pH‐Controlled Multiple Chiral Inversion That Induces Molecular Dimerization in a Gold(I)–Cobalt(III) Coordination System with L‐Cysteinate

Herein, a unique coordination system that exhibits multiple chiral inversions and molecular dimerization in response to a subtle pH change is reported. Treatment of (Δ)₂‐H₃[Au₃Co₂(L ‐cys)₆] (H₃[ 1 a ]) with [Co₃(aet)₆](NO₃)₃ (aet=2‐aminoethanethiolate) in water at pH 7 gave a 1:1 complex salt of [Co₃(aet)₆]³⁺ and [ 1 a ]^3?, retaining the Au^I₃Co^III₂ structure and chiral configurations of [ 1 a ]^3?. Similar treatment at pH 9 led to not only the inversion of all of the chiral Co^III and S centers but also the dimerization of [ 1 a ]^3?, giving a 2:1 complex salt of [Co₃(aet)₆]³⁺ and (Λ)₄(R)₁₂‐[Au₆Co₄(L ‐cys)₁₂]^6? ([ 2 ]^6?). When dissociated from [Co₃(aet)₆]³⁺ in solution, [ 2 ]^6? was converted to (Λ)₂(R)₆‐[Au₃Co₂(L ‐cys)₆]^3? ([ 1 b ]^3?) with retention of the chiral configurations.     

S-bridged complex of <Superscript>99m</Superscript>Tc with <Emphasis Type="Italic">fac</Emphasis>(S)-[Rh(aet)<Subscript>3</Subscript>]: Quality control,characterization and biodistribution studies in rats

fac(S)-[Rh(aet)₃] (aet = 2-aminoethanethiolate) is N₃S₃ metalloligand which can coordinate to transition metal ions to form S-bridge polynuclear complexes. The reaction was carried out between ^99mTcO₄Na and fac(S)-[Rh(aet)₃] in the presence of SnCl₂·2H₂O. A complex analogous to [Re{Rh(aet₃)}₂]³⁺ is formed.⁶ A simple method for radiolabeling of fac(S)-[Rh(aet)₃] with ^99mTc has been developed and radiolabeling efficiency was higher than 99%. Effect of SnCl₂·2H₂O concentration, electrophoresis, HPLC, UV-Visible absorption spectra and biodistribution studies in rats were performed. Higher uptake by kidneys showed rapid distributions of the labeled fac(S)-[Rh(aet)₃]. Liver uptake was significant, stomach, lungs and intestine uptake was high at 4 hours post injection time.     

Thiolato-bridged RuIIAgIRuII trinuclear complex composed of bis(bipyridine)ruthenium(II) units with chelating 2-aminoethanethiolate: conversion to a disulfide-bridged RuIIRuII dinuclear complex

The reaction of [Ru(solvent)2(bpy)2]2+ (bpy = 2,2'-bipyridine) with Haet (2-aminoethanethiol) in ethanol/water in the presence of Ag+ gave a thiolato-bridged RuIIAgIRuII trinuclear complex, [Ag{Ru(aet)(bpy)2}2]3+, in which two [RuII(aet)(bpy)2]+ units are linked by an AgI atom. When this complex was treated with HCl in acetonitrile/water, a disulfide-bridged RuIIRuII dinuclear complex, [Ru2(cysta)(bpy)4]4+ (cysta = cystamine), was produced as a result of the removal of an AgI atom and the autoxidation of thiolato groups. It was found that the dinuclear structure in [Ru2(cysta)(bpy)4]4+ is reverted back to [Ag{Ru(aet)(bpy)2}2]3+ by treatment with Ag+ assisted by Zn reduction.     

The first triple thiol-thiolate hydrogen bond versus triple diselenide bond that bridges two metal centers

