In A Ruthenium Research Articles

Proton-Coupled Electron Transfer in a Ruthenium(II) Bipyrimidine Complex in Its Ground and Excited Electronic States.

Proton-coupled electron transfer (PCET) was studied for the ground and excited electronic states of a [Ru(terpy)(bpm)(OH2)(PF6)2] complex, Ru-bpm. Cyclic voltammetry measurements show that the Ru(II)-aqua moiety undergoes PCET to form a Ru(IV)-oxo moiety in the anodic region, while the bpm ligand undergoes PCET to form bpmH2 in the cathodic region. The photophysical behavior of Ru-bpm was studied using steady-state and femtosecond transient UV-vis absorption spectroscopy, coupled with density functional theory (DFT) calculations. The lowest-lying excited state of Ru-bpm is described as a (Ru → bpm) metal-to-ligand charge-transfer (MLCT) state, while the metal-centered (MC) excited state was found computationally to be close in energy to the lowest-energy bright MLCT state (MC state was 0.16 eV above the MLCT state). The excited-state kinetics of Ru-bpm were found via transient absorption spectroscopy to be short-lived and were fit well to a biexponential function with lifetimes τ1 = 4 ps and τ2 = 65 ps in aqueous solution. Kinetic isotope effects of 1.75 (τ1) and 1.61 (τ2) were observed for both decay components, indicating that the solvent plays an important role in the excited-state dynamics of Ru-bpm. Based on the pH-dependent studies and the results from prior studies of similar Ru-complexes, we hypothesize that the 3MLCT state forms an excited-state hydrogen-bond adduct with the solvent molecules and that this process occurs with a 4 ps lifetime. The formation of such a hydrogen-bond complex is consistent with the electronic density accumulation at the peripheral N atoms of the bpm moiety in the 3MLCT state. The hydrogen-bonded state 3MLCT decays to the ground state with a 65 ps lifetime. Such a short lifetime is likely associated with the efficient vibrational energy transfer from the 3MLCT state to the solvent.

Visible-Light Augmented Lithium Storage Capacity in a Ruthenium(II) Photosensitizer Conjugated with a Dione-Catechol Redox Couple.

Controlling redox activity of judiciously appended redox units on a photo-sensitive molecular core is an effective strategy for visible light energy harvesting and storage. The first example of a photosensitizer - electron donor coordination compound in which the photoinduced electron transfer step is used for light to electrical energy conversion and storage is reported. A photo-responsive Ru-diimine module conjugated with redox-active catechol groups in [Ru(II)(phenanthroline-5,6-diolate)3 ]4- photosensitizer can mediate photoinduced catechol to dione oxidation in the presence of a sacrificial electron acceptor or at the surface of an electrode. Under potentiostatic condition, visible light triggered current density enhancement confirmed the light harvesting ability of this photosensitizer. Upon implementation in galvanostatic charge-discharge of a Li battery configuration, the storage capacity was found to be increased by 100 %, under 470 nm illumination with output power of 4.0 mW/cm-2 . This proof-of-concept molecular system marks an important milestone towards a new generation of molecular photo-rechargeable materials.

Ligand-Field Effects in a Ruthenium(II) Polypyridyl Complex Probed by Femtosecond X-ray Absorption Spectroscopy.

We employ femtosecond X-ray absorption spectroscopy of [Ru(m-bpy)3]2+ (m-bpy = 6-methyl-2,2'-bipyridine) to elucidate the time evolution of the spin and charge density upon metal-to-ligand charge-transfer (MLCT) excitation. The core-level transitions at the Ru L3-edge reveal a very short MLCT lifetime of 0.9 ps and relaxation to the lowest triplet metal-centered state (3MC) which exhibits a lifetime of about 300 ps. Time-dependent density functional theory relates ligand methylation to a lower ligand field strength that stabilizes the 3MC state. A quarter of the 3MLCT population appears to be trapped which may be attributed to intramolecular vibrational relaxation or further electron transfer to the solvent. Our results demonstrate that small changes in the ligand field allow control of the photophysical properties. Moreover, this study underscores the high information content of femtosecond L-edge spectroscopy as a probe of valence charge density and spin-state in 4d transition metals.

Accessing a Long-Lived 3LC State in a Ruthenium(II) Phenanthroline Complex with Appended Aromatic Groups.

