Tris Bipyridine Complex Research Articles

Test of the orbital-based LI3 index as a predictor of the height of the [formula omitted]MLCT [formula omitted][formula omitted]MC transition-state barrier for gas-phase [Ru(N[formula omitted]N)[formula omitted]][formula omitted] polypyridine complexes

Ruthenium(II) polypyridine compounds often luminesce, with ligand-dependant lifetimes. This is the third in a series of papers devoted to finding orbital-based luminescence indices (LI) for predicting luminescence lifetimes. The third attempt (LI3) was based upon a frontier molecular orbital (FMO) like estimate of the height of the barrier to conversion from an initial phosophorescent triplet metal-ligand charge transfer (3MLCT) state to a nonluminescent triplet metal-centered (3MC) state which decays nonradiatively. A linear correlation was found between LI3 and extracted empirical average 3MLCT →3MC transition state (TS) barrier heights (Eaves) which were not believed to be quantitative but which were believed to capture the trends in the true barrier heights correctly. As it is known that Eave is a large underestimate of the true 3MLCT →3MC TS barrier height in the case of the trisbipyridine ruthenium(II) cation { [Ru(bpy)3]2+ }, but accurate TS barrier heights are difficult to obtain experimentally, it was judged useful to verify the ideas used to derive the LI3 index in the present work by calculating the energetics of the gas-phase 3MLCT →3MC reaction for a series of ruthenium(II) tris bipyridine complexes using the same density functional and basis sets used in calculating LI3. Specifically, four closely-related bipyridine complexes { [Ru(N∧N)3]2+ with N∧N = bpy (6), 4,4’-dm-bpy (70), 4,4’-dph-bpy (73), and 4,4’-DTB-bpy (74) } were used for these calculations. In the process, we examined the gas-phase trans dissociation mechanism in greater detail than has been previously done and uncovered a two part mechanism. In the first part, the electron is transferred to a single ligand rather than symmetrically to all three ligands. It is the two Ru-N bonds to this ligand which are equally elongated in the transition state. The intrinsic reaction coordinate then continues down a ridge in hyperspace and bifurcates into one of two symmetry-equivalent 3MC structures with elongated trans bonds. Interestingly, no significant difference is found for the TS barriers for the four complexes treated here. Instead, LI3 is linearly correlated with the energy difference ΔE=E(3MLCT)−E(3MC), different from what was originally intended but still consistent with the FMO arguments underlying the derivation of LI3.

Synthesis of Ruthenium (II) trisbipyridine complex containing ionic liquids immobilized on fibrous CoMn2O4 for isolation of asphaltene from petroleum

The formation of a durable nanoadsorbent, known as DFCoMn2O4/IL@Ru(II), was achieved by binding a complex of Ru (II) trisbipyridine with ionic liquids (IL) to a dendritic fibrous CoMn2O4 (DFCoMn2O4). The resulting DFCoMn2O4/IL@Ru(II) was characterized using various techniques such as X-ray diffraction analysis (XRD), fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and scanning electron microscopy (SEM). DFCoMn2O4/IL@Ru(II) was then employed as an environmentally friendly adsorbent for the removal and adsorption of asphaltene from petroleum. The presence of fibrous CoMn2O4 categories enhanced the adsorption capacity and facilitated the recovery of the adsorbent without significantly reducing the efficiency. The results demonstrated a clear synergistic effect between dendritic fibrous CoMn2O4 and the IL@Ru(II) categories, exhibiting a strong correlation.The utilization of the DFCoMn2O4/IL@Ru(II) system resulted in quasi-second-order adsorption kinetics. The experiment was conducted using the Taguchi method to minimize costs and time. Various amounts of asphaltene, temperatures, and adsorbent quantities were examined. Minitab software was deployed to evaluate the impact of these variables on asphaltene adsorption. The presence of ionic liquid groups enhanced the solubility of the heterogeneous adsorbent in environmentally friendly solvents, thereby enhancing function and reducing the time.

