Bipyridine Ruthenium Research Articles

Spectroelectrochemical and photophysical properties of a (3,4-pyridyl) porphyrazine supermolecule containing four [Ru(bipy) 2Cl] + groups

Tetra(3-pyridyl)porphyrazine has been modified with four peripheral [Ru(bipy) 2CI] + groups, yielding a novel, dark green supramolecular species. The spectroscopic and electrochemical properties of the tetraruthenated porphyrazine have indicated a significant electronic interaction between the central and peripheral groups. In addition, fluorescence emission from the porphyrazine center has been observed at room temperature either by direct excitation at the Soret and Q bands, or by excitation at the peripheral ruthenium–bipyridine complexes, evidencing an efficient antenna effect. The generation of 1 O 2 species from the porphyrazine excited triplet states has also been demonstrated.

Volume Changes Correlate with Enthalpy Changes during the Photoinduced Formation of the 3MLCT State of Ruthenium(II) Bipyridine Cyano Complexes in the Presence of Salts. A Case of the Entropy−Enthalpy Compensation Effect

The total structural volume (ΔVstr) and enthalpy (ΔHstr) changes associated with the formation of the triplet metal-to-ligand charge transfer (3MLCT) state were determined by laser-induced optoacoustic spectroscopy for the complexes Ru(bpy)32+, Ru(bpy)2(CN)2, and Ru(bpy)(CN)42- in aqueous solutions of 0.1 M monovalent salts. For the cyano complexes (bound to water through hydrogen bonds) the values of ΔVstr vs ΔHstr exhibited a linear relationship in the salt series, whereas for Ru(bpy)32+ the values were independent of the salt. This linear correlation is interpreted as arising from an enthalpy−entropy compensation effect of the water structure perturbed by the 0.1 M salts. Since in all cases the intrinsic energy of the 3MLCT state was unperturbed by the salts (as determined by the constancy of the absorption and emission spectra), the plots ΔHstr vs ΔVstr (the latter shown to be proportional to ΔSstr) yield the free energy for the formation of the 3MLCT state, ΔGMLCT = (123 ± 8) kJ/mol for Ru(bpy)2(CN)2 and (67 ± 25) kJ/mol for Ru(bpy)(CN)42-. The higher stability of the 3MLCT state of Ru(bpy)(CN)42- is due to the larger entropic factor which originates in the high flexibility photoinduced in its 3MLCT state by the loosening of four CN-bound water molecules, rather than only two in Ru(bpy)2(CN)2. The correlation ΔVstr vs ΔSstr (a consequence of the correlation between the environment reorganization parameters ΔVsol and ΔSsol) finds support in the proportionality between ΔVstr of the cyano complexes and the calculated water-structuring entropy of the salts, ΔS°str(salt). Water structuring salts [negative ΔS°str(salt) values] afforded a larger ΔVstr, due to the extension of the water network, opposite to structure breaking salts [positive ΔS°str(salt) values] which yielded smaller ΔVstr values. For Ru(bpy)(CN)42- the linear dependence had twice as large a slope as for Ru(bpy)2(CN)2, reflecting the difference in the number of hydrogen-bound CN groups.

Electron Transfer Photofragmentation Reactions in Monolayer Films at the Air/Water Interface

A series of photoinduced electron-transfer fragmentation reactions have been studied in compressed monolayer films at the air/water interface. The reactions investigated involve amphiphilic and polymeric derivatives of fragmentable amino alcohol, 1,2-diamine, and pinacol donors and light-absorbing acceptors, which are reactive in solution-phase studies from their triplet states. For intralayer studies a surfactant anthraquinone derivative was the light-absorbing acceptor. For comparable interfacial studies, the water soluble cation tris(2,2'-bipyridine)ruthenium(II)2+ (Ru(bpy) 32+) was the photoactive acceptor from the subphase. The fragmentation reactions all involve oxidative cleavage of a relatively strong C-C bond in the donor. Reaction was followed in each case by monitoring changes in surface pressure that occur when the compressed film is irradiated and maintained at a constant area. Reaction was readily observed in most cases where the donor and light-absorbing substrate are present; however the consequences were found to be quite dependent upon the specific donor substrate. Thus for simple single-chain amphiphiles containing either amino alcohol or 1,2-diamine donor sites, both intralayer and interfacial reactions result in rapid decrease in surface pressure, consistent with destruction of the film as the more hydrophilic redox products are solubilized into the subphase. For a polymeric diamine, much more complex behavior is observed, consistent with a situation where single fragmentation events do not lead to removal of material from the film but multiple fragmentation reactions culminate in film solubilization. Finally, a double-chain amphiphilic pinacol was found to undergo interfacial fragmentation with Ru(bpy) 32+ in the subphase with a concurrent increase in surface pressure to form stable films that do not dissolve' into the subphase. The isotherms observed following irradiation, decompression, and recompression are consistent with an expansion that occurs as the two-chain amphiphile undergoes redox fragmentation to produce two equivalents of a single-chain amphiphile.

