Fluxional organometallic compound

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Fluxional organometallic compound:-
Fluxional molecules are molecules that undergo dynamics such that some or all of their atoms  interchange between symmetry-equivalent positions. Because virtually all molecules are fluxional in some respects, e.g. bond rotations in most organic compounds, the term fluxional depends on the beyond that dictated by the Heisenberg uncertainty principle) due to context and the method used to assess the dynamics. Often, a molecule is considered fluxional if its spectroscopic signature exhibits line-broadening (chemical exchange. In some cases, where the rates are slow, fluxionality is not detected spectroscopically, but by isotopic labeling.


Dynamic exchange process:-
Classical kinetics can often be used to determine the rate constant and activation energy of a chemical reaction. In a typical study, changes in concentration of products and/or reactants versus time are monitored using any number of experimental techniques (IR, NMR and UV-VIS are the most common).
This analysis becomes more complicated when we have to consider reversible reactions or systems that are at equilibrium. For example:
-If we are interested in the energy barrier to interconversion between two isomers but the two isomers can not be resolved or separated, then we can't use this approach (since their concentrations would be constant with time).
-If the rate of the reaction is very fast, we'd have an equilibrium mixture before we could even obtain the first measurement.
 The prototypical example of such a system is the axial-equatorial interconversion of the chair form of cyclohexane. At room temperature the axial and equatorial protons are interchanged by a dynamic (fluxional) process in which the ring undergoes a "chair-chair" conformation change. As shown here, Ha and Hb are interchanged between axial and equatorial positions:
To understand why this complicates our analysis remember that in the 1H NMR experiment we irradiate the protons to flip their nuclear spins and then wait as they give off this excess energy. The energy (frequency) of this relaxation is what we more commonly call the chemical shift of our proton. It takes time for our protons to relax to their nuclear ground states and this relaxation is governed by both the spin-lattice, T1, and spin-spin, T2, relaxation time. 
 

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