Electronic structure and spectra of binuclear bridged nitrosyl ruthenium complexes

The B3LYP method in the LanL2DZ basis set was used to carry out geometry optimization for the binuclear bridged complexes [RuCl₄(NO)(μ-Pyz)Ru(P)(CO)]^?, [Ru(Bipy)₂(NO)(μ-Pyz)Ru(NH₃)₅]⁵⁺, and [(NC)Ru(Py)₄(μ-CN)Ru(Py)₄NO]³⁺ (Pyz is pyrazine). The electronic spectra of the complexes were calculated by the TDDFT and CINDO-CI methods with allowance for solvation effects. The ground-state electronic configurations of the two ruthenium atoms in these compounds were shown to be different. Among the lower excited states of all complexes, states with essentially weakened Ru-NO bonds were found. The strong absorption in the visible region of the spectrum of [Ru(Py)₄NO-CN-Ru(Py)₄CN]³⁺ is due to the interfragment electron transfer Ru^II → {RuNO} accompanied by weakening of the bond between nitrogen oxide and the complex.     

Studies of the reactions of thiocyanate ion with pentammine dinitrogen ruthenium(II) dibromide at different temperatures

The salts of the linkage isomers of thiocyanatopentammineruthenium(III) [Ru(NH₃)₅(NCS)]²⁺, [Ru(NH₃)₅(SCN)]²⁺ and dithiocyanatotetrammineruthenium(III) [Ru(NH₃)₄(NCS)₂]⁺ along with those of tetrathiocyanatodiammineruthenate(III) [Ru(NH₃)₂(SCN)₄]^? have been synthesized. The insoluble polymeric complex [Ru(NH₃)₂(SCN)₂]_n has also been prepared. The compounds have been characterized by chemical analyses, spectral (IR, UV and visible), magnetic susceptibility, conductivity, cyclic voltammetry and chromatography studies.     

Electronic structure of metastable isomers of Ru nitroso complexes

Geometrical structures of nitroso complexes trans- [Ru(NO)(NH₃)₄(Cl)]²⁺, trans-[Ru(NO)(NH₃)₄(H2O)]³⁺, [Ru(NO)(Cyclam)(Cl)]²⁺(Cyclam is 1,4,8,11-tetraazocyclodecane), and [Ru(NO)(Bipy)₂(Cl)]²⁺ (Bipy is 2,2-bipyridine) are optimized using the density functional method. The potential energy surface of all four complexes was found to contain local minima corresponding to a stable state with the ¹-coordination of NO through the N atom and to two metastable isomers with the ¹-O and ²-NO coordination. For [Ru(NO)Cl₅)]^2-, trans-[Ru(NO)(NH₃)₄(Cl)]²⁺, and trans-[Ru(NO)(NH₃)₄(H₂O)]³⁺, the lowest electronically excited triplet states are calculated, as well as the reduced complexes with one additional electron. It is shown that the electron excitation and reduction are accompanied by bending of the RuNO group with a substantial elongation of the Ru-O and N-O bonds, which makes this group unstable. These processes do not cause any significant changes in the metal or in the nitroso ligand oxidation states because of the electron density delocalization in the RuNO group.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 1, 2005, pp. 32–42.Original Russian Text Copyright © 2005 by Sizova, Lubimova.     

Chemistry of Ruthenium Polypyridine Complexes: IX. Nitro-Nitrosyl Equilibrium in cis-[Ru(2,2'-bpy)2(L)NO2]+ Complexes

Ruthenium(II) bisbipyridyl complexes cis-[Ru(bpy)₂(L)NO₂](BF₄) (bpy is 2,2'-bipyridyl) with 4-substituted pyridine ligands L = 4-(Y)py (Y = NH₂, Me, Ph, and CN) were obtained. The equilibrium constants of the reversible nitro-nitrosyl transition [Ru(bpy)₂(L)NO₂]⁺ + 2H⁺ [Ru(bpy)₂(L)NO]^{3 +} + H₂O were measured in solutions with pH 1.5-8.5 (ionic strength 0.4). The constants correlate with the protonation constants of free ligands 4-(Y)py.     

