Tervalent metal ions

Furthermore, they introduced the metal ion lability constant a as a measure of the effect of the metal ion on lability. The lability constants for various tervalent metal ions obtained by Eq. (8) are summarized in Table 1. 

Table 1. Metal Ion Lability Constant a for Tervalent Metal Ions ...

Al(HE), Ga(HE) as well as In(HE) porphyrin are typical porphyrins incorporated with a tervalent metal ion Characteristic Q and B bands in the visible and near-ultraviolet region, respectively, arise from the (7T,7T ) excitations in the porphyrin ring with only minor perturbation from the outershell electrons of the central metal ion. The Q band is of forbidden character, however, the Q band can borrow the intensity by vibronic couplings from the allowed B band (30). The intensity of the Q(1,0) band is much less sensitive to the peripheral substituents, the axial ligands and the central metal ions, while that of the Q(0,0) band without excitation in the skeletal vibrational modes is rather sensitive to various substituents. 

The temperature dependence of the 1H NMR spectra of many [Cr(S2CNR2)3] complexes has been investigated.1000,1017 There were broad double resonances from the N—CH2 protons indicating that inversion between the A and A isomers is slow on the HNMR time-scale. No exchange broadening was observed up to 84 °C when [Cr(S2CNEt2)3] decomposed. Dithiocar-bamato complexes of other tervalent metal ions do not exhibit this stereochemical rigidity. 

In the presence of acetate ions and the absence of other tervalent metal ions, chromium(III) hydroxide is not precipitated. The precipitation of chromium(III) hydroxide is also prevented by tartrates and by citrates. 

Two studies have been made of the outer-sphere oxidation of iodide by tervalent metal ion complexes. In both cases the reaction is... 

Metals of Valency Three and Higher.— There have been several reports of the measurement by n.m.r. of the kinetic characteristics of complexes of Group IIIA tervalent metal ions. Delpuech et al. have used the spectra associated with the A1 and nuclei to identify the species present in solutions of the metal and a number of phosphorus-containing ligands, and to measure their exchange characteristics. It appears that the major solvates of AP+ in trimethyl (TMPA) and triethyl phosphates (TEPA), dimethyl methyl- (DMMP) and diethyl ethyl-phosphonates (DEEP), and dimethyl hydrogen phosphite (DMHP) are octahedral. In each case the rate law for the exchange process,... 

Following a determination of values of jRTe [equation (22)] for the adducts [(NH3)5CoC204M] + (M = bivalent or tervalent metal ion) in which the oxalate ion is acting as a unidentate ligand, the rates of acid hydrolysis have been measured and the relative catalytic activities found to parallel the thermodynamic stabilities of the dinuclear species Mn Ztf and In similar study of the salicylatopenta-amminecobalt(m) ion was reported earlier and the observed rate constant k found to vary with the metal-ion concentration ([M +]) and the acidity as follows... 

Table 21 Comparison of rate data at 298.1 K for the formation n/[M(HaO)6X] + ions from [M(HaO)6l (M = tervalent metal ion, X = anion) data from ref 10...

The stereochemical rigidity of NN-disubstituted dithiocarbamate complexes, [Cr(R R -dtc)3], has been established by n.m.r. in chloroform solution at temperatures up to 357 K. The relative rates of rearrangement by a trigonal-twist mechanism (resulting in optical inversion) have been established for a series of tervalent metal ions and the order is Ga, In, V > Mn > Cr. These results are discussed further in the next section. 

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