Synthesis, crystal structure, and electron paramagnetic resonance investigations of heteronuclear Co(II)/Zn(II) and Co(II)/Cd(II) coordination polymers

The crystal structures of five new Co(II), Zn(II), and Cd(II) coordination polymers based on pyridine-substituted triazolyl carboxylates are reported. The two isomorphous compounds (∞)3[M(Me-3py-pba)?] (M = Zn, Co) possess {6?} topology (dia). In order to obtain heteronuclear compounds, we synthesized Co(II)-substituted Zn(II) and Cd(II) coordination polymers. At T = 5 K, the powder samples of the diamagnetically diluted Co(II)/Zn(II) and Co(II)/Cd(II) systems [Co/(Zn,Cd) ≈ 0.01] show intense electron paramagnetic resonance spectra, which were analyzed with an effective spin of S' = ?. The g tensor as well as the ??Co hyperfine tensor A(Co) are strongly anisotropic. The g tensor components are used to gain information about the symmetry of the Co(II) coordination sphere and covalency effects. Differential thermal analysis/thermogravimetry-mass spectrometry and temperature-dependent powder X-ray diffraction studies reveal high thermal stability of the three-dimensional coordination polymers up to 390 °C.     

Polarographie der Proteine in Co(II)/Ammoniak-Pufferl?sungen

Ohne Zusammenfassung     

Dinuclear Co(III)/Co(III) and Co(II)/Co(III) mixed-valent complexes: synthetic control of the cobalt oxidation level

The reactivity of cobalt(II) salts towards H(3)L (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) was studied in different reaction conditions. Accordingly, the interaction of cobalt(II) acetate with H(3)L in methanol gives rise to the discrete complex [Co(III)(2)L(OAc)(2)(OMe)]*1.5H(2)O.MeOH, 1. Reaction of cobalt(II) acetylacetonate with H(3)L in the presence of dicarboxylic acids was also investigated. Thus, when cobalt(II) acetylacetonate and H(3)L are mixed with terephthalic or malonic acid in 4 : 2 : 1 molar ratios, the mixed valent [Co(II/III)(2)L(acac)(p-O(2)CC(6)H(4)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*2H(2)O*2MeOH, 2 and [Co(II/III)(2)L(acac)(O(2)CCH(2)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*7H(2)O, complexes are isolated. Decreasing the pH of the medium, by addition of a second mol of dicarboxylic acid, leads to [Co(II/III)(2)L(O(2)CCH(2)CO(2))(MeOH)]*2MeOH, 4, while the reaction with terephthalic acid does not proceed. 1, 2 and 4 were crystallographically characterised and all the complexes are dinuclear, with hydrogen bonds that expand the initial nodes. The magnetic characterisation, as well as the NMR spectroscopy, indicates a diamagnetic nature for 1, in agreement with the presence of Co(III), showing the aerial oxidation suffered by the cobalt(II) ions. Nevertheless, are paramagnetic. Temperature variable magnetic measurements were recorded for the crystallographically characterised complexes 2 and 4 and these studies confirm the mixed valence Co(II)/Co(III) nature of the compounds. The best fits of the magnetic data give an axial distortion parameter Delta = 628.7 cm(-1) for 2 and 698.8 cm(-1) for 4, and spin-orbit coupling constant lambda = -117.8 cm(-1) for 2 and -107.0 cm(-1) for 4. Therefore, this study shows that the oxidation degree of the initial cobalt(ii) salt by atmospheric oxygen can be controlled according to the pH of the medium.     

Discrete Rh(III)/Fe(II) and Rh(III)/Fe(II)/Co(III) cyanide-bridged mixed valence compounds

The heterotrinuclear complexes trans- and cis-[{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) are unprecedented examples of mixed valence complexes based on ferrocyanide bearing three different metal centers. These complexes have been assembled in a stepwise manner from their {trans-III-L(14S)Co(III)}, {cis-VI-L(15)Rh(III)}, and {Fe(II)(CN)(6)} building blocks. The preparative procedure follows that found for other known discrete assemblies of mixed valence dinuclear Cr(III)/Fe(II) and polynuclear Co(III)/Fe(II) complexes of the same family. A simple slow substitution process of [Fe(II)(CN)(6)](4-) on inert cis-VI-[Rh(III)L(15)(OH)](2+) leads to the preparation of the new dinuclear mixed valence complex [{cis-VI-L(15)Rh(III)(μ-NC)}Fe(II)(CN)(5)](-) with a redox reactivity that parallels that found for dinuclear complexes from the same family. The combination of this dinuclear precursor with mononuclear trans-III-[Co(III)L(14S)Cl](2+) enables a redox-assisted substitution on the transient {L(14S)Co(II)} unit to form [{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+). The structure of the final cis-[{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) complex has been established via X-ray diffraction and fully agrees with its solution spectroscopy and electrochemistry data. The new species [{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) and [{cis-VI-L(15)Rh(III)(μ-NC)}Fe(II)(CN)(5)](-) show the expected electronic spectra and electrochemical features typical of Class II mixed valence complexes. Interestingly, in the trinuclear complex, these features appear to be a simple addition of those for the Rh(III)/Fe(II) and Co(III)/Fe(II) moieties, despite the vast differences existent in the electronic spectra and electrochemical properties of the two isolated units.     