New method for the synthesis of trans-hydroxotetraamminenitrosoruthenium(II) dichloride and its characterization

A procedure for the synthesis of mpa h c-[Ru(NO)(NH₃)₄(OH)]Cl₂ in a nearly quantitative yield (～95%) comprising treatment of a solution of (NH₄)₂[Ru(NO)Cl₅] with ammonium carbonate at t ～80°C was developed. It was found that [Ru(NO)(NH₃)₄(H₂O)]Cl₃·H₂O and trans-[Ru(NO)(NH₃)₄Cl]Cl₂ formed in the reaction of [Ru(NO)(NH₃)₄(OH)]Cl₂ with hydrochloric acid at various temperatures most often contain some initial hydroxy complex. The former compound is unstable, even at room temperature, it slowly eliminates water and HCl. A procedure for preparing the latter compound in a pure state in 85–90% yield was proposed. The acidity constant of the complex trans-[Ru(NO)(NH₃)₄(H₂O)]³⁺ at room temperature (K _a = (4 ± 1) × 10^?2) was estimated by ¹⁴N NMR spectroscopy.     

A perchlorate-promoted electrochemically induced nitride coupling reaction

The osmium nitride complex [Os^VI(NH₃)₄N]³⁺ undergoes a one-electron reduction in acetonitrile to give [Os^V(N)(NH₃)₄]²⁺, which further reacts by nitride coupling to give the μ-dinitrogen osmium complex [(CH₃CN)(NH₃)₄Os^II(N₂)Os^II(NH₃)₄(CH₃CN)]⁴⁺. The formation of the μ-dinitrogen osmium complex is promoted by the presence of perchlorate anion, which causes the deposition of [(CH₃CN)(NH₃)₄Os^II(N₂)Os^II(NH₃)₄(CH₃CN)](ClO₄)₄ on the electrode surface upon repetitive voltammetric scans.     

Synthesis,structure, redox property and ligand replacement reaction of ruthenium(II) complexes containing a terpyridyl ligand with a redox active moiety

Ruthenium(II) complexes bearing a redox-active tridentate ligand 4′-(2,5-dimethoxyphenyl)-2,2′:6′,2′′-terpyridine (tpyOMe), analogous to terpyridine, and 2,2′-bipyridine (bpy) were synthesized by the sequential replacement of Cl by CH₃CN and CO on the complex. The new ruthenium complexes were characterized by various methods including IR and NMR. The molecular structures of [Ru(tpyOMe)(bpy)(CH₃CN)]²⁺ and two kinds of [Ru(tpyOMe)(bpy)(CO)]²⁺ were determined by X-ray crystallography. The incorporation of monodentate ligands (Cl, CH₃CN and CO) regulated the energy levels of the MLCT transitions and the metal-centered redox potentials of the complexes. The kinetic data observed in this study indicates that the ligand replacement reaction of [Ru(tpyOMe)(bpy)Cl]⁺ to [Ru(tpyOMe)(bpy)(CH₃CN)]²⁺ proceeds by a solvent-assisted dissociation process.     

Contrasting effects of redox potentials on the rate constants of oxidation and hydrolysis reactions in ruthenium complexes

We report in this work the rate constant of oxidation by peroxydisulfate of the ammine ruthenium center in [(bpy)₂Ru(μ-5-CNphen)Ru(NH₃)₅]⁴⁺ (bpy?=?2,2′-bipyridine and 5-CNphen?=?5-cyano-1,10-phenanthroline) and the rate constant of hydrolysis of coordinated acetonitrile in [Ru(TPTZ)(bpy)(CH₃CN)]²⁺ (TPTZ = 2,4,6-tris(2-pyridil)-1,3,5-triazine). With these data and literature values of related reactions, we establish the existence of contrasting effects of redox potentials of Ru^3+/2+ couples on the rates of both processes.     

1-(2′-Pyridylazo)-2-naphtholate complexes of ruthenium: Synthesis,characterization, and DNA binding properties

