Mixed-valence electron delocalized thiocyanato bridged ruthenium dinuclear complex [{Ru(NH3)5}2SCN]4+

The thiocyanato bridged mixed-valence ruthenium dinuclear species [{Ru(NH₃)₅}2SCN]⁴⁺ has been prepared and characterized. A solvent independent, low intensity intervalence transfer band was observed in the near IR absorption spectrum suggesting a delocalized limit in the [Ru(II)-SCN-Ru(III)] unit.     

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.     

Modeling the solvation shell of complexes in solution for quantum chemical calculations of electronic spectra

A procedure that allows for solvation effects is suggested; it is designed for quantum chemical calculations of the electronic spectra of complex compounds. Based on Monte Carlo (MC) simulation of the solvation shell one can calculate the electrostatic potential created by the solvation shell at the sites of all atoms of the complex; appropriate corrections are added to the diagonal elements of the Fock matrix and to the matrix elements of the Hamiltonian in the configuration interaction method. The method suggested has been implemented based on the semiempirical (CINDO) version of the CI (configuration interaction) technique and tested on the following compounds: [Ru(NH₃)₅(py)]²⁺, [Ru(NH₃)₅(pyz)]²⁺, [Ru(bpy)(CN)₄]^2?, [Ru(NO)(py)₄-NC-Ru(py)₄(CN)]³⁺.     

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.     

Study of nitrosation of hexaammineruthenium(II): Crystal structure of <Emphasis Type="Italic">trans</Emphasis>-[RuNO(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>Cl]Cl<Subscript>2</Subscript>

The nitrosation of [Ru(NH₃)₆]²⁺ in hydrochloric acid and alkaline ammonia media has been studied; the patterns of interconversion of ruthenium complexes in reaction solutions have been proposed. In both cases, nitrogen(II) oxide acts as the nitrosation agent. The procedure for the synthesis of [Ru(NO)(NH₃)₅]Cl₃ · H₂O (yield 75–80%), the main nitrosation product of [Ru(NH₃)₆]²⁺, has been optimized. Thermolysis of [Ru(NO)(NH₃)₅]Cl₃ · H₂O in a helium atmosphere has been studied; the intermediates have been identified. One of these products is polyamidodichloronitrosoruthenium(II) whose subsequent decomposition gives an equimolar mixture of ruthenium metal and dioxide. The structure of trans-[RuNO(NH₃)₄Cl]Cl₂, formed in the second stage of thermolysis and as a by-product in the nitrosation of [Ru(NH₃)₆]Cl₂, has been determined by X-ray diffraction.     

Über Reaktionen oxygenierter Kobalt(II)-Chelate. VI. Präparative Darstellung von diastereoisomeren Tetrakis(äthylendiamin)-μ-peroxo-μ-hydroxodikobalt(III)-perchloraten

On Reactions of oxygenated Cobalt(II) Chelates. VI. Preparation of diastereoisomeric tetrakis(ethylenediamine)-μ-peroxo-μl-hydroxo-dicobalt(III) Perchlorates Oxygenation of Co(en)₂²⁺ leads to a mixture of two isomeric forms of [(en)₂Co(O₂, OH)-Co(en)₂] (ClO₄)₃ · H₂O from which the less soluble meso form can be readily crystallized. Further crystallization from the mother liquor yields the racemate ΔΔ/ΔΔ. The pure racemate may be obtained by either of the following methods: (a) By ligand exchange starting from mono bridged [(NH₃)₅CoO₂Co(NH₃)₅] (NO₃)₄ or from doubly bridged [(SCN) (NH₃)₃Co(O₂, OH)Co(NH₃)₃(SCN)] SCN · 2H₂O. (b) By reaction of cis-[Co(en)₂(OH₂)₂]³⁺ with H₂O₂. Reaction (b) proceeds via an intermediate cis-[Co(en)₂(OOH) (OH₂)] (ClO₄)₂ · H₂O which at higher pH reacts with [Co(en)₂(OH) (OH₂)]²⁺ to yield the desired doubly bridged ΔΔ/ΔΔ tetrakis(ethylenediamine)-μ-peroxo-μ-hydroxodikobalt(III)-perchlorate.     