Molecular dynamics of electrosprayed water nanodroplets containing sodium bis(2‐ethylhexyl)sulfosuccinate

The behavior of aqueous solutions of sodium bis(2‐ethylhexyl)sulfosuccinate (AOTNa) subject to electrospray ionization (ESI) has been investigated by molecular dynamics (MD) simulations at three temperatures (350, 500 and 800 K). We consider several types of water nanodroplets containing AOTNa molecules and composed of a fixed number of water molecules (1000), N⁰_AOT AOT^? anions (N⁰_AOT = 0, 5, 10) and N⁰_Na sodium ions (N⁰_Na = 0, 5, 10, 15, 20): in a short time scale (less than 1 ns), the AOTNa molecules, initially forming direct micelles in the interior of the water nanodroplets, are observed in all cases to diffuse nearby the nanodroplet surface, so that the hydrophilic heads and sodium ions become surrounded by water molecules, whereas the alkyl chains lay at the droplet surface. Meanwhile, evaporation of water molecules and of solvated sodium ions occurs, leading to a decrease of the droplet size and charge. At 350 K, no ejection of neutral or charged surfactant molecules is observed, whereas at 500 K, some fragmentation occurs, and at 800 K, this event becomes more frequent. The interplay of all these processes, which depend on the values of temperature, N⁰_AOT and N⁰_Na eventually leads to anhydrous charged surfactant aggregates with prevalence of monocharged ones, in agreement with experimental results of ESI mass spectrometry. The quantitative analysis of the MD trajectories allows to evidence molecular details potentially useful in designing future ESI experimental conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Phosphonation of arenes with dialkyl phosphites catalyzed by Mn(II)/Co(II)/O2 redox couple

[reaction: see text]. Arylphosphonates were first synthesized through a catalytic phosphonation of various arenes with dialkyl phosphites under the influence of an Mn(OAc)2/Co(OAc)2/O2 redox couple. For instance, the reaction of benzene with diethyl phosphite in the presence of Mn(OAc)2 (5 mol %) and Co(OAc)2 (1 mol %) under a mixed gas of O2 (0.5 atm) and N2 (0.5 atm) at 45 degrees C led to diethyl phenylphosphonate in 81% selectivity at 62% conversion. This is the first successful phosphonation of benzene with dialkyl phosphites through a catalytic radical process.     

2-Aminoisobutyric acid in Co(II) and Co(II)/Ln(III) chemistry: homometallic and heterometallic clusters

