Low spin, diamagnetic [Col_6]^3(which contains a Co^3+ ion) is an example of a c
ID: 474975 • Letter: L
Question
Low spin, diamagnetic [Col_6]^3(which contains a Co^3+ ion) is an example of a complex ion that is thermodynamically unstable with respect to ligand exchange with F^+, but is kinetically inert: [Col_6]^3- + 6 F^+ rightarrow [CoF_6]^3- +6l^- (a) Why is [Col_6]^3- more thermodynamically stable than [Col_6]^3-? (b) Why is [Col_6]^3- kinetically inert? (c) Compete the energy diagram below to illustrate the energy changes that occur in the reaction of [Col_6]^3- with F^- that are consistent with the statements above? (d) The reaction of [Col_6]^3- with F^- generates a reactive intermediate. Draw the structure of this intermediate. (e) If [Col_6]^3- is reduced by one electron to [Col_6]^4- (which now contains a high spin Co^2+ ion), ligand exchange reactions become much more rapid than those of [Col_6]^3-. Explain this observation.Explanation / Answer
The thermodynamic stability of a metal complex depends greatly on the properties of the ligand and the metal ion and on the type of bonding.
(Cobalt +3 = hard acid, F-=hard base, I-=soft base)
[CoF6]3- is thermodynamically more stable than [CoF6]3- .Because the interaction between hard acids and hard bases is primarily electrostatic in nature, the stability of complexes involving hard acid(Co3+) and hard base(F-) increases as the positive charge on the metal ion increases and as its radius decreases.
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