A Few Kinetics Problems
1) Suggest some causes for the ordering of the H2O exchange half-lives for the aqua-cations:
K+, Cu2+ < Fe2+ , V2+ < Ru2+ < Rh3+
3) A certain metal complex can undergo substitution by two different pathways. For pathway-A, the
activation energy is 0.3 kJ/mole, for pathway-B, it's 1.5 kJ/mole. All other things being equal, what
percentage of the molecules proceed by mechanism-B at 25°C ?
5) The rate constants for substitution at the following centres fall in the order given. Suggest reasons for
some of these observations.
[PtCl6]2– < [Cr(NH3)6]3+ < [CrCl6]3– < [VCl6]3– < [Ni(CN)4]2-, [Cu(NH3)5]2+
11) Have a go at estimating the value (in cm-1 and kJ/mol) of the CFAE for the complex ion
[Rh(Pyridine)3Cl3]o undergoing (a) an associative ligand substitution and (b) a dissociative ligand
substitution, in which a chloride is replaced by an ammonia molecule. Obtain the relevant CFSEs using
the Jørgensen f- & g-factors from the CHEM.420 notes, along with the Huheey orbital energies table or
from the Basolo/Pearson CFAE values.
6)  For the following complex molecules, in each case indicate next to it whether the origin of its
color is most likely (which one ?) d-d transition(s), or intraligand transition, or LMCT, or MLCT:
(a) the orange p-nitrophenylazo-ß-naphtholate anion complex of zinc(II) Intraligand
d7d (b) pale pink [Co(OH2) 2+ = LMCI
CT (c) purple MnO2 = MLCT
Yellow absorbed mide
(d) light blue [Ni(NH3)4(OH2)2]'
16) Construct a diagram of energy vs. reaction progress for a square planar d8 complex undergoing
ligand exchange by an (associative) square-pyramidal intermediate/transition state. For your energy
scale, use just the CFSE component of the total energy, expressing it in Dq units. How much is the
CFAE ? If a trigonal-bipyramidal state is added, to allow for reorganization of the intermediate,
does this fall above or below the initial square-pyramid ? By how much ? How might the diagram
change if the process were a substitution involving a "stronger" ligand ?
1)  The complex [Ir(Trien)Br2] 2+ exhibits an absorption band at 375 nm, with 22,000 cm"¹ M'¹.
(Reminder: Trien= triethylenetetramine"; 1,4,7,10-tetraazadecane) Thismost likely to be:
(a) a Br
Ir(d) LMCT transition
(b) an Ir( d) Trien(z*) MLCT transition
a Trien transition
(d) a metal d->d transition, because of the low &-value
2) Which one of the following CT transitions is physically impossible?
(a) Br (o)
Mn(d) in MnBr4
Phen(z*) in Cu(Phen)2
(c) 02- (2p)
Cr(d) in CrO4 2-
(d) Br (o)
Zn(d) in ZnBr4
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