The synthesis and magnetic properties of 13 new homo- and heterometallic Co(II) complexes containing the artificial amino acid 2-amino-isobutyric acid, aibH, are reported: [Co(II)(4)(aib)(3)(aibH)(3)(NO(3))](NO(3))(4)·2.8CH(3)OH·0.2H(2)O (1·2.8CH(3)OH·0.2H(2)O), {Na(2)[Co(II)(2)(aib)(2)(N(3))(4)(CH(3)OH)(4)]}(n) (2), [Co(II)(6)La(III)(aib)(6)(OH)(3)(NO(3))(2)(H(2)O)(4)(CH(3)CN)(2)]·0.5[La(NO(3))(6)]·0.75(ClO(4))·1.75(NO(3))·3.2CH(3)CN·5.9H(2)O (3·3.2CH(3)CN·5.9H(2)O), [Co(II)(6)Pr(III)(aib)(6)(OH)(3)(NO(3))(3)(CH(3)CN)(6)]·[Pr(NO(3))(5)]·0.41[Pr(NO(3))(3)(ClO(4))(0.5)(H(2)O)(1.5)]·0.59[Co(NO(3))(3)(H(2)O)]·0.2(ClO(4))·0.25H(2)O (4·0.25H(2)O), [Co(II)(6)Nd(III)(aib)(6)(OH)(3)(NO(3))(2.8)(CH(3)OH)(4.7)(H(2)O)(1.5)]·2.7(ClO(4))·0.5(NO(3))·2.26CH(3)OH·0.24H(2)O (5·2.26CH(3)OH·0.24H(2)O), [Co(II)(6)Sm(III)(aib)(6)(OH)(3)(NO(3))(3)(CH(3)CN)(6)]·[Sm(NO(3))(5)]·0.44[Sm(NO(3))(3)(ClO(4))(0.5)(H(2)O)(1.5)]·0.56[Co(NO(3))(3)(H(2)O)]·0.22(ClO(4))·0.3H(2)O (6·0.3H(2)O), [Co(II)(6)Eu(III)(aib)(6)(OH)(3)(NO(3))(3)(CH(3)OH)(4.87)(H(2)O)(1.13)](ClO(4))(2.5)(NO(3))(0.5)·2.43CH(3)OH·0.92H(2)O (7·2.43CH(3)OH·0.92H(2)O), [Co(II)(6)Gd(III)(aib)(6)(OH)(3)(NO(3))(2.9)(CH(3)OH)(4.9)(H(2)O)(1.2)]·2.6(ClO(4))·0.5(NO(3))·2.58CH(3)OH·0.47H(2)O (8·2.58CH(3)OH·0.47H(2)O), [Co(II)(6)Tb(III)(aib)(6)(OH)(3)(NO(3))(3)(CH(3)CN)(6)]·[Tb(NO(3))(5)]·0.034[Tb(NO(3))(3)(ClO(4))(0.5)(H(2)O)(0.5)]·0.656[Co(NO(3))(3)(H(2)O)]·0.343(ClO(4))·0.3H(2)O (9·0.3H(2)O), [Co(II)(6)Dy(III)(aib)(6)(OH)(3)(NO(3))(2.9)(CH(3)OH)(4.92)(H(2)O)(1.18)](ClO(4))(2.6)(NO(3))(0.5)·2.5CH(3)OH·0.5H(2)O (10·2.5CH(3)OH·0.5H(2)O), [Co(II)(6)Ho(III)(aib)(6)(OH)(3)(NO(3))(3)(CH(3)CN)(6)]·0.27[Ho(NO(3))(3)(ClO(4))(0.35)(H(2)O)(0.15)]·0.656[Co(NO(3))(3)(H(2)O)]·0.171(ClO(4)) (11), [Co(II)(6)Er(III)(aib)(6)(OH)(4)(NO(3))(2)(CH(3)CN)(2.5)(H(2)O)(3.5)](ClO(4))(3)·CH(3)CN·0.75H(2)O (12·CH(3)CN·0.75H(2)O), and [Co(II)(6)Tm(III)(aib)(6)(OH)(3)(NO(3))(3)(H(2)O)(6)]·1.48(ClO(4))·1.52(NO(3))·3H(2)O (13·3H(2)O). Complex 1 describes a distorted tetrahedral metallic cluster, while complex 2 can be considered to be a 2-D coordination polymer. Complexes 3-13 can all be regarded as metallo-cryptand encapsulated lanthanides in which the central lanthanide ion is captivated within a [Co(II)(6)] trigonal prism. dc and ac magnetic susceptibility studies have been carried out in the 2-300 K range for complexes 1, 3, 5, 7, 8, 10, 12, and 13, revealing the possibility of single molecule magnetism behavior for complex 10.     

Catalytic radical addition of carbonyl compounds to alkenes by Mn(II)/Co(II)/O(2) system

The radical addition of enolizable carbonyl compounds such as malonates and malononitrile to alkenes was successfully achieved through a catalytic process using the Mn(II)/Co(II)/O(2) system to afford the corresponding adducts in fair to good yields. Dimethyl malonate added to 1,5-cyclooctadiene to produce a fused bicycle compound.     

Ion-molecule reactions and fragmentation patterns in helium nanodroplets

A study has been made of the ion chemistry of a series of small molecules that have been embedded in helium nanodroplets. In most instances, the molecules H2O, SO2, CO2, CH3OH, C2H5OH, C3H7OH, CH3F, and CH3Cl have been allowed to form clusters, and reactivity within these has been initiated through electron impact ionization. For two of the molecules studied, CF2Cl2 and CF3I, reactivity is believed to originate from single molecules embedded in the droplets. Electron impact on the droplets is thought to first create a helium ion, and formation of molecular ions is then assumed to proceed via a charge hopping mechanism that propagates though the droplet and terminates with charge-transfer to a molecule or cluster. The chemistry exhibited by many of the cluster ions and at least one of the single molecular ions is very different from that observed for the same species in isolation. In most cases, reactivity appears to be dominated by high-energy bond breaking processes as opposed to, in the case of the clusters, ion-molecule reactions. Overall, charge-transfer from He+ does not appear to be a "soft" ionization mechanism.     

