Diruthenium Complexes Research Articles

Structural and electronic forms of doubly oxido/Pz and triply oxido/(Pz)2 bridged mixed valent and isovalent diruthenium complexes (Pz = pyrazolate).

The article reported on the diastereomeric dinuclear mixed-valent complexes [(acac)2Ru(III)(μ-O)(μ-PzR)Ru(IV)(acac)2] (R = H, Me, meso: ΔΛ, 1a-1c; rac: ΔΔ/ΛΛ, 2a-2c) and rac-[(acac)2Ru(III)(μ-O)(μ-Iz)Ru(IV)(acac)2], (2d) (HPz = pyrazole, HIz = indazole, acac = acetylacetonate). Moreover, the diruthenium(II,II) complexes [(HPz)3Ru(II)(μ-O)(μ-Pz)2 Ru(II)(HPz)3] (3a) and [(HIz)3Ru(II)(μ-O)(μ-Iz)2Ru(II)(HIz)3] (3d) were presented. The analogous form of 3a, i.e., [(HPz)2(Pz)Ru(III)(μ-O)(μ-Pz)2Ru(III)(Pz)(HPz)2], was previously reported. Single crystal X-ray structures of 1a-1c/2a-2d and representative 3a showed their molecular forms, including the diastereomeric nature of the former. The Ru-O-Ru angle decreased appreciably on switching from doubly bridged 1 and 2 (128-135°) to triply bridged 3a (114°). Both series of complexes displayed rhombic symmetry in their EPR spectra, with g1 and g2 being very similar for 1a-1c with an almost axial look. The mixed-valence complex with a Ru(III)Ru(IV) (S = 1/2) state of 1 and 2 would lead to iso-valence complexes of Ru(III)Ru(III) and Ru(IV)Ru(IV) with an EPR inactive state by one electron redox reaction. On the other hand, metal based {Ru(II)Ru(II)/Ru(II)Ru(III), 3a/3a+} and terminal ligand (HPz/HPz-, 3a/3a-) based redox processes displayed anisotropic and free radical EPR, respectively. An IVCT (intervalence charge transfer) band was found for the delocalised mixed valent 1 and 2 {Ru(III)Ru(IV)} or 3a+ {Ru(II)Ru(III)} in the NIR region. The intense metal-to-ligand charge transfer (MLCT) transitions of 1-3 in the visible region varied systematically as a function of the metal oxidation state.

Relative reactivity of the dinuclear ruthenium complex [CpRu(CO)2]2 with diphenylselenyl sulphide and diphenyl disulphide

The reaction of the diruthenium complex [CpRu(CO)2]2 with the diphenyl dichalcogenides was found to proceed through photoinitiation to the [CpRu(CO)2] radical. Reaction with selenyl sulphide was slower than with disulphide, which has implications for the selective targeting of the enzyme thioredoxin reductase.

Redox-Induced Hydrogen Bond Reorientation Mimicking Electronic Coupling in Mixed-Valent Diruthenium and Macrocyclic Tetraruthenium Complexes.

We present the coordination-driven self-assembly of three tetranuclear metallacycles containing intracyclic NH2, OH, or OMe functionalities through the combination of various isophthalic acid building blocks with a divinylphenylene diruthenium complex. All new complexes of this study were characterized by means of nuclear magnetic resonance spectroscopy, ultrahigh-resolution ESI mass spectrometry, cyclic and square wave voltammetry and, in two cases, X-ray diffraction. The hydroxy functionalized macrocycle 4-BOH and the corresponding half-cycle 2-OH stand out, as their intracyclic OH···O hydrogen bonds stabilize their mixed-valent one- (2-OH, 4-BOH) and three-electron-oxidized states (4-BOH). Despite sizable redox splittings between all one-electron waves, the mixed-valent monocations and trications do not exhibit any intervalence charge-transfer band, assignable to through-bond electronic coupling, but nevertheless display distinct IR band shifts of their charge-sensitive Ru(CO) tags. We ascribe these seemingly contradicting observations to a redox-induced shuffling of the OH···O hydrogen bond(s) to the remaining, more electron-rich, reduced redox site.

