CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

water H-bonding network among solvent H 2 O molecules and ionic hydrogen bond
formation between solvent H 2 O molecule and I atom.
Four minimum energy structures predicted for tri-hydrate cluster, I •− 2 .3H 2 O are
displayed in Fig. 2.1-III(A-D). Initial guess structures are considered based on the
optimized minimum energy structures observed in case of di-hydrate cluster, I •− 2 .2H 2 O.
Geometry optimization leads to two different minimum energy structures when the initial
guess structure is designed based on structure II-A adding the third H 2 O forming
symmetrical DHB with two I atoms. When the third H 2 O is kept at a close distance from
one of the H 2 O molecules (r OO ~ 3.5 Å), structure III-A is obtained. On the other hand
when the said distance, r OO is more than 3.5 Å in the initial geometry, structure III-B is
obtained. The initial guess for structure III-C consists of three symmetrical DHB
arrangements. In this particular optimized structure, all the three H 2 O molecules are
directly connected to I atoms without any inter H 2 O interaction. Structure III-D, having
two DHB and one SHB arrangements from axial side of I •− 2 moiety is the least stable
conformer for the tri-hydrate cluster. The surface structure III-A having three H 2 O
molecules connected by inter H 2 O H-bonding network (WHB arrangements) is the most
stable one and has the shortest I-I bond distance among the different conformers of
I •− 2 .3H 2 O cluster. The calculated dihedral angle, δ(O-I-I-O) in the structure III-C is 120 o .
As expected, the number of possible conformers increases with the increase in the
number of solvent water molecules. Initial guess structures are considered with a bottomup
approach based on the predicted stable structures from the smaller size hydrated
clusters. Thus the initial guess structures for I •− 2 .4H 2 O cluster is designed based on the
predicted minimum energy structures of I •− 2 . nH 2 O (n=1-3), keeping different numbers of
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