Luis M. Baraldo

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).

Ruthenium polypyridyl phototriggers: from beginnings to perspectives

Octahedral Ru(II) polypyridyl complexes constitute a superb platform to devise photoactive triggers capable of delivering entire molecules in a reliable, fast, efficient and clean way. Ruthenium coordination chemistry opens the way to caging a wide range of molecules, such as amino acids, nucleotides, neurotransmitters, fluorescent probes and genetic inducers. Contrary to other phototriggers, these Ru-based caged compounds are active with visible light, and can be photolysed even at 532 nm (green), enabling the use of simple and inexpensive equipment. These compounds are also active in the two-photon regime, a property that extends their scope to systems where IR light must be used to achieve high precision and penetrability. The state of the art and the future of ruthenium polypyridyl phototriggers are discussed, and several new applications are presented.

Class III Delocalization in a Cyanide‐Bridged Trimetallic Mixed‐Valence Complex

The NIR and IR spectroscopic properties of the cyanide-bridged complex, trans-[Ru(dmap)4 {(μ-CN)Ru(py)4 Cl}2 ](3+) (py=pyridine, dmap=4-dimethylaminopyridine) provide strong evidence that this trimetallic ion behaves as a Class III mixed-valence species, the first example reported of a cyanide-bridged system. This has been accomplished by tuning the energy of the fragments in the trimetallic complex to compensate for the intrinsic asymmetry of the cyanide bridge. Moreover, (TD)DFT calculations accurately predict the spectra of the trans-[Ru(dmap)4 {(μ-CN)Ru(py)4 Cl}2 ](3+) ion and confirms its delocalized nature.

Structure effects of self-assembled Prussian blue confined in highly organized mesoporous TiO2 on the electrocatalytic properties towards H2O2 detection

Here we report the derivatization of mesoporous TiO2 thin films for the preparation of H2O2 amperometric sensors. The coordination of the bifunctional ligand 1,10 phenantroline, 5,6 dione on the surface Ti(IV) ions provides open coordination sites for Fe(II) cations which are the starting point for the growth of a layer of Prussian blue polymer. The porous structure of the mesoporous TiO2 allows the growth, ion by ion of the coordination polymer. Up to four layer of Prussian blue can be deposit without losing the porous structure of the film, which results in an enhanced response of these materials as H2O2 sensors. These porous confined PB modified electrodes are robust sensors that exhibit good reproducibility, environmental stability and high sensitivity towards H2O2 detection.

Communication between Remote Moieties in Linear Ru−Ru−Ru Trimetallic Cyanide-Bridged Complexes

In this article, we report the structural, spectroscopic, and electrochemical properties of the cyanide-bridged complex salts trans-[(NC)Ru(II)(L)4(μ-CN)Ru(II)(py)4Cl]PF6 and trans-[Ru(II)(L)4{(μ-CN)Ru(II)(py)4Cl}2](PF6)2 (L = pyridine or 4-methoxypyridine). The mixed-valence forms of these compounds show a variety of metal-to-metal charge-transfer bands, including one arising from charge transfer between the remote ruthenium units. The latter is more intense when L = 4-methoxypyridine and points to the role of the bridging ruthenium unit in promoting mixing between the dπ orbitals of the terminal fragments.

Exchange coupling across the cyanide bridge: structural and DFT interpretation of the magnetic properties of a binuclear chromium(III) complex

The reaction of [Cr(CN)6]3- with a mixture of trans-[Cr(cyclam)(OH)2]Cl, [Cr(cyclam)(OH)Cl]Cl and [Cr(cyclam)Cl2]Cl affords the cyanide bridged dimer, trans-[HO-Cr(cyclam)-NC-Cr(CN)5]-. The tetraphenylphosphonium salt of the anion crystallizes in space group P2(1)/n and shows a bent arrangement of the Cr1-CN-Cr2 unit with the Cr1-CN bond angle at 166.9 degrees and CN-Cr2 at 160.32 degrees . The Cr2-O bond, trans to the hexacyanide fragment, is very short at 1.902 A. Two dimers are held together by two hydrogen bonds connecting the Cr2-OH group of each dimer with one of the NH groups of the cyclam ligand of an adjacent molecule, leading to an almost linear configuration. These dimers of dimers get packed parallel to each other, generating layers separated by the tetraphenylphosphonium cations. Four of the cyanide groups of the anion are engaged in H-bonds with the four water molecules present in the structure or with a NH group of the macrocycle of an adjacent molecule. From magnetic susceptibility measurements, the dimer was found to exhibit antiferromagnetic interaction between the Cr(III) centers with J=-16 cm(-1)(H=-2JS(A)S(B)). Structural and magnetic parameters have been calculated by density functional theoretical methods at the B3LYP level. The exchange coupling constant, J, calculated for the dimer at the X-ray geometry is -23.2 cm(-1) which is in excellent agreement with the experimental value.

