Synthesis,Photophysical, and Electrochemical Properties of RuII Polypyridyl Complexes Bridged with two Tetrapodal Symmetric and one Asymmetric Ligands

Two symmetric tetrapodal ligands L^1–2 and one asymmetric tetrapodal ligand L³ based on 4,5‐diazafluoren have been synthesized and characterized. Ligands L^1–2 formed by the condensation of pentaerythrityl tetratosylate with 4,5‐diazafluoren‐9‐oxime and 9‐(4‐hydroxy)phenylimino‐4,5‐diazafluorene, respectively. L³ was prepared by two steps, 9‐(4‐hydroxy)phenylimino‐4,5‐diazafluorene reacted with pentaerythrityl tetratosylate affording 1,1′,1"‐tris[(4,5‐diazafluoren‐9‐ylimino)phenoxymethyl]‐1"′‐(p‐tosyloxymethyl)‐methane, which reacted with 4,5‐diazafluoren‐9‐oxime affording the asymmetric ligand L³. Three tetranuclear Ru^II complexes [(bpy)₈L^1–3Ru₄](PF₆)₈ (bpy = bipyridine) were obtained by the reaction of Ru(bpy)₂Cl₂ · 2H₂O with ligands L^1–3. Spectroscopic studies of these complexes exhibit metal‐to‐ligand charge transfer absorptions at 440–445 nm and emissions at 575–579 nm. The electrochemical behaviors of these complexes are consistent with one Ru^II‐based oxidation couple and three ligand‐centered reduction couples.     

“Off‐on‐off” Fluorescence pH Switch of Three Trinuclear RuII Complexes Containing Imidazole Rings

Three tripodal ligands H₃L^1–3 containing imidazole rings were synthesized by the reaction of 1,10‐phenanthroline‐5,6‐dione with 1,3,5‐tris[(3‐formylphenoxy)methyl]benzene, 1,3,5‐tris[(3‐formylphenoxy)methyl]‐2,4,6‐trimethylbenzene, and 2,2′,2"‐tris[(3‐formylphenoxy)ethyl]amine, respectively. Trinuclear Ru^II polypyridyl complexes [(bpy)₆Ru₃H₃L^1–3](PF₆)₆ were prepared by the condensation of Ru(bpy)₂Cl₂ · 2H₂O with ligands H₃L^1–3. The pH effects on the UV/Vis absorption and fluorescence spectra of the three complexes were studied, and ground‐ and excited‐state ionization constants of the three complexes were derived. The three complexes act as “off‐on‐off” fluorescence pH switch through protonation and deprotonation of imidazole ring with a maximum on‐off ratio of 5 in buffer solution at room temperature.     

Synthesis,Photophysical, and Electrochemical Properties of Ruthenium(II) Polypyridyl Complexes containing Open‐Chain Crown Ether

Four polypyridyl bridging ligands BL¹⁻⁴ containing open‐chain crown ether, where BL¹⁻³ formed by the condensation of 4,5‐diazafluoren‐9‐oxime with diethylene glycol di‐p‐tosylate, triethylene glycol di‐p‐tosylate, and tetraethylene glycol di‐p‐tosylate, respectively. BL⁴ formed by the reaction of 4‐(1,10‐phenanthrolin‐5‐ylimino)methylphenol with triethylene glycol di‐p‐tosylate, have been synthesized. Reaction of Ru(bpy)₂Cl₂·2H₂O with BL, respectively, afforded four bimetallic complexes [(bpy)₂RuBL¹⁻⁴Ru(bpy)₂]⁴⁺ as [PF₆]⁻ salts. Electrochemistry of these complexes is consistent with one Ru^II‐based oxidation and several ligand‐based reductions. These complexes show metal‐to‐ligand charge transfer absorption at 439‐452 nm and emission at 570‐597 nm.     

Preparation, photophysical, and electrochemical properties of two tetranuclear ruthenium(II) polypyridyl complexes containing 4,5-diazafluorene

Two tetrapodal ligands L¹ and L² containing 4,5-diazafluorene units have been synthesized and characterized. Both ligands are composed of two kinds of nonequivalent coordinating sites: one involves the 4-(4,5-diazafluoren-9-ylimino)phenoxy moiety, and the other one involves the 2-(4,5-diazafluoren-9-ylimino)phenoxy moiety. The Ru(II) complexes [(bpy)₈Ru₄(L¹)](PF₆)₈ and [(bpy)₈Ru₄(L²)](PF₆)₈ (bpy = 2,2′-bipyridine) have been obtained by refluxing Ru(bpy)₂Cl₂·2H₂O and each ligand in 2-methoxyethanol. Both complexes exhibit metal-to-ligand charge transfer (MLCT) absorptions at around 443 nm and emission at around 574 nm. Electrochemical studies of both complexes display one Ru(II)-centered oxidation at around 1.33 V and three ligand-centered reductions.     

