Bryantsev Vyacheslav S, Diallo Mamadou S, van Duin Adri C T, Goddard William A
Materials and Process Simulation Center, Beckman Institute 139-74, California Institute of Technology, Pasadena, California 91125, USA.
J Phys Chem A. 2008 Sep 25;112(38):9104-12. doi: 10.1021/jp804373p. Epub 2008 Sep 3.
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 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 core stabilized by an unpaired electron in the Cu(II) ion d(x(2)-y(2)) 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 (approximately 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.
铜（II）离子的水合结构一直是文献中持续争论的主题。在本文中，我们使用密度泛函理论（B3LYP）和COSMO连续介质溶剂模型来表征Cu(H₂O)ₙ团簇的结构和稳定性，该稳定性是配位数（4、5和6）和团簇大小（n = 4 - 18）的函数。我们发现，气相中热力学上最有利的铜（II）配合物具有非常开放的四配位结构。它们由一个稳定的平面正方形Cu(H₂O)₈核心形成，该核心由铜（II）离子d(x² - y²)轨道中的一个未成对电子稳定。这与最近质谱实验所暗示的团簇几何形状一致。在水相中，我们发现更紧凑的五配位正方锥几何形状比四配位或六配位团簇更稳定，这与最近对铜（II）水溶液的EXAFS和XANES联合研究结果一致。然而，在金属离子周围有两个完整水合壳的五配位和六配位模型之间存在较小的能量差异（约1.4千卡/摩尔），这表明两种形式可能在溶液中共存。