The first X‐ray structure of a hexa­ammine­cobalt(III) salt with two different complex chloro­cadmium anions: synthesis,characterization and crystal structure of [Co(NH3)6]4[CdCl6][CdCl4(SCN)(H2O)]2Cl2·2H2O

In the title complex salt, tetra­kis[hexa­ammine­cobalt(III)] hexa­chloro­cadmate(II) bis­[aqua­tetra­chloro­thio­cyanato­cad­mate(II)] dichloride dihydrate, the discrete ions, i.e. [Co(NH₃)₆]³⁺, Cl⁻, [CdCl₆]⁴⁻ (located on an inversion centre) and [CdCl₄(SCN)(H₂O)]³⁻, together with cocrystallized water mol­ecules, are assembled by means of a network of hydrogen‐bonding inter­actions. This is the first X‐ray structure determination of a hexa­amminecobalt(III) salt with two different complex chloro­cadmium anions.     

Darstellung und Charakterisierung der Pentammin-Komplexe [Os(NH3)5(NCS)]2+ und [Os(NH3)5(NCSe)]2+

Preparation and Characterization of the Pentammine Complexes [Os(NH₃)₅(NCS)]²⁺ and [Os(NH₃)₅(NCSe)]²⁺ The new pentammine complexes [Os(NH₃)₅(NCS)]²⁺ and [Os(NH₃)₅(NCSe)]²⁺ are prepared from the reaction of [Os(NH₃)₅(CF₃SO₃)](CF₃ SO₃)₂ with NH₄SCN and KSeCN, respectively, in acetone, and subsequent purification by ion exchange chromatography on carboxymethyl cellulose. Evidence of N-bonding in both cases is given by the vibrational spectra, indicating that Os³⁺ is in terms of Lewis acidity harder than Ru³⁺, Rh³⁺, and Ir³⁺. I.r. and Raman spectra are interpreted according to local C_4v symmetry around Os, and the presumed assignments are confirmed by comparison with the i.r. spectra of the perdeuterated compounds. In the electronic spectra of both complexes charge transfer bands at 412 nm (NCS) and 498 nm (NCSe) are observed, respectively. Further weak absorptions near 4500 and 5100 cm^?1, which are in correlation with electronic Raman bands, are assigned to intraconfigurational transitions within the ²T_2g (O_h) ground term, split into three Kramers doubletts by spin-orbit coupling and lowered symmetry. Electrochemical measurements demonstrate a stabilisation of +III and +II oxidation states by π-back donation to —NCS and —NCSe ligands.     

Redox properties of bis(1,10-phenanthroline)-(pyridine)ruthenium(II) complexes

The redox properties of a series of [Ru(phen)₂(py)X]ⁿ⁺ cations (X = pyridine, NH₃, Cl, Br, I, CN, SCN, N₃ and NO₂) have been investigated in acctonitrile. Two reversible reduction steps are seen at ? 1.35 and ? 1.6 V vs Ag/AgCl; the invariance of these processes with X-group is indicative of electron addition to molecular orbitals mainly of phenanthroline ligand π^* origin. Irreversible multi-electron reductions follow below ? 2.20 V. The Ru(II)/Ru(III) couple is seen as a reversible wave near + 0.8 V vs the normal hydrogen electrode, from calibration with ferrocene, except in the cases of the NO₂ and SCN complexes, where rapid reactions involving these ligands occur.     

