Electrocatalytic hydrogen evolution at low overpotentials by cobalt macrocyclic glyoxime and tetraimine complexes

Cobalt complexes supported by diglyoxime ligands of the type Co(dmgBF2)2(CH3CN)2 and Co(dpgBF2)2(CH3CN)2 (where dmgBF2 is difluoroboryl-dimethylglyoxime and dpgBF2 is difluoroboryl-diphenylglyoxime), as well as cobalt complexes with [14]-tetraene-N4 (Tim) ligands of the type [Co(TimR)X2]n+ (R=methyl or phenyl, X=Br or CH3CN; n=1 with X=Br and n=3 with X=CH3CN), have been observed to evolve H2 electrocatalytically at potentials between -0.55 V and -0.20 V vs SCE in CH3CN. The complexes with more positive Co(II/I) redox potentials exhibited lower activity for H2 production. For the complexes Co(dmgBF2)2(CH3CN)2, Co(dpgBF2)2(CH3CN)2, [Co(TimMe)Br2]Br, and [Co(TimMe)(CH3CN)2](BPh4)3, bulk electrolysis confirmed the catalytic nature of the process, with turnover numbers in excess of 5 and essentially quantitative faradaic yields for H2 production. In contrast, the complexes [Co(TimPh/Me)Br2]Br and [Co(TimPh/Me)(CH3CN)2](BPh4)3 were less stable, and bulk electrolysis only produced faradaic yields for H2 production of 20-25%. Cyclic voltammetry of Co(dmgBF2)2(CH3CN)2, [Co(TimMe)Br2]+, and [Co(TimMe)(CH3CN)2]3+ in the presence of acid revealed redox waves consistent with the Co(III)-H/Co(II)-H couple, suggesting the presence of Co(III) hydride intermediates in the catalytic system. The potentials at which these Co complexes catalyzed H2 evolution were close to the reported thermodynamic potentials for the production of H2 from protons in CH3CN, with the smallest overpotential being 40 mV for Co(dmgBF2)2(CH3CN)2 determined by electrochemistry. Consistent with this small overpotential, Co(dmgBF2)2(CH3CN)2 was also able to oxidize H2 in the presence of a suitable conjugate base. Digital simulations of the electrochemical data were used to study the mechanism of H2 evolution catalysis, and these studies are discussed.     

Theoretical analysis of mechanistic pathways for hydrogen evolution catalyzed by cobaloximes

The mechanistic pathways for hydrogen evolution catalyzed by cobalt complexes with supporting diglyoxime ligands are analyzed with computational methods. The cobaloximes studied are Co(dmgBF(2))(2) (dmg = dimethylglyoxime) and Co(dpgBF(2))(2) (dpg = diphenylglyoxime) in acetonitrile. The reduction potentials and pK(a) values are calculated with density functional theory in conjunction with isodesmic reactions, incorporating the possibility of axial solvent ligand loss during the reduction process. The solvent reorganization energies for electron transfer between the cobalt complex and a metal electrode and the inner-sphere reorganization energies accounting for intramolecular rearrangements and the possibility of ligand loss are also calculated. The relative reduction potentials agree quantitatively with the available experimental values. The pK(a)s and reorganization energies agree qualitatively with estimates based on experimental data. The calculations suggest that a peak measured at ca. -1.0 V vs SCE in cyclic voltammetry experiments for Co(dmgBF(2))(2) is more likely to correspond to the Co(II)H/Co(I)H reduction potential than the Co(III)H/Co(II)H reduction potential. The calculations also predict pK(a) values of Co-hydride complexes and reduction potentials for both cobaloximes that have not been determined experimentally. The results are consistent with a mechanism in which the Co(III) and Co(II) complexes have two axial solvent ligands and the Co(I) complex has a single axial ligand along the reaction pathway. Analysis of the free energy diagrams generated for six different monometallic and bimetallic hydrogen production pathways identified the most favorable pathways for Co(dmgBF(2))(2) and tosic acid. The thermodynamically favored monometallic pathway passes through a Co(III)H intermediate, and Co(II)H reacts with the acid to produce H(2). The thermodynamically favored bimetallic pathways also pass through the Co(III)H intermediate, but the pathways in which two Co(III)H or two Co(II)H complexes react to produce H(2) are not thermodynamically distinguishable with these methods. On the basis of the electrostatic work term associated with bringing the two cobalt complexes together in solution, the preferred bimetallic pathway involves the reaction of two Co(III)H complexes to produce H(2). This mechanistic insight is important for designing more effective catalysts for solar energy conversion.     