Light Harvesting and Directional Energy Transfer in Long‐Lived Homo‐ and Heterotrimetallic Complexes of FeII,RuII, and OsII

A new family of trimetallic complexes of the form [(bpy)₂M(phen‐Hbzim‐tpy)M′(tpy‐Hbzim‐phen)M(bpy)₂]⁶⁺ (M=Ru^II, Os; M′=Fe^II, Ru^II, Os; bpy=2,2′‐bipyridine) derived from heteroditopic phenanthroline–terpyridine bridge 2‐{4‐[2,6‐di(pyridin‐2‐yl) pyridine‐4‐yl]phenyl}‐1H‐imidazole[4,5‐f][1,10]phenanthroline (phen‐Hbzim‐tpy) were prepared and fully characterized. Zn²⁺ was used to prepare mixed‐metal trimetallic complexes in situ by coordinating with the free tpy site of the monometallic precursors. The complexes show intense absorptions throughout the UV/Vis region and also exhibit luminescence at room temperature. The redox behavior of the compounds is characterized by several metal‐centered reversible oxidation and ligand‐centered reduction processes. Steady‐state and time‐resolved luminescence data show that the potentially luminescent Ru^II‐ and Os^II‐based triplet metal‐to‐ligand charge‐transfer (³MLCT) excited states in the triads are quantitatively quenched, most likely by intercomponent energy transfer to the lower lying ³MLCT (for Ru and Os) or triplet metal‐centered (³MC) excited states of the Fe^II subunit (nonluminescent). Interestingly, iron did not adversely affect the photophysics of the respective systems. This suggests that the multicomponent molecular‐wire‐like complexes investigated here can behave as efficient light‐harvesting antennas, because all the light absorbed by the various subunits is efficiently channeled to the subunit(s) in which the lowest‐energy excited states are located.     

Controlling Metal–Ligand–Metal Oxidation State Combinations by Ancillary Ligand (L) Variation in the Redox Systems [L2Ru(μ‐boptz)RuL2]n,boptz=3,6‐bis(2‐oxidophenyl)‐1,2,4,5‐tetrazine,and L=acetylacetonate, 2,2′‐bipyridine,or 2‐phenylazopyridine

The new compounds [(acac)₂Ru(μ‐boptz)Ru(acac)₂] ( 1 ), [(bpy)₂Ru(μ‐boptz)Ru(bpy)₂](ClO₄)₂ ( 2 ‐(ClO₄)₂), and [(pap)₂Ru(μ‐boptz)Ru(pap)₂](ClO₄)₂ ( 3 ‐(ClO₄)₂) were obtained from 3,6‐bis(2‐hydroxyphenyl)‐1,2,4,5‐tetrazine (H₂boptz), the crystal structure analysis of which is reported. Compound 1 contains two antiferromagnetically coupled (J=?36.7 cm^?1) Ru^III centers. We have investigated the role of both the donor and acceptor functions containing the boptz^2? bridging ligand in combination with the electronically different ancillary ligands (donating acac^?, moderately π‐accepting bpy, and strongly π‐accepting pap; acac=acetylacetonate, bpy=2,2′‐bipyridine pap=2‐phenylazopyridine) by using cyclic voltammetry, spectroelectrochemistry and electron paramagnetic resonance (EPR) spectroscopy for several in situ accessible redox states. We found that metal–ligand–metal oxidation state combinations remain invariant to ancillary ligand change in some instances; however, three isoelectronic paramagnetic cores Ru(μ‐boptz)Ru showed remarkable differences. The excellent tolerance of the bpy co ‐ ligand for both Ru^III and Ru^II is demonstrated by the adoption of the mixed ‐ valent form in [L₂Ru(μ‐boptz)RuL₂]³⁺, L=bpy, whereas the corresponding system with pap stabilizes the Ru^II states to yield a phenoxyl radical ligand and the compound with L=acac^? contains two Ru^III centers connected by a tetrazine radical‐anion bridge.     