The photophysical properties of a series of heteroleptic Ru(II) complexes of the form [Ru(phen)2(phen-5,6-R2)]2+, where phen = 1,10-phenanthroline and R = phenyl (Ph), p-tert-butylbenzene (p-Ph-tBu), p-methoxybenzene (p-Ph-OMe), and 2-naphthalene (2-naph), have been measured. Variation of the R group does not greatly perturb the electronic properties of the ground state, which were explored with electronic absorption and resonance Raman spectroscopy and are akin to those of the archetypal parent complex [Ru(phen)3]2+. All complexes were shown to possess emissive 3MLCT states, characterized through transient absorption and emission spectroscopy. However, an additional, long-lived excited state was observed in the Ru(II) naphthalene complex. The naphthalene substituents facilitate population of a 40 μs dark state which decays independently to that of the emissive 3MLCT state. This state was characterized as 3LC in nature, delocalized over the naphthalene substituted ligand.

Front Cover: Stabilization of Pristine Low Resistive State in a Ruthenium(II)‐Polymer of a Hexadentate Schiff Base Ligand: Synthesis, Characterization, and Application as Non‐Volatile Memory Device (Eur. J. Inorg. Chem. 32/2020)

Front Cover: Stabilization of Pristine Low Resistive State in a Ruthenium(II)‐Polymer of a Hexadentate Schiff Base Ligand: Synthesis, Characterization, and Application as Non‐Volatile Memory Device (Eur. J. Inorg. Chem. 32/2020)

Stabilization of Pristine Low Resistive State in a Ruthenium(II)‐Polymer of a Hexadentate Schiff Base Ligand: Synthesis, Characterization, and Application as Non‐Volatile Memory Device

Metallo‐supramolecular polymers offer ample opportunity to develop new emergent materials with the potential for applications as future memories. In this context, we have synthesized a novel hybrid polymer of our developed Schiff base ligand with Ru(II)‐metal ion. The main objective of this study is to understand the effect of changing central metal ion on the ligand field stabilization energy, and the band gap of material as the biting angle of organic moiety changes accordingly with a change in cationic radius of the central metal ion. Furthermore, we have also investigated the application in non‐volatile memory devices. Complete characterization of the newly synthesized hybrid polymer has been performed to establish its structure as well as oxidation state of the central metal ion. A comparative study of the present case and the previously reported Fe(II)‐polymer provides a clear insight into the effect of incorporating a bigger size metal ion in the polymer chain. Non‐volatile memory properties of the polymer have shown a rare behaviour of Negative Differential Resistance (NDR) along with the Low Resistive State (LRS) as its pristine state. Remarkable charge retention and endurance test have also been demonstrated.

Metal-ligand cooperativity in a ruthenium(II) complex of bis-azoaromatic ligand for catalytic dehydrogenation of alcohols

Herein a new Ru-phosphine complex (1) with molecular formula [RuL(PPh3)Cl2] is reported where L is a redox active pincer ligand 2,6-bis(phenylazo)pyridine. The isolated complex has been characterized by usual spectroscopic techniques including single crystal X-ray crystallographic analysis. Complex 1 efficiently catalyzes aerobic oxidation of a wide range of primary and secondary benzylic, allylic, heterocyclic, alicyclic alcohols under mild conditions and is found to be superior over several other Ru (0, +2 and +3), Ru-H and Ru-PPh3 catalysts. Mechanistic studies indicate that a transient Ru-H intermediate is formed in the catalytic cycle which gets switched into a Ru-hydrazo intermediate via hydrogen-walking mechanism. The catalyst is regenerated by aerial oxidation producing H2O2 as a by-product.

One pot conversion of acetyl chloride to dehydroacetic acid and its coordination in a ruthenium(II) arene complex

The reaction of [(η6-p-cymene)RuCl(κ2N,O-l-serinate)], 1, with CH3C(O)Cl/NEt3, in chloroform at reflux temperature, led to the serendipitous isolation of the dehydroacetate complex [(η6-p-cymene)RuCl(κ2O,O′-dha)], 2, in low amount. Then, dehydroacetic acid (dhaH) was prepared in one pot by self condensation of acetyl chloride in the presence of NEt3 at room temperature, this reaction being unusual in the landscape of the chemistry of acyl chlorides. Complex 2 was synthesized in 89% yield from [(η6-p-cymene)RuCl2]2 and dhaH, and fully characterized by means of X-ray diffraction, IR and NMR spectroscopy. Complex 2 underwent fast and extensive dissociation of the dehydroacetate ligand in dmso/water solution, the degree of dissociation being substantially higher than that observed for the acetylacetonate ligand from [(η6-p-cymene)RuCl(κ2O,O′-acac)], 3.

