Lear Benjamin J, Kubiak Clifford P
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0358, USA.
J Phys Chem B. 2007 Jun 21;111(24):6766-71. doi: 10.1021/jp068964l. Epub 2007 Apr 18.
The electronic effects resulting from noncovalent host-guest interactions between calix[6]arene and a ruthenium dimer, [Ru3O(OAc)6(CO)(ppy)]2-mu-pz (ppy=4-phenyl pyridine, pz=pyrazine), are presented. The noncovalent interaction is between the calix[6]arene and the ppy ligands of the dimer. The dimer can bind 2 equiv of calix[6]arene. The complex [Ru3O(OAc)6(CO)(ppy)]2-mu-pz forms a highly stable mixed valence ion with strong electronic coupling between the two Ru3 clusters. The strength of the electronic interaction is found to be moderated by calix[6]arene binding. Addition of calix[6]arene to the mixed valence ion causes the electronic coupling to decrease. The binding of calix[6]arene is found to be cooperative. The origins of cooperative binding are developed in terms of the potential energy surfaces associated with the symmetric and asymmetric mixed valence ion. In particular, it is found that symmetry breaking (through the binding of a single calix[6]arene) destabilizes the mixed valence state. Restoration of symmetry (through the binding of a second calix[6]arene) increases the stability of the mixed valence ion and provides an additional driving force for the binding of the second calix[6]arene.
本文介绍了杯[6]芳烃与钌二聚体[Ru3O(OAc)6(CO)(ppy)]2-μ-pz（ppy = 4-苯基吡啶，pz = 吡嗪）之间非共价主客体相互作用产生的电子效应。非共价相互作用发生在杯[6]芳烃与二聚体的ppy配体之间。该二聚体可以结合2当量的杯[6]芳烃。配合物[Ru3O(OAc)6(CO)(ppy)]2-μ-pz形成了一种高度稳定的混合价离子，两个Ru3簇之间具有强电子耦合。发现电子相互作用的强度受杯[6]芳烃结合的调节。向混合价离子中加入杯[6]芳烃会导致电子耦合降低。发现杯[6]芳烃的结合具有协同性。协同结合的起源是根据与对称和不对称混合价离子相关的势能面来阐述的。特别地，发现对称性破缺（通过单个杯[6]芳烃的结合）会使混合价态不稳定。对称性的恢复（通过第二个杯[6]芳烃的结合）增加了混合价离子的稳定性，并为第二个杯[6]芳烃的结合提供了额外的驱动力。
