Octahedral complexes with chemical change

Table 27 lists the 29Si chemical shifts for the high coordination complexes. Triphenyl-silane serves as a tetracoordinate model for the complexes 197 and 200, for comparison. It can be seen that the increased coordination in the latter complexes effects a small upheld shift, much smaller than is normally observed upon going from tetra- to penta- (Table 11, Section III.A.2.b) and hexacoordination (Table 24, Section VI.A.2). This is in accord with the crystallographic results, which show that no significant change in hybridization takes place in these compounds, in contrast to TBP and octahedral complexes.

In the assessment of the refining performance of uranium, systematic data has been reported for the chemical properties of uranium complex in various alkali chlorides such as LiCl-RbCl and LiCl-CsCl mixtures [3-5], Information on the coordination circumstance of solute ions is also important since it should be correlated with stability. The polarizing power of electrolyte cations controls the local structure around neodymium trivalent Nd " " as an example of f-elements and the degree of its distortion from octahedral symmetry is correlated with thermodynamic properties of NdClg " complex in molten alkali chlorides [6]. On the other hand, when F coexists with Cr in melts, it is well-known that the coordination circumstances of solute ions are drastically changed because of the formation of fluoro-complexes [7-9]. A small amount of F stabilizes the higher oxidation states of titanium and induces a negative shift in the standard potentials of the Ti(IV)ITi(ni) and Ti(III)ITi(II) couples [7, 8], The shift in redox potentials sometimes causes specific electrochemical behavior, for example, the addition of F to the LiCl-KCl eutectic leads to the disproportionation of americium Am into Am " and Am metal [9],... 

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