Crystal Structure of a Lantern-type Diruthenium(II,III) Complex with Axial Thiocyanato and DMF Ligands, [Ru<sub>2</sub>(O<sub>2</sub>CCMe<sub>3</sub>)<sub>4</sub>(NCS)(DMF)

Crystal Structure of a Lantern-type Diruthenium(II,III) Complex with Axial Thiocyanato and DMF Ligands, [Ru<sub>2</sub>(O<sub>2</sub>CCMe<sub>3</sub>)<sub>4</sub>(NCS)(DMF)

Chiral paddle-wheel diruthenium complexes for asymmetric catalysis

The development of robust and reactive chiral catalysts is a fundamental aim in asymmetric catalysis, and crucial for providing efficient methods for synthesizing chiral molecules. Chiral paddle-wheel bimetallic complexes provide a highly tunable chiral environment in rhodium-catalysed asymmetric carbene/nitrene transfer reactions and Lewis acid-catalysed reactions. Chiral paddle-wheel complexes having other transition metals as the reactive metal centre, however, have not yet been identified in asymmetric catalysis. Here, we report the synthesis, structures and high catalytic performances of chiral paddle-wheel diruthenium complexes. The cationic chiral diruthenium complex [Ru2((S)-BPTPI)4]+ exhibited remarkable reactivity as a Lewis acid catalyst for asymmetric hetero-Diels–Alder reactions, achieving a turnover number of up to 1,880,000 with high enantioselectivity (>90% e.e.). The chiral diruthenium complexes also exhibited good reactivity and high enantioselectivity in C–H amination and cyclopropanation reactions under oxidizing conditions, indicating their high tolerance towards oxidation. Our results reveal the chiral paddle-wheel diruthenium scaffold as a promising platform for asymmetric catalysis. The development of chiral catalysts is of fundamental importance in asymmetric catalysis. Now, chiral paddle-wheel diruthenium complexes are reported that are stable under oxidizing conditions and effective in asymmetric C–C and C–N bond-forming reactions with turnover numbers of up to 1,880,000.

Interactions of Cationic Diruthenium Trithiolato Complexes with Phospholipid Membranes Studied by NMR Spectroscopy.

To apprehend the possible mechanisms involved in the cellular uptake and the membrane interactions of cytotoxic dinuclear p-cymene trithiolato ruthenium(II) complexes, the interactions of the complexes [(η6-p-MeC6H4Pri)2Ru2(R1)2(R2)]+ (R1 = R2 = SC6H4-m-Pri:1; R1 = SC6H4-p-OMe, R2 = SC6H4-p-OH:2; R1 = SCH2C6H4-p-OMe, R2 = SC6H4-p-OH:3) with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) vesicles and 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) micelles were studied using nuclear magnetic resonance (NMR) spectroscopy. 1H NMR, nuclear Overhauser effect (NOE), diffusion ordered spectroscopy (DOSY), and T1 and T2 relaxation data provided information on interactions between the complexes and the model membranes and on the submolecular localization of the complexes at the membrane interface. The results suggest that (a) the interaction takes place without new covalent adduct formation, (b) the cationic diruthenium complexes interact with DOPC head groups most likely involving electrostatic interactions while remaining structurally unchanged, (c) the changes indicating interactions are more pronounced for the most lipophilic complex 1, and (d) the diruthenium complexes remain at the exterior vesicle surface and are unlikely inserted between the phospholipid chains. The complexes also interact with micellar/free DHPC and seem to induce micellization or aggregation in solutions below critical micelle concentration (CMC). Our study suggests high affinity of the Ru complexes for the membrane surface that likely plays a key role in cellular uptake and possibly also in redistribution in mitochondria.

