Effect of cobalt bis(dicarbollides) on electrochemical oxygen reduction on Pt electrode in methanol-acid solution

Electrochemical oxygen reduction on a platinum electrode has been investigated in methanol-0.05 M H₂SO₄ aqueous solutions in the presence of acids of cobalt bis(dicarbollide) (H⁺B⁻, H⁺[(1,2-C₂B₉H₁₁)₂-3-Co]⁽⁻⁾) or its hexachlorinated derivative (H⁺BCl⁻, H⁺ [(8,8′,9,9′,12,12′-Cl₆-(1,2-C₂B₉H₈)₂-3-Co)]⁽⁻⁾). Methanol oxidation was suppressed with H⁺BCl⁻ significantly, and selective oxygen reduction was achieved on a platinum electrode. The efficiency of oxygen reduction to H₂O, which depended on the electrode potential, was lower by 2% to 20% than that without H⁺BCl⁻. The mechanism was investigated by surface-enhanced infrared absorption spectroscopy (SEIRAS). H⁺BCl⁻ suppresses formation of both the catalytic poison, linear CO (ads.), from methanol and the formate, the intermediate of the non-CO path of methanol oxidation.     

Iron versus ruthenium oxidation in 1,1′-bis(diphenylphosphino)ferrocene–ruthenium(II) complexes: EPR and spectroelectrochemical evidence

Oxidation of [Cp^*RuH(dppf)] (1), dppf=1,1′-bis(diphenylphosphino)ferrocene, and [(Cym)RuCl(dppf)](PF₆) (2), Cym=p-cymene, occurs at ruthenium for 1 but yields a ferrocenium species for compound 2.     

Models of intermediates in metallocene-catalyzed alkene polymerizations: observation of a d0 cationic titanium–alkyl-alkene complex and decomposition by β-allyl elimination

Low temperature activation of Cp^*₂Ti[η¹,η¹- CH₂CH(CH₂CHCH₂)CH₂] (3) with [HN(CH₃)(C₆H₅)₂] [B(C₆F₅)₄] led to the formation of Cp^*₂Ti[η¹,η²-CH₂CH(CH₃)CH₂CHCH₂][B(C₆F₅)₄] (6) as determined by ¹H NMR spectroscopy. Cp^*₂Ti[η¹,η²-CH₂CH(CH₃)CH₂CHCH₂][B(C₆F₅)₄] undergoes rapid quantitative β-allyl elimination at temperatures as low as −140 °C. The resulting cationic titanium allyl complex [Cp^*₂Ti(η³-CH₂CHCH₂)][B(C₆F₅)₄] (4) exhibits a static structure at low temperatures, but interconversion of η³–η¹ binding modes can be observed at higher temperatures. Lineshape analysis of this process yielded ΔG³(−10 °C)= 13.7 ± 0.6 kcal mol⁻¹, ΔH³=9.8 ± 0.6 kcal mol⁻¹, and ΔS³=−15 ± 3 eu. The use of neutral borane B(C₆F₅)₃ also resulted in β-allyl elimination with the formation of [Cp^*₂Ti(η³-CH₂CHCH₂)][CH₂=CHCH₂B(C₆F₅)₃] (8).     

Syntheses and structures of the first two tetra-scandium substituted polyoxometalates

The first two tetra-Sc-substituted polyoxotungstates H₂K₂Na₂[Sc₄(H₂O)₁₀(B-β-SbW₉O₃₃)₂]·21H₂O (1) and H₂₀K₂Na₆[Sc₄(C₂O₄)₄(B-β-SbW₉O₃₃)₂][Sc₄(H₂O)₂(C₂O₄)₄(B-β-SbW₉O₃₃)₂]·64H₂O (2) have been synthesized and characterized by IR spectroscopy, AC impedance measurements, TG, PXRD, and single-crystal X-ray diffractions. Compound 1 represents an isolated inorganic sandwich-type dimeric POM constructed from two trilacunary Keggin [B-β-SbW₉O₃₃]^9 − moieties and four Sc^3 + ions, while compound 2 shows an extended organic–inorganic hybrid POM which composes of two kinds of distinct tetra-Sc-substituted polyoxotungstate building units and oxalate ligands. Notably, these two compounds also are the first Sc-containing polyoxotungstates based on trilacunary Keggin [B-β-SbW₉O₃₃]^9 − clusters. Electrochemical study showed that compound 2 has good proton conductivity.     

