Thiocyanate linkage isomerism in a ruthenium polypyridyl complex

Ruthenium polypyridyl complexes have seen extensive use in solar energy applications. One of the most efficient dye-sensitized solar cells produced to date employs the dye-sensitizer N719, a ruthenium polypyridyl thiocyanate complex. Thiocyanate complexes are typically present as an inseparable mixture of N-bound and S-bound linkage isomers. Here we report the synthesis of a new complex, [Ru(terpy)(tbbpy)SCN][SbF(6)] (terpy = 2,2';6',2'-terpyridine, tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine), as a mixture of N-bound and S-bound thiocyanate linkage isomers that can be separated based on their relative solubility in ethanol. Both isomers have been characterized spectroscopically and by X-ray crystallography. At elevated temperatures the isomers equilibrate, the product being significantly enriched in the more thermodynamically stable N-bound form. Density functional theory analysis supports our experimental observation that the N-bound isomer is thermodynamically preferred, and provides insight into the isomerization mechanism.     

Hydrolytic cleavage of DNA by a ruthenium(II) polypyridyl complex

The complex [Ru(bpy)2(BPG)]Cl2 (1) containing hydrogen-bond donor (N-H atoms) and acceptor (O atoms) groups mediates hydrolytic cleavage of plasmid pBR322 DNA in an enzyme-like manner. The kinetic aspects of DNA cleavage under pseudo- and true-Michaelis-Menten conditions are detailed.     

Rapid electrochemically induced linkage isomerism in a ruthenium(II) polypyridyl complex

Rapid and complete switching between the N6 and the N5O donor set induced by changing the metal oxidation state has been observed for a new structural motif based on a ruthenium(II) polypyridyl complex.     

Underlying spin-orbit coupling structure of intervalence charge transfer bands in dinuclear polypyridyl complexes of ruthenium and osmium

The mixed-valence systems meso- and rac-[{M(bpy)2}2(mu-BL)]5+ {M = Ru, Os; BL = a series of polypyridyl bridging ligands such as 2,3-bis(2-pyridyl)benzoquinoxaline (dpb)} are characterized by multiple intervalence charge transfer (IVCT) and interconfigurational (IC) bands in the mid-infrared and near-infrared (NIR) regions. Differences in the relative energies of the IC transitions for the fully oxidized (+6) states of the osmium systems demonstrate that stereochemical effects lead to fundamental changes in the energy levels of the metal-based dpi orbitals, which are split by spin-orbit coupling and ligand-field asymmetry. An increase in the separation between the IC bands as BL is varied reflects the increase in the degree of electronic coupling through the series of ruthenium and osmium complexes. The increase in the IVCT bandwidths for the former is therefore attributed to the increase in the separation of the three underlying components of the bands. Stark effect measurements reveal small dipole moment changes accompanying IVCT excitation in support of the localized-to-delocalized or delocalized classification for the dinuclear ruthenium and osmium systems.     

Assessment of intercomponent interaction in phenylene bridged dinuclear ruthenium(II) and osmium(II) polypyridyl complexes

The synthesis and characterisation of [Ru(bipy)(2)(L1)](2+) and the homodinuclear complexes [M(bipy)(2)(L1)M(bipy)(2)](4+)(where M = Ru or Os), employing the ditopic ligand, 1,4-phenylene-bis(1-pyridin-2-ylimidazo[1,5-a]pyridine)(L1), are reported. The complexes are identified by elemental analysis, UV/Vis, emission, resonance Raman, transient resonance Raman and (1)H NMR spectroscopy, mass spectrometry and electrochemistry. The X-ray structure of the complex [Ru(bipy)(2)(L1)(bipy)(2)Ru](PF(6))(4) is also reported. DFT calculations, carried out to model the electronic properties of the compounds, are in good agreement with experiment. Minimal communication between the metal centres is observed. The low level of ground state electronic interaction is rationalized in terms of the poor ability of the phenyl spacer in facilitating superexchange interactions. Using the electronic and electrochemical data a detailed picture of the electronic properties of the RuRu compound is presented.     

