Chemistry Reference
In-Depth Information
TABLE 9.4 (Table VI of the Reference)
Isomerization (Δ
E
iso
) and Activation
(Δ
E
act
) Energies (in kJ/mol) for the
Transformation of Acetylene to
Vinylidene on Iron Clusters, Fe
q
n
(
n
= 1 − 4
and q = 0 − 1) Calculated with the PP86
and the PLAP3 Functionals
Δ
E
iso
Δ
E
act
q
n
PP86
PLAP3
PP86
PLAP3
0
1
62.7
53.4
233.9
249.2
0
2
−12.5
225.9
258.7
0
3
13.0
−22.9
252.8
288.1
0
4
4.0
1.0
a
1
1
77.9
224.2
236.1
1
2
46.9
24.1
b
277.8
308.3
1
3
25.7
3.4
c
1
4
24.5
18.9
d
Source:
. Reprinted. from. Chretien,. S.. et. al.,.
J. Chem.
Phys
.,.119(23),.December.5,.12279,.2003..With.
permission.
a.
The.lower.state.of.Fe
4
(C
2
H
2
).is.different.from.the.one.
with.the.PP86.
b.
The.lower.state.of.Fe
2
(C
2
H
2
)
+
.is.different.from.the.one.
with.the.PP86.
c.
The.lower.state.of.Fe
3
(CCH
2
)
+
.is.different.from.the.one.
with.the.PP86.
d.
The.lower.state.of.Fe
4
(C
2
H
2
)
+
.is.different.from.the.one.
with.the.PP86.
Analysis.of.these.results.indicates.that.with.respect.to.the.proposed.mechanism.
(Figure.9.33),.the.formation.of.a.cyclobutadiene.complex.is.unlikely,.the.cyclobuta-
diene.complexes.being.much.less.stable.than.the.complexes.containing.two.acetylene.
molecules. or. an.
n
-C
4
H
4
. ligand.. The. calculations. also. show. that. the. formation. of.
benzene.is.thermodynamically.possible.
The.above.studies.have.shed.light.on.several.aspects.of.the.reaction.mechanism,.
but.they.have.not.allowed.us.to.understand.the.reason.that.benzene.is.formed.on.Fe
+
.
and.
Fe
4
+
.but.not.on.
Fe
2
+
.or.
Fe
3
+
..The.answer.does.not.appear.to.lie.in.the.thermodynam-
ics.of.the.systems,.so.we.must.await.a.future.study.that.will.look.deeply.at.the.kinetics.
9.6.2 o
xidation
of
co
With
c
ationic
i
ron
o
xide
c
luSterS
Over. the. last. years,. several. combined. experimental. and. theoretical. studies. on. the.
oxidation. of. CO. to. CO
2
. with. TM. oxide. clusters. were. realized. with. deMon2k,.
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