Synthesis, characterization, and pH-induced luminescence switching of two trinuclear Ru(II) polypyridyl complexes containing imidazole

Two tripodal ligands H₃L¹ and H₃L² containing imidazole rings have been prepared by the reaction of 1,10-phenanthroline-5,6-dione with 1,3,5-tris[(4-formylphenoxy)methyl]benzene and 1,3,5-tris[(2-formylphenoxy)methyl]benzene, respectively. Trinuclear Ru(II) complexes [(bpy)₆Ru₃H₃L^1?C2](PF₆)₆ (bpy=2,2??-bipyridine) have been obtained by the condensation of Ru(bpy)₂Cl₂?·?2H₂O with ligands H₃L¹ and H₃L², respectively. The pH effects on the UV?CVis absorption and emission spectra of both complexes have been studied, and ground- and excited-state ionization constants of both complexes have been derived. The photophysical properties of both complexes are strongly dependent on the solution pH. They act as pH-induced switchable luminescence sensors through protonation and deprotonation of the imidazole groups, with a maximum on?Coff ratio of 6 in buffer solution at room temperature.     

一系列Ru(II)配合物电致化学发光性质的比较研究

比较研究了以C₂O₄^2－为共反应物时5个结构相关的Ru(II)配合物[Ru(bpy)₂L¹]^2＋, [Ru(bpy)₂L²]^2＋, [Ru(bpy)₂L³]^2＋, [Ru(phen)₂L¹]^2＋和[Ru(phen)₂L²]^2＋(其中bpy＝2,2′-联吡啶, phen＝1,10-邻菲啰啉, L¹＝4-羧基苯基咪唑[4,5-f][1,10]邻菲啰啉, L²＝3-羧基-4-羟基苯基咪唑[4,5-f][1,10]邻菲啰啉, L³＝3,4-二羟基苯基咪唑[4,5-f][1,10]邻菲啰啉)的电致化学发光(ECL)性质. 结果表明, 酚羟基的存在能有效地淬灭Ru(II)配合物[Ru(bpy)₂L²]^2＋, [Ru(bpy)₂L³]^2＋和[Ru(phen)₂L²]^2＋的ECL, 其它Ru(II)配合物的ECL量子效率与[Ru(bpy)₃]^2＋相差不大.     

Near‐IR Absorbing Ruthenium Complexes of Non‐Innocent 6,12‐Di(pyridin‐2‐yl)indolo[3,2‐b]carbazole: Variation as a Function of Co‐Ligands

This article deals with the hitherto unexplored metal complexes of deprotonated 6,12‐di(pyridin‐2‐yl)‐5,11‐dihydroindolo[3,2‐b]carbazole (H₂L). The synthesis and structural, optical, electrochemical characterization of dimeric [{Ru^III(acac)₂}₂(μ‐L^.?)]ClO₄ ([ 1 ]ClO₄, S=1/2), [{Ru^II(bpy)₂}₂(μ‐L^.?)](ClO₄)₃ ([ 2 ](ClO₄)₃, S=1/2), [{Ru^II(pap)₂}₂(μ‐L^2?)](ClO₄)₂ ([ 4 ](ClO₄)₂, S=0), and monomeric [(bpy)₂Ru^II(HL^?)]ClO₄ ([ 3 ]ClO₄, S=0), [(pap)₂Ru^II(HL^?)]ClO₄ ([ 5 ]ClO₄, S=0) (acac=σ‐donating acetylacetonate, bpy=moderately π‐accepting 2,2’‐bipyridine, pap=strongly π‐accepting 2‐phenylazopyridine) are reported. The radical and dianionic states of deprotonated L in isolated dimeric 1 ⁺/ 2 ³⁺ and 4 ²⁺, respectively, could be attributed to the varying electronic features of the ancillary (acac, bpy, and pap) ligands, as was reflected in their redox potentials. Perturbation of the energy level of the deprotonated L or HL upon coordination with {Ru(acac)₂}, {Ru(bpy)₂}, or {Ru(pap)₂} led to the smaller energy gap in the frontier molecular orbitals (FMO), resulting in bathochromically shifted NIR absorption bands (800–2000 nm) in the accessible redox states of the complexes, which varied to some extent as a function of the ancillary ligands. Spectroelectrochemical (UV/Vis/NIR, EPR) studies along with DFT/TD‐DFT calculations revealed (i) involvement of deprotonated L or HL in the oxidation processes owing to its redox non‐innocent potential and (ii) metal (Ru^III/Ru^II) or bpy/pap dominated reduction processes in 1 ⁺ or 2 ²⁺/ 3 ⁺/ 4 ²⁺/ 5 ⁺, respectively.     