Proton-coupled redox properties and water oxidation catalysis of an aqua-coordinated (µ-oxo)diruthenium(III) complex

The electronic absorption and redox properties as well as the catalysis for water oxidation reaction (WOR) of an aqua-coordinated oxo-bridged diruthenium(III) complex trans(µ-O,OH2)-[Ru2(µ-O)(µ-CH3COO)2(bpy)2(H2O)2](PF6)2·3H2O ([1](PF6)2·3H2O; bpy = 2,2′-bipyridine) in aqueous media are reported. [1]2+ displays a visible absorption band at 566 nm ascribed to metal-to-metal charge transition (MMCT) within the Ru2O core. This visible band redshifts due to the deprotonation of the terminal aqua ligands of [1]2+ in alkaline solutions. [1]2+ shows proton-coupled electron transfer behaviors in aqueous solutions at pH 0–14. The oxidation of RuIIIRuIII in [1]2+ has successfully reached the higher oxidation states including RuIVRuIV and RuVRuV which are stabilized by the deprotonation of the terminal aqua ligands and are important for catalytic water oxidation. WOR catalyzed by [1]2+ in acidic solutions was studied using electrochemical and chemical oxidation. In the solution of [1]2+ at pH 1.0, the overpotential for WOR was ~0.38 V. A turnover number of 23 was obtained by using (NH4)2Ce(NO3)6 as the oxidant. A nucleophilic-attack catalytic mechanism was proposed.

Role of Substituents at 3-position of Thienylethynyl Spacer on Electronic Properties in Diruthenium(II) Organometallic Wire-like Complexes.

A series of organometallic complexes [Cl(dppe)2 Ru-C≡C-(3-R-C4 H2 S)-C≡C-Ru(dppe)2 Cl] (3-R-C4 H2 S=3-substituted thienyl moiety; R=-H, -C2 H5 , -C3 H7 , -C4 H9 , -C6 H13 , -OMe, -CN in 5 a-5 g respectively) have been synthesized by systematic variation of 3-substituents at the thienylethynyl bridging unit. The diruthenum(II) wire-like complexes (5 a-5 g) have been achieved by the reaction of thienylethynyl bridging units, HC≡C-(3-R-C4 H2 S)-C≡CH (4 a-4 g) with cis-[Ru(dppe)2 Cl2 ]. The wire-like diruthenium(II) complexes undergo two consecutive electrochemical oxidation processes in the potential range of 0.0 - 0.8 V. Interestingly, the wave separation between the two redox waves is greatly influenced by the substituents at the 3-position of the thienylethynyl. Thus, the substitution on 3-position of the thienylethynyl bridging unit plays a pivotal role for tuning the electronic properties. To understand the electronic behavior, density functional theory (DFT) calculations of the selected diruthenium wire-like complexes (5 a-5 e) with different alkyl appendages are performed. The theoretical data demonstrate that incorporation of alkyl groups to the thienylethynyl entity leaves unsymmetrical spin densities, thus affecting the electronic properties. The voltammetric features of the other two Ru(II) alkynyl complexes 5 f and 5 g (with -OMe and -CN group respectively) show an apparent dependence on the electronic properties. The electronic properties in the redox conjugate, (5 a+ ) with Kc of 3.9×106 are further examined by UV-Vis-NIR and FTIR studies, showing optical responses in NIR region along with changes in "-Ru-C≡C-" vibrational stretching frequency. The origin of the observed electronic transition has been assigned based on time-dependent DFT (TDDFT) calculations.

Fused N-Heterocyclic-Bridged Isomeric Diruthenium Complexes [(acac)2Ru(μ-DIPQD)Ru(acac)2]n, n = +2, + 1, 0, -1, -2.

