostatic charges in the positions occupied by the MM atoms, introducing in practice a term in the monoelectronic Hamiltonian (8). Qne problem with this kind of approach is the choice of the electrostatic charges, which is by no means trivial, since its validity is usually confined to the consis-... 

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