Chemistry Reference
In-Depth Information
TABLE 4.2
Speciic Structural Parameters for the
Aqueous Solutions of the Cr
3+
and the
Fe
3+
Ions
Cr
3+
Fe
3+
R
Cr−O
2
.(Å)
3.91.±.0.03
R
Fe−O
2
.(Å)
3.96.±.0.04
R
O
2
−H
2
.(Å)
0.98.±.0.01
R
O
2
−H
2
.(Å)
0.99.±.0.01
R
O
1
−O
2
.(Å)
2.63.±.0.03
R
O
1
−O
2
.(Å)
2.64.±.0.02
R
HB
.(Å)
1.65.±.0.04
R
HB
.(Å)
1.63.±.0.05
HB.denotes.the.hydrogen.bond.distance.between.the.irst.and.
second. shell. water. molecules. in. the. vicinity. of. these. two.
transition.metal.ions.
4.3.2 S
ingle
i
on
and
d
imerization
S
tudieS
of
a
l
3+
in
W
ater
For.the.studies.of.the.Al
3+
.ion.in.water,.we.performed.several.simulations..To.model.
Al.ions.in.water.at.the.pH.of.interest.(3.<.pH.<.7),.we.used.the.octahedral.Al(H
2
O)
3+
.
structure. (Figure. 4.2A). obtained. from. our. simulations. with. 58. water. molecules,.
removing.one.H.atom.from.a.irst.shell.water.molecule.that.is.coordinated.to.the.Al
3+
.
ion.. The. resulting. aqueous. Al(H
2
O)
5
OH
2+
. structure. loses. one. water. molecule. and.
becomes. a. penta-coordinate. Al(H
2
O)
4
OH
2+
. structure. (Figure. 4.2B). within. 0.8.ps..
This.inding.is.in.excellent.agreement.with.recent.kinetics.experiments.and.CPMD.
simulations,.which.report.a.penta-coordinated.Al(OH)(H
2
O)
2+
.complex.in.aqueous.
solution..Our.studies.show.that.the.penta-coordinated.complex.converts.to.a.trigonal.
bipyramidal.structure.(Figure.4.2C).in.water.within.the.following.1.7.ps.
Additional.CPMD.simulations.involving.breaking.a.HO-H.bond.of.a.irst.shell.
water.molecule.were.performed.in.order.to.understand.the.impact.of.the.free.proton.
on. the. solution. dynamics. and. coordination. chemistry.. This. simulation. shows. that.
the. proton. moves. to. the. second. shell. and. forms. a. Zundel-like. structure.. However,.
(A)
(B)
(C)
FIGURE 4.2
Octahedral. Al(H
2
O)
3+
(A),. square. pyramidal. Al(OH)(H
2
O)
2+
. (B),. and. tri-
gonal. bipyramidal. Al(OH)(H
2
O)
2+
. (C). species. in. aqueous. solution,. obtained. from. CPMD.
simulations.
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