Parameters metal centre

For transition metals compounds, excited states are often extremely important, and this should be reflected in any parameterisation scheme. We have shown that one way such information can be incorporated into a given parameterisation strategy is by fitting the one-centre parameters (t/ss, f/pp, Ua, Gss, Gsd, Gm, Hsd) to experimental excitation and ionisation energies of the neutral and charged metal atom (as a starting point for future parameterisations these parameters have been reported elsewhere for... 

More recent approaches to the effects of the ligands on the redox activity of metal complexes are based upon the assumption that the electrode potential of a redox change involving a metal complex is determined by the additivity of the electronic contribution of all the ligands linked to the metal centre, or to the overall balance between the c-donor and the 7r-acceptor capability of each ligand.3 In particular two ligand electrochemical parameters have gained popularity ... 

Many attempts have been undertaken to define a reliable steric parameter complementary to the electronic parameter. Most often Tolman s parameter 0 (theta) is used. Tolman proposed to measure the steric bulk of a phosphine ligand from CPK models in the following way. From the metal centre, located at a distance of 2.28 A from the phosphorus atom in the appropriate direction, a cone is constructed which embraces all the atoms of the substituents on the phosphorus atom (see Figure 1.6). 

This section intends to provide the reader with some examples of how the high relaxivity challenge has been tackled for Gd(III) complexes so far. For the sake of clarity, this section has been divided in three sub-sections in relation to the specific relaxation parameter considered for relaxivity enhancement, namely the hydration state of the metal centre, the tumbling rate of the CA, and the exchange rate of the mobile protons coordinated to the paramagnetic center. 

The attempt to stabilize transients in the formation reaction of phosphasilenes by transition metal centres directly bound to the precursors was not successful392. The metal substituent was either cleaved or behaved like a normal substituent, as is shown for the synthesis of phosphasilene 842 from 841 (equation 291). The NMR parameters for 842... 

An account has appeared on the preparation, structure and reactivity of a series of metallaphosphoranes. For example, the transition metal complex (2) reacts with (3ab) to form (4ab). X-ray crystallographic analysis and spectroscopic data for these metallaphosphoranes reveal that the transition metal fragment serves as a strong n donor towards the phosphorane fragment. The account also reports the activation parameters for pseudorotation about phosphorus in several metallaphosphoranes with values ranging from 67.8 to 89.7 kJmoP dependent upon the metal centre (Co, Ru or Fe) and the substituents in the Cp ring. 

While the dependence on phosphine concentration and carbon monoxide strongly depends on the reaction parameters, it is important to note most catalyst systems will show a first-order dependence in alkene and rhodium concentration. A recent study involving fluoroalkylphosphine ligands illustrates this once again [37]. Thus, with very few exceptions, complexation of alkene to the metal centre is the rate-determining step. One exception was discussed above. 

Studies of this type are frequently performed to investigate configurational variations, e.g. at metal centres. The obvious initial parameters are the relevant valence angles L-M-L, where L represents a ligating atom. Such studies may then be broken down chemically according to the nature of L. However, it is often more informative to study the deviations of observed coordination geometries from some idealized symmetric form [7, 8, 9], as described in Chapter 2. This requires use of symmetry-adapted deformation coordinates which can readily be calculated, using the CSD System, for instance, as simple linear combinations of standard internal coordinates. 

This is called the nucleophilicity sequence for substitution at square planar Pt(II) and the ordering is consistent with Pt(II) being a soft metal centre (see Table 6.9). A nucleophilicity parameter, Kpt, is defined by equation 25.19 where kf is the rate constant for reaction 25.18 with Y = MeOH (i.e. for Y = MeOH, npt = 0). 

The structure of the major diastereomer 4.18a in sample 1 was determined by X-ray diffraction analysis. Complex 4.18a crystallizes in the chiral space group P2i, a view of the complex is shown in Figure 4.10. The absolute configuration of the molecules in the structure was confirmed by refining the Flack s x parameter and was equal to —0.02(1), attesting to the enantiopure character of the crystal.This complex possesses planar chirality and the absolute configuration of the metal centres in the cationic species... 

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