Syntheses And Crystal Structures Of Novel Adducts Based On POMs And Crown Ethers, And Properties Of Their Modified Carbon Paste Electrodes

Six new polyoxometalate-crown ethers adducts have been synthesized in the organic solvent based on polyoxoanions and crown ether building blocks. They are determined structurally by single crystal X-ray diffractions and characterized by elemental analysis, IR spectroscopy, TG-DTA analysis.In these adducts mentioned above, crown ethers are able to combine with sodium cation by O-Na bonds or H3O⁺ to form [(H₃O)crown ethers]⁺1-2 building blocks by hydrogenbonds. There are dominantly the electrostatic interactions between these complex cations and polyanions in these adducts. In adduct 1, the CH3CN molecules connect polyanions Mo₆O₁₉^2- with [Na(Benzo-15-Crown-5)(H2O)]⁺ by C-H(CH₃CN)…Ob hydrogen bond and Na-N(CH3CN) bond. In 2, the Dicyclohexyl-18-Crown-6 molecules are more flexible and the Na⁺ ions are wholly enwrapped by the contorted crown ether moieties, the Mo₆O₁₉^2- anions are packed in the AB…AB layers along the c axis. In adducts 3 and 6, there are hydrogen interactions between the H3O⁺ ions of [(H₃O)(Benzo-15-Crown-5)]⁺ and the terminal or bridged oxygen atoms of polyoxoanions. In three [(H₃O)(Benzo-15-Crown-5)2]⁺ complex cations of adduct 4, the opposite positions of the two crown ether molecules are different from each other. In 5, there are hydrogen interactions between the CH3OH molecules and the teminal oxygen of GeW12O404- polyoxoanions as well as the H3O⁺ ions of [Na(Benzo-15-Crown-5)(H₃O)]⁺.These polyoxometalate-crown ether hybrid compounds mentioned above were firstly used as a bulk-modifier to fabricate a renewable three-dimensional chemically modified carbon paste electrode (MCPE) by directly mixing. The electrochemical and electrocatalytic properties of the MCPEs were investigated. The peak currents are proportional to the scan rates. With increasing pH, the peak potentials shift towards the negative direction. They display electrocatalytic activity toward to reduction of nitrite or hydrogen peroxide, and also exhibited an advantage of reused ability in the vent of surface fouling. Another advantage of the MCPE is its stability due to insolubility of these adducts, the affinity of the crown ethers toward the paste and the adsorption of polyoxometalate on graphite, which is important for practical application.