Electrochemical recognition of alkali metal cations by electrodes modified withpoly[tris-(2,2′-bipyridine) ruthenium(II)] films

The electrochemical behavior of tris-substituted bipyridine ruthenium (II) complexes containing the aza-crown-substituted 2,2′-bipyridine ligands L 2 and L 3 (L 2 is 4,4′-disubstituted by 1-aza-18-crown-6 moieties; L 3 is bridged at its 4,4′-positions by a 4,13-diaza-18-crown-6 group), has been studied by cyclic voltammetry in acetonitrile electrolyte, and in the presence of alkali metal cations (Li +, Na +, K +). Cyclic voltammetry curves show that these complexes are able to recognize potentiometrically a metal cation. The L 2-based complex is sensitive to Li + and Na + cations, while the L 3-based complex is only sensitive to the presence of potassium ions. Glassy carbon electrodes have been modified by electropolymerization ofthe related complexes containing pyrrole-substituted bipyridine ligands. The electrochemical behavior of the resulting redox-active films in the presence of the surveyed alkali metal cations shows that the electrochemical recognition properties of these complexes are mainly retained after their immobilization onto an electrode surface, which is a prerequisite to the construction of new prototypes of electrochemical sensor.

Chemiluminescence occurring upon decomposition of dimethyldioxirane adsorbed from the gas phase onto a silipor surface in the presence of tris(bipyridine)ruthenium(II) and 9,10-diphenylanthracene

Chemiluminescence arising upon decomposition of dimethyldioxirane adsorbed from the gas phase onto a silipor surface containing tris(bipyridine)ruthenium(II) and 9,10-diphenylanthracene has been found and some mechanisms of activation have been suggested.

Unprecedented luminescence behaviour and structural characterization of a novel class of ruthenium(II) 2,2′-bipyridine complexes with orthometallated aminocarbene ligands

Novel luminescent ruthenium(II) bipyridine complexes with orthometallated aminocarbene ligands have been prepared and their photophysical properties studied.

Ruthenium(II) bipyridine complexes with modified phenolic Schiff base ligands. Synthesis, spectroscopic characterization and Redox properties

A group of stable new ruthenium(II) mixed-ligand tris-chelated complexes of the type [Ru(bpy) 2L]ClO 4 ( 1–6), (bpy = 2,2′-bipyridine; L = deprotonated form of the HL ligands, o-(HO)C 6H 3(R)C(R′)NCH 2C 6H 5 or o-(HO)C 6H 3(R)C(R′)NNHC 6H 5; where R = H, p-NO 2 and R′ = H, CH 3) have been synthesized and characterized. The complexes are essentially diamagnetic and behave as 1 : 1 electrolytes in acetonitrile solution. They display two metal-to-ligand-charge-transfer (MLCT) transitions near 500 and 400 nm respectively and intra ligand π-π ∗ transitions in the UV-region. In acetonitrile solution the complexes exhibit weak emission from the lowest energy MLCT band at room-temperature. The quantum yields of the complexes are found to be in the range 0.0004–0.01. In acetonitrile solution the complexes show quasi-reversible ruthenium(II)-ruthenium(III) oxidation couples in the range 0.33 a ̊ 0.70 V and irreversible ruthenium(III)-ruthenium(IV) oxidations in the range 1.53 a ̊ 1.95 V vs SCE . Two successive reversible bipyridine reductions are observed for each complex in the ranges −1.4 a ̊ −1.62 V and −1.59 a ̊ −1.85 V vs SCE respectively. The presence of trivalent ruthenium in the oxidized solution for one complex 5 is evidenced by the rhombic EPR spectrum with g values, g 1 = 2.389, g 2 = 2.081 and g 3 = 1.810. The EPR spectrum of the coulometrically oxidized species, 5 + has been analyzed to furnish values of axial ( Δ = 4745 cm −1) and rhombic (V = 3692 cm −1) distortion parameters as well as the energies of the two expected ligand field transitions ( ν 1 = 3071 cm −1 and ν 2 = 6819 cm −1) within the t 2 shell. One of the ligand field transitions has been observed experimentally at 6578 cm −1 by near-IR spectrum which is close to the computed ν 2 value.

