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Reduction of [U(NN'(3))I] [NN'(3) = N(CH2CH2NSiMe2But)(3)] with potassium in pentane gives the purple trivalent monomer [U(NN'(3))] in good yield, this compound having previously been synthesised via fractional vacuum sublimation of mixed-valent [{U(NN'(3))}(2)(mu-Cl)]. The magnetic susceptibility of this compound is consistent with the presence of U(III) centres, and this is confirmed by a characteristic near IR spectrum. Its reactions with Lewis bases to give e.g. [U(NN'(3))(Py)] and [U(NN'(3))(HMPA)] are reported, along with the molecular structure of the latter. The complex [U(NN'3)] is readily oxidised, imido and hydrazido complexes being formed readily by reaction with trimethylsilyl-azide and -diazomethane, respectively. The reaction with methylene trimethylphosproane however led to the formation of an addition compound [U(NN'(3))(CH2PMe3)]. Reaction of this latter complex with air gave a few crystals of the unusual hydroxo complex [U(NN'(3))(OH)(CH2PMe3)] which was structurally characterised. Reaction of [U(NN'(3))(CH2PMe3)] with trimethylamine N-oxide gave pentavalent [U(NN'(3))(O)], or perhaps a dimer thereof. The latter complex reacted with [U(NN'(3))] to give the bridging oxo complex [{U(NN'(3))}(2)(mu-O)] which could also be prepared directly by reaction of trimethylamine N-oxide with [U(NN'(3))]

Different PEDOT-based counter electrodes, obtained by potentiostatic electropolymerization of 3,4-ethylenedioxythiophene (EDOT) monomer on fluorine tin oxide (FTO) surfaces, were compared to platinum- and gold-coated electrodes in order to evaluate the potential use of PEDOT counter electrodes in dye-sensitized photoelectrochemical cells (DSCs). In particular, a series of DSC devices utilizing Co(III)/(II) polypyridine redox mediators ([Co(bpy)3]3+/2+, [Co(phen)3]3+/2+, [Co(dtb)3]3+/2+; bpy = 2,2′-bipyridine; dtb = 4,4′ditert-butyl-2,2′-bipyridine; phen = 1,10-phenanthroline) having distinct electrochemical characteristics were evaluated. Electrochemical impedance spectroscopy (EIS) measurements reveal that [Co(bpy)3]3+/2+ and [Co(phen)3]3+/2+ mediators exhibit relatively fast heterogeneous electron transfer rates with porous PEDOT/ClO4 electrodes (k = 7 × 10–3 cm s–1 and 2.1 × 10–3 cm s–1, respectively) and correspondingly low charge transfer resistances (<1 Ω) that are competitive with results obtained for Au and Pt coated electrodes. The bulkier [Co(dtb)3]3+/2+ mediator exhibits a more complex surface dependent electrochemistry yielding somewhat faster electron transfer kinetics on gold (3.8 × 10–4 cm s–1) relative to PEDOT/ClO4 (1.7 × 10–4 cm s–1) coated counter electrodes. Nevertheless, this work establishes that porous PEDOT/ClO4 counter electrodes, because in part of their enhanced electroactive surface area and reduced charge transfer resistance, possess sufficient electrocatalytic properties when paired with cobalt-based redox mediators to make PEDOT-based counter electrodes attractive for use in DSC applications.

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