π-Conjugated bridged isomeric diruthenium(II) complexes [(acac)2RuII(μ-DIPQD)RuII(acac)2], 1 (trans) and 2 (cis) (acac- = acetylacetonate, (8E,16E)-N8,N16-diphenylindeno[1,2-b]indeno[2',1':5,6]pyrazino[2,3-g]quinoxaline-8,16-diimine (trans-DIPQD), and (12E,16E)-N12,N16-diphenylindeno[1,2-b]indeno[1',2':5,6]pyrazino[2,3-g]quinoxaline-12,16-diimine (cis-DIPQD) were separated and structurally characterized. The structures of the rac (ΔΔ/ΛΛ) forms of 1 and 2 exhibit two units of {Ru(acac)2}, linked to adjacent pyrazine and imine nitrogen donors of the bridge (DIPQD) in trans and cis modes, with metal-metal separations of 9.050 and 6.330 Å, respectively. The packing diagrams of 1 and 2 revealed an intermolecular π···π stacking interaction (3.202-3.398 Å) involving the face-to-face arrangement of the aromatic rings of DIPQD in adjacent molecules and varying solid-state packing modes, slipped stacking in the former versus brick-layer stacking in the latter. The electronic forms associated with multiple reversible one-electron redox steps of 1 and 2 were addressed by DFT (MO composition, Mulliken spin density distribution), supported by EPR of intermediate paramagnetic states and by UV-vis-NIR spectroelectrochemistry in all redox states. The results reveal similar electronic forms along the redox series irrespective of their isomeric identities in 1 and 2, viz., primarily metal-based oxidations ([(acac)2RuII(μ-DIPQD)RuIII(acac)2]+, 1+/2+, S = 1/2; [(acac)2RuIII(μ-DIPQD)RuIII(acac)2]2+, 12+/22+, S = 1) and bridge-based reductions ([(acac)2RuII(μ-DIPQD•-)RuII(acac)2]-, 1•-/2•-, S = 1/2; [(acac)2RuII(μ-DIPQD2-)RuII(acac)2]2-, 12-/22-, S = 1). TD-DFT analysis of the electronic transitions in the complexes suggests bridge-targeted mixed metal/ligand-based multiple charge transfer transitions over the visible to NIR region in all redox states, while a weak band involving the radical bridge appeared in the long-wavelength region (∼2000 nm) in 1•-/2•-.

DFT/TD-DFT investigation on the photoinduced electron transfer of diruthenium and viologen complexes

Photoinduced electron transfer, chemical stability, and redox property of diruthenium−viologen complexes were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Target systems include a series of diruthenium and viologen complexes consisting of Ru(bpy)3-viologen-Ru(bpy)3; Ru–V–Ru, Ru(bpy)3-viologen-Ru(bpy)(dcbpy)2; Ru–V–RuCOOH, and Ru(bpy)3-viologen-viologen-Ru(bpy)3; Ru–V–V–Ru, where bpy = 2,2′-bipyridyl and dcbpy = 4,4′-dicarboxyl-2,2-bipyridyl. The B3LYP functional was used to investigate the ground state properties for the three diruthenium and viologen complexes and for two parent complexes: ruthenium-bipyridine (Ru(bpy)32+) and methyl viologen (MV2+) as well as their oxidized states. Singlet excited states were examined using the TD-DFT calculations with CAM-B3LYP functional in acetonitrile using conductor polarizable continuum model (CPCM). The TD-DFT calculations reproduced the experimentally observed variation of the absorption spectra due to oxidation states. The correlation between the calculated UV–Vis transition and molecular orbitals for the excited state clearly established that the viologen dication (V2+) changed their reductive product into the radical cation (V•+) and neutral (V0), whereas ruthenium retained its formal Ru(bpy)32+ oxidation state. The metal to ligand charge transfer state of Ru(bpy)32+ was shown to undergo electron transfer quenching by methyl viologen dication (MV2+). These findings are relevant for the development of novel optoelectronic materials owing to a combination of chemical stability, redox activity, and long-lived excited states.

A mixed-valence diruthenium(II,III) complex endowed with high stability: from experimental evidence to theoretical interpretation.

We herein report the synthesis and multi-technique characterization of [Ru2Cl((2-phenylindol-3-yl)glyoxyl-l-leucine-l-phenylalanine)4], a novel diruthenium(ii,iii) complex obtained by reacting [Ru2(μ-O2CCH3)4Cl] with a dual indolylglyoxylyl dipeptide anticancer agent. We soon realised that the compound is very stable under several different conditions including aqueous buffers or organic solvents. It is also completely unreactive toward proteins. The high stability is also suggested by cellular experiments in a glioblastoma cell line. Indeed, while the parent ligand exerts high cytotoxic effects in the low μM range, the complex is completely non-cytotoxic against the same line, most probably because of the lack of ligand release. To investigate the reasons for such high stability, we carried out DFT calculations that are fully consistent with the experimental findings. The results highlight that the stability of [Ru2Cl((2-phenylindol-3-yl)glyoxyl-l-leucine-l-phenylalanine)4] relies on the nature of the ligand, including its steric hindrance that prevents the reaction of any nucleophilic group with the Ru2 core. Ligand displacement is the key step to allow reactivity with the biological targets of metal-based prodrugs. Accordingly, we discuss the implications of some important aspects that should be considered when active molecules are chosen as ligands for the synthesis of paddle-wheel-like complexes with medicinal applications.