The solid state reaction between hexaamminechromium(III) complexes and L-α-alanine

The solid reaction between [Cr(NH₃)₆]X₃(X^? = Cl, I, SCN and NO₃) and L-α-alanine was studied under continuous rise in temperature and isothermal heating. Under continuous rise in temperature, the main products were [Cr(NCS)₃-(NH₃)₃] (X^? = NCS) and [Cr(L-ala)₃] (X^? = NO₃), when [Cr(NH₃)₆]Cl₃ and [Cr(NH₃)₆]I₃ as starting complexes were used; in both cases only the decomposition proceeds. Under isothermal heating at 150°C the main products were [CrCl(NH₃)₅]-Cl₂ (X^? = Cl), [Cr(NH₃)₆]I₂ (X^? = I), [Cr(NCS)₃(NH₃)₃] (X^? = SCN) and [Cr(L-ala)₃] (X^? = NO₃). In those matrix reactions, the ease of anion coordination was: SCN^? > Cl^? > I^? > alanine. For the synthesis of tris(alaninato)chromium(III) complex the most desirable starting complex was [Cr(NH₃)₆](NO₃)₃.The solid state reaction between [Cr(en)₃]X₃ type complexes and NH₄X (X^? = F, Cl, Br, I and SCN), KX (X^? = Cl, Br and I), and NaSCN have been reported by Wendlandt and Stembridge¹. They reported that the reaction product in most cases, was cis-[Cr(en)₂Y₂]X, where Y and X are the same or different anions, depending upon the matrix material employed and the thermal matrix method appears to be a useful new route for the synthesis of bis(ethylendiamine(chromium(III) complexes.In the previous paper², the solid state reaction between [Cr(NH₃)₆](NO₃)₃ and L-amino acids has been utilized in the preparation of tris(amino acidato)chromium(III) complexes. The preparation of [Cr(L-ala)₃] by the solid state reaction between [Cr(NH₃)₆](NO₃)₃ and L-alanine have been reported. No studies on the effect of the counter-ion have been reported.In this paper, various hexaamminechromium(III) complexes, [Cr(NH₃)₆]X₃ (X^? = Cl, I, SCN and NO₃), were heated with L-α-alanine under continuous rise in temperature and under isothermal heating at 150°C for studies on the ease of anion coordination. It will seen that the anion which replaces the ammonia in the hexaamminechromium(III) complex comes from either the alanine or counter-ion.     

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.     

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.     

Double complexes [Co(NH3)5(H2O)]2[Zr3F18]·6H2O and [Co(NH3)6]2[Zr3F18]·6H2O

The structures of orthorhombic bis[pentaammineaquacobalt(III)] tetra‐μ₂‐fluorido‐tetradecafluoridotrizirconium(IV) hexahydrate (space group Ibam), [Co(NH₃)₅(H₂O)]₂[Zr₃F₁₈]·6H₂O, (I), and bis[hexaamminecobalt(III)] tetra‐μ₂‐fluorido‐tetradecafluoridotrizirconium(IV) hexahydrate (space group Pnna), [Co(NH₃)₆]₂[Zr₃F₁₈]·6H₂O, (II), consist of complex [Co(NH₃)_x(H₂O)_y]³⁺ cations with either m [in (I)] or and 2 [in (II)] symmetry, [Zr₃F₁₈]⁶⁻ anionic chains located on sites with 222 [in (I)] or 2 [in (II)] symmetry, and water molecules.     

Coordination chemistry of the [Pt2(μ-S)2(PPh3)4] metalloligand with π-hydrocarbon derivatives of d ruthenium(II), osmium(II), rhodium(III) and iridium(III)

The reactivity of [Pt₂(μ-S)₂(PPh₃)₄] towards [RuCl₂(η⁶-arene)]₂ (arene=C₆H₆, C₆Me₆, p-MeC₆H₄Prⁱ=p-cymene), [OsCl₂(η⁶-p-cymene)]₂ and [MCl₂(η⁵-C₅Me₅)]₂ (M=Rh, Ir) have been probed using electrospray ionisation mass spectrometry. In all cases, dicationic products of the type [Pt₂(μ-S)₂(PPh₃)₄ML]²⁺ (L=π-hydrocarbon ligand) are observed, and a number of complexes have been prepared on the synthetic scale, isolated as their BPh₄⁻ or PF₆⁻ salts, and fully characterised. A single-crystal X-ray structure determination on the Ru p-cymene derivative confirms the presence of a pseudo-five-coordinate Ru centre. This resists addition of small donor ligands such as CO and pyridine. The reaction of [Pt₂(μ-S)₂(PPh₃)₄] with RuClCp(PPh₃)₂ (Cp=η⁵-C₅H₅) gives [Pt₂(μ-S)₂(PPh₃)₄RuCp]⁺. In addition, the reaction of [Pt₂(μ-S)₂(PPh₃)₄] with the related carbonyl complex [RuCl₂(CO)₃]₂, monitored by electrospray mass spectrometry, gives [Pt₂(μ-S)₂(PPh₃)₄Ru(CO)₃Cl]⁺.     