Hybrid Cyclic Water–Chloride Cluster Self-assembled in a Ruthenium(II) Polypyridyl Complex

A two-dimensional cyclic water–chloride anionic {[H2O)18(Cl)8]8−}n network has been identified in a ruthenium(II) complex [Ru(bpy)2(tdzp)]2·tdzp·Cl4·9H2O (bpy = 2,2′-bipyridine, tdzp = [1,2,5]-thiadiazolo-[3,4-f]-[1,10]-phenanthroline). The compound crystallized in monoclinic space group P21/c. A two-dimensional cyclic water-chloride anionic {[H2O)18(Cl)8]8−}n network has been identified in a ruthenium(II) complex [Ru(bpy)2(tdzp)]2⋅tdzp⋅Cl4⋅9H2O (bpy=2,2′-bipyridine, tdzp=[1,2,5]-thiadiazolo-[3,4-f]-[1,10]-phenanthroline).

Visible-Light-Driven Photoisomerization and Increased Rotation Speed of a Molecular Motor Acting as a Ligand in a Ruthenium(II) Complex.

Toward the development of visible-light-driven molecular rotary motors, an overcrowded alkene-based ligand and the corresponding ruthenium(II) complex is presented. In our design, a 4,5-diazafluorenyl coordination motif is directly integrated into the motor function. The photochemical and thermal isomerization behavior has been studied by UV/Vis and NMR spectroscopy. Upon coordination to a Ru(II) bipyridine complex, the photoisomerization process can be driven by visible (λmax = 450 nm) instead of UV light and furthermore, a large increase of the speed of rotation is noted. DFT calculations point to a contraction of the diazafluorenyl lower half upon metal-coordination resulting in reduced steric hindrance in the "fjord region" of the molecule. Consequently, it is shown that metal-ligand interactions can play an important role in the adjustment of both photophysical and thermodynamic properties of molecular motors.

Visible‐Light‐Driven Photoisomerization and Increased Rotation Speed of a Molecular Motor Acting as a Ligand in a Ruthenium(II) Complex

AbstractToward the development of visible‐light‐driven molecular rotary motors, an overcrowded alkene‐based ligand and the corresponding ruthenium(II) complex is presented. In our design, a 4,5‐diazafluorenyl coordination motif is directly integrated into the motor function. The photochemical and thermal isomerization behavior has been studied by UV/Vis and NMR spectroscopy. Upon coordination to a RuII bipyridine complex, the photoisomerization process can be driven by visible (λmax=450 nm) instead of UV light and furthermore, a large increase of the speed of rotation is noted. DFT calculations point to a contraction of the diazafluorenyl lower half upon metal‐coordination resulting in reduced steric hindrance in the “fjord region” of the molecule. Consequently, it is shown that metal‐ligand interactions can play an important role in the adjustment of both photophysical and thermodynamic properties of molecular motors.

1,2,3-Triazolylidene ruthenium(II)(η⁶-arene) complexes: synthesis, metallation and reactivity.

Three bis(1,2,3-triazolylidene) silver(I) complexes were synthesized, and the ruthenium complexes ([RCH2N2(NMe)C2Ph)]RuCl2(p-cymene) (R = C6H2Me3 4a₁, C6H2iPr3 4b₁) were isolated as major products with the minor C(sp(2))-H activated products ([RCH2N2(NMe)C2C6H4)]RuCl(p-cymene) (R = C6H2Me3 4a₂, C6H2iPr3 4b₂). In the related case where R = Ph, the species ([PhCH2N2(NMe)C2Ph)]RuCl2(p-cymene) 4c₁ was obtained with two C(sp(2))-H activated products [PhCH2N2(NMe)C2C6H4)]RuCl(p-cymene) 4c₂ and [(C6H4)CH2N2(NMe)C2Ph)]RuCl(p-cymene) 4c₃ derived from metallation of the N and C-bound arene rings. Heating a solution of 4a₁ at 45 °C over three weeks resulted in a ruthenium(II)(1,2,3-triazolylidene) complex [(C6H2Me3)CH2N2(NMe)C2Ph)]RuCl2 5a, where the pendant mesityl group on the triazolylidene moiety displaced the p-cymene ligand. The complexes 4a₁, 4b₁, 4c₁ and 5a displayed moderate catalytic activities in base-free oxidation of benzyl alcohols to benzaldehydes and oxidative homocoupling of benzyl amines to imines using oxygen as oxidant.

