Syntheses, Structures And Properties Of Metal Complexes Of Tricarboxylic Acid And Calixarenes

Calixarenes are a kind of macrocyclic compounds constructed by bridging the phenol units with other groups such as methylene, sulfur, nitrogen and oxygen atoms. Due to the fact that their phenolic hydroxyl groups, heteroatom bridges and/or functional groups after modification can bind metal ions, and the coordination models differ much with their changeable comformation, calixarenes are good ligands for the construction of coordination compounds. This paper applied thiacalix[4]arene and its derivatives as the main ligand and tricarboxylic acids as the auxiliary ligands to react with different metal salts under solvothermal condition for the construction of the target complexes. All the compounds were characterized by single crystal X-ray diffraction, elemental analysis, thermogravimetry and infrared spectra. Gas sorption properties were also studied for some compounds.（1） A Zn₂（COO）₃ paddle-wheel-based metal-organic aggregate, namely {Zn₂Cl₂（BBC）}n（1; BBC = 4,4′,4′′-（benzene-1,3,5-triyl-tris（benzene-4,1-diyl））） was obtained by solvothermal synthesis, which is featured with a（6,3） network with some hexagonal pores being of 2.4 × 2.4 nm2. However, the pores are blocked when different layers are stacked with some shifts so that this compound exhibits no N2 adsorption. Different from those 2D networks obtained with hydrated zinc nitrate as the zinc source, this compound has some chloride anions bonded the layer structure rather than additional water molecules. It is found that the water content in the zinc source and even in the solvent plays a crucial role in the formation of the target compound and no target compounds can be obtained with higher water content. This compound can be easily dissolved in alkaline solution and exfoliated into isolated sheets by ultrasonic dispersion, which might be helpful to the potential application of these 2D networks.（2） A novel Co（II）-based metal-organic framework, namely {[Co₅（OH）（H₂O）（DMF）₄]（BTE）₃}（2a; BTE = 4,4′,4′′-（benzene-1,3,5-triyltris-（ethyne-2,1-diyl））tribenzoate） was obtained by solvothermal synthesis. This compound is featured with some 12-connected Co5 cluster nodes which are interconnected by some triangular tricarboxylic acid ligands into an interpenetrating metal-organic framework. After soaked in methanol, 2a was turned into another compound 2b, namely {[Co₅（OH）（H₂O）2（CH3OH）4]（BTE）3}, through single crystal-to-single crystal transform. These two compounds can take small molecular gas such as N₂ and H₂.（3） Three different heterometallic compounds were obtained by the reaction of tetra-（tetrabutylammonium） octamolybdate and p-tert-butylthiacalix[4]arene under solvothermal condition, namely, trinuclear one [（C₄H₉）₄N]{Na Mo₂（TC₄A）₂（CH₃O）₂（OH）₄}（3）, fourteen nuclear one [（C₄H₉）₄N]2{[Na₃Mo₄O₂（TC₄A）2（H₂O）₅]₂（H₂O）₄}（4） and another containing tetranuclear and eight nuclear units [（C₄H₉）₄N]4{Mo₄（TC₄A）₂Cl（CH₃OH）}2{Mo₈（TC₄A）4Cl₂}（5）. The trinuclear unit in compound 3 is constructed by connecting two shuttlecock-like mononuclear Mo-TC4 A motifs through a sodium cation. The fourteen nuclear unit in compound 4 looks like the eight nuclear one in 5, but there is obvious difference. The distance between two calixarene molecules in a sandwich-like subunit was stretched and a C-shaped unit with in-between Mo4Na3 clusters formed. Two such units are bridged into a fourteen nuclear motif by water molecules. Compound 5 contains two kinds of isolated units, one tetranuclear sandwich-like unit and one eight nuclear motif. The tetranuclear sandwich-like unit is constructed by two tail-to-tail calixarene molecules bridged by four molybdenum atoms while the eight nuclear unit is constructed by linking two such tetranuclear units by two chloride anions.（4） A sandwich-like structure {Mo₂Na₄O₃（TC₄A-SO₂）₂}（6） was obtained by the reaction of sodium molybdate and p-tert-butylsulfonylcalix[4]arene（H₄TC₄A-SO₂） under solvothermal conditions. It structure is similar to the typical tetranuclear sandwich-like motif, i.e. two calixarene molecules in tail to tail arrangement are bridged by four sodium cations to form a sandwich-like structure. At the same time two molybdenum atoms are located in the calixarene cavities and bonded by four phenolic hydroxyl groups. Two molybdenum atoms are connected by an oxygen bridge.