Properties of the mixed-valence binuclear complex ion, (NH3)5RuIII-NC-OsII(CN)5]−

Abstract The mixed-valence ion, [(NH 3 ) 5 Ru III -NC-Os II (CN) 5 ] − , was prepared in solution from [Ru(NH 3 ) 5 H 2 O] 3+ and [Os(CN) 6 ] 4− and was isolated as a potassium salt. A kinetic study of the formation reaction shows that a dissociative mechanism is operative, the process being rate-controlled by the loss of water from the Ru(III) moiety, as in related reactions with [Fe(CN) 6 ] 4− and [Ru(CN) 6 ] 4− . The binuclear ion shows a distinctive intervalence band, associated to charge transfer from Os(II) to Ru(III), at 830 nm (ϵ=3450 M −1 cm −1 ), with a noticeable asymmetry, probably associated to spin-orbit coupling. Shifts in the redox potentials at the metal centers on dimer formation are consistent with the Os(II)-Ru(III) formulation. By measuring solution Raman spectra in post-resonance conditions with respect to the IT band, activation of the bridging CN stretching, as well as of the terminal stretching modes, is observed; absolute distortion values for both of the modes can be calculated by applying a time-dependent analysis of the scattering problem. IR and Raman results of the solid samples are also presented. Theoretical models were applied to IT data, allowing an estimation of the delocalization parameter, α 2 , and the electronic coupling parameter, H AB . The results are compared with other valence-trapped binuclear systems.

Reactivity and spectroscopy of the {Ru(DMAP)5} fragment: an {Ru(NH3)5} analogue.

Reaction of trans-Ru(DMSO)4Cl2 with DMAP (DMAP = 4-dimethylaminopyridine) yields the yellow [Ru(DMAP)6](2+) cation in good yield. The crystal and molecular structure of [Ru(DMAP)6]Cl2.6CH3CH2OH was determined by X-ray diffraction methods. The complex crystallizes in the trigonal R3 space group with a = b = 16.373(1), c = 20.311(1) A, gamma = 120 degrees , and Z = 3 molecules per unit cell. The reaction of [Ru(DMAP)6](2+) in aerobic water gives the red [Ru(III)(DMAP)5(OH)](2+) cation. This complex shows a chemical behavior similar to [Ru(III)(NH3)5Cl](2+) and allows the preparation of a family of [Ru(DMAP)5L](n+) complexes. Their electronic properties indicate that the {Ru(II)(DMAP)5} fragment is a weaker pi-donor than {Ru(II)(NH 3)5}. Our density functional theory (DFT) calculations show that in {Ru(II)(DMAP)5} the DMAP ligands can compete for the pi electron density of the ruthenium making the fragment a weaker pi-donor.

4,4'-Bis(N,N-diethylamino)-2,2'-bipyridine.

The title compound, C(18)H(26)N(4), contains two almost identical independent molecules that lie about inversion centres. Each molecule has a planar bipyridine nucleus and two terminal diethylamine groups oriented at almost right angles to the core. These diethylamine branches act as spacers, producing a very open structure with one of the lowest densities reported among related compounds. The most important intermolecular interactions are of the C-H...pi type, which connect non-equivalent moieties.

A complex containing three different kinds of Ru-N bonds: Ethoxydinitronitrosyl(N, N, N', N'-tetramethylethylenediamine-κ2N, N')ruthenium(II)

The octahedral title compound, [Ru(C(2)H(5)O)(NO)(NO(2))(2)(C(6)H(16)N(2))], crystallizes in the rhombohedral space group P3(1) with an ethoxy ligand axially coordinated trans to the nitrosyl ligand. The RuII ion is equatorially coordinated by a tetramethylethylenediamine group acting as a bidentate ligand, and to two nitro moieties whose planes are tilted with respect to the mean equatorial plane. Each nitrogen ligand bonded to the metallic centre has a different hybridization state.