Positional and compositional disorder in a ruthenium(II) piano-stool complex

In (η⁶-p-cymene)(difluorophosphinato-κO){2-[(1H-pyrazol-1-yl)methyl-κN²]pyridine-κN}ruthenium(II) 0.85-hexafluorophosphate 0.15-tetrafluoroborate, [Ru(PO₂F₂)(C₁₀H₁₄)(C₉H₉N₃)](PF₆)0.85(BF₄)0.15, (I), the [PO₂F₂]⁻ ligand exhibits positional disorder due to one F atom and one O atom sharing the same two positions related by a mirror reflection across the O-P-F plane. The correct composition of this coordinated anion was successfully determined to be [PO₂F₂]⁻ by refining the complex with various tetrahedral anions in which terminal atoms have similar atomic form factors. The noncoordinated counter-ion is compositionally disordered between [PF₆]⁻ and [BF₄]⁻. The difficulty in determining the correct composition of this anion illustrates the importance of a crystallographer remaining impartial and open to encountering unexpected moieties in the process of elucidating a structure.

Photoinduced Singlet Charge Transfer in a Ruthenium(II) Perylene-3,4:9,10-bis(dicarboximide) Complex

Elucidation of photoinduced charge transfer behavior in organic dye/metal hybrids is important for developing photocatalytic systems for solar energy conversion. We report the synthesis and photophysical characterization of a perylene-3,4:9,10-bis(dicarboximide) (PDI)-ruthenium(II) complex, bis-PDI-2,2'-bipyridineRu(II)Cl(2)(CN(t)butyl)(2), which has favorable energetics, ΔG(CS) ≈ -1.0 eV, for singlet electron transfer from the Ru complex to PDI. Time-resolved optical spectroscopy reveals that upon selective photoexcitation of PDI, ultrafast charge transfer (<150 fs) from the Ru complex to (1*)PDI generates the Ru(III)-PDI(-•) ion pair. The resulting vibrationally hot Ru(III)-PDI(-•) ion pair exhibits fast relaxation (τ = 3.9 ps) and charge recombination (τ(CR) = 63 ps). Our experimental and computational (DFT and TDDFT) studies show that energy-preserving photodriven singlet electron transfer can dominate in properly designed organic dye/metal complexes, making them of particular interest for use in artificial photosynthetic systems for solar fuels formation.

Influence of Urea N–H Acidity on Receptor–Anionic and Neutral Analyte Binding in a Ruthenium(II)–Polypyridyl‐Based Colorimetric Sensor

AbstractA new ruthenium(II)–polypyridyl complex {[Ru(bpy)2L]2+; bpy = 2,2′‐bipyridyl, L = 1‐(6‐nitro‐1,10‐phenanthrolin‐5‐yl)‐3‐phenylurea} having a urea functionality as a receptor fragment for anionic analytes was synthesized. Its binding affinity towards various oxy anions and halides was studied. This complex was found to act as a selective colorimetric sensor for F– among halides and CH3COO–/H2PO4– among oxy anions. The relative binding affinity of different anions towards this receptor was examined by using quantum chemical calculations. This complex was also found to act as a colorimetric sensor for neutral molecules like DMSO and DMF, though the binding affinity was weaker than that of the three anions mentioned above. The relative acidity of two HNurea atoms was compared with that of one from the related complex by using pKa calculations, and its influence on binding affinities towards different analytes is discussed. Results of the time‐resolved fluorescence studies reveal that two nonequilibrated excited states exist involving two different 3MLCT transitions, namely Rudπ → bpyπ* and Rudπ → Lπ*.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2009)

