Dear
Professor
Ahmed El-Nahas and allThanks for reply. According to
IUPAC, the defination of solvation energy is "The change
in Gibbs energy when an ion or molecule is transferred from a
vacuum
(or the gas phase) to a solvent. The main contributions to
the solvation
energy come from: (a) the cavitation energy of formation of
the
hole which preserves the dissolved species in the solvent; (b)
the
orientation energy of partial orientation of the dipoles; (c)
the isotropic
interaction energy of electrostatic and dispersion origin;
and (d)
the anisotropic energy of specific interactions, e.g.
hydrogen
bonds, donor-acceptor interactions etc."
However, I
calculated Ni2+ cation in water, please see this part of
output:
Variational PCM
results
=======================
<psi(f)|
H
|psi(f)>
(a.u.) = -1507.146446
<psi(f)|H+V(f)/2|psi(f)>
(a.u.) = -1507.887943
Total free energy in
solution:
with all non electrostatic
terms (a.u.)
=
-1507.882504
--------------------------------------------------------------------
(Polarized
solute)-Solvent
(kcal/mol) =
-465.30 --------------------------------------------------------------------
Cavitation
energy
(kcal/mol) = 3.41
Dispersion
energy
(kcal/mol) = 0.00
Repulsion
energy
(kcal/mol) = 0.00
Total non
electrostatic
(kcal/mol) =
3.41
--------------------------------------------------------------------
Did you mean by solvation energy the highlight one?
Thanks,
CCG1
People add solvent (in term of PCM) to the reactants and
products; the solvation of bar metal ions releases a lot of
kcal/mols at the expense of the total reaction enthalpy. If you look
at the energy of solvation of the ligand, metal ion and complex, separately, you
will realize this fact. I have a similar situation with a difference of about
150-300 kcal/mol between gas phase and solution, depending of your metal ion,
ligand and the resulting complex.
=============================
Professor Ahmed El-Nahas
Physical Chemistry (Quantum
Chemistry)
Computational Chemistry Unit
(CCU)
Chemistry
Department
Faculty
of Science
El-Menoufia
University
Shebin
El-Kom
Egypt
Email: amelnahas:_:http://hotmail.com"
target="_blank">hotmail.com
Tel:
+2-016-4607974; +81-09062124377
==============================
> From: owner-chemistry:_:
ccl.net> To: amelnahas:_:
hotmail.com>
Subject: CCL: Binding Enthalpy in vacuum and solvent
> Date: Wed, 12 May 2010 09:29:15 -0400
>
>
> Sent to CCL
by: "Comp Chem Group " [compchemgroup1 a
gmail.com]
> Dear All,
>
By surveying on "Interaction Enthalpy" of transition metal complex in
vacuum and solvent (PCM or other model), I found in all cases that the enthalpy
change in vacuum is larger than that solvent. For example, if delta H in vacuum=
-1000 kcal/mol, in solvent= -200 kcal/mol. Could anyone explain why?
> Regards,
> CCG1
>
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;
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