Treatment of fac(S)-[Rh(aet)3] (aet = 2-aminoethanethiolate) with aqueous HBF4 in air led to the protonation at coordinated thiolato groups to give a rhodium(III) dimer, [{Rh(aet)2(Haet)}{Rh(aet)(Haet)2}](BF4)3 ([1](BF4)3). On the other hand, similar treatment of fac(Se)-[Rh(aes)3] (aes = 2-aminoethaneselenolate) produced a dinuclear rhodium(III) complex, [Rh2(selenocystamine)3](BF4)6 ([2](BF4)6), because of the autoxidation of coordinated selenolato groups by air. The crystal structures of [1](BF4)3, DeltaDelta-[1](BF4)3, and [2](BF4)6 were determined by X-ray crystallography. In [1]3+ two RhIII octahedrons are connected through a strong triple thiol-thiolate S-H...S hydrogen bond, while two RhIII octahedrons are directly joined by a triple diselenide bond in [2]6+. The cyclic voltammetry indicated that in acidic media the RhIII center in fac(Se)-[Rh(aes)3] is more easily oxidized to RhIV than that in fac(S)-[Rh(aet)3], which is responsible for the formation of coordinated diselenide bonds.     

Heterometallation of Photoluminescent Silver(I) Sulfide Nanoclusters Protected by Octahedral Iridium(III) Thiolates

The recently-increasing interest in coinage metal clusters stems from their photophysical properties, which are controlled via heterometallation. Herein, we report homometallic Ag^I₄₆S₁₃ clusters protected by octahedral fac-[Ir(aet)₃] (aet=2-aminoethanethiolate) molecules and their conversion to heterometallic Ag^I₄₃M^I₃S₁₃ (M=Cu, Au) clusters. The reactions of fac-[Ir(aet)₃] with Ag⁺ and penicillamine produced [Ag₄₆S₁₃{Ir(aet)₃}₁₄]²⁰⁺ ([ 1 ]²⁰⁺), where a spherical Ag^I₄₆S₁₃ cluster is covered by fac-[Ir(aet)₃] octahedra through thiolato bridges. [ 1 ]²⁰⁺ was converted to [Ag₄₃M₃S₁₃{Ir(aet)₃}₁₄]²⁰⁺ ([ 1^M ]²⁰⁺) with an Ag^I₄₃M^I₃S₁₃ cluster by treatment with M⁺, retaining its overall structure. [ 1 ]²⁰⁺ was photoluminescent and had an emission band ca. 690 nm that originated from an S-to-Ag charge transfer. While [ 1^Cu ]²⁰⁺ showed an emission band with a slightly higher energy of ca. 650 nm and a lower quantum yield, the emission band for [ 1^Au ]²⁰⁺ shifted to a much higher energy of ca. 590 nm with an enhanced quantum yield.     

Bis(μ‐cyst­amine‐κ4N,S:S′,N′)­bis­[(2‐amino­ethane­thiol­ato‐κ2N,S)­iridium(III)] tetrabromide dihydrate

In the complex cation of the title compound, [Ir₂(C₂H₆NS)₂(C₄H₁₂N₂S₂)₂]Br₄·2H₂O, which was obtained by rearrangement of [Re{Ir(aet)₃}₂]³⁺ (aet is 2‐amino­ethane­thiol­ate) in an aqueous solution, two approximately octahedral fac(S)‐[Ir(NH₂CH₂CH₂S)₃] units are linked by two coordinated di­sulfide bonds. The complex cation has a twofold axis, and the two non‐bridging thiol­ate S atoms in the complex are located on opposite sides of the two di­sulfide bonds. Considering the absolute configurations of the two octahedral units (Δ and Λ) and the four asymmetric di­sulfide S atoms (R and S), the complex consists of the Δ_RRΔ_RR and Λ_SSΛ_SS isomers, which combine to form the racemic compound.     

Facile Carbon–Fluorine Bond Activation and Subsequent Functionalisation of 1,1‐Difluoroethylene and Tetrafluoroethylene Promoted by Adjacent Metal Centres

