Tuning Reactivity of Platinum(II) Complexes

pressure on a reaction mixture. 15,25 The rate of reaction becomes sensitive to pressure
changes only under extremely vey high pressures 100-200 MPa.
Assuming there is no variation in T, the derivative of the thermodynamic equation for
free energy is obtained as:
(∂ΔG # /dP) o T =
#
Δ V
(2.29)
Differentiating equation (2.29) with respect to pressure and recognizing that
( T )
k b
is independent of pressure gives
h
(∂lnK/∂P) o T = (∂(ΔG #/RT)/ ∂P) o T (2.30)
#
= - Δ V /RT (2.31)
Integration of equation (2.31) taking into consideration that the equilibrium constant is
K = k2/k-2, results in:
#
lnk2 = ln(k-2)0 − ( ΔV
)P .
(2.32)
RT
where, ∆V # is the volume of activation for the forward step of the reaction
and is the difference in molar volumes of the activated complex and
the reactants under the experimental conditions; (k-2)0 coefficient
of compressibility of the solvent.
A plot of lnk2 against pressure (P) is linear, and
#
ΔV takes values in the range 20 ≤ ≥10
whereby:
i.
ii.
15
#
Δ V is calculated from the slope.
− x (cm 3 mol -1) , through zero,
#
Δ V = -20 cm3 mol-1 signifies electrostriction of the solvent due to the formation
of ions in the transition-state.
#
Δ V ≈ -10 cm3 mol-1 is characteristic of an associative mechanism, in which the
activated complex is dominated by the formation of M---Y bond and not by the
dissociation of the M---X bond.