Probing the strong electron-acceptor property of pyridine-appended 1,2,3-benzotriazole ligand in tris-homoleptic Ru(II) and Fe(II) complexes

In order to probe the σ-donor/π-acceptor properties of the fused triazolo-based pyridine-appended bidentate ligand, 1-(pyridin-2-yl)-1H-benzo[d][1–3]triazole (BTZ-2P), two discrete octahedral tris-homoleptic complexes, [Ru(BTZ-2P)3](PF6)2 (1) and [Fe(BTZ-2P)3](ClO4)2 (2) were synthesized and well characterized for the first time. Crystal structures of the complexes revealed the key geometrical parameters which highlighted the metal-ligand bonding characteristics in the complexes, especially the strong π-acceptor property of the ligand. The bonding with the BTZ-2P ligand resulted in simultaneous stabilization of the HOMO and destabilization of the LUMO of both the metal complexes, leading to anodic shift of the MII/III redox potential and blue shift of the MLCT band in absorption spectroscopy in comparison to their analogous Ru(II) and Fe(II) tris-bipyridine complexes. Experimental results and theoretical calculations confirmed that in addition to being a good σ-donor, the BTZ-2P ligand exhibits strong π-acceptor property as well compared to the classic 2,2′-bipyridine ligand. This disclosure can have future implications in stabilizing low-valent transition metal complexes with the BTZ-2P ligand.

Electrocatalyst decomposition pathways: torsional strain in a second sphere proton relay shuts off CO2RR in a Re(2,2'-bipyridyl)(CO)3X type electrocatalyst.

Group 7 tris(carbonyl) bipyridine complexes have been well explored as important CO2 reduction reaction (CO2RR) electrocatalysts and now represent an excellent platform for catalyst design. Recent synthetic focus has been on the installation of proton sources/relays within the primary/secondary coordination sphere. These proton sources have been implicated in directly assisting catalysis by acting as shuttles for proton transfer or through the stabilization of transition states through hydrogen bonding. Herein, we report a new ligand system for CO2RR electrocatalysts, which features an aryl amine appended to a quinoline-bipyridine core. While the geometrical arrangement of the aryl amine seems amenable to assisting CO2RR electrocatalysis, we find, through spectroelectrochemical and chemical reduction studies, the torsional strain imposed on the ligand induces a structural reorganization through loss of a hydrogen atom radical. This new complex, which utilizes the anionic nitrogen as a donor atom, and other Re complexes with the same coordination motif, have been found to be entirely inactive for CO2RR. Subsequent reduction yields hydrogenation of the complex through dearomatization of the quinoline backbone concomitant with decomposition products. While the electrocatalytic capability of the reported complexes is moderate, the study represents an important investigation into the deactivation of CO2RR electrocatalysts as a consequence of typical proton shuttle moieties and guides future ligand design by highlighting an oft overlooked structural parameter.

Imbroglio at a photoredox-iron-porphyrin catalyst dyad for the photocatalytic CO 2 reduction

We have covalently connected the ruthenium trisbipyridine complex (bpyRu) as a photoredox module to an iron porphyrin catalyst (porFe) through an amido function for investigating the synergistic action to power the photocatalytic CO2 reduction. The electrochemical studies of the porFe-bpyRu dyad did not show any marked effect on the redox properties of the constitutive units. However, the photophysical properties of the porFe-bpyRu dyad point to the complete extinction of the photoredox module that undergoes ultrafast quenching processes with the porFe acolyte, the unavoidable dilemma in this type of molecular assemblies. Nevertheless, when exogenous bpyRu and a sacrificial electron donor were added to this dyad, we found that it exhibits much higher turnover number and selectivity towards CO2 photocatalytic reduction to CO than with the iron porphyrin analogue (porFe). Comprehensive analyses of the data suggest that this catalytic enhancement displayed by the dyad can be attributed to an interesting electron relay role played by the appended bpyRu moiety.

