Syntheses, Structures And Properties Of Novel Metal-organic Rotaxane Frameworks

Metal-organic rotaxane frameworks (MORFs), as a new family of solid statecrystal materials containing mechanical bond, has drawn tremendous attention ofsupramolecular and material chemists, due to their structural designability andexcellent performance. Mechanically interlocked molecules (MIMs), especially thosemulti-stable ones with stimuli-responsive characteristics, have found potentialapplications in sensor, small molecules delivery, molecular electronics, catalysis andintellectual materials. Now, the incorporation of interlocked supramolecules intohighly ordered lattice has not only become a new growing point of the coordinationchemistry, but also become a bridge for the supramolecular chemistry leading to the“bionics”. In this paper, a series of novel MORFs have been synthesized by the use ofcucurbit[6]uril-based pseudorotaxane and transition metal cations with/withoutgeometry varied rigid carboxylate ligands, by exploiting the concepts of dynamiccombinatorial chemistry (DCC) and mixed ligands. The synthesis conditions of thesecompounds were discussed. Then, the non-covalent interactions, the site of terminalfunctional groups in pseudorotaxanes, geometrically different auxiliary ligands andvarious metal ions on the resulted frameworks of these compounds have beeninvestigated. Furthermore, the relationships between the functionality andcorresponding structures of related compounds have been analyzed.Twelve metal-organic rotaxane framework compounds have been synthesized byhydrothermal technique, and structurally characterized by IR, elemental analyses,TGA, FL and single crystal X-ray diffractions, etc. The thermal stabilities,electrochemical properties and solid state sensitization of visible light emitting ions ofsome compounds have been studied.1. Two long yet flexible pseudorotaxane [PCN6n]2+2[NO3-](n=3,4) withterminal cyano groups were designed and synthesized. Three novel isostructurallyself-catenated4-connected uninodal (65.8)-mok MORFs containing cucurbit[6]urilwere constructed from the in-situ trans/cis-configuration (1:1) of rotaxanes by takingadvantage of d10metal ion directed synthesis. It is revealed that the effects ofhydrogen bonds and the π-π stacking interactions play significant roles in theself-assembly process. Meanwhile, the thermal stability and electrochemical propertyof compound1has been investigated.[Cu(PCA64)(PCA642-)]13H2O (1)[Zn(PCA64)(PCA642-)]13H2O (2)[Cd(PCA64)(PCA642-)]13H2O (3) 2. Pseudorotaxane [PR6n](n=3,4) with pyridine groups at the terminals wereselected and synthesized to combine with geometry varied rigid carboxylate ligandsand transition metal ions under hydrothermal conditions. As a result, nine MORFshave been obtained: one3D fameworks, five2D nets and three1D polymers. Inaddition, the synergistic effects of supramolecular building blocks and auxiliaryligands as well as the coordination tendency of metal ions on the topologies ofresulted frameworks have been discussed, during the coordination drivenself-assembly process.[Co(BTC)(PR64)0.5(H2O)4]6H2O (4)[Ni(BTC)(PR64)0.5(H2O)3]6H2O.(5)[La(m-BDC)(m-HBDC)(NO3-)(PR64)0.5(H2O)2]7H2O (6)[Zn(BPDC)(PR64)0.5(H2O)]2.5H2O (7)[Zn(PR64)0.5(m-BDC)(H2O)]3H2O (8)[Cd2(BDC)3(PR64)]9H2O.(9)[Cd(BDC)(PR63)(NO3-)2(H2O)]8.5H2O (10)[Co(BDC)(PR63)(NO3-)2(H2O)2]4.5H2O.(11)[Co(BTC)(PR63)0.5(H2O)2]6H2O (12)Compounds4-8were obtained by the combination of pseudorotaxane[PR64],trimesic acid or m-phthalic acid or diphenyldicarboxylic acid and four kinds of metalions. Compound6representsed a supramolecular framework with pseudorotaxane[PR64] sandwiched between adjacent layers. While, compound7was the first“staircase” like polyrotaxanes. Compound8has two dimensional flat hexagon sheets.When terephthalic acid was used, compound9was isolated, which representsed thefirst MORFs where pseudorotaxanes were used as pillar ligands to fabricatethree-dimensional MOFs containing MIMs. Compounds10-12with two dimensionalquadrangle nets, were obtained by the combination of pseudorotaxane[PR64],terephthalic acid or trimesic acid and metal ions. Furthermore, compound8showedgood sensitization behavior for lanthanide ions.