de Visser Sam P, Kumar Devesh, Danovich Mark, Nevo Nir, Danovich David, Sharma Pankaz K, Wu Wei, Shaik Sason
The Manchester Interdisciplinary Biocenter, School of Chemical Engineering and Analytical Science, The University of Manchester, Sackville Street, PO Box 88, Manchester M60 1QD, UK.
J Phys Chem A. 2006 Jul 13;110(27):8510-8. doi: 10.1021/jp055125a.
Density functional theoretic studies are performed for the high-spin copper clusters (n)(+1)Cu(n) (n = 2-14), which are devoid of electron pairs shared between atoms, hence no-pair clusters (J. Phys. Chem. 1988, 92, 1352; Isr. J. Chem. 1993, 33, 455; J. Am. Chem. Soc. 1999, 121, 3165). Despite the lack of electron pairing, it is found that the bond dissociation energy per atom (BDE/n) is significant and converges (to within 1 kcal mol(-1)), around a cluster size (11)Cu(10), to a value of BDE/n = 19 kcal mol(-1). This is a very large bonding energy, much larger than has previously been obtained for no-pair clusters of lithium, BDE/n = 12 kcal mol(-1), or sodium clusters, BDE/n = 3 kcal mol(-1). This bonding, so-called ferromagnetic bonding (FM-bonding) is analyzed using a valence bond (VB) model (J. Phys. Chem. A 2002, 106, 4961; Phys. Chem. Chem. Phys. 2003, 5, 158). As such, FM-bonding in no-pair clusters is described as an ionic fluctuation, of the triplet pair, that spreads over all the close neighbors of a given atom in the clusters. Thus, if we refer to each triplet pair and its ionic fluctuations as a local FM-bond, we can regard the electronic structure of a given (n)(+1)M(n) cluster as a resonance hybrid of all the local FM-bonds between close neighbors. The model shows how a weak interaction in the diatomic triplet molecule can become a remarkably strong binding force that binds together mono-valent atoms without even a single electron pair. This is achieved because the growing number of VB structures exerts a cumulative effect of stabilization that is maximized when the cluster has a compact structure with an optimal coordination number for the atoms.
对高自旋铜簇(n)(+1)Cu(n)（n = 2 - 14）进行了密度泛函理论研究，这些铜簇中原子间不存在共享电子对，因此是无对簇（《物理化学杂志》1988年，92卷，1352页；《以色列化学杂志》1993年，33卷，455页；《美国化学会志》1999年，121卷，3165页）。尽管不存在电子配对，但发现每个原子的键解离能（BDE/n）很大，并且在簇尺寸为(11)Cu(10)左右收敛（在1千卡摩尔⁻¹范围内），达到BDE/n = 19千卡摩尔⁻¹的值。这是一个非常大的结合能，比之前锂的无对簇（BDE/n = 12千卡摩尔⁻¹）或钠簇（BDE/n = 3千卡摩尔⁻¹）所得到的结合能大得多。这种键合，即所谓的铁磁键合（FM键合），使用价键（VB）模型进行了分析（《物理化学杂志A》2002年，106卷，4961页；《物理化学化学物理》2003年，5卷，158页）。因此，无对簇中的FM键合被描述为三重态对的离子涨落，它扩展到簇中给定原子的所有近邻。这样，如果我们将每个三重态对及其离子涨落视为一个局部FM键，那么我们可以将给定的(n)(+1)M(n)簇的电子结构视为近邻之间所有局部FM键的共振杂化体。该模型展示了双原子三重态分子中的弱相互作用如何能成为一种非常强的结合力，将单价原子结合在一起，甚至没有一个单电子对。之所以能实现这一点，是因为越来越多的VB结构产生了稳定的累积效应，当簇具有紧凑结构且原子具有最佳配位数时，这种效应达到最大。