General Method for Reducing Adaptive Laser Pulse-Shaping Experiments to a Single Control Variable

Adaptive laser pulse shaping has proven to be expeditious for discovering laser pulse shapes capable of manipulating complex systems. However, if adaptive control is to be a valuable interrogative technique that informs physical and chemical research, methods that make it possible to infer mechanistic information from experimental results must be developed. Here, we demonstrate multivariate statistical analysis to extract a single control variable from results of a 137-parameter adaptive laser pulse-shaping optimization of multiphoton electronic excitation in a ruthenium(II) coordination complex in solution. We show that this single variable can be used to linearly manipulate the observed fitness, which is determined by the ratio of molecular emission to second harmonic generation of the laser pulse, over the range explored during the adaptive optimization. Further, manipulation of this variable reveals the latent control mechanism. For this system, that mechanism entails focusing the second harmonic power spectrum of the laser field in a spectral region where the probability of two-photon absorption by the molecule is also large. The statistical tools developed are general and will help elucidate control mechanisms in future adaptive pulse-shaping experiments.

Light-driven machine prototypes based on dissociative excited states: photoinduced decoordination and thermal recoordination of a ring in a ruthenium(II)-containing [2]catenane.

Light-driven machine prototypes based on dissociative excited states: photoinduced decoordination and thermal recoordination of a ring in a ruthenium(II)-containing [2]catenane.

Toward a photochemical and thermal molecular machine: reversible ligand dissociation and binding in a ruthenium(II)-2,2'-bipyridine complex with tris(2-pyridylmethyl)amine.

A Ru(II) complex having tris(2-pyridylmethl)amine (TPA) and 2,2'-bipyridine (bpy), [Ru(TPA)(bpy)]X(2) (X = ClO(4), PF(6)), exhibited a severe distortion of the coordination of the axial pyridine moiety of TPA due to steric hindrance. The complex showed interesting dissociation-binding behavior of the axial pyridine arm to form a solvent adduct with TPA ligation in a unique meridional tridentate fashion. The complex undergoes thermal dissociation to form solvent-coordinated species via an S(N)2-like mechanism with activation energy of 117 kJ/mol. In contrast, the complex showed reversible photochemical dissociation and rebinding via an S(N)1-like mechanism by MLCT irradiation. The photochemical dissociation was accelerated approximately 200-fold faster than the thermal process. The dissociation process involves selective binding behavior toward external ligands (solvents) with pi-acceptor character, which is indispensable, and no sigma-donating molecules could bind to the Ru(II) center. The guest molecule can be released upon photoirradiation after its thermal binding.

Crystal Structure of Chloro(2,2'-bipyridine)[3-(1,10-phenanthroline-2-yl)-5,6-diphenyl-as-triazine]ruthenium(II) Perchlorate

The reaction between Ru(dppt)Cl3 (dppt = 3-(1,10-phenanthroline-2-yl)-5,6-diphenyl-as-triazine), 2,2′-bipyridine (bpy), LiCl and triethylamine in ethanol-H2O resulted in a ruthenium(II) complex, [Ru(dppt)(bpy)Cl](ClO4)·1.5C7H8. Crystallographic studies show that the Ru(II) ion is octahedrally coordinated to one dppt, one bpy and a Cl atom in a trans-axial position at a distance of 2.3996(5)A.

The formation of [RuCl( p-cymene)(Me 2HPz)(PPh 2OR)]Cl (Me 2HPz=3, 5-dimethylpyrazole; R=H, Me and p-Tol) complexes from the cleavage of the P–N bond of a P-coordinated P(Me 2Pz)Ph 2 ligand by ROH molecules in a ruthenium(II) complex. Crystal structure of [RuCl( p-cymene)(Me 2HPz)(PPh 2OH)]Cl

The complex [RuCl 2( p-cymene)] 2 reacts with 1-(3,5-dimethyl)pyrazolyldiphenylphosphine (P(Me 2Pz)Ph 2) to give the complex RuCl 2( p-cymene)(P(Me 2Pz)Ph 2). This compound reacts with ROH molecules (R=H, Me and p-Tol) to give [RuCl( p-cymene)(Me 2HPz)(PPh 2OR)]Cl (R=H, Me and p-Tol) complexes, which contain both Me 2HPz and PPh 2OR coordinated molecules.