Eight-coordination in nitrato manganese(II) complexes with tetradentate di-Schiff bases derived from 2-pyridyl ketones: preparation,characterization and catalytic activity for alkene epoxidation

The reactions of Mn(NO₃)₂·6H₂O with the tetradentate Schiff bases N,N′-bis[1-(pyridin-2-yl)ethylidene]ethane-1,2-diamine (L_A) and N,N′-bis[1-(pyridin-2-yl)benzylidene]ethane-1,2-diamine (L_B) afforded the novel eight-coordinate complexes [Mn(NO₃)₂(L_A)] (1) and [Mn(NO₃)₂(L_B)] (2), which have a distorted dodecahedral coordination geometry. The catalytic activity of 1 and 2 for alkene epoxidation is reported and discussed.     

New estertin derivatives based on trivacant Keggin-type [β-SbW9O33]9− cluster

Two new polyoxometalate-based estertin derivatives, Na₆K₄[{Sn(C₃H₄O₂)}₂{Sn(C₃H₄O₂)(H₂O)}₂·(B-β-SbW₉O₃₃)₂]·14H₂O (1) and Na₄K₆[{Sn(C₄H₆O₂)(H₂O)}₂(WO₂)₂(B-β-SbW₉O₃₃)₂]·19H₂O (2), have been synthesized by the reaction of Na₉[B-α-SbW₉O₃₃]?19.5H₂O with Cl₃Sn(CH₂)₂COOCH₃ or Cl₃SnCH₂CH(CH₃)COOCH₃ in an aqueous KCl solution. Both compounds exhibit the sandwich-type structural feature, in which the carboxyethyltin fragments are sandwiched by two B-β-[SbW₉O₃₃]^9? units. Structural analyses reveal that the reaction process involves α → β isomerization of [SbW₉O₃₃]^9? unit and the hydrolysis of estertin into carboxyethyltin group. Both compounds display good electrocatalytic activities toward the reduction of hydrogen peroxide, and compound 1 also shows good anti-tumoral activities in vitro.     

The C-substituted charge-compensated dicarbollide [7-SMe2-7,8-C2B9H10]−: Synthesis and room-temperature rearrangement of the iridium complex

The reaction of [7-SMe₂-7,8-C₂B₉H₁₀]⁻ with [(cod)IrCl]₂ at room temperature affords iridacarborane 1-cod-8-SMe₂-1,2,8-IrC₂B₉H₁₀. The metal insertion is accompanied by polyhedral rearrangement of the carborane ligand with migration of the substituted carbon atom from the metal bonded pentagonal face. The electronic factors rather than steric ones play the main role in the ligand rearrangement. According to DFT calculations the final iridacarborane is more stable by 6–7 kcal mol^− 1 than the transient pseudocloso-1-cod-2-SMe₂-1,2,3-IrC₂B₉H₁₀ complex. Structures of 7-SMe₂-7,8-C₂B₉H₁₁ and 2 were determined by X-ray diffraction.     

The synthesis and crystal structure of [M{H2B(tz*)2}2(H2O)] (M=Cu,Zn and tz*=3,5-dimethyl-1,2,4-triazole)

New ligand [KH₂B(tz^*)₂] (tz*=3,5-dimethyl-1,2,4-triazolyl) has been synthesized and the reactions of two different metal salts (copper and zinc) with the new ligand in agar gave two similar crystalline polymorphic forms: [Cu{H₂B(tz^*)₂}₂(H₂O)] (1) and [Zn{H₂B(tz^*)₂}₂(H₂O)] (2). A single crystal X-ray study revealed that the compound 1 was the monoclinic system with space group C2/c and a=8.462(3) Å, b=14.039(6) Å, c=19.991(8) Å, β=94.622(7)°, Z=4, R₁=0.0451, wR₂=0.1110. And the compound 2 was the monoclinic system with space group C2/c and a=8.4214(4) Å, b=13.8765(7) Å, c=20.2969(6) Å, β=95.615(2)°, Z=4, R₁=0.0667, wR₂=0.1375. The metal(II) ion in the complex is five-coordinated with four nitrogen atoms which come from triazolyl and one oxygen atom which come from water molecular. In both compounds, the hydrogen atoms of water molecule are connected by hydrogen bonding with N atoms of two adjacent complex molecules to form 2-D planes. The spectroscopic results are consistent with the crystallographic study.     