The bridging fluoroolefin ligands in the complexes [Ir₂(CH₃)(CO)₂(μ‐olefin)(dppm)₂][OTf] (olefin=tetrafluoroethylene, 1,1‐difluoroethylene; dppm=μ‐Ph₂PCH₂PPh₂; OTf^?=CF₃SO₃^?) are susceptible to facile fluoride ion abstraction. Both fluoroolefin complexes react with trimethylsilyltriflate (Me₃SiOTf) to give the corresponding fluorovinyl products by abstraction of a single fluoride ion. Although the trifluorovinyl ligand is bound to one metal, the monofluorovinyl group is bridging, bound to one metal through carbon and to the other metal through a dative bond from fluorine. Addition of two equivalents of Me₃SiOTf to the tetrafluoroethylene‐bridged species gives the difluorovinylidene‐bridged product [Ir₂(CH₃)(OTf)(CO)₂(μ‐OTf)(μ‐C?CF₂)(dppm)₂][OTf]. The 1,1‐difluoroethylene species is exceedingly reactive, reacting with water to give 2‐fluoropropene and [Ir₂(CO)₂(μ‐OH)(dppm)₂][OTf] and with carbon monoxide to give [Ir₂(CO)₃(μ‐κ¹:η²‐C?CCH₃)(dppm)₂][OTf] together with two equivalents of HF. The trifluorovinyl product [Ir₂(κ¹‐C₂F₃)(OTf)(CO)₂(μ‐H)(μ‐CH₂)(dppm)₂][OTf], obtained through single C? F bond activation of the tetrafluoroethylene‐bridged complex, reacts with H₂ to form trifluoroethylene, allowing the facile replacement of one fluorine in C₂F₄ with hydrogen.     

Reactions of [Cp*Ru(H2O)(NBD)]+ with alkynes

Formal [2 + 2 + 2] addition reactions of [Cp*Ru(H₂O)(NBD)]BF₄ (NBD = norbornadiene) with PhC?CR (R = H, COOEt) give [Cp*Ru(η⁶‐C₆H₅? C₉H₈R)] BF₄ (1a, R = H; 2a, R = COOEt). Treatment of [Cp*Ru(H₂O)(NBD)]BF₄ with PhC?C? C?CPh does not give [2 + 2 + 2] addition product, but [Cp*Ru(η⁶‐C₆H₅? C?C? C?CPh)] BF₄(3a). Treatment of 1a, 2a, 3a with NaBPh₄ affords [Cp*Ru(η⁶‐C₆H₅? C₉H₈R)] BPh₄ (1b, R = H; 2b, R = COOEt) and [Cp*Ru(η⁶‐C₆H₅? C?C? C?CPh)] BPh₄(3b). The structures of 1b, 2b and 3b were determined by X‐ray crystallography. Copyright © 2007 John Wiley & Sons, Ltd.     

On the Design of Radical–Radical Cocrystals

Formation of radical–radical cocrystals is an important step towards the design of organic ferrimagnets. We describe a simple approach to generate radical–radical cocrystals through the identification and implementation of well‐defined supramolecular synthons which favor cocrystallization over phase separation. In the current paper we implement the structure‐directing interactions of the E?E bond (E=S, Se) of dithiadiazolyl (DTDA) and diselenadiazolyl (DSDA) radicals to form close contacts to electronegative groups. This is exemplified through the preparation and structural characterization of three sets of radical cocrystals; the 2:2 cocrystal [PhCNSSN]₂[MBDTA]₂ ( 4 ) [MBDTA=methyl benzodithiazolyl] and the 2:1 cocrystals [C₆F₅CNEEN]₂[TEMPO] (E=S, 5 ; E=Se, 6 ). In 4 the two types of radical are linked via bifurcated inter‐dimer ^δ+S???N^δ? interactions whereas 5 and 6 exhibit a set of five‐centre ^δ+E???O^δ? contacts (E=S, Se).     

The Effect of C4H and C5H on the Microstructure of Aqueous Solutions of 1‐Alkyl‐3‐methylimidazolium Tetrafluoroborate Ionic Liquids

As is well‐known, the C2?H proton of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ([Emim]BF₄) and 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([Bmim]BF₄) has a strong ability to form hydrogen bonds. The purpose of this work is to evaluate the effect of the interactions of the C4?H and C5?H protons on the microstructure of [Emim]BF₄ and [Bmim]BF₄ with water by using ¹H NMR spectroscopy. The differences between the relative ¹H NMR chemical shifts of C2?H, C4?H, and C5?H and between the interaction‐energy parameters obtained from these chemical shifts are minor, thus suggesting that the interactions of C4?H and C5?H may have a considerable effect on the microstructure. To confirm this, the viscosities of the systems are estimated by using the interaction‐energy parameters obtained from the ¹H NMR chemical shifts of the three studied aromatic protons and water, showing that the interactions of C4?H and C5?H also play an important role in the microstructure.     

