Optimized Structures for the and Clusters

Lowest energy SCF-MI optimized structure of the octahedral complex of the K+ cation with six ammonia molecules 

Because the ionic radius of Li+ is smaller than that of K+, the Li+ cation allows solvent molecules to come closer to it. In addition because of its smaller size, Li+ is able to accommodate fewer ammonia molecules in its first coordination shell. 

The complexes with n=5 and n=6 exhibit marked differences from the corresponding K+ systems with the fifth and sixth molecules located in the second coordination shell forming bifurcated H-bonds with the first solvation sphere (as shown in Figs. 7 and 8). 

From the computed Ldwdin charge of Li+ for clusters of different sizes, it follows that Li+ complexes behave as K+ complexes, but a greater amount of charge is transferred in this case. 

The interaction energy increases as the size of the cluster grows. In order to examine the variation of the interaction energy in the process of formation of the clusters, the difference between the energy in the clusters containing n and n-1 ligands was plotted against n (see Fig. 9 ). 

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