Reaction of 1-(2′-pyridylazo)-2-naphthol (Hpan) with [Ru(dmso)₄Cl₂] (dmso = dimethylsulfoxide), [Ru(trpy)Cl₃] (trpy = 2,2′,2″-terpyridine), [Ru(bpy)Cl₃] (bpy = 2,2′-bipyridine) and [Ru(PPh₃)₃Cl₂] in refluxing ethanol in the presence of a base (NEt₃) affords, respectively, the [Ru(pan)₂], [Ru(trpy)(pan)]⁺ (isolated as perchlorate salt), [Ru(bpy)(pan)Cl] and [Ru(PPh₃)₂(pan)Cl] complexes. Structures of these four complexes have been determined by X-ray crystallography. In each of these complexes, the pan ligand is coordinated to the metal center as a monoanionic tridentate N,N,O-donor. Reaction of the [Ru(bpy)(pan)Cl] complex with pyridine (py) and 4-picoline (pic) in the presence of silver ion has yielded the [Ru(bpy)(pan)(py)]⁺ and [Ru(bpy)(pan)(pic)]⁺ complexes (isolated as perchlorate salts), respectively. All the complexes are diamagnetic (low-spin d⁶, S = 0) and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a Ru(II)–Ru(III) oxidation on the positive side of SCE. Except in the [Ru(pan)₂] complex, a second oxidative response has been observed in the other five complexes. Reductions of the coordinated ligands have also been observed on the negative side of SCE. The [Ru(trpy)(pan)]ClO₄, [Ru(bpy)(pan)(py)]ClO₄ and [Ru(bpy)(pan)(pic)]ClO₄ complexes have been observed to bind to DNA, but they have not been able to cleave super-coiled DNA on UV irradiation.     

Quantum chemical study of the bond orders in the ruthenium,diruthenium and dirhodium nitrosyl complexes

Density functional calculations with the B3LYP functional were carried out for the [Ru(NO)Cl₅]²⁻, [Ru(NO)(NH₃)₅]³⁺, [Ru(NO)(CN)₅]²⁻, [Ru(NO)(CN)₅]³⁻, [Ru(NO)(hedta)]^q (hedta = N-(hydroxyethyl)ethylenediaminetriacetate triple-charged anion; q = 0, −1, −2), Rh₂(O₂CR)₄, Rh₂(O₂CR)₄(NO)₂, Ru₂(O₂CR)₄, Ru₂(O₂CR)₄(NO)₂, Ru₂(dpf)₄, and Ru₂(dpf)₄(NO)₂ (dpf = N,N′-diphenylformamidinate ion; R = H, CH₃, CF₃) complexes. The electronic structure was analyzed in terms of Mayer and Wiberg bond order indices. The technique of bond order indices decomposition into σ-, π-, and δ-contributions was proposed.     

Stereospecific synthesis and redox properties of ruthenium(II) carbonyl complexes bearing a redox-active 1,8-naphthyridine unit

Two stereoisomers of cis-[Ru(bpy)(pynp)(CO)Cl]PF₆ (bpy = 2,2′-bipyridine, pynp = 2-(2-pyridyl)-1,8-naphthyridine) were selectively prepared. The pyridyl rings of the pynp ligand in [Ru(bpy)(pynp)(CO)Cl]⁺ are situated trans and cis, respectively, to the CO ligand. The corresponding CH₃CN complex ([Ru(bpy)(pynp)(CO)(CH₃CN)]²⁺) was also prepared by replacement reactions of the chlorido ligand in CH₃CN. Using these complexes, ligand-centered redox behavior was studied by electrochemical and spectroelectrochemical techniques. The molecular structures of pynp-containing complexes (two stereoisomers of [Ru(bpy)(pynp)(CO)Cl]PF₆ and [Ru(pynp)₂(CO)Cl]PF₆) were determined by X-ray structure analyses.     

Structural Characterization of a Series of N5-Ligated MnIV-Oxo Species

Analysis of extended X-ray absorption fine structure (EXAFS) data for the Mn^IV-oxo complexes [Mn^IV(O)(^DMMN4py)]²⁺, [Mn^IV(O)(2pyN2B)]²⁺, and [Mn^IV(O)(2pyN2Q)]²⁺ (^DMMN4py=N,N-bis(4-methoxy-3,5-dimethyl-2-pyridylmethyl)-N-bis(2-pyridyl)methylamine; 2pyN2B=(N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine, and 2pyN2Q=N,N-bis(2-pyridyl)-N,N-bis(2-quinolylmethyl)methanamine) afforded Mn=O and Mn−N bond lengths. The Mn=O distances for [Mn^IV(O)(^DMMN4py)]²⁺ and [Mn^IV(O)(2pyN2B)]²⁺ are 1.72 and 1.70 Å, respectively. In contrast, the Mn=O distance for [Mn^IV(O)(2pyN2Q)]²⁺ was significantly longer (1.76 Å). We attribute this long distance to sample heterogeneity, which is reasonable given the reduced stability of [Mn^IV(O)(2pyN2Q)]²⁺. The Mn=O distances for [Mn^IV(O)(^DMMN4py)]²⁺ and [Mn^IV(O)(2pyN2B)]²⁺ could only be well-reproduced using DFT-derived models that included strong hydrogen-bonds between second-sphere solvent 2,2,2-trifluoroethanol molecules and the oxo ligand. These results suggest an important role for the 2,2,2-trifluoroethanol solvent in stabilizing Mn^IV-oxo adducts. The DFT methods were extended to investigate the structure of the putative [Mn^IV(O)(N4py)]²⁺⋅(HOTf)₂ adduct. These computations suggest that a Mn^IV-hydroxo species is most consistent with the available experimental data.     