{μ‐PbSe}: A Heavy CO Homologue as an Unexpected Ligand

Reactions of [K(18‐crown‐6)]₂[Pb₂Se₃] and [K([2.2.2]crypt)]₂[Pb₂Se₃] with [Rh(PPh₃)₃Cl] in en (ethane‐1,2‐diamine) afforded ionic compounds with [Rh₃(PPh₃)₆(μ₃‐Se)₂]^? and [Rh₃(CN)₂(PPh₃)₄(μ₃‐Se)₂(μ‐PbSe)]^3? anions, respectively. The latter contains a PbSe ligand, a rather uncommon homologue of CO that acts as a μ‐bridge between two Rh atoms. Quantum chemical calculations yield a significantly higher bond energy for PbSe than for CO, since the size of the ligand orbitals better matches the comparably rigid Rh‐Se‐Rh angles and the resulting Rh???Rh distance. To rationalize the bent coordination of the ligand, orbitals with significant ligand contributions and their dependence on the bonding angle were investigated in detail.     

Dissociation of disulfide‐intact somatostatin ions: the roles of ion type and dissociation method

The dissociation chemistry of somatostatin‐14 was examined using various tandem mass spectrometry techniques including low‐energy beam‐type and ion trap collision‐induced dissociation (CID) of protonated and deprotonated forms of the peptide, CID of peptide‐gold complexes, and electron transfer dissociation (ETD) of cations. Most of the sequence of somatostatin‐14 is present within a loop defined by the disulfide linkage between Cys‐3 and Cys‐14. The generation of readily interpretable sequence‐related ions from within the loop requires the cleavage of at least one of the bonds of the disulfide linkage and the cleavage of one polypeptide backbone bond. CID of the protonated forms of somatostatin did not appear to give rise to an appreciable degree of dissociation of the disulfide linkage. Sequential fragmentation via multiple alternative pathways tended to generate very complex spectra. CID of the anions proceeded through CH₂? S cleavages extensively but relatively few structurally diagnostic ions were generated. The incorporation of Au(I) into the molecule via ion/ion reactions followed by CID gave rise to many structurally relevant dissociation products, particularly for the [M+Au+H]²⁺ species. The products were generated by a combination of S? S bond cleavage and amide bond cleavage. ETD of the [M+3H]³⁺ ion generated rich sequence information, as did CID of the electron transfer products that did not fragment directly upon electron transfer. The electron transfer results suggest that both the S? S bond and an N? C_α bond can be cleaved following a single electron transfer reaction. Copyright © 2009 John Wiley & Sons, Ltd.     

Electrochemical Investigations Give Some Insights into the Coordination Chemistry of New Stable Iridium(+1), Iridium(0), and Iridium(−1) Complexes

The redox chemistry of the stable tetracoordinated 16 valence electron d⁸‐[Ir^+I(tropp^Ph)₂]⁺(PF₆)^? and pentacoordinated 18 valence d⁸‐[Ir^+I(tropp^Ph)₂Cl] complexes was investigated by cyclic voltammetry (tropp^Ph=dibenzotropylidenyl phosphine). The experiments were performed using a platinum microelectrode varying scan rates (100 mV/s–10 V/s) and temperatures (? 40 to 20 °C) in tetrahydrofuran, THF, or acetonitrile, ACN, as solvents. In THF, the overall two‐electron reduction of the 16 valence electron d⁸‐[Ir^+I(tropp^Ph)₂]⁺(PF₆)^? proceeds in two well separated slow heterogeneous electron transfer steps according to: d⁸‐[Ir^+I (tropp^Ph)₂]⁺+e^?→d⁹‐[Ir⁰(tropp^Ph)₂]+e^?→d¹⁰‐[Ir^?I(tropp^Ph)₂]^?, [k^s₁=2.2×10^?3 cm/s for d⁸‐Ir^+I/d⁹‐Ir⁰ and k^s₂=2.0×10^?3 cm/s for d⁹‐Ir⁰/d¹⁰‐Ir^?I]. In ACN, the two redox waves merge into one “two‐electron” wave [k^s_1,2=7.76×10^?4 cm/s for d⁸‐Ir^+I/d⁹‐Ir⁰ and d⁹‐Ir⁰/d¹⁰‐Ir^?I] most likely because the neutral [Ir⁰(tropp^Ph)₂] complex is destabilized. At low temperatures (ca. ? 40 °C) and at high scan rates (ca. 10 V/s), the two‐electon redox process is kinetically resolved. In equilibrium with the tetracoordianted complex [Ir^+I(tropp^Ph)₂]⁺ are the pentacoordinated 18 valence [Ir^+I(tropp^Ph)₂L]⁺ complexes (L=THF, ACN, Cl^?) and their electrochemical behavior was also investigated. They are irreversibly reduced at rather high negative potentials (? 1.8 to ? 2.4 V) according to an ECE mechanism 1) [Ir^+I(tropp^Ph)₂(L)]+e^?→[Ir⁰(tropp^Ph)₂(L)]; 2) [Ir⁰(tropp^Ph)₂(L)]→[Ir(tropp^Ph)₂]+L, iii) [Ir⁰(tropp^Ph)₂]+e^?→[Ir^?I(tropp^Ph)₂]^?. Since all electroactive species were isolated and structurally characterized, our measurements allow for the first time a detailed insight into some fundamental aspects of the coordination chemistry of iridium complexes in unusually low formal oxidation states.     