Intervalence charge transfer in the stereoisomers of a dinuclear ruthenium complex containing the bridging ligand dibenzoeilatin

The dinuclear species [{Ru(bpy)2}2(micro-dbneil)]4+(bpy = 2,2'-bipyridine; dbneil = dibenzoeilatin) was separated into its three stereoisomeric forms by cation-exchange chromatographic techniques. The NMR characteristics of the two diastereoisomers (meso and rac) are very similar, consistent with the decreased anisotropic interactions between the terminal bpy ligands located on different ruthenium centres because of their large spatial separation. Spectroelectrochemical measurements of the IVCT transitions in the mixed valence (5+) species show the system to be in the class II-III regime with substantial electronic communication between the metal centres. There is no significant difference in IVCT behaviour between the two diastereoisomers.     

A photosensitizer dinuclear ruthenium complex: intramolecular energy transfer to a covalently linked fullerene acceptor

A fullerene derivative (5) in which a dinuclear ruthenium complex is covalently linked to a fulleropyrrolidine (FP) through a rigid spacer has been prepared through azomethine ylide cycloaddition to C60. Electrochemical and photophysical studies revealed that ground-state electronic interactions between the bimetallic ruthenium chromophore and the FP moiety are small. The absorption spectrum of 5 displays a metal-to-ligand charge transfer (MLCT) transition at about 620 nm in CH2Cl2 which is shifted by nearly 160 nm relative to that of a previously reported mononuclear dyad (8). The photophysical investigations have also shown that both in dichloromethane and acetonitrile the photoexcited MLCT state of dyad 5 transforms into the fullerene triplet excited state with a quantum yield of 0.19 and that, contrary to mononuclear dyad 8, electron transfer, if any under the applied conditions, is negligible relative to energy transfer.     

Formation of a dinuclear imido complex from the reaction of a ruthenium(VI) nitride with a ruthenium(II) hydride

The treatment of [Ru(L(OEt))(N)Cl(2)] (1; L(OEt)(-) = [Co(η(5)-C(5)H(5)){P(O)(OEt)(2)}(3)](-)) with Et(3)SiH affords [Ru(L(OEt))Cl(2)(NH(3))] (2), whereas that with [Ru(L(OEt))(H)(CO)(PPh(3))] (3) gives the dinuclear imido complex [(L(OEt))Cl(2)Ru(μ-NH)Ru(CO)(PPh(3))(L(OEt))] (4). The imido group in 4 binds to the two ruthenium atoms unsymmetrically with Ru-N distances of 1.818(6) and 1.952(6) ?. The reaction between 1 and 3 at 25 °C in a toluene solution is first order in both complexes with a second-order rate constant determined to be (7.2 ± 0.4) × 10(-5) M(-1) s(-1).     

Synthesis and characterization of a dinuclear iron(II) spin crossover complex with wide hysteresis

The magnetic properties and results from X-ray structure analysis for a new pair of iron(II) spin-crossover complexes [FeL1(meim) 2](meim) ( 1(meim)) and [Fe 2L2(meim) 4](meim) 4 ( 2(meim) 4), with L1 being a tetradentate N 2O 2 (2-) coordinating Schiff-base-like ligand [([3,3']-[1,2-phenylenebis(iminomethylidyne)]bis(2,4-pentane-dionato)(2-)N,N',O (2),O (2)'], L2 being an octadentate, dinucleating N 2O 2 (2-) coordinating Schiff-base-like ligand [3,3',3',3']-[1,2,4,5-phenylenetetra(iminomethylidyne)]tetra(2,4-pentanedionato)(2-) N, N', N', N', O (2), O (2) ', O (2) ', O (2) '], and meim being N-methylimidazole, are discussed in this work. Crystalline samples of both complexes show a cooperative spin transition with an approximately 2-K-wide thermal hysteresis loop in the case of 1(meim) ( T 1/2 increase = 179 K and T 1/2 decrease = 177 K) and an approximately 21-K-wide thermal hysteresis loop in the case of dinuclear complex 2(meim) 4 ( T 1/2 increase= 199 K and T 1/2 decrease= 178 K). For a separately prepared powder sample of 2, a gradual spin transition with T 1/2 = 229 K is observed that was additionally followed by Mossbauer spectroscopy. The results from X-ray structure analysis give a deeper insight into the molecule packing in the crystal and, by this, help to explain the increase of cooperative interactions during the spin transition when going from the mononuclear to the dinuclear complex. Both compounds crystallize in the triclinic space group P1, and the X-ray structure was analyzed before and after the spin transition. The change of the spin state at the iron center is accompanied by a change of the O-Fe-O angle, the so-called bite of the equatorial ligand, from about 109 degrees in the high-spin state to 89 degrees in the low-spin state. The cooperative interactions responsible for the thermal hysteresis loop are due to elastic interactions between the complex molecules in both cases. However, due to the higher symmetry of the dinucleating ligand in 2(meim) 4, a 3D network of short contacts is formed, while for mononuclear complex 1(meim), a 2D layer of linked molecules is observed. The spin transition was additionally followed in solution using (1)H NMR spectroscopy for both complexes. In both cases, a gradual spin transition is observed, and the increase of cooperative interactions when going from the mononuclear to the dinuclear system is solely attributed to the extended network of intermolecular contacts.     