H2mbpdc-funcationalized CdII6 cage captures protonated water clusters: Chloride-templated assembly and applications in recognition and separation

Assembly of CdCl₂ and 3,3′-dimethoxy-2,2′-bipyridine-6,6′-dicarboxylic acid (H₂mbpdc) under hydrothermal condition affords a chloride-centered discrete Cd^II₆ cage [Cd₆(mbpdc)₆Cl]·[H(H₂O)_14.5] (1), in which a cationic water cluster H⁺(H₂O)₁₀ is present. Our anion-templated assembly system exhibits exclusive encapsulation of Cl⁻ ion, and thus displays potentially applications in the separation of Cl⁻ ion with other halide ions.     

A strategy for controlling charge and conformation in 2,2′-bipyridine complexes for use in photonic applications

The complex [ⁿBu₄N][Cu(H1)₂]·H₂O (H₂1 = 3,3′-dihydroxy-6,6′-dimethyl-2,2′-bipyridine) is readily formed from the reaction of H₂1 with [Cu(MeCN)₄][PF₆] in the presence of [ⁿBu₄N]Br; in the solid state the anion comprises a discrete dinuclear {[Cu(H1)₂](H₂O)₂[Cu(H1)₂]}^2– unit in which two oxygen atoms of each [H1]^– ligand and two water oxygens form a chair shaped hydrogen-bonded six-membered ring.     

Self-assembly of an organo-palladium molecular basket that encapsulates cobalticarborane anion in water

Two [M₃L₃]^6 +-type organo-palladium(II) macrocyclic host molecules, {[(phen)Pd]₃(4,7-phen)₃}(NO₃)₆, 1·6NO₃⁻; {[(dtod-phen)Pd]₃(4,7-phen)₃}(NO₃)₆, 2·6NO₃⁻, (where M = (4,7-phen)Pd, (dtod-phen)Pd; 4,7-phen = 4,7-phenanthroline (L), phen = 1,10-phenanthroline, dtod-phen = 5,6-di(1′,4′,7′,10′-tetraoxododecanoxy)-1,10-phenanthroline), have been synthesized by metal-directed self-assembly in aqueous solution. These basket-shaped hosts bearing syn, syn, syn orientations and their anion complexes, have been fully characterized by ¹H NMR, cold-spray ionization mass spectrometry (CSI-MS) and in the case of basket-shaped host 1*PF₆⁻ by X-ray single-crystal diffraction analysis. On the basis of anion binding structure within the cavity of 1, the molecule basket 2 possessing a hydrophobic inner cavity expanded with hydrophilic polyethyleneglycol chains was successfully designed for encapsulating one giant anion [(C₂B₉H₁₁)₂Co]⁻ in water and the host–guest interaction was studied by ¹H NMR titration and CSI-MS.     

Binuclear, 2D grid and 3D interlocking coordination polymers based on 1,2,4,5-benzenetetracarboxylic acid and 4,4′-azobispyridine

Three new nickel(II) complexes [Ni₂(btec)(azopy)₂(H₂O)₈]·2H₂O (1), {[Ni(H₂btec)(azopy)(H₂O)₂]·(azopy)}_n (2) and {[Ni₄(btec)₂(azopy)₃(H₂O)₁₀]·8H₂O}_n (3) (H₄btec = 1,2,4,5-benzenetetracarboxylic acid; azopy = 4,4′-azobispyridine) have been synthesized by tuning the reaction temperature and the metal–ligand ratio. They were characterized by single-crystal X-ray diffraction and elemental analysis. 1 shows a binuclear structure, 2 exhibits a 2D grid, and 3 features an interesting 3D framework with (6³)(4.6²)(4².6².8²) topology formed by two types of interlocked 2D layers.     