Cobaloximes as functional models for hydrogenases. 2. Proton electroreduction catalyzed by difluoroborylbis(dimethylglyoximato)cobalt(II) complexes in organic media

Cobaloximes are effective electrocatalysts for hydrogen evolution and thus functional models for hydrogenases. Among them, difluoroboryl-bridged complexes appear both to mediate proton electroreduction with low overpotentials and to be quite stable in acidic conditions. We report here a mechanistic study of [Co(dmgBF2)2L] (dmg2- = dimethylglyoximato dianion; L = CH3CN or N,N-dimethylformamide) catalyzed proton electroreduction in organic solvents. Depending on the applied potential and the strength of the acid used, three different pathways for hydrogen production were identified and a unified mechanistic scheme involving cobalt(II) or cobalt(III) hydride species is proposed. As far as working potential and turnover frequency are concerned, [Co(dmgBF2)2(CH3CN)2], in the presence of p-cyanoanilinium cation in acetonitrile, is one of the best synthetic catalysts of the first-row transition-metal series for hydrogen evolution.     

Fe4 cluster and a buckled macrocycle complex from the reduction of [(dmgBF2)2Fe(L)2] (L = MeCN, (t)Bu(i)NC)

We report the syntheses, X-ray structures, and reductive electrochemistry of the Fe(II) complexes [(dmgBF(2))(2)Fe(MeCN)(2)] (1; dmg = dimethylglyoxime, MeCN = acetonitrile) and [(dmgBF(2))Fe((t)Bu(i)NC)(2)] (2; (t)Bu(i)NC = tert-butylisocyanide). The reaction of 1 with Na/Hg amalgam led to isolation and the X-ray structure of [(dmgBF(2))(2)Fe(glyIm)] (3; glyIm = glyimine), wherein the (dmgBF(2))(2) macrocyclic frame is bent to accommodate the binding of a bidentate apical ligand. We also report the X-ray structure of a rare mixed-valence Fe(4) cluster with supporting dmg-type ligands. In the structure of [(dmg(2)BF(2))(3)Fe(3)((1)/(2)dmg)(3)Fe(O)(6)] (4), the (dmgBF(2))(2) macrocycle has been cleaved, eliminating BF(2) groups. Density functional theory calculations and electron paramagnetic resonance data are in accordance with a central Fe(III) ion surrounded by three formally Fe(II)dmg(2)BF(2) units.     

P538萃取Co(II)的平衡研究

研究了P538-煤油于25±0.5℃时从硫酸钠介质中萃取Co(II)的平衡,并提出萃取机理.     

Sulphuric acid influence on liquid-liquid extraction of Co(II) and Zn(II) by MIBK from NH(4)SCN medium

Liquid-liquid extraction of Co(II) and Zn(II) by methylisobutylcetone (MIBK) has been studied systematically from NH(4)SCN/H(2)SO(4) media. The influence of sulphuric acid concentration on the percentage of extraction of Co(II) and Zn(II) has been discussed. It is shown that sulphuric acid concentration has not the same effect on distribution curves of Co(II) and Zn(II). Thus, it is possible to have a separation of Zn(II) of Co(II) when [NH(4)SCN] is 0.5 mol l(-1) and [H(2)SO(4)] is about 2 mol l(-1). Under these conditions the separation factor (S(Zn/Co)) is around 580. The results are treated in terms of thermodynamic activities in aqueous phase, to determine the composition of the extracted complexes (M:SCN(-)) and to discuss the extraction mechanism.     