ルテニウム（ＩＩ）多核金属錯体のＥＳＩ‐ＭＳ

A number of polynuclear ruthenium(II), rhodium(III), and cobalt(III) bipyridine complexes have been examined by electrospray ionization mass spectrometry (ESI-MS). ESI-MS is shown to be a powerful tool for the identification of polymetallic complexes and for detecting the contamination, because ESI mass spectra for the complexes showed a simple enough mass pattern for easy structural assignment. Multiply charged ions with the charge state from 8+ to 3+ were observed in the full scan ESI mass spectra of star-burst type tetranuclear complexes denoted by [Met(II)(bpy)2B]3RuX8 (Met=Ru, Os, and bpy=2,2′-bipyridine, B=bridging ligands, X=ClO4-). Different charged ions were found to be generated by the combination of counterion loss and protonation/deprotonation at the proton site of the bridging ligand B. These ion intensities are qualitatively explained in terms of acidity of metal complexes depending upon bridging ligand structures and the charge of metal ions. Ions produced by a removal of ligands were not observed in the ESI spectra unlike the FAB spectra. For tetranuclear complexes, collision-induced dissociation (CID) of the multiply charged ions has made it clear that loss of one or more HX neutral is a major process for lower charge states, while complete fragmentation takes place for higher charge states and the fragments are based on a subunit group of [Met(II)(bpy)2B]2+. Insertion of formal O2- produced from ClO4- counterion was observed for the complexes without active protons even if low energy CID experiments, but not for the complexes with active protons. Advantages of ESI mass spectrometry are demonstrated for these polynuclear compounds and CID chemistry of the investigated ions will be discussed.

Intercalation of Tris(2,2′-bipyridine)ruthenium(II) into Magadiite

Intercalation of Tris(2,2′-bipyridine)ruthenium(II) into Magadiite

ELECTROCHEMISTRY OF CALIXARENE AND ITS ANALYTICAL APPLICATIONS

The electrochemistry of calixarene as a redox-dependent ionophore and its structural dependence are described. One or more redox-centers such as quinone, ferrocene, cobaltocenium and ruthenium bipyridine moieties have been introduced into the calixarene frame of the lower or upper rim. Although the electrochemical behavior depends mainly on the inherent redox property of these electrochemically active groups, the structural effect and solvent also play important roles, especially, in the presence of charged guests. When cationic species such as metal ions and ammonium ion are added to a quinone-functionalized calixarene solution, electron transfer to quinone is enhanced by the electrostatic effect or the formation of hydrogen bonds. In addition to redox-active hosts for voltammetric use, a number of calixarenes with novel structures have been developed as ionophores for potentiometric analysis and found to be successful for some target ions. In terms of Na+, Cs+ and Ca2+ selective ionophores for ion-selective electrodes, calixarenes are found to be excellent compared to crown ether derivatives or cryptands. Calixarenes can be also utilized to construct chemically modified electrodes, which are sensitive to gas species and biologically important compounds. The sophisticated design and synthesis of calixarenes are essential to specific potential applications to diverse fields.

Quinoxaline‐based conjugated polymers containing ruthenium(II) bipyridine metal complex

AbstractA series of novel quinoxaline‐based conjugated polymers which contain a ruthenium(II) bipyridine complex were synthesized by the Suzuki coupling reactions. UV/VIS spectroscopy showed that the spectral features of the polymers are dependent on the amount of metal complex present. Results from excitation and emission spectroscopy suggest an energy transfer between the backbone and the metal complex. The polymers exhibit hole carrier mobilities of ≈ 10−5 cm2 · V−1 · s−1, which is comparable to organic photoconductors.

Molecular Recognition and Reactivity of Ruthenium(II) Bipyridine Barbituric Acid Guests in the Presence of Complementary Hosts: Ruthenium(II) Promoted Enolization of Barbituric Acids in Guest−Host Complexes