Analysis of Iron (III) Perchlorate at Magnetically Modified Electrodes

Electrochemical reactions drive many chemical processes using well established protocols and hardware. Most improvements of electrochemical reactions require substantial changes to existing protocols and equipment, However, our previous work has shown that electrochemical systems may be impacted by the presence of magnetic field gradients at the electrode surface. Using ion exchange polymer films with embedded magnetic microparticles, it is possible to improve reaction kinetics. Previous cyclic voltammetric studies of metal tris-bipyridine complexes at electrodes modified with composite films of Nafion and magnetized microparticles exhibit substantially higher currents than at electrodes modified with simple Nafion films.The aim of this study is to show magnetic field gradients can enhance currents for redox probes other than metal tris-bipyridine complexes and to use methods alternative to cyclic voltammetry (CV). Iron (III) perchlorate is the first transition metal species evaluated by impedance to exhibit enhanced electron transfer rates at electrodes modified with magnetized microparticles in Nafion. The enhancement is attributed to improvements in kinetics of heterogeneous exchange rate and self exchange rate.Electrochemical impedance spectroscopy (EIS) and CV studies at magnetically modified electrodes are compared to non-magnetic analogs for the iron (III) perchlorate redox couple. This redox couple shows kinetic rate enhancements for the magnetically modified electrodes over the non-magnetic analogs.

FPS/[Fe(Bpy)3]2+ NPs as a nanocatalyst for production of quinoline-2-ones through the annulation of ortho-heteroaryl anilines and CO2

Carbon dioxide (CO2) play a basic role as a sustainable feedstock during chemical synthesis. The considered approach should be moderated to be viable. Iron(II) trisbipyridine complex [Fe(Bpy)3]2+ supported over fibrous phosphosilicate (FPS) utilizing dipyridin ligands has been determined as highly valuable catalysts of cycloaddition of ortho-heteroaryl anilines with CO2 during the synthesis of quinoline-2-ones. The mentioned materials possess various eco-friendly properties like high catalytic activity and easy to recovery from the reaction mixture using the method of filtration, and various reuse times without losing the efficiency.

Synthesis and characterization of a novel ruthenium(ii) trisbipyridine complex magnetic nanocomposite for the selective oxidation of phenols.

Anchoring ruthenium(ii) trisbipyridine complex [Ru(Bpy)3]2+ into a magnetic dendritic fibrous silica nanostructure produces an unprecedented strong nanocatalyst, FeNi3/DFNS/[Ru(Bpy)3]2+. Impressive oxidation of phenols to 1,4-benzoquinones catalyzed by FeNi3/DFNS/[Ru(Bpy)3]2+ is obtained in acetonitrile and water solution with molecular dioxygen as oxidant. Exclusively, apparently inert phenols such as phenol itself and mono-alkyl-substituted phenols are impressively oxidized to produce 1,4-benzoquinones through activation of the C–H bond in the position para to the carbon–oxygen bond under mild conditions. In addition, the production of industrially significant quinones that are known intermediates for vitamin combinations is investigated and studied FeNi3/DFNS/[Ru(Bpy)3]2+ magnetic nanoparticles were produced, and their properties were investigated by AFM, FTIR, XRD, TGA, SEM, TEM, and VSM.

Visible‐Light‐Driven Reduction of CO2 to CO and Its Subsequent Valorization in Carbonylation Chemistry and 13C Isotope Labeling

AbstractA convenient and safe approach in valorizing carbon monoxide (CO) produced from the photocatalytic reduction of carbon dioxide (CO2) has been investigated. Visible light was used to drive an optimized photocatalytic reduction using a ruthenium trisbipyridine complex as a sensitizer and a rhenium bipyridyl carbonyl complex as a catalyst to perform an efficient reduction of CO2 to CO, which was then simultaneously utilized in a palladium‐catalyzed aminocarbonylation reaction at room temperature. This approach provides safe handling of the produced CO which also opens the way for a more efficient application of 13C‐isotope and 14C‐radioisotope‐labeled CO2 in pharmaceutically relevant drug labeling.

Covalent and Non-covalent Conjugation of Few-Layered Graphene Oxide and Ruthenium(II) Complex Hybrids and Their Energy Transfer Modulation via Enzymatic Hydrolysis.

