Alejandro R. Parise

Advances in the coordination chemistry of [M(CN)5L]n− ions (M=Fe, Ru, Os)

Abstract New developments in the synthesis, crystal and molecular structure, spectroscopy and kinetic properties of the [M(CN) 5 L] n − ions (M II,III =Fe, Ru, Os; L=H 2 O, NH 3 , amines, CN − , N -heterocyclic ligands, etc.), performed over the last decade, are reviewed. The properties of dinuclear complexes containing pentacyano-fragments bridged by pyrazine, cyanide or other bridging ligands, are also considered, with emphasis on mixed-valent systems. The influence of the solvent and other medium effects on the electronic structure, as well as on the modification of the reactivity of L upon coordination is addressed particularly. Some catalytic processes relevant to bioinorganic chemistry are discussed, involving either ligand oxidation (hydrazine, thiolates) or reduction (nitrosyl).

The valence-localized decacyanodiruthenium(III,II) analogue of the Creutz–Taube ion. Completing the full d5/d6 triad [(NC)5M(μ-pz)M(CN)5]5−, M=Fe,Ru,Os; pz=pyrazine

Abstract The new ruthenium(II) complex ion [(NC) 5 Ru(μ-pz)Ru(CN) 5 ] 6− has been prepared and studied as the hexakis(tetraethylammonium) salt. Although spectroelectrochemical experiments in dichloromethane were affected by adsorption as they were in other solvents, the compound could be oxidized via two reversible one-electron steps with a mixed-valent pentaanionic intermediate. In comparison with the iron and osmium analogues, the system [(NC) 5 Ru(μ-pz)Ru(CN) 5 ] 5− is distinguished by less negative redox potentials, a smaller comproportionation constant K c of only 10 4.7 , a very broad (Δ ν 1/2 =4200 cm −1 ) symmetrical IVCT band at 1760 nm ( e =2600 M −1 cm −1 ) conforming with the Hush model for weakly coupled mixed-valent systems, the absence of an EPR signal even at 3.5 K and the appearance of infrared bands (CN, pyrazine ring vibrations) indicating localized valence on the time scale of 10 −12 s. Together with the high MLCT energies these results suggest a weaker metal–pyrazine interaction for the ruthenium system in comparison with the Fe and Os analogues reported previously. In relation to the Creutz–Taube ion, the substitution of ammine ligands by non-innocent cyanide ions attenuates the metal–metal interaction across the π accepting pyrazine bridge.

Charge transfer properties of Tröger base derivatives

Two triarylamine centers bridged through an aliphatic bridge feature unexpected charge transfer properties, bearing an important electronic coupling between them in the absence of a π linker; EPR, electrochemistry, electronic spectroscopy and first principles molecular calculations are combined to study the electronic structure of this compound.

The crystal and molecular structure of sodium pentacyanoammineferrate(II) heptahydrate. Role of intermolecular hydrogen-bond interactions

Abstract The crystal and molecular structures of sodium pentacyanoammineferrate(II) heptahydrate have been determined by X-ray diffraction. The FeN distance is longer than in the analogous iron(III) complex by 0.06 A; the FeC and CN distances are similar to those for the hexacyanoferrate(II) species, although with a significant relative shortening of the trans FeC bonds. The anions display a chain-like arrangement, with interlinking sodium ions and water molecules H-bonded to cyanide N atoms. By comparing with related structures of pentacyano-L-ferrate(II) ions (L=NO + , CN − ), it results that the binding mode of the L ligand influences strongly both the first- and second-sphere metal–ligand interactions.