The binding of the host H1 (N,N‘-bis(6-pivalamidopyrid-2-yl)-3,5-pyridinedicarboxamide) to three different ruthenium polypyridine complexes with an attached barbituric acid and barbital moieties (RuG1, RuG2, RuG3) (where G1 = 5-[4-(4‘-methyl)-2,2‘-bipyridylidene]-2,4,6-(1H,3H,5H)-pyrimidinetrione, G2 = 5-[4-(4‘-methyl)-2,2‘-bipyridyl]methyl-2,4,6-(1H,3H,5H)-pyrimidinetrione, and G3 = 5-ethyl, 5-[4-(4‘-methyl)-2,2‘-bipyridyl]methyl-2,4,6-(1H,3H,5H)-pyrimidinetrione) and Ru = (4,4‘-di-tert-butyl-bpy)2Ru (bpy = 2,2‘-bipyridine) has been studied in chlorinated solvents by NMR and fluorescence titrations. Significant binding was only observed between H1 and the RuG2 series, while steric hindrance significantly diminished binding between H1 and RuG1 or RuG3. The high binding constant for RuG2 was related to the presence of the enolate form of the barbituric acid guest which forms strong H-bonds with the complementary host H1. For the organic barbituric acid and barbital guests, the keto and enol bind only weakly to H1 (K ∼ 102 M-1); binding is further increased in the presence of base to generate the enolate. In contrast, formation of the RuG2 enolate occurs upon binding to H1 without any additional base. The ruthenium polypyridine cation (compared to the organic barbituric acid derivatives) facilitates ionization of the enol to enolate thus producing a better complementary H-bonding site between the guest and host. Molecular mechanics calculations confirmed the experimental observatons that the enolate has the highest binding constant to the Host H1, while the corresponding enol form has the weakest binding.

Microfluorometry and image analysis of peritoneal mast cells reveal differences in the morphology and content of sulfated polyanions between normal and tumor-bearing mice

Mast cells (MC) are frequently increased in neoplasias. Recently, we observed that MC from peritoneal cavity of normal mice (NMC) and one of their mediators (heparin) decreased M3 tumor incidence and tumor cell proliferation in vitro, while MC from peritoneal cavity of tumor-bearing mice (TMC) had no effect. The purpose of this study was to evaluate the differences in morphology and content of sulfated glycosaminoglycans between NMC and TMC. Both were stained with Mayer's haematoxylin-Rubipy [tris (2,2'-bipyridine) ruthenium (II)] sequence, a specific technique to detect sulfated polysaccharides. Image processing and analysis (IPA) confirmed densitometric and microfluorometric studies and revealed several structural characteristics of MC. TMC were partially degranulated with smaller surface and greater perimeter than NMC. Shape factor, which reflects the sphericity grade of the cell (1 = spherical), was three-fold increased in TMC in relation to NMC (6.15 vs 1.76, respectively). Also, TMC had less than a half sulfated polysaccharides compared to NMC. We conclude that subcutaneous tumor grafts mediate degranulation of MC from peritoneal cavity with the consequent release of MC mediators such as heparin. This may be one of the factors for the absence of antitumoral effect of TMC.

Excited-State Processes in Ruthenium(II) Bipyridine Complexes Containing Covalently Bound Arenes

The photophysical properties of a series of ruthenium trisbipyridine complexes covalently linked to aromatic chromophores of the type [Ru(bpy)2(4-methyl-4‘-(2-arylethyl)-2,2‘-bipyridine)]2+(ClO4)2,...

Temperature and viscosity dependence of the electron-transfer reaction between plastocyanin and cytochrome c labeled with a ruthenium(II) bipyridine complex

The temperature and viscosity dependence of the photo-induced electron-transfer reaction between plastocyanin and cytochrome c labeled at Lys13 with Ru(4,4′-dicarboxybipyridine)(bipyridine) 2 +2 have been investigated. In these studies, a short pulse of 450 nm light was used to excite the ruthenium complex which was oxidatively quenched by the iron center of cytochrome c. The resulting Fe(II) cytochrome c was then rapidly reoxidized by plastocyanin. The reactions were investigated over a temperature range of 3.5 to 37°C under low ionic strength conditions such that protein/protein complex formation was favored. The enthalpy of activation was 7 kcal mol −1 and the entropy of activation was −20 cal mol −1 K −1. Increasing the viscosity by the addition of sucrose up to 70% resulted in a 4-fold decrease in the rate constant for electron transfer. The overall results suggest a rate-limiting step that involves either dissociation of the dominant protein/protein complex or surface diffusion of the associated proteins.

Oxidation of Disulfides by 4-Electron Transfer to O2: A Ru(bpy)3 2+-Catalyzed Photo-Oxidation System for Selective Formation of Polythioethers

Tris(2,2′-bipyridine)ruthenium(II) chloride catalyzed the photo-oxidative polymerization of diaryl disulfides by O2, by which poly(thioarylene)s were efficiently produced. The polymerization proceeded through the electrophilic reaction of the sulfonium cation which was produced selectively by the photo-redox system.

