Solvent-, Cation- and Anion-Induced Structure Variations in Manganese-Based TCNQF(4) Complexes: Synthesis, Crystal Structures, Electrochemistry and Their Catalytic Properties

摘要

The reaction of Mn(BF4)(2 center dot)xH(2)O with (Pr4N)(2)TCNQF(4) (TCNQF(4)=2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) in a mixture of CH3OH/CH2Cl2 gives a 2:3 stoichiometric complex of (Pr4N)(2)[Mn-2(TCNQF(4))(3)(CH3OH)(2)] (1). If the solvent system used for the crystallisation of 1 is changed to CH3OH/DMF, then a different product, [Mn(TCNQF(4))(DMF)(2)](CH3OH)(2) (2), is obtained. The use of Li(2)TCNQF(4) instead of (Pr4N)(2)TCNQF(4) leads to the generation of [Mn-2(TCNQF(4))(2)(DMF)(4)]center dot 3DMF (3). An unexpected mixed oxidation state network with a composition of [(Mn4Mn16O10)-Mn-II-O-III(OH)(6)(OCH3)(24)(TCNQF(4))(2)](NO3)(2 center dot)24CH(3)OH (4), is formed if Mn(NO3)(2 center dot)xH(2)O is used in place of Mn(BF4)(2 center dot)xH(2)O in the reaction that leads to the formation of 3. Compounds 1-3 have been characterised by X-ray crystallography; FTIR, Raman and UV/Vis spectroscopy; and electrochemistry. Compound 4 has only been analysed by X-ray crystallography and vibrational spectroscopy (Raman, FTIR), owing to rapid deterioration of the compound upon exposure to air. These results indicate that relatively minor changes in reaction conditions have the potential to yield products with vastly different structures. Compound 1 adopts an anionic 2D network with unusual -stacked dimers of the TCNQF(4)(2-) dianion, whereas 2 and 3 are composed of similar neutral sheets of [Mn(TCNQF(4))(DMF)(2)]. Interestingly, the solvent has a significant influence on the stacking of the sheets in the structures of 2 and 3. In compound 4, clusters with a composition of [(Mn4Mn16O10)-Mn-II-O-III(OH)(6)(OCH3)(24)(CH3OH)(4)](6+) serve as eight-connecting nodes, whereas TCNQF(4)(2-) ligands act as four-connecting nodes in a 3D network that has the same topology as fluorite. Compound 3 exhibits an exceptionally high super-catalytic activity for the electron-transfer reaction between ferricyanide and thiosulfate ions in aqueous media.