Oxidized divinyl oligoacene-bridged diruthenium complexes: bridged localized radical characters and reduced aromaticity in bridge cores.

A series of bimetallic ruthenium vinyl complexes 1-5 bridged by oligoacenes were synthesized and characterized in this study. Comparative cyclic voltammetry results from 1-5 indicated that the first oxidation potential decreased gradually with the extension of conjugate ligands. Upon oxidation to singly oxidized species 1+-5+, rather small ν(CO) changes in the infrared (IR) spectra and the characteristic bands of metal-to-ligand charge transfer absorptions in the near IR (NIR) region predicted via time-dependent DFT calculations suggested that strong bridged ligands participate in redox processes. NIR absorptions were not observed in complexes 4+ and 5+ possibly because of instability in their twisted and noncoplanar geometry. Electron paramagnetic resonance results and spin density distribution demonstrated that the bridged localized degrees of 1+-5+ successively increased with the extension of oligoacene from benzene to tetracene. Further comparative analysis of neutral molecules and monocations to the aromaticity and π-electron density of bridge cores indicated a step-by-step transformation process from an aromatic to quinoidal radical upon oxidation.

Ring size matters: supramolecular isomerism in self-assembled redox-active tetra- and hexaruthenium macrocycles.

Self-assembly of a divinylthiophene-bridged diruthenium complex with 2,5-furandicarboxylate leads to the formation of two macrocyclic structures that differ solely with regard to their respective nuclearities. Both supramolecular isomers were fully characterized and the conversion of the hexa- to the tetraruthenium macrocycle was followed by NMR monitoring.

Dinuclear RuII complexes with quinonoid bridges: tuning the electrochemical and spectroscopic properties of redox-switchable NIR dyes through judicious bridge design.

Bridging quinonoid ligands are important platforms for generating metal-based switchable optoelectronic and magnetic materials. A possible sound way of influencing the properties of the aforementioned materials is to modify the direct metal-ligand interface. We present herein a series of dinuclear RuII complexes where the set of donor atoms at the bridging quinonoid ligands range from [O,O,O,O], [O,O,O,N], [O,N,O,N] and [O,N,O,N']. Additionally, the substituents on the N-donors were varied as well (a total of eight different quinonoid bridges are compared). We also present a mononuclear RuII complex for comparison purposes. The dinuclear complexes act as switchable NIR dyes, absorbing in the NIR region in their mixed-valent RuII/RuIII form but not in the neighboring RuII/RuII and RuIII/RuIII states. The switching potentials (the potentials at which NIR absorptions appear) and the λmax of the NIR band can be fine-tuned by varying the donor atoms as well as the electron-donating ability of the substituents on the nitrogen atoms (tuning E by ca. 0.4 V and λmax by ca. 450 nm). Introducing more electron-rich substituents at the nitrogen atoms of the bridge results in higher band energies and more cathodic redox potentials. Unsymmetrical bridging ligands increase the thermodynamic stability of the mixed-valent state. Whereas almost all of the mixed-valent species presented here belong to the delocalised type III of the Robin-Day classification, the most unsymmetrical complex 2O,N(Mes) shows characteristic signs of a borderline Class-II-III compounds. This comprehensive study thus establishes the lesser used unsymmetrically substituted quinones as excellent bridges for generating and tuning a series of properties in their corresponding metal complexes.

Framework Conversion of Oxido-Bridged Dinuclear Ruthenium Complexes.