Synthesis and characterization of constrained-geometry half-sandwich sila- and germacarboranes derived from a trianionic C(cage)-appended alkyloxo-C2B9-carborane ligand

The reaction of the [nido-7-(OCH₂)-8-Me-7,8-C₂B₉H₉]³⁻ trianion with anhydrous MeMCl₃ (M=Si, Ge) in 1:1 molar ratio in dry toluene, followed by re-crystallization from a solution of toluene/heptane, resulted in the formation of the corresponding novel half-sandwich constrained-geometry group 14 metallacarboranes, closo-1-M(Me)-2-(1-η¹(σ)-OCH₂)-3-Me-η⁵-2,3-C₂B₉H₉ [M=Si (3), Ge (4)] in 48% and 56% yields, respectively.     

1,1′-Ferrocene dicarboxylic acid pyridin-4-yl ester: A new bidentate ligand in arene ruthenium chemistry

1,1′-Ferrocene dicarboxylic acid pyridin-4-yl ester (1) is prepared from 1,1′-ferrocene dicarbonyl chloride and 4-hydroxypyridine. This new bidentate ferrocenoyl ligand reacts with the monocationic complex [(η⁶-p-cymene)₂Ru₂(μ-OH)₃]⁺ to give the dicationic complex [(η⁶-p-cymene)₂Ru₂(μ-OH)₂(1,1′- (NC₅H₄–OOC)₂–Fc)]²⁺ (2) (Fc: C₅H₄–Fe–C₅H₄), isolated as a tetrafluoroborate salt. The single-crystal X-ray structure analysis of [2][BF₄]₂ reveals the ferrocenoyl pyridine ligand 1 to act as μ₂-η² chelating ligand in the dinuclear complex, having replaced a μ₂-η¹-hydroxo ligand.     

Synthesis,crystal structure and third-order nonlinear optical properties of the hetero-metallic cluster {Cp1Ir[S2C2(B10H10)]}2Mo(CO)2

A hetero-metallic cluster {Cp¹Ir[S₂C₂(B₁₀H₁₀)]}₂Mo(CO)₂ (2) has been synthesized and structurally characterized, and their third-order nonlinear optical (NLO) properties have been investigated by Z-scan technique. The results indicate that 2 exhibit good NLO absorption and self-focusing effects. The hyperpolarizability γ value is calculated to be 2.60 × 10⁻²⁹ esu for 2.     

Silyl group mediated linkage of closo-C2B10-cage to nido-C2B4-carborane: synthesis of the novel carborane ligand, 1-R-2-[5′-(SiMe2CH2)-2′,3′-(SiMe3)2-2′,3′-C2B4H5]-1,2-C2B10H10 (R=Me,Ph)

The reaction of the sodium salt of the monoanion, nido-[2,3-(Si(CH₃)₃)₂-2,3-C₂B₄H₅]⁻, with (chloromethyl)dimethylchlorosilane in a 1:1 molar ratio produced the B_(cage)-substituted cluster, nido-5-ClCH₂Si(CH₃)₂-2,3-(Si(CH₃)₃)₂-2,3-C₂B₄H₅ (1), in 81% yield. This product (1) was reacted further with the lithium salt of [closo-1-R-1,2-C₂B₁₀H₁₀]⁻ monoanion (R=Me, Ph) to give the novel linked and mixed C₂B₄/C₂B₁₀ carborane species, 1-Me-2-[5^′-SiMe₂CH₂-2^′,3^′-(SiMe₃)₂-2^′,3^′-C₂B₄H₅]-1,2-C₂B₁₀H₁₀ (2), 1-Ph-2-[5^′-SiMe₂CH₂-2^′,3^′-(SiMe₃)₂-2^′,3^′-C₂B₄H₅]-1,2-C₂B₁₀H₁₀ (3), in yields of 76% and 81%, respectively.     

Reaction of the titanocene alkyne complex Cp2Ti(η2-Me3SiC2SiMe3) with selenium dioxide: Preparation and characterization of a novel tetranuclear titanium complex with selenium and oxo bridges

The low valent titanocene(II) source Cp₂Ti(η²-Me₃SiC₂SiMe₃) 1 reacts with selenium dioxide (2) to obtain a tetranuclear selenium and oxygen bridged titanocene(IV) [{Cp₂Ti(µ²-O; µ²-Se)CpTi}₂(µ²-O)] 6. The molecular structure was confirmed by X-ray analysis.     

