Actinyl ions (AnO(2)(+) and AnO(2)(2+)) are strongly complexed by CO(3)(2)(-) in aqueous solution, and tricarbonato complexes of UO(2)(2+) and NpO(2)(+), in particular, have been widely studied. Cyclic voltammetry shows that, whereas the Np(V)/Np(VI) couple is reversible in aqueous CO(3)(2)(-) solution, the analogous U couple is irreversible, suggesting significant conformational change on one-electron reduction of [UO(2)(CO(3))(3)](4)(-). EXAFS spectroscopy has been used to define the coordination geometry of the reduced species and shows that both axial and equatorial U-O distances increase on reduction, from 1.80 to 1.90 Å and from 2.43 to 2.50 Å, respectively. The basic geometry of the U complex is apparently unchanged by reduction so any conformational change which does occur must be subtle.

The electronic structures of the prototypical bimetallic buta-1,3-diyn-1,4-diylbridged radical cation complexes [{M(dppe)Cp´} 2 (µ-C≡CC≡C)] + (M= Fe, Cp´ = Cp* (1a), Cp (1b); M = Ru, Cp´ = Cp* (2a), Cp (2b)) have been (re-)investigated using a combination of UV-vis-NIR and IR spectroelectrochemistry, and quantum chemical calculations based on both dispersion-corrected global (BLYP35-D3) and local (Lh-SsirPW92-D3) hybrid functionals. Following analysis of new and existing data, including the IR-active ν(C≡C) bands, the iron compounds [1] + are reclassified as valence-trapped (Robin and Day Class II) mixed-valence complexes, in contrast to the ruthenium complexes [2] + , which are delocalized (Robin and Day Class III) systems. All members of the series exist as a thermally populated distribution of conformers in solution, and the overlapping spectroscopic profiles make the accurate extraction of the parameters necessary for the analysis of [1] + and [2] + within the framework of the Marcus-Hush model extremely challenging. Analysis of the spin-density distributions from a range of conformational minima provides an alternative representation of

A series of molybdenum alkynyl complexes [Mo(CCR)(dppe)(η-C7H7)] featuring a range of alkynyl substituents R with varying electron-donating and -withdrawing properties have been prepared. Oxidation of representative members of the series to the corresponding 17-electron radical cations has been achieved through both chemical oxidation and in situ spectroelectrochemical methods. The largely metal-centered character of the HOMO in this class of compounds has been established through a combination of experimental measurements (IR, UV−vis−NIR, EPR spectroscopies) and DFT-based calculations and rationalized in terms of the stabilization of the metal d xy , d yz , d xz , and dx2-y2 through π- and δ-interactions with the C7H7 ring and concomitant destablization of the dz2 orbital.

International audienceReaction of [FeCl(dppe)Cp*] with [Mo(C≡CC6H4-4-C≡CH)(dppe)(η-C7H7)], 1, and NaBPh4 in methanol gives the alkynylvinylidene complex [{Fe(dppe)Cp*}{μ-C≡CC6H4(H)C═C}{Mo(dppe)(η-C7H7)}]BPh4, [2A]BPh4, which is deprotonated to form the heterobimetallic, 1,4-diethynylbenzene-bridged complex [{Fe(dppe)Cp*}(μ-C≡CC6H4C≡C){Mo(dppe)(η-C7H7)}], 3. The alkynylvinylidene compound [2A]BPh4 exists as the major component of an equilibrium mixture with [Fe(dppe)Cp*}{μ-C═C(H)C6H4C≡C}{Mo(dppe)(η-C7H7)}]BPh4, [2B]BPh4, and is formed as a consequence of proton migration between the Cβ carbons of the vinylidene and alkynyl ends of the bridging ligand. Cyclic voltammetric investigations reveal that 3 undergoes two reversible one-electron oxidations to cationic [3]+ and [3]2+, which have been isolated as the [PF6]− salts after chemical oxidation. Computational (DFT) studies on [3]n+ indicate that while the HOMO of neutral 3 is rather heavily localized on the Mo center, in [3]+ the frontier orbitals are more evenly distributed over both metals, with the concentration of spin density being sensitive to the relative disposition of the metal end-cap fragments about the diethynylbenzene ligand. Experimental investigations on [3]PF6 by IR and EPR spectroscopy provide evidence for the coexistence of redox isomers [3A]+ and [3B]+, in which spin density is localized at the molybdenum or iron center, respectively. The solution IR spectrum of [3]PF6 exhibits an unusual four-band pattern in the ν(C≡C) region, consistent with the observation of two isomeric forms of [3]PF6, which are "valence trapped" on the short time scale of IR spectroscopy. In the frozen solution EPR spectrum, at 120 K, the spectroscopic signatures of both paramagnetic end-caps Mo(dppe)(η-C7H7) and Fe(dppe)Cp* are observed. The properties of [3]n+ are discussed with reference to the parent homobimetallics [{MLx}2(μ-C≡CC6H4C≡C)]n+ [MLx = Fe(dppe)Cp*, [4]n+, and Mo(dppe)(η-C7H7), [5]n+, n = 0, 1, 2]

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