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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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ABSTRACT:The deposition of perylene diimide-based aggregates (PDI) onto wide band gap n-type Sb-doped SnO 2 (ATO) was investigated with the aim of finding efficient and versatile dye-sensitized platforms for photoelectrochemical solar fuel generation. These ATO-PDI photoanodes displayed hydrolytic stability in a wide range of pH (from 1 to 13) and revealed superior performances (up to 1 mA/cm 2 net photocurrent at 1 V vs SCE) compared to both WO 3 -PDI and undoped SnO 2 -PDI when used in a photoelectrochemical setup for HBr splitting. Although ATO, SnO 2 , and WO 3 are endowed with similar conduction band edge energetics, in ATO the presence of a significant density of intrabandgap states, whose occupancy varies with the applied potential, plays a substantial role in tuning the efficiency of photoinduced charge separation and collection. Furthermore, the investigation of the charge injection kinetics confirmed that, even in the absence of applied bias, ATO and WO 3 are the best substrates for the oxidative quenching of poorly reducing PDI excited states, with at least a fraction of them injecting within <200 fs. The charge-separated states recombination occurs on longer time scales, allowing for their exploitation to drive demanding chemical reactions, as confirmed in photoelectrochemical water oxidation using IrO 2 -modified ATO-PDI photoanodes.

The intramolecular metalation of a b-silyl methyl group in [U{N(CH 2 CH 2 NSiMe 2 Bu t ) 3 }(CH 2 Ph)] occurs rapidly, despite the conformational demands of the triamidoamine ligand, to produce a highly strained metallacycle (U-C ca. 2.75 Å); this complex reacts cleanly with a range of carbon and other acids to give, for example, an alkynyl with a bent (156°) U-C•C unit.

The first Fe(ii)-based sensitizer to give 1% efficiency in a DSSC.

The reaction of the lithiated triamidoamine [Li(3)(NN'(3))(THF)(3)] [NN'(3) = N(CH(2)CH(2)NSiMe(2)Bu(t))(3)] with AnCl(4) (An = U, Th) followed by sublimation gives monomeric [An(NN'(3))Cl]. Reaction of these complexes with SiMe(3)X (X = Br, I) gives [An(NN'(3))X]. The amido derivatives [An(NN'(3))(NEt(2))] are prepared from H(3)(NN'(3)) and [U(NEt(2))(4)] and from [Th(NN'(3))Cl] and [Li(NEt(2))]. In each case, the complexes [U(NN'(3))X] (X = Cl, Br, I, NEt(2)) are shown by X-ray crystallography to contain a triamidoamine ligand disposed with 3-fold symmetry about the metal center. The structures are distorted from trigonal bipyramidal by displacement of the uranium atoms out of the equatorial plane of the three amido nitrogen atoms by ca. 0.8 Å. The ligand backbone is distorted in such a manner as to cause the tert-butyldimethylsilyl groups to encircle the equatorial plane of the metal atom rather than surround the apical coordination site as is observed in the transition metal complexes of this type. Variation of the auxiliary ligand has little effect on the orientation, bond lengths, and angles within the (triamidoamine)uranium fragment. The tert-butydimethysilyl-substituted triamidoamine ligand is thus ideally suited for coordination to large metals since it stabilizes the formation of 3-fold symmetric structures while also allowing reactivity at the fifth coordination site.