Zhang Jun, Dolg Michael
Institute for Theoretical Chemistry, University of Cologne , Greinstraße 4, D-50939 Cologne, Germany.
J Phys Chem A. 2015 Jan 29;119(4):774-80. doi: 10.1021/jp511043c. Epub 2015 Jan 14.
For a wide range of trivalent lanthanide ion coordination complexes of tricapped trigonal prism or monocapped square antiprism configurations, the bonds between the central lanthanide ions and the capping ligands are found to violate Badger's rule: they can get weaker as they get shorter. We demonstrate that this observation originates from the screening and repulsion effect of the prism ligands. Both effects enhance as the electric field of the central ion or the softness of the prism ligands increases. Thus, for heavier lanthanides, despite the fact that the capping bond could be shorter, it is more efficient to be weakened by the prism ligands, being inherently labile. This concept of "labile capping bonds phenomenon" is then successfully used to interpret many problems in lanthanide(III) hydration, e.g., why the water exchange rate of a lanthanide(III) complex is much higher in a twisted square antiprism than in square antiprism configuration. Thus, the theory proposed in this paper offers new insights in understanding chemical problems.
对于一系列具有三帽三棱柱或单帽反方棱柱构型的三价镧系离子配位络合物，发现中心镧系离子与帽配体之间的键违反了巴杰尔规则：它们可能会随着键长缩短而变弱。我们证明这一观察结果源于棱柱配体的屏蔽和排斥效应。随着中心离子的电场或棱柱配体的柔软度增加，这两种效应都会增强。因此，对于较重的镧系元素，尽管帽键可能更短，但棱柱配体使其变弱的效率更高，本质上是不稳定的。然后，“不稳定帽键现象”这一概念成功地用于解释镧系（III）水合作用中的许多问题，例如，为什么镧系（III）络合物在扭曲的反方棱柱构型中的水交换速率比在反方棱柱构型中高得多。因此，本文提出的理论为理解化学问题提供了新的见解。
