A solution and solid state study of niobium complexes University of ...

5. Formation kinetics of
Synopsis...
[NbCl(acac)(OMe)3]
A complete discussion of the reaction kinetics as well as the reaction mechanism of
the formation of [NbCl(acac)(OMe)3] is given. The use of 93 Nb NMR is also included
as this was used to identify the nature of the niobium halide starting reagent.
5.1 Introduction
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Chemical kinetics comprises the study of the rates of chemical reactions, which
involves the precise measurement of the variation of concentrations of the reacting
species with time. These measurements are conducted in such a way that a certain
aspect of the chemical reaction may be studied, such as the influence of
temperature, concentration and pressure variation on the reaction time, or the
catalytic effect of one species involved in the reaction pathway.
An important aim of this project was to identify and clarify the ligand coordination
mechanism for niobium and O,O’-bidentate ligands. A few general trends have been
observed in this study:
The coordination of only one acac moiety to niobium(V) even in the presence
of an excess of acacH.
Several chlorido ligands are immediately substituded by solvents like
methanol upon dissolution of [NbCl5]2 which creates some doubt of the true
identity of the starting complex in the reaction with acacH.
The process of mathematical prediction of reaction rate conditions is discussed
along with the observations from the kinetic experiments. It is important to note that
the available literature on the reactions of niobium(V) is very limited which highlights
the importance of this study.
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