Aqueous Solutions of Metal Ions - Metallic Systems: A Quantum Chemist's Perspective - page 121

Initially,.the.Al.ion.centers.are.separated.from.one.another.by.7.1.Å..After.5.2.ps,.
the. distance. between. the. Al. ions. decreases. to. 5.2. Å.. The. calculations. of. the. free.
energy.indicate.that.Al.ions.separated.by.two.water.molecules.at.a.distance.of.5.2.
Å.from.one.another.(Figure.4.3B).are.slightly.more.stable.(4.6.kJ.mol −1 ).than.the.Al.
ions. separated. by. 7.1. Å. (Figure. 4.3A).. However,. this. free. energy. change. value. is.

(A)

(B) (C) (D)

(E) (F) (G)

FIGURE 4.3 Two.Al(OH)(H 2 O) 2+ .species.in.aqueous.solution.(A),.two.trigonal.bipyrami-
dal Al(OH) 2+ .ions.at.a.distance.of.7.1.Å.(B),.water-separated.Al(OH) 2+ .ions.at.a. r Al-Al .distance.
of.5.2.Å.(C),.formation.of.a.Zundel.complex.(H 5 O + ).and.loss.of.one.water.molecule.from.one.
Al.center.(D),.formation.of.one.OH.bridge.between.the.Al.centers.and.formation.of.a.second.
Zundel-like. complex. (E),. loss. of. one. water. molecule. coordinated. to. the. Al. center. and. the.
formation.of.an.Eigen-like.aqua.complex.(F),.and.formation.of.OH-bridged.Al 2 (OH) 2 (H 2 O) 4+ .
complex.in.water.(G).obtained.from.the.CPMD.simulations.