Proton‐Induced Generation of Remote N‐Heterocyclic Carbene–Ru Complexes

The proton‐induced Ru?C bond variation, which was previously found to be relevant in the water oxidation, has been investigated by using cyclometalated ruthenium complexes with three phenanthroline (phen) isomers. The designed complexes, [Ru(bpy)₂(1,5‐phen)]⁺ ([ 2 ]⁺), [Ru(bpy)₂(1,6‐phen)]⁺ ([ 3 ]⁺), and [Ru(bpy)₂(1,7‐phen)]⁺ ([ 4 ]⁺) were newly synthesized and their structural and electronic properties were analyzed by various spectroscopy and theoretical protocols. Protonation of [ 4 ]⁺ triggered profound electronic structural change to form remote N‐heterocyclic carbene (rNHC), whereas protonation of [ 2 ]⁺ and [ 3 ]⁺ did not affect their structures. It was found that changes in the electronic structure of phen beyond classical resonance forms control the rNHC behavior. The present study provides new insights into the ligand design of related ruthenium catalysts.     

Ring‐to‐Cage Structural Conversion via Template Effect in a Gold(I) Metallosupramolecular System

A unique example of a ring‐to‐cage structural conversion in a multinuclear gold(I) coordination system with d ‐penicillamine (d ‐H₂pen) is reported. The reaction of [Au₂Cl₂(dppe)] (dppe=1,2‐bis(diphenylphosphino)ethane) with d ‐H₂pen in a 1:1 ratio gave [Au₄(dppe)₂(d ‐pen)₂] ([ 1 ]), in which two [Au₂(dppe)]²⁺ units are linked by two d ‐pen S atoms in a cyclic form so as to have two bidentate‐N,O coordination arms. The subsequent reaction of [ 1 ] with Cu(OTf)₂ afforded [Au₄Cu(dppe)₂(d ‐pen)₂]²⁺ ([ 2 ]²⁺), in which a Cu^II ion is chelated by the two coordination arms in [ 1 ] to form an Au^I₄Cu^II bicyclic metallocage. A similar reaction using Cu(NO₃)₂ was accompanied by the ring expansion of [ 1 ] to [Au₈(dppe)₄(d ‐pen)₄], leading to the production of [Au₈Cu₂(dppe)₄(d ‐pen)₄]⁴⁺ ([ 3 ]⁴⁺). In [ 3 ]⁴⁺, two Cu^II ions are each chelated by the two coordination arms to form an Au^I₈Cu^II₂ tricyclic metallocage, accommodating a nitrate ion. The use of Ni(NO₃)₂ or Ni(OAc)₂ instead of Cu(NO₃)₂ commonly gave a tricyclic metallocage of [Au₈Ni₂(dppe)₄(d ‐pen)₄]⁴⁺ ([ 4 ]⁴⁺), but a water molecule was accommodated inside the Au^I₈Ni^II₂ metallocage.     