Kinetic Study of the Ru(II) Catalyzed Oxidation of Pentacyanoferrate(ll) Complexes by Peroxydisulfate

The oxidation reactions of Fe(CN)₅L^3? (L = 4-ampy, py, dpa) complexes by S₂O₈^2? were catalyzed upon the addition of a trace amount of Ru(NH₃)₅L′²⁺ (L′ = pz, py or dcb) complex, and the reaction becomes zero-order in Fe(II). The reaction time is ～10² fold faster than the simple Fe(CN)₅L^3?-S₂O₈^2? system. The mechanism of this Ru(II) catalyzed redox reaction is proposed as Ru(NH₃)₅L′²⁺ + 1/2 S₂O₈^2? → Ru(NH₃)₅L′³⁺ + SO₄^2? Ru(NH₃)₅L′³⁺ + Fe(CN)₅L^3? ? Ru(NH₃)₅L′²⁺ + Fe(CN)₅L^2?     

Evidence for symmetry reduction in excited states of [Ru(bpy)3]+ and related compounds

Photoselection and other spectroscopic data for [Ru(bpy)₃]²⁺, [Ru(phen)₃]²⁺, [Ru(bpy)(py)₄]²⁺ and [Os(bpy)₃]²⁺ suggest that the emitting state for the tris compounds may be localized on a single ring.     

Mechanism of oxidation of benzaldehyde by polypyridyl oxo complexes of Ru(IV)

The oxidation of benzaldehyde and several of its derivatives to their carboxylic acids by cis-[Ru(IV)(bpy)2(py)(O)]2+ (Ru(IV)=O2+; bpy is 2,2'-bipyridine, py is pyridine), cis-[Ru(III)(bpy)2(py)(OH)]2+ (Ru(III)-OH2+), and [Ru(IV)(tpy)(bpy)(O)]2+ (tpy is 2,2':6',2'-terpyridine) in acetonitrile and water has been investigated using a variety of techniques. Several lines of evidence support a one-electron hydrogen-atom transfer (HAT) mechanism for the redox step in the oxidation of benzaldehyde. They include (i) moderate k(C-H)/k(C-D) kinetic isotope effects of 8.1 +/- 0.3 in CH3CN, 9.4 +/- 0.4 in H2O, and 7.2 +/- 0.8 in D2O; (ii) a low k(H2O/D2O) kinetic isotope effect of 1.2 +/- 0.1; (iii) a decrease in rate constant by a factor of only approximately 5 in CH3CN and approximately 8 in H2O for the oxidation of benzaldehyde by cis-[Ru(III)(bpy)2(py)(OH)]2+ compared to cis-[Ru(IV)(bpy)2(py)(O)]2+; (iv) the appearance of cis-[Ru(III)(bpy)2(py)(OH)]2+ rather than cis-[Ru(II)(bpy)2(py)(OH2)]2+ as the initial product; and (v) the small rho value of -0.65 +/- 0.03 in a Hammett plot of log k vs sigma in the oxidation of a series of aldehydes. A mechanism is proposed for the process occurring in the absence of O2 involving (i) preassociation of the reactants, (ii) H-atom transfer to Ru(IV)=O2+ to give Ru(III)-OH2+ and PhCO, (iii) capture of PhCO by Ru(III)-OH2+ to give Ru(II)-OC(O)Ph+ and H+, and (iv) solvolysis to give cis-[Ru(II)(bpy)2(py)(NCCH3)]2+ or the aqua complex and the carboxylic acid as products.     

