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Published September 25, 2008 | Supplemental Material
Journal Article Open

Hydration of Copper(II): New Insights from Density Functional Theory and the COSMO Solvation Model

Abstract

The hydrated structure of the Cu(II) ion has been a subject of ongoing debate in the literature. In this article, we use density functional theory (B3LYP) and the COSMO continuum solvent model to characterize the structure and stability of [Cu(H2O)n]2+ clusters as a function of coordination number (4, 5, and 6) and cluster size (n = 4−18). We find that the most thermodynamically favored Cu(II) complexes in the gas phase have a very open four-coordinate structure. They are formed from a stable square-planar [Cu(H2O)8]2+ core stabilized by an unpaired electron in the Cu(II) ion dx2−y2 orbital. This is consistent with cluster geometries suggested by recent mass-spectrometric experiments. In the aqueous phase, we find that the more compact five-coordinate square-pyramidal geometry is more stable than either the four-coordinate or six-coordinate clusters in agreement with recent combined EXAFS and XANES studies of aqueous solutions of Cu(II). However, a small energetic difference (~1.4 kcal/mol) between the five- and six-coordinate models with two full hydration shells around the metal ion suggests that both forms may coexist in solution.

Additional Information

© 2008 American Chemical Society. Received: May 17, 2008. Revised Manuscript Received: July 22, 2008. Web Release Date: September 3, 2008. Funding for this work was provided by the National Science Foundation (NIRT CTS Award # 0506951) and by the US Environmental Protection Agency (STAR Grant RD-83252501). The computational facilities used in these studies were funded by grants from ARO-DURIP, ONR-DURIP and NSF-MRI. Supporting Information Available: Cartesian coordinates and absolute energies for all [Cu(H2O)n]2+ complexes optimized at the B3LYP/6-311++G(d,p) level of theory. This material is available free of charge via the Internet at http://pubs.acs.org.

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