Organometallic boxes built from 5,10,15,20-tetra(4-pyridyl)porphyrin panels and hydroxyquinonato-bridged diruthenium clips

Self-assembly of 5,10,15,20-tetra(4-pyridyl)porphyrin (tpp-H₂) tetradentate panels with dinuclear arene ruthenium clips [Ru₂(η⁶-arene)₂(dhbq)Cl₂] (arene = C₆H₅Me, p-PrⁱC₆H₄Me, C₆Me₆; dhbq = 2,5-dihydroxy-1,4-benzoquinonato) affords the cationic organometallic boxes [Ru₈(η⁶-C₆H₅Me)₈(tpp-H₂)₂(dhbq)₄]⁸⁺ ([1]⁸⁺), [Ru₈(η⁶-p-PrⁱC₆H₄Me)₈(tpp-H₂)₂(dhbq)₄]⁸⁺ ([2]⁸⁺) and [Ru₈(η⁶-C₆Me₆)₈(tpp-H₂)₂(dhbq)₄]⁸⁺ ([3]⁸⁺). These octanuclear cations have been isolated as their triflate salts and characterised by mass spectrometry, NMR and IR spectroscopy. The molecular structure of these systems was deduced by one-dimensional and two-dimensional NMR experiments (ROESY, COSY, HSQC).     

First use of the maleamate(−1) ligand in coordination chemistry: Dinuclear copper(II) complexes with N-donors and their interesting ‘organic’ chemistry

A systematic investigation of the reactions of 3d-metal ions with the maleamate(−1) ligand (HL⁻) in the presence of mono- , bi- or tridentate chelating N-donors has been initiated and the first results are described. Reaction schemes involving Cu(ClO₄)₂ · 6H₂O, HL⁻ and 1,10-phenanthroline or 2,6-bis(pyrazol-1-yl)pyridine (bppy) in MeCN gave complexes [Cu₂(HL)₃(phen)₂](ClO₄) (1) and [Cu₂(HL)₂(bppy)₂](ClO₄)₂ (3), respectively. The same reaction systems in MeOH afforded the new complexes [Cu₂L′₂(ClO₄)(phen)₂(MeOH)](ClO₄) (2b) and [Cu₂L′₂(bppy)₂](ClO₄)₂ (4) in which the maleamate(−1) ion has been transformed to the monomethyl maleate(−1) ligand L′⁻ via a novel, metal ion-assisted process. The reaction that leads to 2b takes place through the formation of the 1D coordination polymer [Cu(ClO₄)(phen)(MeOH)₂]_n(ClO₄)_n (2a), whose structure was assigned on the basis of its spectral similarity with the structurally characterized complex [Cu(ClO₄)(phen)(MeCN)₂]_n(ClO₄)_n (2c). Only the carboxylate oxygen atoms of HL⁻ and L′⁻ are coordinated to copper(II) in 1, 2b, 3 and 4.     

A 3D Cu(II) coordination polymer constructed from BIBP (BIBP = 5,5′-bis(1H-imidazol-1-yl)-2,2′-bithiophene) ligand with semiconductive property

Hydrothermal reaction of Cu(NO₃)₂·3H₂O with BIBP and H₂hfipbb at 105 °C yielded a novel 3D Cu(II) coordination polymer, {[Cu₂(BIBP)_0.5(hfipbb)₂(CH₃CN)]·5H₂O}_n (1) [BIBP = 5,5′-bis(1H-imidazol-1-yl)-2,2′-bithiophene, H₂hfipbb = 4,4′-(hexafluoroisopropylidene)bis(benzoic acid)]. Compound 1 displays a 3D 2-fold interpenetrating framework with {4⁴.6⁶} sqp topology, containing interesting ⋯LRLR⋯ double helical chains. The compound 1 was characterized by IR spectra, elemental analysis, thermal analysis and single crystal X-ray diffraction. In addition, solid-state UV–vis spectra experiment shows that compound 1 exhibits semiconductive property with a band gap of 2.46 eV.