Pyrene-containing ruthenium(II) tris-bipyridine complexes have been prepared. These complexes have been non-covalently attached onto the few-layered graphene oxide (GO) sheets through their high binding affinity for flat π-surfaces. Alternatively, the reduced graphene oxide (rGO) sheets have also been covalently functionalized with the ruthenium(II) tris-bipyridine complex. The prepared conjugates have been characterized by transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy, thermogravimetric analysis (TGA), and UV-visible absorption spectroscopy. The energy transfer properties of the resulted conjugates between the graphene and transition metal complexes have been studied via esterase hydrolysis. The energy transfer efficiencies were found to vary with the separation between the donor and the acceptor units.

Silica-Based Nanoparticles as Bifunctional and Bimodal Imaging Contrast Agents.

New bifunctional and bimodal nanoparticles (NPs) have been elaborated and characterised. They are based on silica NPs that incorporate a silylated ruthenium tris-bipyridine complex. The resulting suspension of amine-modified NPs with diameters of 20 nm was post-functionalised with a stable gadolinium ion complex. Interest in these NPs lies mainly in the confinement of optical and magnetic imaging agents (Ru and Gd complexes, respectively) within the NP volume. Their potential use as a bimodal probe (luminescence/magnetic resonance imaging) and theranostic agent (photodynamic therapy/imaging) is described. The biological potential of these NPs has been studied on HCT-116 cells and microscopy and cytotoxicity results are given.

Ultrafast Spin Crossover in [FeII (bpy)3 ]2+ : Revealing Two Competing Mechanisms by Extreme Ultraviolet Photoemission Spectroscopy.

Photoinduced spin-flip in FeII complexes is an ultrafast phenomenon that has the potential to become an alternative to conventional processing and magnetic storage of information. Following the initial excitation by visible light into the singlet metal-to-ligand charge-transfer state, the electronic transition to the high-spin quintet state may undergo different pathways. Here we apply ultrafast XUV (extreme ultraviolet) photoemission spectroscopy to track the low-to-high spin dynamics in the aqueous iron tris-bipyridine complex, [Fe(bpy)3 ]2+ , by monitoring the transient electron density distribution among excited states with femtosecond time resolution. Aided by first-principles calculations, this approach enables us to reveal unambiguously both the sequential and direct de-excitation pathways from singlet to quintet state, with a branching ratio of 4.5:1.

Synthesis, characterization and photophysical studies of novel pyrene labeled ruthenium (II) trisbipyridine complex cored dendrimers

Abstract Two new bipyridine ligands containing, respectively, two and four pyrene units were prepared. The obtained compounds were employed to synthesize new pyrene labeled ruthenium (II) trisbipyridine complex as well as a pyrene labeled ruthenium (II) trisbipyridine cored dendrimer. The obtained bipyridine ligands and the ruthenium complexes were characterized by NMR spectroscopy and MALDI-TOF mass spectroscopy. The optical and photophysical properties of the luminescent macromolecules were studied by absorption and fluorescence spectroscopy. It was noticed that the absorption spectra of the obtained complexes correspond to the sum of the absorption spectra of their components, which indicates a lack of interaction in the ground state. Efficient energy transfer was observed from pyrene units to the metal complex core resulting in the observation of the characteristic ruthenium bipyridine emission band upon excitation at the pyrene absorption wavelength. Moreover, efficient protection to oxygen quenching was remarked in the first generation dendrimer.

A combined computational and experimental study of the [Co(bpy)3]2+/3+ complexes as one-electron outer-sphere redox couples in dye-sensitized solar cell electrolyte media

A combined experimental and computational investigation conducted to understand the nature of the interactions between cobalt II/III redox mediators ([Co(bpy)3](2+/3+)) and their impact on the performance of the corresponding dye-sensitized solar cells (DSCs) is reported. The fully optimized equilibrium structures of cobalt(II/III)-tris-bipyridine complexes in the gas phase and acetonitrile solvent are obtained by the density functional B3LYP method using LanL2DZ and 6-31G(d,p) basis sets. The harmonic vibrational frequencies, infrared intensities and Raman scattering activities of the complexes are also calculated. The scaled computational vibrational wavenumbers show very good agreement with the experimental values. Calculations of the electronic properties of the complexes are also performed at the TD-B3LYP/6-31G(p,d)[LanL2DZ] level of theory. Detailed interpretations of the infrared and Raman spectra of the complexes in different phases are reported. Detailed atomic orbital coefficients of the frontier molecular orbitals and their major contributions to electronic excitations of the complexes are also reported. These results are in good agreement with the experimental electrochemical values. Marcus diagram is derived for the electron transfer reaction Co(II) + D35(+)→ Co(III) + D35 using the Co-N bond length as a reaction coordinate.