Preparation, photophysical, and electrochemical properties of two polynuclear Ru(II) polypyridyl complexes containing imidazole-based ligands

A tripodal ligand L¹ and dipodal ligand L² containing imidazole rings have been synthesized by the reaction of 1,10-phenanthroline-5,6-dione with 2,2??-bipyridine-4,4??-dicarbaldehyde and 4-methyl-2,2??-bipyridine-4??-carbaldehyde, respectively, in the presence of ammonium acetate. Both ligands have two kinds of nonequivalent coordinating sites: one involving the phenanthroline moiety and the other involving the 2,2??-bipyridine moiety. The Ru(II) complexes, [(bpy)₆Ru₃(L¹)](PF₆)₆ and [(bpy)₄Ru₂(L²)](PF₆)₄ (bpy?=?2,2??-bipyridine), have been obtained by refluxing Ru(bpy)₂Cl₂·2H₂O with each ligand in solution. The two complexes display MLCT absorptions at 465 and 480?nm, respectively, and emission at 665 and 675?nm, respectively, in CH₃CN solution. Electrochemical studies of both complexes show one Ru(II)-centered oxidation at around 1.29?V and three ligand-centered reductions.     

Efficient Electronic Communication of Two Ruthenium Centers through a Rigid Ditopic N‐Heterocyclic Carbene Linker

A ditopic benzobis(carbene) ligand precursor was prepared that contained a chelating pyridyl moiety to ensure co‐planarity of the carbene ligand and the coordination plane of a bound octahedral metal center. Bimetallic ruthenium complexes comprising this ditopic ligand [L₄Ru‐C,N‐bbi‐C,N‐RuL₄] were obtained by a transmetalation methodology (C,N‐bbi‐C,N=benzobis(N‐pyridyl‐N′‐methyl‐imidazolylidene). The two metal centers are electronically decoupled when the ruthenium is in a pseudotetrahedral geometry imparted by a cymene spectator ligand (L₄=[(cym)Cl]). Ligand exchange of the Cl^?/cymene ligands for two bipyridine or four MeCN ligands induced a change of the coordination geometry to octahedral. As a consequence, the ruthenium centers, separated through space by more than 10 Å, become electronically coupled, which is evidenced by two distinctly different metal‐centered oxidation processes that are separated by 134 mV (L₄=[(bpy)₂]; bpy=2,2′‐bipyridine) and 244 mV (L₄=[(MeCN)₄]), respectively. Hush analysis of the intervalence charge‐transfer bands in the mixed‐valent species indicates substantial valence delocalization in both complexes (delocalization parameter Γ=0.41 and 0.37 in the bpy and MeCN complexes, respectively). Spectroelectrochemical measurements further indicated that the mixed‐valent Ru^II/Ru^III species and the fully oxidized Ru^III/Ru^III complexes gradually decompose when bound to MeCN ligands, whereas the bpy spectators significantly enhance the stability. These results demonstrate the efficiency of carbenes and, in particular, of the bbi ligand scaffold for mediating electron transfer and for the fabrication of molecular redox switches. Moreover, the relevance of spectator ligands is emphasized for tailoring the degree of electronic communication through the benzobis(carbene) linker.     

Three trinuclear Ru(II) complexes containing 4,5-diazafluorene and 2,2′-bipyridine: synthesis,absorption spectrum,luminescence, and redox behavior