Syntheses, properties, and reactions of hydroxido- or oxido-bridged dinuclear ruthenium complexes bearing a tridentate auxiliary ligand, ethylbis(2-pyridylmethyl)amine (ebpma) or benzylbis(2-pyridylmethyl)amine (bbpma), have been investigated. Reduction reactions of a singly oxido-bridged diruthenium complex bearing ebpma, [{RuIII,IVCl2(ebpma)}2(μ-O)]+ ([2Cl]+), by zinc in acetonitrile afforded an acetonitrile-substituted singly oxido-bridged complex in the RuIII-RuIII isovalent state, [{RuIII,IIICl(NCCH3)(ebpma)}2(μ-O)]2+ ([2CH3CN]2+). Chlorido ligand abstraction reactions using silver salts have also been attempted. Through a reaction of [2Cl]+ with two equimolar amounts of AgNO3 in water-acetone, a singly oxido-bridged complex having an aqua and a hydroxido, [{RuIIICl(OH2)(ebpma)}(μ-O){RuIVCl(OH)(ebpma)}]2+ ([2H2O-OH]2+), was obtained. Reactions with four equimolar amounts of AgL (L = CH3COO- or NO3-) in water-acetone gave doubly oxido- and bidentate oxygen donor ligand-bridged diruthenium complexes of Ru(III)-Ru(IV), [{RuIII,IV(ebpma)}2(μ-O)2(μ-L)]2+ ([3L]2+; L = O2CCH3; [3CH3COO]2+, L = O2NO; [3NO3]2+). Reactions of [3L]2+ under acidic conditions afforded a corresponding one-protonated species having the {Ru2(μ-O)(μ-OH)} core. Reactivity and electronic structure of the oxido-bridged diruthenium complexes were studied by electrochemical, spectroscopic, and theoretical methods.

Chiral Self-Sorting in Truxene-Based Metallacages

Two chiral face-rotating metalla-assembled polyhedra were constructed upon self-assembling achiral components, i.e., a tritopic ligand based on a truxene core (10,15-dihydro-5H-diindeno[1,2-a;1′,2′-c]fluorene) and two different hydroxyquinonato–bridged diruthenium complexes. Both polyhedra were characterized in solution as well as in the solid state by X-ray crystallography. In both cases, the self-sorting process leading to only two homo-chiral enantiomers was governed by non-covalent interactions between both truxene units that faced each other.

Reactions of [Ru3(CO)12] with thiosaccharin: Synthesis and structure of di-, tri-, tetra- and penta-ruthenium complexes containing a thiosaccharinate ligand(s)

Reactions of [Ru3(CO)12] with thiosaccharin (tsacH) at different temperatures have been investigated. At 40 °C, the diruthenium complex [Ru2(CO)6(μ-N,S-tsac)2] (1) is produced and whose ruthenium atoms are bridged by two tsac ligands that are oriented in a head-to-tail fashion. When this reaction is carried out at 66 °C, the tri-, tetra- and penta-ruthenium complexes [H2Ru3(CO)7(μ-N,S-tsac)(μ-C,N–C6H4CNSO2)(μ3-S)] (2), [Ru4(CO)12(μ-N,S-tsac)2(μ4-S)] (3) and [H2Ru5(CO)13(μ-N,S-tsac)(μ-C,N–C6H4CNSO2)(μ3-S)(μ4-S)] (4), respectively, are also isolated in addition to 1. The triruthenium complex 2 exhibits an arachno SRu3 polyhedron containing edge-bridging tsac and C6H4CNSO2 ligands. The tetraruthenium complex 3 consists of two [Ru2(CO)6(μ-N,S-tsac)] fragments linked via a μ4-S ligand, while the pentaruthenium complex 4 is composed of individual Ru3 and Ru2 units linked via a μ4-S ligand. At 81 °C, the same reaction furnishes the pentaruthenium complex [HRu5(CO)15(μ-N,S-tsac)(μ5-S)] (5) containing tsac and μ5-S bridging ligands. The molecular structures of the new complexes have been determined by single-crystal X-ray diffraction analyses, and the bonding in each product has been examined by DFT.