Ruthenium polypyridine complexes as sensitizers in NiO based p-type dye-sensitized solar cells: Effects of the anchoring groups

In this contribution, we investigate the photovoltaic performances of four ruthenium trisbipyridine complexes in NiO based dye-sensitized solar cells (DSSC). The four complexes differ by the nature of the anchoring groups, which are either carboxylic acids, biscarbodithioic acids catechol or methyl phosphonic acids. The properties of the dyes were studied by electrochemistry, absorption and emission spectroscopies, surface binding measurements, time-dependent density functional theory (TDDFT) as well as by determining their photoconversion efficiencies in DSSCs under AM 1.5. We show that these simple dyes are relatively efficient sensitizers in NiO-based DSSCs, since some of them give photoconversion efficiencies comparable to that of a standard benchmark dye coumarin C343. We also demonstrate that both catechol and methyl phosphonic acid are promising binding groups for NiO sensitizers to replace classical carboxylic acids in NiO sensitizers and finally we report molecular design rules to elaborate a new generation of better performing ruthenium polypyridine sensitizers.

A theoretical study on the exciton circular dichroism of propeller-like metal complexes of bipyridine and tripodal tris(2-pyridylmethyl)amine derivatives

Time-dependent density functional theory (TD-DFT) has been employed to simulate the circular dichroism (CD) spectra of bipyridyl ruthenium(II) complexes as well as zinc(II) and copper(II) complexes containing tris(2-pyridylmethyl)amine (TPA) derivatives. A qualitative model is used to account for the mechanism by which the bis- and tris-bipyridine complexes (or analogous systems) exhibit exciton CD. The model is further used to predict the sign of the exciton CD bands. The predictions are in agreement with experiment and DFT calculations. A comprehensive analysis is presented of the subtle differences in the CD spectra of this series of related complexes.

Structural Study of Mixed Crystals of [Zn1−xRux(bpy)3][NaCr(ox)3] Probed by High-Resolution Absorption Spectroscopy and High-Pressure Experiments

In the mixed crystal series of the cubic three-dimensional networks of composition [Zn(1-x)Ru(x)(bpy)(3)][NaCr(ox)(3)] (0 <or= x <or=1, ox = C(2)O(4)(2-), bpy = 2,2'-bipyridine), high-resolution absorption spectroscopy in the region of the (4)A(2)-->(2)E transition (R-lines) reveals the creation of five specific spectroscopic sites for the [Cr(ox)(3)](3-) complex. The concentration of these spectroscopic sites follows a binomial distribution of [Zn(bpy)(3)](2+) and [Ru(bpy)(3)](2+) among the four nearest neighbors of a given [Cr(ox)(3)](3-) complex within the network. The tris-bipyridine complexes occupying those positions have an optimal pi-pi interaction with the oxalate ligands of the tris-oxalate chromophore. The energy of each spectroscopic [Cr(ox)(3)](3-) site depends on the total concentration of [Ru(bpy)(3)](2+) in the mixed crystal and on its specific distribution among the four nearest neighbors. Single crystal X-ray diffraction indicates a reduction of the unit cell volume when [Zn(bpy)(3)](2+) (a = 15.6365(18) A) is substituted by [Ru(bpy)(3)](2+) (a = 15.5098(6) A). This alone would lead to a red-shift of the R lines in analogy to the red-shift of 25.2 cm(-1)/GPa due to the decrease of the metal ligand Cr-O bond length as observed in high-pressure luminescence experiments. However, specific pi-pi interactions with the nearest neighbors have the opposite effect and shift the transition in discrete jumps to higher energies with increasing [Ru(bpy)(3)](2+) mole fraction.