Three heterotopic ligands L¹, L², and L³ have been prepared by the reaction of 4,4′-bis(bromomethyl)-2,2′-bipyridine with 4,5-diazafluoren-9-oxime, 9-(2-hydroxy)phenylimino-4,5-diazafluorene, and 9-(4-hydroxy)phenylimino-4,5-diazafluorene, respectively, in DMF. The three ligands consist of two 4,5-diazafluorene units and one 2,2′-bipyridine unit. Ru(II) complexes [{Ru(bpy)₂}₃(μ₃-L^1?3)](PF₆)₆ (bpy = 2,2′-bipyridine) were prepared by refluxing Ru(bpy)₂Cl₂·2H₂O and the ligands in 2-methoxyethanol. The three Ru(II) complexes display metal-to-ligand charge-transfer absorption at 445–450 nm and one Ru(II)-centered oxidation at 1.32 V in CH₃CN solution at room temperature. Upon excitation into the metal-to-ligand charge-transfer band, the emission intensities of [{Ru(bpy)₂}₃(μ₃-L²)]⁶⁺ and [{Ru(bpy)₂}₃(μ₃-L³)]⁶⁺ are almost equal to that of [{Ru(bpy)₂}₃(μ₃-L¹)]⁶⁺ in CH₃CN solution at room temperature, but weaker than that of [{Ru(bpy)₂}₃(μ₃-L¹)]⁶⁺ in EtOH–MeOH (4?:?1, v/v) glassy matrix at 77 K.     

Synthesis and structures of ruthenium di‐ and tricarbonyl complexes derived from 4,5‐diazafluoren‐9‐one

Carbon monoxide (CO) has recently been shown to impart beneficial effects in mammalian physiology and considerable research attention is now being directed toward metal–carbonyl complexes as a means of delivering CO to biological targets. Two ruthenium carbonyl complexes, namely trans‐dicarbonyldichlorido(4,5‐diazafluoren‐9‐one‐κ²N,N′)ruthenium(II), [RuCl₂(C₁₁H₆N₂O)(CO)₂], (1), and fac‐tricarbonyldichlorido(4,5‐diazafluoren‐9‐one‐κN)ruthenium(II), [RuCl₂(C₁₁H₆N₂O)(CO)₃], (2), have been isolated and structurally characterized. In the case of complex (1), the trans‐directing effect of the CO ligands allows bidentate coordination of the 4,5‐diazafluoren‐9‐one (dafo) ligand despite a larger bite distance between the N‐donor atoms. In complex (2), the cis disposition of two chloride ligands restricts the ability of the dafo molecule to bind ruthenium in a bidentate fashion. Both complexes exhibit well defined ¹H NMR spectra confirming the diamagnetic ground state of Ru^II and display a strong absorption band around 300 nm in the UV.     

Synthesis,photophysical, and electrochemical properties of two polynuclear ruthenium(II) polypyridyl complexes containing diazafluorene

Two polypodands, tetrakis[2-(4,5-diazafluoren-9-ylimino)phenoxymethyl]methane (L¹) and 1,1,1-tris[2-(4,5-diazafluoren-9-ylimino)phenoxymethyl]propane (L²), and their corresponding Ru(II) polypyridyl complexes have been synthesized and characterized. The photophysical behaviors of the two complexes were investigated by UV–vis absorption and emission spectroscopy. They display metal-to-ligand charge transfer (MLCT) absorptions at around 443 nm in MeCN solution at room temperature and emission at around 573 nm in EtOH:MeOH (4:1) glassy matrix at 77 K. Electrochemical studies of the two complexes show one Ru(II)-centered oxidation at around 1.35 V and three ligand-centered reductions.     

Mono‐, bis‐ and tris‐piperidine fused imidazolinium salts: their in situ catalytic applications for C?C bond formation in aqueous solutions

The 1,5,6,7,8,8a‐hexahydroimidazo[1,5‐a]pyridine, 3, was quaternized with 2‐(bromomethyl‐1,3,5‐trimethylbenzene, 1,4‐bis(bromomethyl)‐2,3,5,6‐tetramethylbenzene, 2,4‐bis(bromomethyl)‐1,3,5‐trimethylbenzene, 1,3,5‐tris(bromomethyl)‐2,4,6‐trimethylbenzene and 1,3,5‐tris(bromomethyl)‐2,4,6‐triethylbenzene to obtain mono‐, bis‐ and tris‐imidazolinium salts (4–7) which were characterized by elemental analysis and NMR spectroscopy. In order to understand the effects of these changes on the N‐substituent and how they translate to catalytic activity, these new salts (4–7) with Pd(OAc)₂ were applied as in situ catalysts for Suzuki‐Miyaura and Heck‐Mirozoki cross‐coupling reactions of aryl chlorides and aryl bromides, respectively. The tris‐imidazolinium salts (7) were found to be more efficient than the related analogs 4–6. Copyright © 2009 John Wiley & Sons, Ltd.     