Conversion of oxido-bridged dinuclear ruthenium complex to dicationic dinitrosyl ruthenium complex using proton and nitric oxide: completion of NO reduction cycle

The hydroxido-bridged dinuclear ruthenium complex 4, which is supported by Tp ligands, has been prepared from protonation of the oxido-bridged dinuclear ruthenium complex 3. Additional protonation of 4, affording the aqua-bridged dinuclear ruthenium complex 5 in situ, and subsequent treatment with NO gave rise to the dicationic dinitrosyl complex 2. These indicate completion of the NO reduction cycle on the dinuclear ruthenium complex.     

A dinuclear ruthenium(II) complex that functions as a label-free colorimetric sensor for DNA

A dinuclear ruthenium(II) complex groove binds to DNA and this interaction results in distinctive color changes that are dependent on both DNA sequence and structure.     

Molecular conductance switch-on of single ruthenium complex molecules

Thiol-tethered Ru(II) terpyridine complexes were synthesized for a voltage-driven molecular switch and used to understand the switch-on mechanism of the molecular switches of single metal complexes in the solid-state molecular junction in a vacuum. Molecularly resolved scanning tunneling microscopy (STM) images revealed well-defined single Ru(II) complexes isolated in the highly ordered dielectric monolayer. When a negative sample-bias was applied, the threshold voltage to the high conductance state in the molecular junctions of the Ru(II) complex was consistent with the electronic energy gap between the Fermi level of the gold substrate and the lowest ligand-centered redox state of the metal complex molecule. As an active redox center leading to conductance switching in the molecule, the lowest ligand-centered redox state of Ru(II) complexes was suggested to trap an electron injected from the gold substrate. Our suggestions for a single-molecule switch-on mechanism in the solid state can provide guidance in a design that improves the charge-trapping efficiency of the ligands with different metal substrates.     

Highly selective photo-catalytic dimerization of alpha-methylstyrene by a novel palladium complex with photosensitizing ruthenium(II) polypyridyl moiety

A novel dinuclear complex containing the photo-sensitizing Ru unit and a Pd center is effective toward selective catalytic dimerization of alpha-methylstyrene leading to 2,4-diphenyl-4-methyl-1-pentene under visible-light irradiated conditions.     

A binuclear ruthenium polypyridyl complex: synthesis,characterization, pH luminescence sensor and electrochemical properties

Transition Metal Chemistry - The binuclear ruthenium complex [Ru2(bpy)4L](PF6)4 [Ru1(PF6)4, where L?=?9,10-bis(3-(1H-imidazo[4,5-f] [1,10] phenanthrolin-2-yl)phenyl)anthracene and...     

Molecular chemistry in a zeolite: genesis of a zeolite Y-supported ruthenium complex catalyst

Dealuminated zeolite Y was used as a crystalline support for a mononuclear ruthenium complex synthesized from cis-Ru(acac)2(C2H4)2. Infrared (IR) and extended X-ray absorption fine structure spectra indicated that the surface species were mononuclear ruthenium complexes, Ru(acac)(C2H4)2(2+), tightly bonded to the surface by two Ru-O bonds at Al(3+) sites of the zeolite. The maximum loading of the anchored ruthenium complexes was one complex per two Al(3+) sites; at higher loadings, some of the cis-Ru(acac)2(C2H4)2 was physisorbed. In the presence of ethylene and H2, the surface-bound species entered into a catalytic cycle for ethylene dimerization and operated stably. IR data showed that at the start of the catalytic reaction, the acac ligand of the Ru(acac)(C2H4)2(2+) species was dissociated and captured by an Al(3+) site. Ethylene dimerization proceeded approximately 600 times faster with a cofeed of ethylene and H2 than without H2. These results provide evidence of the importance of the cooperation of the Al(3+) sites in the zeolite and the H2 in the feed for the genesis of the catalytically active species. The results presented here demonstrate the usefulness of dealuminated zeolite Y as a nearly uniform support that allows precise synthesis of supported catalysts and detailed elucidation of their structures.     

