Metal Vector Manipulated Molecular Self-Assembly from Werner System to Cotton System

摘要

A definition of metal vector was given to coordinatively unsaturated metals or asymmetrically coordinated metal complexes in which the metal center is partly blocked by inert chelating ligand(s), thus possess specific reactivity and directionality, such as cis-coordinated square Pd(Ⅱ) or Pt(Ⅱ) complexes. Metal vectors have been extensively used in coordination catalysis and molecular assembly. In 1990, Fujita [ 1 ] first demonstrated the utility of cis-coordinated square Pd(Ⅱ)or Pt(Ⅱ) complexes as a right angular 2D metal vector in the formation of molecular square, a cyclic tetramer with nano-cavity and unique molecular recognition. So far, much attention has been paid to the use of the mononuclear coordination centers (Werner-type metal vectors) in molecular assembly.As late as 1999, Cotton et al. [2] reported the use of cis-coordinated metal-metal bonded dimetal units (Cotton-type metal vectors) to direct assembly of molecular squares.This presentation includes two parts: 1) Werner-type metal vector directed molecular assembly; [3]2) Cotton-type metal vector directed molecular assembly.[4]Firstly, the Werner-type metal vector, cis-coordinated Pd(Ⅱ) nitrate, was used to direct a 6-component self-assembly. This leads to the formation of a molecular bowl or crown with syn,syn,syn conformation. These structures are analogues of calix[3]arenes and can function as anion receptors. Interestingly, an nitrate is found to distort from a trigonal plane into a trigonal pyramid when binding to the bottom of the molecular bowl.Secondly, the Cotton-type metal vector, cis-diRh(Ⅱ, Ⅱ), was used to assemble di- or poly-carboxylate anions into neutral supermolecules. Most interestingly, a calixarene-based carceplex with four cis-diRh(Ⅱ, Ⅱ) fastners was obtained[5].All self-assembling entities were studied by both X-ray crystallographic analysis and solution NMR spectra, which are consistent with the presence of assembling structures even in solution.