Stereospecific π–π stacking interactions between pseudo-enantiomeric sulfur-bridged dinuclear Co(III)–Pd(II) and Co(III)–Pt(II) complexes with optically active propanediamines

Assemblies between pseudo-enantiomers with different d⁸ metal centers, Δ-[M(bpy){Co(aet)₂(R-pn)}]³⁺ (M?=?Pd or Pt, bpy?=?2,2′-bipyridine, aet?=?2-aminoethanethiolate, pn?=?1,2-propanediamine), and Λ-[M′(bpy){Co(aet)₂(S-pn)}]³⁺ (M′ ≠ M, M′?=?Pd or Pt), have been examined from stereo- and spectrochemical aspects. A mixture of equimolar amounts of the optically active sulfur-bridged dinuclear complex, Δ-[M(bpy){Co(aet)₂(R-pn)}](NO₃)₃·7H₂O, and its pseudo-enantiomer, Λ-[M′(bpy){Co(aet)₂(S-pn)}](NO₃)₃·7H₂O, in H₂O crystallizes as [M(bpy){Co(aet)₂(R-pn)}][M′(bpy){Co(aet)₂(S-pn)}](NO₃)₆·4H₂O, in which two complex cations with imperfect enantiomorphisms form a 1?:?1 π–π stacked unit.     

Manganese cationic pyrazolylamidino complexes

The reactions of fac-[MnBr(CO)₃(NHC(CH₃)pz^∗-κ²N,N)] (pz^∗ = pz, dmpz; pzH = pyrazole; dmpzH = 3,5-dimethylpyrazole) with wet AgBF₄ in a 1:1 ratio lead to the cationic pyrazolylamidino complexes fac-[Mn(OH₂)(CO)₃(NHC(CH₃)pz^∗-κ²N,N)]BF₄. The aquo ligand is readily substituted by 2,6-xylylisocyanide (CNXyl) to give fac-[Mn(CNXyl)(CO)₃(NHC(CH₃)pz^∗-κ²N,N)]BF₄. The pyrazole complexes fac-[Mn(pz^∗H)(CO)₃(NHC(CH₃)pz^∗-κ²N,N)]BF₄ are obtained by treating fac-[MnBr(CO)₃(NCMe)₂] with AgBF₄ and then with pyrazole (pzH or dmpzH), in a 1:1:2 ratio. A similar reaction using 1:1:1 ratio and AgClO₄ leads to the acetonitrile complexes fac-[Mn(NCMe)(CO)₃(NHC(CH₃)pz^∗-κ²N,N)]ClO₄. The X-ray structures of the complexes show moderate hydrogen bonds interactions between the N-bond hydrogen of the pyrazolylamidino ligand and the anion. In the aquo complex, one of the hydrogens of the coordinated water molecule is also involved in a hydrogen bond.     

Catalytic Four‐Electron Oxidation of Water by Intramolecular Coupling of the Oxo Ligands of a Bis(ruthenium–bipyridine) Complex

A bis(ruthenium–bipyridine) complex bridged by 1,8‐bis(2,2′:6′,2′′‐terpyrid‐4′‐yl)anthracene (btpyan), [Ru₂(μ‐Cl)(bpy)₂(btpyan)](BF₄)₃ ([ 1 ](BF₄)₃; bpy=2,2′‐bipyridine), was prepared. The cyclic voltammogram of [ 1 ](BF₄)₃ in water at pH 1.0 displayed two reversible [Ru^II,Ru^II]³⁺/[Ru^II,Ru^III]⁴⁺ and [Ru^II,Ru^III]⁴⁺/[Ru^III,Ru^III]⁵⁺ redox couples at E_1/2(1)=+0.61 and E_1/2(2)=+0.80 V (vs. Ag/AgCl), respectively, and an irreversible anodic peak at around E=+1.2 V followed by a strong anodic currents as a result of the oxidation of water. The controlled potential electrolysis of [ 1 ]³⁺ ions at E=+1.60 V in water at pH 2.6 (buffered with H₃PO₄/NaH₂PO₄) catalytically evolved dioxygen. Immediately after the electrolysis of the [ 1 ]³⁺ ion in H₂¹⁶O at E=+1.40 V, the resultant solution displayed two resonance Raman bands at $\tilde \nu $ =442 and 824 cm^‐1. These bands shifted to $\tilde \nu $ =426 and 780 cm^?1, respectively, when the same electrolysis was conducted in H₂¹⁸O. The chemical oxidation of the [ 1 ]³⁺ ion by using a Ce^IV species in H₂¹⁶O and H₂¹⁸O also exhibited the same resonance Raman spectra. The observed isotope frequency shifts (Δ$\tilde \nu $ =16 and 44 cm^?1) fully fit the calculated ones based on the Ru? O and O? O stretching modes, respectively. The first successful identification of the metal? O? O? metal stretching band in the oxidation of water indicates that the oxygen–oxygen bond at the stage prior to the evolution of O₂ is formed through the intramolecular coupling of two Ru–oxo groups derived from the [ 1 ]³⁺ ion.     