Dearomatization of naphthalene: novel stereoselective cyclization reactions promoted by Osmium(II)

A series of Michael acceptors has been combined with the Os(II) eta(2)-naphthalene complex (1) to form stable 1H-naphthalenium species. Under acidic conditions, these complexes undergo ring closure at C2 to form the phenanthrenone core. In contrast, the corresponding 1-methylnaphthalene complex (15) upon addition of MVK at C8 undergoes ring closure at C5 to form a bridged tricyclic complex (18). Michael addition of MVK to the naphthalene complex (1) followed by deprotonation, an inter-ring linkage isomerization, and ring closure forms a 9-methylphenalene complex (21). In all cases, the organic cyclization products may be decomplexed by heating with silver triflate and isolated in moderate yield.     

On Mn(Hg)/Mn(II) equilibria and reactions in aqueous solution

The title subject has been studied through galvanostatic single-pulse and chronopotentiometric measurements on the Mn(Hg)/Mn(II) electrode and equilibrium measurements on the same and the Ag/AgCl electrode, all in x MMnCl₂+(0.5?x)M MgCl₂ solutions of pH 4.3–4.9 at 25°C. The Mn(Hg)/Mn(II) reactions are found to occur in two consecutive steps, an unsymmetric (α_c near 0.8) ion-transfer step Mn(Hg)/Mn(I) and an essentially symmetric (α_c near 0.5) electron-transfer step Mn(I)/Mn(II). Besides charge transfer, no sluggishness other than diffusion is observed, but the dispersed precipitate Mn₂Hg₅ of saturated amalgam serves as an ageing-dependent source of anodic reactant Mn(Hg). Quantitative kinetic and thermodynamic data are presented and discussed. Comparisons are made to corresponding reactions for the succeeding elements iron, cobalt, nickel, copper, and zinc.     

Layered Uranyl Phosphonates Encapsulating Co(II)/Mn(II)/Zn(II) Ions: Exfoliation into Nanosheets and Its Impact on Magnetic and Luminescent Properties

Layered heterometallic 5f–3d uranyl phosphonates can exhibit unique luminescent and/or magnetic properties, but the fabrication and properties of their 2D counterparts have not been investigated. Herein we report three heterobimetallic uranyl phosphonates, namely, [(UO₂)₃M(2-pmbH)₄(H₂O)₄] ⋅ 2H₂O [ MU , M=Co(II), CoU ; Mn(II), MnU ; Zn(II), ZnU ; 2-pmbH₃=2-(phosphonomethyl)benzoic acid]. They are isostructural and display two-dimensional layered structures where the M(II) centers are encapsulated inside the windows generated by the diamagnetic uranyl phosphonate layer. Each M(II) has an octahedral geometry filled with four water molecules in the equatorial positions and two phosphonate oxygen atoms in the axial positions. The uranium atoms adopt UO₇ pentagonal bipyramidal and UO₆ square bipyramidal geometries. The lattice and coordination water molecules can be released by thermal treatment and reabsorbed in a reversible manner, accompanied with changes of magnetic dynamics. Interestingly, the bulk samples of MU can be exfoliated in acetone via freezing and thawing processes forming nanosheets with single-layer or two-layer thickness ( MU-ns ). Magnetic studies revealed that the CoU and MnU systems exhibited field-induced slow magnetization relaxation at low temperature. Compared with crystalline CoU , the magnetic relaxation of the CoU-ns aggregates is significantly accelerated. Moreover, photoluminescence measured at 77 K showed slight red-shift of the five characteristic uranyl emission bands for ZnU-ns in comparison with those of the crystalline ZnU . This work gives the first examples of 2D materials based on 5f–3d heterometallic uranyl phosphonates and illustrates the impact of dimension reduction on their magnetic/optical properties.     

On Cu(Hg)/Cu(II) equilibria and reactions in aqueous sulphate solution

Combined thermodynamic and kinetic studies have revealed amalgam properties, solution activities, and diffusion data besides charge-transfer parameters and exchange rates for either step of the Cu(Hg)/Cu(II) electrode in aqueous solutions of xM CuSO₄+(0.5?x) M MgSO₄+H₂SO₄ (to pH about 2.5) at 25°C. The studies allow separation of mean ionic activities into convenient single-ion ones. The kinetic results demonstrate the consecutive two-step mechanism involved. Comparison is made to the solid Cu/Cu(II) electrode, and double-layer effects are discussed.     