Near-infrared electrochromism of multilayer films of a cyclometalated diruthenium complex prepared by layer-by-layer deposition on metal oxide substrates

A cyclometalated diruthenium complex 2 bridged by 1,2,4,5-tetra(pyrid-2-yl)benzene with six carboxylic acid groups at two ends was synthesized. Monolayer and multilayer films FTO/TiO2/( 2 ) n (Zr) ( n =1, 2) and FTO/SnO2:Sb/( 2 ) n (Zr) ( n =1–4) have been prepared via interfacial layer-by-layer coordination assembly of 2 with zirconium(IV) ions. All films show two consecutive redox couples in the potential range between 0 and +1.0 V vs. Ag/AgCl. These films exhibit reversible near-infrared electrochromism upon switching of redox potential. The response time of the films on SnO2:Sb is around a few seconds, while that on TiO2 is around a few tens of seconds. The film deposition cycles were found to have a great impact on the electrochromic performance. Among six films examined, the two-layered film on SnO2:Sb displays the best balanced performance with a contrast ratio of 56% at 1,150 nm and good cyclic stability (9% loss of contrast ratio after 1,000 continuous double-potential-switching cycles), which is superior to that of the previously reported electropolymerized films of a related diruthenium complex with the same bridging ligand. In addition, the X-ray photoelectron spectroscopy, scanning electron microscopy, and electron transfer mechanism of these films have been investigated.

A Diruthenium Complex of an N-Pyridyl-o-aminophenol Derivative: A Route to Mixed Valency.

An N-pyridyl-o-aminophenol derivative that stabilises mixed-valence states of ruthenium ions is disclosed. A diruthenium complex, [(LIQ 0 )Ru2 Cl5 ]⋅MeOH (1⋅MeOH) is successfully isolated, in which LIQ 0 is the o-iminobenzoquinone form of 2-[(3-nitropyridin-2-yl)amino]phenol (LAP H2 ). In 1, LIQ 0 oriented towards one ruthenium centre is a non-innocent NO-donor redox ligand, whereas another oriented towards another ruthenium centre is an innocent pyridine-donor redox ligand. Complex 1 is a diruthenium(II,III) mixed-valence complex, [RuII (LIQ 0 )(μ-Cl)2 RuIII ], with a minor contribution from the diruthenium(III,III) state. [RuIII (LISQ .- )(μ-Cl)2 RuIII ] contains LISQ .- , which is the o-iminobenzosemiquinonate anion radical form of the ligand. Complexes 1- and 1+ are diruthenium(II,II), [RuII (LIQ 0 )(μ-Cl)2 RuII ], and diruthenium(III,III), [RuIII (LIQ 0 )(μ-Cl)2 RuIII ], complexes, respectively, of LIQ 0 . Complex 12- is a diruthenium(II,II) complex of the o-iminobenzosemiquinonate anion radical (LISQ .- ), [RuII (LISQ .- )(μ-Cl)2 RuII ], with a minor contribution from the diruthenium(III,II) form, [RuIII (LAP 2- )(μ-Cl)2 RuII ]. Complex 12+ is a diruthenium(III,IV) mixed-valence complex of LIQ 0 , [RuIII (LIQ 0 )(μ-Cl)2 RuIV ]. Complexes 1 and 12+ exhibit inter-valence charge-transfer transitions at λ=1300 and 1370 nm, respectively.

The First Bis(μ‐acetato)(μ‐oxido)diruthenium(III) Complexes Containing Sulfur Donor Ligands

AbstractNovel diruthenium(III) complexes of general formula [RuIII2(μ‐O)‐(μ‐CH3CO2)2(bpy)2L2](PF6)2 (L: tetrahydrothiophene, (3); 4,5‐dihydro‐3(2H)‐thiophenone, (4); thiazole, (5); 4‐methylthiazole, (6); bpy: 2,2’‐bipyridine), which contain sulfur or nitrogen donor ligands at the trans‐to‐oxido sites, have been synthesized. The Ru–S bond distance in 4 is determined by X‐ray crystallography to be 2.447 Å, and the Ru–N(trans‐to‐oxido) length in 5 (2.157 Å) is similar to that of the complex having pyridine as the L ligand, 1. The spectroscopic properties and redox behavior of the complexes bearing sulfur donor ligands have been investigated and compared with those containing nitrogen donor ligands. The potentials of the redox couples of Ru2II,III/Ru2III,III and Ru2III,III/Ru2III,IV for 3 and 4 shift to positive regions compared with those of complexes with nitrogen donor ligands, 1, 5 and 6. The density functional theory (DFT) calculations reveal that the contribution of the trans ligand to the visible absorption is larger in 3 and 4 than in 1, 2 (L: CH3CN), 5 and 6.