Singlet and triplet energy transfer processes in ruthenium(II) bipyridine complexes containing covalently bound arenes

Singlet and triplet energy transfer processes in [Ru(bipy) 2(4-methyl-4′-(2-arylethyl)-2,2′-bipyridine)] 2+ have been investigated, where aryl = 2-naphthyl (Ru-Naph), 9-anthryl (Ru-Anth) and 1-pyrenyl (Ru-Pyrene). In each case fluorescence from the aromatic chromophore is quenched by intramolecular energy transfer to Ru(bipy) 3 2+ whereas emission from the Ru(bipy) 3 2+ moiety is controlled by the relative energy of its 3MLCT state and the pendant arene triplet states. Consequently 3MLCT emission is observed for Ru-Naph whereas it is fully quenched for Ru-Anth. When the two states are isoenergetic (e.g. Ru-Pyrene) a long-lived 3MLCT emission is observed which delays with the same lifetime as the pyrene triplet state (5.23 μs).

Control of the co-ordination mode of 1,8-naphthyridine ligated to ruthenium(II) bipyridine complexes

The complexes [Ru(bipy)2(napy-N)(MeCN)][PF6]21 and [Ru(bipy)2(napy-N,N′)][PF6]22(bipy = 2,2′-bipyridine, napy = 1,8-naphthyridine) were prepared, and their crystal structures determined by X-ray analysis. The crystal structure of 1 displays an octahedral co-ordination with monodentate napy, acetonitrile and two chelating bipy. Despite the inequivalency of two nitrogens of napy in 1 in the solid state, the 1H NMR spectra in the aromatic region resemble those of 2 over the range –90 to 60 °C, which implies dynamic behaviour of napy in 1 in solution. Both 1 and 2 were reduced irreversibly at –0.98 V (vs. Ag–AgCl) in dimethylformamide at –20 °C, and the process gradually becomes a reversible redox reaction on increasing the temperature to 30 °C. An EPR study revealed that one-electron reduction of 1 takes place in the napy-localized orbital without appreciable increase in electron density on one of the nitrogens of napy. The distinct inequivalence in the charge density between the two nitrogen atoms of singly reduced napy results in stabilization of the N rather than N,N′ co-ordination mode.

Raman spectroscopy of adsorbates on semiconductors by means of SERS effect

An application of surface enhanced Raman scattering (SERS) to the surface characterization of semiconductors is reported by evaporating an Ag island film onto the surface of the materials. The surface sensitivity of the Raman effect at the metal surface is used for the study of molecules absorbed onto the semiconductors. With this method there is enhanced Raman scattering from the surface because the discontinuous Ag layer produces large electromagnetic enhancement at each Ag particle. SERS spectra are observed from tris(bipyridine)ruthenium, Ru(bpy) 3 2+ , molecules adsorbed on Si, GaAs, InP, silver, and glass substrates onto which an Ag island film has been evaporated. The spectral differences observed between the spectra from the molecules adsorbed on the semiconductors and on the glass and silver substrates allow us to affirm that the SERS signals arise from the substrate surface and not from the Ag island film. Raman scattering cannot be detected from surfaces without the deposited Ag film because the vibrational spectra of molecules adsorbed on the surface are too weak to be detected. These results prove that by using the Ag overlayer method is should be possible to study the properties of adsorbed species on semiconductor surfaces. This suggests the possibility of utilizing the SERS effect as a new surface probe of the semiconductor surface considering that Raman spectroscopy can give detailed information about the state of chemical species on the surface.

Crystal structure, physical, and photophysical properties of a ruthenium(II) bipyridine diazafluorenone complex

The complex [Ru(bpy)2(dafo)](PF6)2, where bpy is 2,2′-bipyridine and dafo is diazafluorenone crystallizes in the space group P21/n witha=9.505(3) A,b=14.002(4) A andc=25.783(8) A. The coordination geometry of the Ru atom is that of a distorted octahedron with a RuN6 core. The two Ru-N bond distances to the dafo ligand are 2.13(1) and 2.15(1) A; the four Ru-N bond distances to the bipyridine ligands are 2.03(1), 2.05(1), 2.06(1), and 2.07(1) A. The three shortest Ru-N distances aretrans to the three longest Ru-N distances. The complex is oxidized and reduced reversibly at 1.41 and −0.65 V vs. SSCE, respectively. It displays absorptions at 438 nm (1.6×104), 285 nm (6.2×104), and 240 nm (4.1×104) and a broad emission centered at 626 nm in water at room temperature. The emission lifetime is 420 ns and the emission quantum yield is 5.3×10−4.