Ammine parameters

Table 4.22. Geometrical and NBO parameters for ammine, phosphine, and carbonyl coordination complexes of Os and Re hydrides, showing bond angles, valence Lewis accuracy (%p ), and metal bond hybrid (Iim) and polarization (%cm2) of oml and omh NBOs...

Rate constants and activation parameters (AH, AS, and AV ) for base hydrolysis of [Pg.80]

The ex model has been elaborated in a number of ways. An electrostatic perturbation was added (33) to account for band splittings in the d-d spectra of tetragonal copper(II) ammine complexes where the simple AOM predicted accidental degeneracy the merits of this refinement will be discussed in 2.5.1. Another development has been the introduction of d—s and d—p mixing, which is apparently necessary to account for the d-d spectra of chlorocuprates(II) (34). This requires the additional parameters e, edpa and edpv. 

Figure 2. Deuterium isotope effect for electron transfer between ammine complexes as a function of the reduced electronic energy gap AE/EC where Er is the total reorganization energy E, = Eg + Ec. Key for parameters — —, hci)H/kBT — 2.0 and Es/Ec = 0 ------------------, Es/Ec = 1 and-------, Es/Ec = 2.

Both the electronic couphng matrix element and the outer-sphere component of the nuclear reorientation parameter are thought to vary with donor-acceptor separation and orientation [29, 49]. It has been shown in studies of Os and Ru-ammines bridged by polyproline spacers that the distance dependence of X can be greater than that of [50]. Dielectric continuum models of solvent reorganization predict that Xg will increase with... 

Bertini et al.497 and Lever et al.495 measured the electronic spectra of a series of tetragonal nickel(II) ammine complexes and found a relationship between the Ni—N distance and the ea parameter, e decreasing when the Ni—N distance increases. 

Some progress is possible if an appeal to chemical experience is made. Suppose a metal hexa-ammine ion M(NH3) + is involved. The NH3 molecule is known to be close to sp3 hybridization on the N atom, with the lone pair occupying the fourth position. Consequently, there are no orbitals of n symmetry available on the N atom. In this situation it can be proposed with some confidence the n-bonding involving the central atom is negligible and consequently the AOM parameter e is zero.59 Then... 

Kinetic Parameters for Bridge-Formation and Water-Exchange Reactions of Ammine Complexes at 25°C in 1.0 A/(Na,H)CI04 ... 

The data in Table XXXV show that common features for these ammonia and amine complexes are very fast isomerization between the cis and trans isomers of the diaqua species and the fact that the trans diaqua isomers are generally more stable than the cis isomers. In the ammine system the activation parameters for k2 and k 2 are consistent with an isomerization process at cobalt(III), but it is at present not clear how this occurs. It need not be a simple cis-trans isomerization occurring at one of the Co(III) centers, but might involve the participation of both metal centers. The isomerization reaction may proceed via intramolecular proton transfer between a water ligand and one of the two hydroxo bridges with simultaneous bridge cleavage and formation... 

There is an extensive literature on ammines and the Chemical Abstracts 10th Collective Index (1977-81) has four pages under this heading. One important parameter for this class of compound is the metal-nitrogen bond length and Table 1 lists some of the available data. Transition metal-NH, bond energies have also been calculated.100... 

TABLE 1 Parameters for Three ET Models That Fit ZnP/Ru(III) Ammine ET Rate vs. Free Energy of Reaction Data from Refs. 54, 55, 57, 59, 60... 

Figure 3. Driving force-dependence of intramolecular electron transfer rates in Ru-ammine-His33 modified Zn-substituted cytochrome c ( ), and Ru-bpy-His33 modified Fe-cytochrome c ( ). Solid lines were generated using Eq. 1 and the following parameters Ru-ammine,, i=1.15 eV, Hab = 0.10 cm Ru-bpy, X = 0.74 eV, Hab = 0.095 cm". ...

As always, the photooxidation of water to 2 has received much less attention than the much easier photoreduction of water to H2 However, some notable achievements have appeared and genuine progress has been made. The mechanisms for oxidation of water by metalloporphyrins and cobalt(III) ammines have been studied, with particular attention being given to kinetic parameters. Several new 02 evolving catalysts have been... 

This work lead to an interest in the luminescence of lower symmetry chromium ammine complexes. In these complexes, the 2Eg state is split into two components by the lower symmetry ligand field. The tetragonal ligand field parameters for many of these compounds were well known or easily available from optical spectroscopy, but the splitting of the 2Eg as measured by the absorption and emission spectroscopy... 

The final and, in many cases probably, decisive parameters in determining which metal ammine is optimal for an application will be the price and availability of the metal salt, i.e. NaCl, MgCl2 or CaCl2 are cheap and abundant, while Bel2 or CoBr2 would be much harder to come by (http // www.sigmaaldrich.com). 

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