The pH-induced emission switching and interesting DNA-binding properties of a novel dinuclear ruthenium(II) complex

A novel dinuclear Ru(II) complex, [(bpy)(2)Ru(ebipcH(2))Ru(bpy)(2)](ClO(4))(4), where bpy = 2,2'-bipyridine and ebipcH(2) = N-ethyl-4,7-bis([1,10]-phenanthroline[5,6-f]imidazol-2-yl)carbazole, has been newly synthesized. The pH effects on UV-vis absorption and emission spectra of the complex are studied, and ground- and excited-state ionization constants of the complex are derived. The binding of the complex to calf thymus (ct) DNA is investigated with absorption and luminescence titrations, steady-state emission quenching, and viscosity measurements. The complex acts as a pH-induced "on-off" emission switch between pH 8.0 and pH 10.0 with a maximum on-off ratio of approximately 100 which is favorably compared with the other imidazole-containing Ru(II) complex congeners, and a strong ct-DNA intercalator with an intrinsic binding constant of 1.31(+/-0.08) x 10(6) M(-)(1) in buffered 50 mM NaCl.     

Synthesis and characterization of rigid +2 and +3 heteroleptic dinuclear ruthenium(II) complexes

Synthesis and characterization of the dinuclear ruthenium coordination complexes with heteroleptic ligand sets, [Cl(terpy)Ru(tpphz)Ru(terpy)Cl](PF₆)₂(7) and [(phen)₂Ru(tpphz)Ru(terpy)Cl](PF₆)₃(8), are reported. Both structures contain a tetrapyrido[3,2-α:2′,3′-c:3′′,2′′-h:2′′,3′′-j]phenazine (tpphz) (6) ligand bridging the two metal centers. Complex 7 was obtained via ligand exchange between, RuCl₂(terpy)DMSO (5) and a tpphz bridge. Complex 8 was obtained via ligand exchange between, [Ru(phen)₂tpphz](PF₆)₂(4) and RuCl₂(terpy)DMSO (5). Metal-to-ligand-charge-transfer (MLCT) absorptions are sensitive to ligand set composition and are significantly red-shifted due to more electron donating ligands. Complexes 7–9 have been characterized by analytical, spectroscopic (IR, NMR, and UV–Vis), and mass spectrometric techniques. The electronic spectral properties of 7, 8, and [(phen)₂Ru(tpphz)Ru(phen)₂](PF₆)₄(9), a previously reported +4 analog, are presented together. The different terminal ligands of 7, 8, and 9 shift the energy of the MLCT and the π–π* transition of the bridging ligand. These shifts in the spectra are discussed in the context of density functional theory (DFT). A model is proposed suggesting that low-lying orbitals of the bridging ligand accept electron density from the metal center which can facilitate electron transfer to nanoparticles like single walled carbon nanotubes and colloidal gold.     

Ground- and excited-state electronic structure of an emissive pyrazine-bridged ruthenium(II) dinuclear complex

The synthesis, characterization, and electrochemical, photophysical, and photochemical properties of the binuclear compounds [(Ru(H8-bpy)2)2((Metr)2Pz)](PF6)2 (1) and [(Ru(D8-bpy)2)2((Metr)2Pz)](PF6)2 (2), where bpy is 2,2'-bipyridine and H2(Metr)2Pz is the planar ligand 2,5-bis(5'-methyl-4'H-[1,2,4]triaz-3'-yl)pyrazine, are reported. Electrochemical and spectro-electrochemical investigations indicate that the ground-state interaction between each metal center is predominantly electrostatic and in the mixed-valence form only a low level of ground-state delocalization is present. Resonance Raman, transient, and time-resolved spectroscopies enable a detailed assignment to be made of the excited-state photophysical properties of the complexes. Deuteriation is employed to both facilitate spectroscopic characterization and investigate the nature of the lowest excited states.