Hetero‐ and homo‐leptic Ru(II) catalyzed synthesis of cyclic carbonates from CO2; Synthesis,spectroscopic characterization and electrochemical properties

Based on the a ligand BDPPZ [(9a,13a‐dihydro‐4,5,9,14‐tetraaza‐benzo[b]triphenylene‐11‐yl)‐phenyl‐methanone] (1) and its polypyridyl hetero‐ and homoleptic Ru(II) metal complexes, [Ru(bpy)₂L](PF₆)₂ (2), [Ru(phen)₂L](PF₆)₂ (3), [Ru(dafo)₂L](PF₆)₂ (4), [Ru(dcbpy)₂L](PF₆)₂ (5) and [RuL₃](PF₆)₂ (6) (where, L = ligand, bpy = 2,2′‐bipyridine, phen = 1,10‐phenantroline, dafo = 4,5‐diazafluoren‐9‐one and dcbpy = 3,3′‐dicarboxy‐2,2′‐bipyridine), have been synthesized and characterized by elemental analysis, UV–vis, FT‐IR, ¹H and ¹³C‐NMR spectra (for ligand), molar conductivity measurements and X‐ray powder techniques. The electrochemical parameters of the substituted ligand and its polypyridyl hetero‐ and homoleptic Ru(II) metal complexes are reported by cyclic voltammetry. UV–vis spectroscopy is used to compare the differences between the conjugated π systems in this ligand and its Ru(II) metal complexes. The polypyridyl hetero‐ and homoleptic Ru(II) metal complexes also tested as catalysts for the formation of cyclic organic carbonates from carbon dioxide and liquid epoxides which served as both reactant and solvent. The results showed that the [Ru(L)₃](PF₆)₂ (6) complex is more efficient than the other Ru(II) complexes for the formation of cyclic organic carbonates from carbon dioxide. Copyright © 2010 John Wiley & Sons, Ltd.     

Tuning the Electronic Properties in Ruthenium–Quinone Complexes through Metal Coordination and Substitution at the Bridge

A rare example of a mononuclear complex [(bpy)₂Ru(L¹_?H)](ClO₄), 1 (ClO₄) and dinuclear complexes [(bpy)₂Ru(μ‐L¹_?2H)Ru(bpy)₂](ClO₄)₂, 2 (ClO₄)₂, [(bpy)₂Ru(μ‐L²_?2H)Ru(bpy)₂](ClO₄)₂, 3 (ClO₄)₂, and [(bpy)₂Ru(μ‐L³_?2H)Ru(bpy)₂](ClO₄)₂, 4 (ClO₄)₂ (bpy=2,2′‐bipyridine, L¹=2,5‐di‐(isopropyl‐amino)‐1,4‐benzoquinone, L²=2,5‐di‐(benzyl‐amino)‐1,4‐benzoquinone, and L³=2,5‐di‐[2,4,6‐(trimethyl)‐anilino]‐1,4‐benzoquinone) with the symmetrically substituted p‐quinone ligands, L, are reported. Bond‐length analysis within the potentially bridging ligands in both the mono‐ and dinuclear complexes shows a localization of bonds, and binding to the metal centers through a phenolate‐type “O^?” and an immine/imminium‐type neutral “N” donor. For the mononuclear complex 1 (ClO₄), this facilitates strong intermolecular hydrogen bonding and leads to the imminium‐type character of the noncoordinated nitrogen atom. The dinuclear complexes display two oxidation and several reduction steps in acetonitrile solutions. In contrast, the mononuclear complex 1 ⁺ exhibits just one oxidation and several reduction steps. The redox processes of 1 ¹⁺ are strongly dependent on the solvent. The one‐electron oxidized forms 2 ³⁺, 3 ³⁺, and 4 ³⁺ of the dinuclear complexes exhibit strong absorptions in the NIR region. Weak NIR absorption bands are observed for the one‐electron reduced forms of all complexes. A combination of structural data, electrochemistry, UV/Vis/NIR/EPR spectroelectrochemistry, and DFT calculations is used to elucidate the electronic structures of the complexes. Our DFT results indicate that the electronic natures of the various redox states of the complexes in vacuum differ greatly from those in a solvent continuum. We show here the tuning possibilities that arise upon substituting [O] for the isoelectronic [NR] groups in such quinone ligands.     