Selective Protein‐Surface Sensing Using Ruthenium(II) Tris(bipyridine) Complexes

Inhibition of protein–protein interactions (PPIs) with designed molecules represents a key challenge in modern bio-organic chemistry.[1–3] In contrast to competitive enzyme inhibition,[4] in which small molecules are optimised to masquerade as a substrate (or transition-state analogue) and fit a well defined concave pocket or cleft, competitive inhibition of PPIs requires a molecule that must make discontinuous, noncovalent contacts over a much larger (>800 A2), surface-lacking, defined shape. Whilst high-throughput screening has identified inhibitors of some PPIs,[5,6]—these are generally regarded as ‘low-hanging fruit’[2]—there remains a need to develop our basic understanding of how to design molecules that possess the features needed for protein-surface recognition. Building on fundamental studies of short peptide recognition,[7–9] a number of approaches in which a scaffold is used to project groups capable of making multivalent hydrophobic,[10] ion-pairing[11–29] and metal–ligand interactions[30–33] with proteins have been described. In the current manuscript we illustrate that functionalised RuII tris-bipyridine complexes can be used as selective and low nanomolar sensors for cytochrome c (cyt c).[34] Receptors for cyt c have been described[11–13,16–18,20–26] in addition to inhibitors of its PPIs.[35–37] The current system, however, offers significant advantages for fundamental studies of protein-surface recognition. Binding to metalloproteins and nonmetalloproteins can be detected by using simple fluorescence quenching or anisotropy changes, respectively, whilst structure–affinity studies and screening against a panel of proteins point to specific interactions with the target. Importantly, the highest affinity receptor binds cyt c with 1:1 stoichiometry and an affinity of 2 nm.

Transition-Metal Tris-Bipyridines Containing Three Dithienylcyclopentenes: Synthesis, Photochromic, and Electrochromic Properties

Designed prototype molecules for making a three-terminal single-molecule device, star-shaped Fe(II), Co(II), and Ru(II) tris-bipyridine complexes containing three dithienylcyclopentenes, have been synthesized and characterized. All complexes displayed reversible photochromic behavior when irradiated with UV or visible light. The open form of these complexes could be cyclized electrochemically as revealed by cyclic voltammetric studies and bulk electrolysis experiments.

Photoinduced electron transfer in ruthenium(ii) trisbipyridine complexes connected to a naphthalenebisimidevia an oligo(phenyleneethynylene) spacer

The preparation and the characterization of three new dyads composed of a ruthenium trisbipyridine complex linked to a naphthalene bisimide electron acceptor via a phenyleneethynylene spacer of different length (one or two units) are reported. The dyads also differ by the anchoring position of the spacer on the bipyridine, which is appended either at the 4-position or the 5-position. Cyclic voltammetry and the UV-Vis absorption spectroscopy suggested that the spacer linked at the 5-position ensures a longer π-conjugation length but the electron transfer rates indicate a lower electronic coupling, than in 4-position. Photoinduced emission yields indicate a significant quenching of the MLCT excited-state of the ruthenium complex in these dyads. Except for the dyad linked in 5 position with one phenyleneethynylene unit, the transient absorption spectroscopy of all the other dyads evidences that the MLCT excited-state decays almost exclusively by electron transfer to form the charge-separated state RuIII–NBI−. This state could not be observed, presumably because the subsequent recombination to the ground state was much faster than its formation. In the dyad linked in 5 position with only one phenyleneethynylene unit, at room temperature, the 3MLCT* state is in equilibrium with the 3NBI* state, and it also decays via electron transfer. The notable feature of these dyads is first the occurrence of a relatively long-range electron transfer reaction via a bis(phenylethynylene) linking unit anchored at the 5 position. Secondly, we show within these series of compounds that subtle variations in the structure of the dyads (length of the spacer and anchoring position on bipy) have a strong impact on the rates and in the mechanism of decay of the 3MLCT* state. The photophysical properties of the dyads can be explained in terms of energy proximity of different excited states and magnitude of the electronic coupling according to the anchoring position.