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.     

Double complex salts [M(NH3)5Cl][M′Br4] (M = Rh, Ir, Co, Cr, Ru; M′ = Pt, Pd): Synthesis, x-ray diffraction characterization, and thermal properties

Double complex salts (DCSs) with [M(NH₃)₅Cl]²⁺ (M = Rh, Ir, Co, Cr, Ru) cations and [PtBr₄]^2? anions were prepared in high yields. The salts were two-phase mixtures of the anhydrous and monohydro DCSs. Anhydrous analogues containing [PdBr₄]^2? anions with M = Cr or Ru were synthesized. All the compounds were characterized using a set of physicochemical methods. The crystal structure of chloropentaamminechromium(III) tetrabromopalladate(II) was solved: space group Pnma, Z = 4, a = 17.068(2) Å, b = 8.315(12) Å, c = 9.653(14) Å. The [M(NH₃)₅Cl][M′X₄] (M = Rh, Ir, Co, Cr, Ru; M′ = Pd, Pt; X = Cl, Br) compounds were shown to be isostructural. The [M(NH₃)₅Cl][PtBr₄] · H₂O monohydrates are isostructural to the [M(NH₃)₅Cl][PdCl₄] · H₂O monohydrates (space group P2₁/c, z = 4). The properties of the compounds were comparatively analyzed. The tendencies of the thermal stability of the complexes were elucidated. The thermolysis products of the double complex salts obtained under a helium or hydrogen atmosphere were studied.     

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.     

Electronic structure, spectrum, and intramolecular electron transfer model of [(NH3)5Ru-(4,4’-bipy)-Ru(NH3)5]5+

The electronic structure of the ground and excited states of the binuclear mixed-valence complex [Ru(NH₃)₅]₂(4,4’-bipy)⁵⁺ is calculated by the semiempirical INDO + CI method, and an electronic spectrum assignment is given. A theoretical model of electron transfer between the Ru(II) and Ru(III) metal centers is constructed on the basis of many-electron wave functions. The dependence of the electron transfer characteristics on the angles between the planes of the pyridine rings and also between the pyridine rings and the planes of cis(NH₃)-Ru-cis(NH₃) is analyzed. Translated fromZhumal Struktumoi Khimii, Vol. 38, No. 3, pp. 447–456, May–June, 1997.     

Attempts of synthesis of Hg(SCN)4-based coordination polymers in conjunction with [Cu(L–L)2] building blocks

Five novel heterobimetallic compounds [Cu(bpzm)₂Hg(SCN)₄]_n (1), [Cu(bdmpzm)₂(μ-SCN)Hg(SCN)₃] (2), [Cu(pybzim)₂(μ-SCN)Hg(SCN)₃]·H₂O (3), [Cu(bipy)₂(μ-SCN)Hg(SCN)₃][Cu(bipy)₂(μ-SCN)₂Hg(SCN)₂] (4) and [Cu(bipy)(NCS)]₂[Hg(SCN)₄] (5) have been synthesized and structurally characterized (bpzm-bis(pyrazol-1-yl)methane, bdmpzm-bis(3,5-dimethylpyrazol-1-yl)methane, pybzim-2-(2-pyridyl)benzimidazole, phen-1,10-phenantroline and bipy-2,2′-bipyridine). The compounds 2, 3, 4 and 5 are molecular complexes, whereas 1 is an alternating 1-D zigzag chain of [Cu(bpzm)₂]²⁺ and Hg(SCN)₄]²⁻ moieties in which the metal atoms are bridged via thiocyanate ions. The polymer 1 has been studied by magnetic measurement.     

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.