The goal of this research was to study the electrochemical behavior of tri-nuclear clusters of molybdenum and tungsten. In addition, the feasibility of using these clusters as catalysts for the purpose of oxidizing ethanol was investigated. Four tri-nuclear cluster compounds were studied: hexa-µ2-acetatotriaquadi-µ3-oxotrimolybdenum (IV, IV, IV) trifluoromethanesulfonate [Mo3O2(O2CCH3)6(H2O)3](CF3SO3)2, hexa-µ2-acetatotriaquadi-µ3-oxodimolybdenum (IV, IV) tungsten (IV) trifluoromethanesulfonate [Mo2W2O2(O2CCH3)6(H2O)3](CF3SO3)2, hexa-µ2-acetatotriaquadi-µ3-oxomolybdenum (IV) ditungsten (IV, IV) trifluoromethanesulfonate [MoW2O2(O2CCH3)6(H2O)3](CF3SO3)2, and hexa-µ2-acetatotriaquadi-µ3-oxotritungsten (IV, IV, IV) trifluoromethanesulfonate [W3O2(O2CCH3)6(H2O)3](CF3SO3)2.
Data was gathered from experimental results with cyclic voltammetry for the four tri-nuclear clusters. Initially, an ionic liquid, EMIBF4 (1-ethyl-3-methylimidazolium tetrafluoroborate), was used as the solvent. Subsequent solvents for use with these clusters were investigated, including ACN (acetonitrile) and NMF (N-methylformamide). The secondary solvent system settled on was the DMSO-TBAHFP solvent system. Each tri-nuclear cluster displayed a reversible redox reaction and one or more irreversible reduction reactions. The redox peak potentials were found to be Ep,a: -0.44V and Ep,c: -0.42V for Mo3, Ep,a: -0.32V and Ep,c: -0.43V for Mo2W, Ep,a: -0.31 V and Ep,c: -0.44 V for MoW2, and Ep,a: -0.42 and Ep,c: -0.46 for the W3 tri-nuclear cluster. The irreversible reduction reactions for each tri-nuclear cluster were observed at Ep,c(2): -0.74 for Mo3, Ep,c(2): -1.15 for Mo2W, Ep,c(2): -1.14 for MoW2, and Ep,c(2): -0.84 for the W3 tri-nuclear cluster. The diffusion coefficients in DMSO were determined to be DMo3 = 9.105E-06 cm2s-1, DMo2W = 1.743E-05 cm2s-1, DMoW2 = 1.764E-05 cm2s-1, and DW3 = 1.991E-05 cm2s-1.
Exploring the electrocatalytic capability of these compounds was another effort made, by attempting to electroplate the compounds on platinum electrodes. Although some types of deposition events did appear to occur, it is unlikely they were of the intact tri-nuclear clusters. Thus far, the ethanol molecule has been partially oxidized, but breaking the carbon-carbon bond in the molecule proved to be a challenge that was not achieved.