Ruthenium(II) complexes of 2-phenylimidazo[4,5-f] [1,10]phenanthroline. Synthesis,characterization and third order nonlinear optical properties

Three Ru^II complexes [Ru(bpy)₂(PIP)]²⁺, [Ru(PIP)₂(bpy)]²⁺ and [Ru(PIP)₃]²⁺ (PIP = 2-phenylimidazo[4,5-f][1,10]phenanthroline, bpy = 2,2-bipyridine) were prepared and characterized by electrospray mass spectrometry, ¹H-n.m.r, u.v.–vis. and electrochemistry. The nonlinear optical properties (NLO) of the Ru^II complexes were investigated by Z-scan techniques with 12 ns laser pulses at 540 nm, and all of them exhibit both NLO absorption and self-defocusing effects. The corresponding effective NLO susceptibility |³| of the complexes is in the (4.15 – 4.86) × 10^–12 e.s.u. range.     

Catalysis of Mononuclear Aquaruthenium Complexes in Oxygen Evolution from Water: A New Radical Coupling Path using Hydroxocerium(IV) Species

The mechanism of O₂ evolution from water catalyzed by a series of mononuclear aquaruthenium complexes, [Ru(terpy)(bpy)(OH₂)]²⁺, [Ru(tmtacn)(R₂bpy)(OH₂)]²⁺ (R=H, Me, and OMe; R₂bpy=4,4′‐disubstituted‐2,2′‐bipyridines), and [Ru(tpzm)(R₂bpy)(OH₂)]²⁺ (R=H, Me, and OMe), is investigated, where terpy=2,2′:6′,2′′‐terpyridine, bpy=2,2′‐bipyridine, tmtacn=1,4,7‐trimethyl‐1,4,7‐triazacyclononane, and tpzm=tris(1‐pyrazolyl)methane. The kinetics of O₂ evolution is investigated as a function of either the catalyst concentration or the oxidant concentration by employing Ce(NH₄)₂(NO₃)₆ as an oxidant; these catalysts can be classified into two groups that have different rate laws for O₂ evolution. In one class, the rate of O₂ evolution is linear to both the catalyst and Ce⁴⁺ concentrations, as briefly reported for [Ru(terpy)(bpy)(OH₂)]²⁺ (S. Masaoka, K. Sakai, Chem. Lett. 2009 , 38, 182). For the other class, [Ru(tmtacn)(R₂bpy)(OH₂)]²⁺, the rate of O₂ evolution is quadratic to the catalyst concentration and independent of the Ce⁴⁺ concentration. Moreover, the singlet biradical character of the hydroxocerium(IV) ion was realized by experimental and DFT investigations. These results indicate that the radical coupling between the oxygen atoms of a Ru^V?O species and a hydroxocerium(IV) ion is the key step for the catalysis of [Ru(terpy)(bpy)(OH₂)]²⁺ and [Ru(tpzm)(R₂bpy)(OH₂)]²⁺, while the well‐known oxo‐oxo radical coupling among two Ru^V?O species proceeds in the catalysis of [Ru(tmtacn)(R₂bpy)(OH₂)]²⁺. This is the first report demonstrating that the radical character provided by the hydroxocerium(IV) ion plays a crucial role in the catalysis of such ruthenium complexes in the evolution of O₂ from water.     

Evaluation of the Oxo‐bridged Dinuclear Ruthenium Ammine Complex as Redox Mediator in an Electrochemical Biosensor

The mediation of electron‐transfer by oxo‐bridged dinuclear ruthenium ammine [(bpy)₂(NH₃)Ru^III(µ‐O)Ru^III(NH₃)(bpy)₂]⁴⁺ for the oxidation of glucose was investigated by cyclic voltammetry. These ruthenium (III) complexes exhibit appropriate redox potentials of 0.131–0.09 V vs. SCE to act as electron‐transfer mediators. The plot of anodic current vs. the glucose concentration was linear in the concentration range between 2.52×10^?5 and 1.00×10^?4 mol L^?1. Moreover, the apparent Michaelis‐Menten kinetic (K_M^app) and the catalytic (K_cat) constants were 8.757×10^?6 mol L^?1 and 1,956 s^?1, respectively, demonstrating the efficiency of the ruthenium dinuclear oxo‐complex [(bpy)₂(NH₃)Ru^III(µ‐O)Ru^III(NH₃)(bpy)₂]⁴⁺ as mediator of redox electron‐transfer.