A Dodecalanthanide Wheel Supported by p‐tert‐Butylsulfonylcalix[4]arene

A dodecaholmium wheel of [Ho₁₂(L)₆(mal)₄(AcO)₄(H₂O)₁₄] ( 1 ; mal=malonate) was synthesized by using p‐tert‐butylsulfonylcalix[4]arene (H₄L) as a cluster‐forming ligand. The wheel consists of three fragments of mononuclear A^3? ([Ho(L)(mal)(H₂O)]^3?), trinuclear B^3? ([Ho(H₂O)₂(mal)(Ho(L)(AcO))₂]^3?), and C³⁺ ([Ho(H₂O)₂]³⁺), and an alternate arrangement of these fragments (A^3?? C³⁺? B^3?? C³⁺? A^3?? C³⁺? B^3?? C³⁺? ) results in a wheel structure. The longest and shortest diameters of the core were estimated to be 17.7562(16) and 13.6810(13) Å, respectively, and the saddle‐shaped molecule possesses a pocketlike cavity inside.     

Redox non-innocence of thioether crowns: spectroelectrochemistry and electronic structure of formal nickel(III) complexes of aza-thioether macrocycles

The Ni^II complexes [Ni([9]aneNS₂‐CH₃)₂]²⁺ ([9]aneNS₂‐CH₃=N‐methyl‐1‐aza‐4,7‐dithiacyclononane), [Ni(bis[9]aneNS₂‐C₂H₄)]²⁺ (bis[9]aneNS₂‐C₂H₄=1,2‐bis‐(1‐aza‐4,7‐dithiacyclononylethane) and [Ni([9]aneS₃)₂]²⁺ ([9]aneS₃=1,4,7‐trithiacyclononane) have been prepared and can be electrochemically and chemically oxidized to give the formal Ni^III products, which have been characterized by X‐ray crystallography, UV/Vis and multi‐frequency EPR spectroscopy. The single‐crystal X‐ray structure of [Ni^III([9]aneNS₂‐CH₃)₂](ClO₄)₆?(H₅O₂)₃ reveals an octahedral co‐ordination at the Ni centre, while the crystal structure of [Ni^III(bis[9]aneNS₂‐C₂H₄)](ClO₄)₆?(H₃O)₃? 3H₂O exhibits a more distorted co‐ordination. In the homoleptic analogue, [Ni^III([9]aneS₃)₂](ClO₄)₃, structurally characterized at 30 K, the Ni? S distances [2.249(6), 2.251(5) and 2.437(2) Å] are consistent with a Jahn–Teller distorted octahedral stereochemistry. [Ni([9]aneNS₂‐CH₃)₂](PF₆)₂ shows a one‐electron oxidation process in MeCN (0.2 M NBu₄PF₆, 293 K) at E_1/2=+1.10 V versus Fc⁺/Fc assigned to a formal Ni^III/Ni^II couple. [Ni(bis[9]aneNS₂‐C₂H₄)](PF₆)₂ exhibits a one‐electron oxidation process at E_1/2=+0.98 V and a reduction process at E_1/2=?1.25 V assigned to Ni^II/Ni^III and Ni^II/Ni^I couples, respectively. The multi‐frequency X‐, L‐, S‐, K‐band EPR spectra of the 3+ cations and their 86.2 % ⁶¹Ni‐enriched analogues were simulated. Treatment of the spin Hamiltonian parameters by perturbation theory reveals that the SOMO has 50.6 %, 42.8 % and 37.2 % Ni character in [Ni([9]aneNS₂‐CH₃)₂]³⁺, [Ni(bis[9]aneNS₂‐C₂H₄)]³⁺ and [Ni([9]aneS₃)₂]³⁺, respectively, consistent with DFT calculations, and reflecting delocalisation of charge onto the S‐thioether centres. EPR spectra for [⁶¹Ni([9]aneS₃)₂]³⁺ are consistent with a dynamic Jahn–Teller distortion in this compound.