Addition of carboxyalkyl radicals to alkenes through a catalytic process,using a Mn(II)/Co(II)/O2 redox system

A novel strategy for production of mono- and dicarboxylic acids by the addition of carboxyalkyl radicals to alkenes and dienes, respectively, was successfully developed through a catalytic process with use of Mn(II)/Co(II)/O(2) system. Thus, a variety of carboxylic acids were prepared by the reaction of alkenes and dienes with acid anhydrides in the presence of a very small amount of Mn(OAc)(2) (0.5 mol %) and Co(OAc)(2) (0.1 mol %) under dilute dioxygen.     

Iron(II)/copper(I)-mediated stereoselective carbozincation of ynamides. One-pot synthesis of α-allyl-tetrasubstituted-enamides

The iron(II) chloride- and copper(I) iodide-mediated carbozincation of a panel of substituted ynamides is described in this article. The reaction is totally regio- and stereoselective. Experiments showed that the reaction mediated with Fe(II) was more substrate dependent than the reaction performed with Cu(I). Interestingly, in the presence of allylbromide, stereoselective carboallylation can be achieved for the first time in a one-pot procedure, leading to skipped dienamides.     

Orbital interactions in Fe(II)/Co(III) heterobimetallocenes: single versus double bridge

Ferrocenyl cobaltocenium hexafluorophosphate (1) and ferrocenylene cobaltocenylenium hexafluorophosphate (2) are investigated by a range of spectroscopic methods. Both compounds are diamagnetic, in contrast to an earlier report indicating a temperature-dependent paramagnetism of 2. Electronic absorption spectra of 1 and 2 are presented and fully assigned up to 50 000 cm(-1) on the basis of electronic structure (DFT) calculations and spectral comparisons with ferrocene and cobaltocenium. The lowest-energy bands, I, of both 1 and 2 correspond to metal-to-metal CT (MMCT) transitions; further intermetallocene charge-transfer bands are identified at higher energy (bands III and V). On the basis of the spectroscopic properties, a trans geometry and a twisted structure are derived for 1 and 2, respectively, in solution. Analysis of the I bands gives orbital mixing coefficients, alpha, electronic-coupling matrix elements, V(AB), and reorganization energies, lambda. Importantly, alpha and V(AB) are larger for 1 than for 2 (0.07 and 1200 cm(-1) vs 0.04 and approximately 600 cm(-1), respectively), apparently in contrast to the presence of one bridge in 1 and two bridges in 2. This result is explained in terms of the respective electronic and geometric structures. Reorganization energies are determined to be 7600 cm(-1) for 1 and 4600 cm(-1) for 2, in qualitative agreement with the analogous Fe(II)-Fe(III) compounds. The general implications of these findings with respect to the spectroscopic and electron-transfer properties of bimetallocenes are discussed.     

Electrochemical and magnetic properties of inorganic polymers constructed from Mn(II)/Co(II)-substituted heteropolymolybdates

Two inorganic polymers constructed from transition metal-substituted heteropolymolybdates, [(CH₃)₃NH]_5n[PMo₁₁MO₃₉]_n·xH₂O (M = Mn²⁺, x = n (1); M = Co²⁺, x = 2n (2)), have been synthesized in aqueous solutions and characterized by IR, TGA, and single-crystal X-ray diffraction analysis. Crystal data: 1, monoclinic, C2/c, a = 17.1322(7) Å, b = 17.6062(7) Å, c = 17.6459(7) Å, β = 103.2220(10)°, V = 5181.5(4) Å³ and Z = 4; 2, triclinic, P-1, a = 12.1986(7) Å, b = 13.0973(7) Å, c = 16.7736(9) Å, α = 97.1810(10)°, β = 98.5040(11)°, γ = 96.3920(10)°, V = 2606.5(2) Å³ and Z = 2. The cyclic voltammograms of 1 and 2 show irreversible redox peaks in DMF solution and there are three reversible couples after addition of 0.1 M H₂SO₄ aqueous solutions. The cyclic voltammograms of 1/2-modified carbon paste electrode (1-CPE/2-CPE) show two consecutive reversible two-electron redox processes. Especially, 2-CPE shows good electrocatalytic activity toward the reduction of nitrite and hydrogen peroxide. The magnetic properties of the two complexes have also been investigated.