Chelate Effect And Its Thermodynamic Origin Pdf Download |VERIFIED|
In fact, the breakdown of the ΔG⦵ into ΔH⦵and TΔS⦵ shows that the two terms are nearly equal (-29cf. -25 kJ mol-1) with the ΔH⦵ term a littlelarger! The entropy term found is still much larger than for ordinaryreactions involving substitution of a non-chelating ligand at a metal ion.How can we explain this enhanced contribution from entropy? Oneexplanation is to count the number of species on the left andright hand side of the equation above.It will be seen that on the left-hand-side there are 4 species,whereas on the right-hand-side there are 7 species, that is a netgain of 3 species occurs as the reaction proceeds. This canaccount for the increase in entropy since it represents anincrease in the disorder of the system.An alternative view comes from trying to understand how thereactions might proceed. To form a complex with 6 monodentatesrequires 6 separate favourable collisions between the metal ionand the ligand molecules. To form the tris-bidentate metalcomplex requires an initial collision for the first ligand toattach by one arm but remember that the other arm is always goingto be nearby and only requires a shift in position of the other end toenable the ligand to form the chelate ring.If you consider dissociation steps, then when a monodentate groupis displaced, it is lost into the bulk of the solution. On theother hand, if one end of a bidentate group is displaced theother arm is still attached and it is only a matter of the armshifting around and it can be reattached again.Both sets of conditions favour the formation of the complex withbidentate groups over that with monodentate groups.For a problem relating to metal complex formation andcalculations of thermodynamic values, try your hand at CALCULATION # TWO. Once again, further problemscan be found in the Tutorialpapers for this course.
Chelate Effect And Its Thermodynamic Origin Pdf Download
Chapter 2. Metal-Ligand Equilibria in Solution: Stepwise and overall formation constants and their interactions, Trends in stepwise constants, Factors affecting stability of metal complexes with reference to the nature of metal ion and ligand, Chelate effect and its thermodynamic origin, Determination of binary formation constants by pH-metry and spectrophotometry.
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