Ligand Exchange Processes on Solvated Beryllium Cations. II [Be(solvent)(12‐Crown‐4)]2+

The solvation and solvent exchange mechanism of [Be(12‐crown‐4)]²⁺ in water and ammonia was studied by DFT calculations (RB3LYP/6‐311+G**). In solution, five‐fold coordinated Be²⁺ species of quadratic pyramidal [Be(H₂O)(12‐crown‐4)]²⁺ and [Be(NH₃)(12‐crown‐4)]²⁺ exist. The water and ammonia exchange reactions follow an associative interchange mechanism, similar to that found for the pure solvent complexes [Be(H₂O)₄]²⁺ and [Be(NH₃)₄]²⁺. The activation barriers are clearly smaller than for the pure solvent complexes, viz. [Be(H₂O)(12‐crown‐4)]²⁺: 6.0 kcal/mol and [Be(NH₃)(12‐crown‐4)]²⁺: 15.3 kcal/mol.     

Behavior of nitrite forms of nitrosylruthenium on extraction and back extraction of heterometalic Ru/Zn complexes with trioctylphosphine oxide

The state of ruthenium in conjugated phases upon extraction of trans-[Ru(¹⁵NO)(¹⁵NO₂)₄(OH)]^2? complex with tri-n-octylphosphine oxide (TOPO) in the presence of Zn²⁺ and subsequent back extraction with H¹⁵NO₃ and NH₃(concd.) solutions was studied by ¹⁵N NMR. Binuclear complexes [Ru(NO)(NO₂)_5?n (μ-NO₂) _n?1(μ-OH)Zn(TOPO) _n ] and [Ru(NO)(NO₂)_4?n (ONO)(μ-NO₂) _n?1(μ-OH)Zn(TOPO) _n ], where n = 2, 3, are predominant forms in extract. Kinetic restrictions for ruthenium extraction with TOPO solution in hexane and its back extraction with aqueous solutions of nitric acid and ammonia are eliminated in the absence of direct coordination of extractant to ruthenium. fac-Dinitronitrosyl forms [Ru(NO)(H₂O)₃(NO₂)₂]⁺, [Ru(NO)(H₂O)₂(NO₂)₂(NO₃)]⁰ (3 and 6 M HNO₃) and [Ru(NO)(H₂O)(NO₂)₂(NO₃)₂]^? (6 M HNO₃) prevail in nitric acid back extracts. Equilibrium constant at ambient temperature (0.05 ± 0.01) was assessed for the coordination of second nitrate ion to nitrosylruthenium dinitronitrato complex. Complex species [Ru(NO)(NO₂)₄(OH)]^2? and [Ru(NO)(NO₂)₃(ONO)(OH)]^2? prevail in ammonia back extract.     

Electrostatic bending and outer-sphere intervalence transfer in a flexible ligand-bridged ruthenium(III)-iron(II) complex

Abstract

In the mixed-valence complex [Ru^III(NH₃)₅(μ-dpypn)Fe^II(CN)₅] with the flexible bridging ligand 1,3-di(4-pyridyl)propane (dpypn), electrostatic interactions between the {Ru(NH₃)₅}³⁺ and {Fe(CN)₅}^3? moieties drive a strong bending of dpypn and approximation of the Ru^III and Fe^II centers, from which the enhanced electronic coupling between metal ions produces an intense intervalence-transfer absorption in the near-infrared region. Density functional theory calculations corroborate both the electrostatic bending in this heterobinuclear complex and a linear geometry in the homobinuclear counterparts [Ru(NH₃)₅(μ-dpypn)Ru(NH₃)₅]⁵⁺ and [Fe(CN)₅(μ-dpypn)Fe(CN)₅]^5?, for which no evidence of electronic coupling was found because of the separation between metal centers. Furthermore, the heterobinuclear species formed an inclusion complex with β-cyclodextrin where the imposed linear geometry prevents significant electronic coupling and intervalence charge transfer between the Ru^III and Fe^II centers.     

Metastable States of Ruthenium Nitrosyl Complexes. Density Functional Quantum-Chemical Calculations

Geometry optimization for the ground state and metastable isomers of the nitrosyl complexes trans-[Ru(NO)(NH₃)₄(L)]^{3 +} (L = imidazole, pyridine, pyrazine, nicotinamide), [Ru(NO)(CN)₅]^{2 -}, and [Ru(NO)Cl₅]^{2 -} was performed in terms of the density functional theory (SVWN/LanL2DZ + 6-31G). The energy gap between the stable structure and the isomer with linear coordination of NO via the oxygen atom is practically independent of the nature of ligand L in the series of ammonia complexes with the same charge, and the energy gap between the stable structure and the isomer with side ² coordination of NO gets slightly smaller if ligand L possesses -acceptor properties.