Water octamer

Stillinger FH, David CW (1980) Study of the water octamer trsing the polarization model of molecular irrteractiorrs. J Chem Phys 73 3384-3389... 

F. H. Stillinger and C. W. David, J. Chem. Phys., 73, 3384 (1980). Study of the Water Octamer Using the Polarization Model of Molecular Interactions. 

The variation of the uncorrected (soiid circies) and BSSE-corrected (open circles) binding energy from MP2 caicuiations with different basis sets for the water octamer (n = 8). The figure is reprinted with permission from reference Xantheas and Apra (2004). 2004 American Institute of Physics... 

Xantheas, S. S., 8c AprS, E. (2004). The binding energies of the Dzd 2nd S4 water octamer isomers High-level electronic structure and empirical potential results. Journal of Chemical Physics, 120, 823-828. 

In the relevant crystal structure, these one-dimensional chains are laterally linked by a supramolecular water octamer (vide infra) resulting in a two-dimensional layer-like arrangement as shown in Figure 6. The other transition-metal complexes that are supported by the octamolybdate isopolyanion are also known in the literature. " ... 

FIGURE 6. Two-dimensional supramolecular hydrogen bonded array in compound [ Cu(phen)(H2O)2 2(M0sO26)] 8H2O that is exclusively formed by lateral hydrogen bonding interactions between one-dimensional chains. One of the water octamers is shown in solid lines (center of structure) for clarity. The polyhedral representations of the octamolybdates are given for a clear view of the water octamer. 

The stabilization of such unusual and disfavored conformation of water octamer is thus achieved through supramolecular hydrogen bonding interactions with its surroundings, which include terminal oxygen atoms 0(1) and 0(5) attached to Mo(l) and Mo(5), respectively, of the isopolyanion. This situation is shown in Figure 46. 

FIGURE 45. (a) Water octamer formed from the copper-coordinated waters and lattice waters. 0(14) and 0(15) are copper-coordinated water molecules. Cu ions are not shown, (b) Water octamer showing water coordination to the copper ions. (Reprinted... 

FIGURE 46. The immediate environment of the water octamers, (H20)g, which includes the oxo groups of the POM anion. (Reprinted with permission from ref. 31.)... 

The use of the double expansion (Sect. 3.3) in the description of the electron correlation and the orbital basis set allows for the accurate computation of water cluster binding energies. These are important data, which are currently not available experimentally, and can be used to assess the accuracy of interaction potentials for water. Table 2 shows a comparison between the MP2 and CCSD(T) binding energies obtained with the aug-cc-pVDZ and aug-cc-pVTZ basis sets for the D2d isomer of the water octamer [104]. We note that the difference between the MP2 and CCSD(T) binding energies for this cluster for each basis set is <0.1 kcal/mol. This result, together with additional calculations on medium size (n = 3-6) clusters [105,106], sug-... 

Table 2 Binding energies (kcal/mol) of the water octamer obtained at the MP2 and CCSD(T) levels of theory with the aug-cc-pVDZ and aug-cc-pVTZ basis sets...

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