abstract
Several novel compounds with 1-alkyl-3-methylimidazolium cations (alkyl = butyl and octyl) and first row transition metal-substituted Keggin polyoxoanions were synthesised, having the general formula (cation)(m)[PW11O39M(H2O)]center dot xH(2)O or (cation)(m-1)H[PW11O39M(H2O)]center dot xH(2)O, M = Co, Fe, Mn and m = anion charge. All compounds were characterized by spectroscopic and analytical techniques. These studies indicated that both the polyoxometalates and the cations are present in the solids without major alterations. Cyclic voltammetry studies were performed for compounds with 1-butyl-3-methylimidazolium. Disregarding the loss of crystallization or coordinated water, the compounds were found to be stable up to near 300 degrees C. The onset of the decomposition of the organic cations, as determined by thermogravimetry, occurred in the 300-350 degrees C range. The metal-substituted polyoxoanions are stable up to around 300 degrees C, but after this temperature the anions transform into the parent [PW12O40](3-) anion, with loss of the substituting metal. Final decomposition to a mixture of oxides occurred only above 600 degrees C. It was also possible to obtain the crystalline compounds Na2K(Bmim)(2)[PW11O39Co(H2O)]center dot 7.5H(2)O and Na(Bmim)(4)[PW11O39Co(H2O)]center dot 2H(2)O and determine their structures by single crystal X-ray diffraction. Compounds with substituted imidazolium cations and metal-substituted polyoxometalates are expected to present a set of properties that make them interesting in many fields, like catalysis. This study aimed at contributing to the understanding the effect of altering the substituting metal and the counter-cation in the properties of this type of compounds. (C) 2015 Elsevier Ltd. All rights reserved.
keywords
METAL-SUBSTITUTED POLYOXOTUNGSTATES; HOMOGENEOUS CATALYTIC-OXIDATION; POLYOXOMETALATE-BASED MATERIALS; IONIC LIQUID; HYDROGEN-PEROXIDE; ELECTROCATALYTIC PROPERTIES; HETEROGENEOUS PERFORMANCE; ELECTROCHEMICAL-BEHAVIOR; SELECTIVE OXIDATION; FILMS
subject category
Chemistry; Crystallography
authors
Santos, FM; Brandao, P; Felix, V; Nogueira, HIS; Cavaleiro, AMV
our authors
Ana Maria Vieira Silva Viana Cavaleiro
Full professor
Filipe Miguel de Almeida Marques dos Santos
Post-doc Fellowship
Helena Isabel Seguro Nogueira
Assistant Professor with Aggregation
Paula Cristina Ferreira da Silva Brandão
Assistant Researcher
Vítor Félix
Associate Professor with Aggregationacknowledgements
Thanks are due to the University of Aveiro and CICECO for financial support. This work was developed in the scope of the project CICECO-Aveiro Institute of Materials (Ref. FCT UID /CTM/50011/2013), financed by national funds through the FCT/MEC and when applicable co-financed by FEDER under the PT2020 Partnership Agreement. F.M. Santos acknowledges FCT for his PhD grant SFRH/BD/40857/2007.