Maleate-fumarate conversion and other novel aspects of the reaction of a Co(II) maleate with pyridine and bipyridine

Reaction of a molecular Co(II) maleate, [Co(Hmal)2(H2O)4], with pyridine yields a Co(II) fumarate, [Co(fum)(H2O)4], with a chain structure and a chiral pyridylsuccinic acid zwitter ion, (-)OOC-CH(N+C5H5)-CH2-COOH, in almost quantitative yields, while the reaction of 4,4'-bipyridine (bipy) with the Co(II) maleate, on the other hand, almost quantitatively generates a polylmeric Co(II) maleate, [Co(mal)(bipy)]n.(n/2)H2O along with the adduct of fumaric acid with bipyridine.     

Rational enantioselective design of chiral heterobimetallic single-chain magnets: synthesis, crystal structures and magnetic properties of oxamato-bridged M(II)Cu(II) chains (M=Mn, Co)

A new series of neutral oxamato-bridged M(II)Cu(II) chiral chains of general formula [MCuL(x)(S)(m)(H(2)O)(n)]·aS·bH(2)O [L(1)=(M)-1,1'-binaphthalene-2,2'-bis(oxamate) with M=Mn (1a) and Co (1b); L(2)=(P)-1,1'-binaphthalene-2,2'-bis(oxamate) with M=Mn (2a) and Co (2b)] and the analogous racemic chains of formula [MCuL(3)(S)(m)(H(2)O)(n)]·aS·bH(2)O [L(3)=1,1'-binaphthalene-2,2'-bis(oxamate) with M=Mn (3a) and Co (3b)] have been prepared by reaction of the corresponding dianionic oxamatocopper(II) complex [Cu(L(x))](2-) with Mn(2+) or Co(2+) cations in either dimethylformamide (DMF) or dimethyl sulfoxide (DMSO). Solid circular dichroism (CD) spectra of the bimetallic chain compounds were recorded to establish their chiral and enantiomeric nature. They exhibit maximum positive and negative Cotton effects, each pair of enantiomeric chains being non-superimposable mirror images. The crystal structures of the Mn(II)Cu(II) (1a-3a) and the Co(II)Cu(II) (1b and 2b) chain compounds were solved by single-crystal X-ray diffraction methods. Our attempts to obtain X-ray quality crystals of 3b were unsuccessful. The values of the shortest interchain Mn···Mn and Co···Co distances are indicative of a good isolation of neighbouring chains in the crystal lattice, which is caused by the bulky aromatic ligand. Although all the Mn(II)Cu(II) and Co(II)Cu(II) chains exhibit ferrimagnetic behaviour (-J(MnCu)=18.9-26.6 cm(-1) and -J(CoCu)=19.5-32.5 cm(-1)), only the enantiopure Co(II)Cu(II) chains (1b and 2b) show slow magnetic relaxation at low temperatures (T(B)=0.6-1.8 K), which is a characteristic of single-chain magnets (SCMs) and is related to the magnetic anisotropy of the high-spin Co(II) ion. Analysis of the SCM behaviour of 1b and 2b, based on Glauber's theory for an Ising one-dimensional system, shows a thermally activated mechanism for the magnetic relaxation (Arrhenius law dependence). The energy barriers (E(a)) to reverse the magnetisation direction are 8.2 (1b) and 8.1cm(-1) (2b), whereas the pre-exponential factor (τ(0)) is 1.9×10(-8) (1b) and 6.0×10(-9) s (2b). Interestingly, the racemic Co(II)Cu(II) chain analogue, 3b, showed no evidence of SCM behaviour.     

Proton electroreduction catalyzed by cobaloximes: functional models for hydrogenases

Cobaloximes have been examined as electrocatalysts for proton reduction in nonaqueous solvent in the presence of triethylammonium chloride. [Co(III)(dmgH)2pyCl], working at moderate potentials (-0.90 V/(Ag/AgCl/3 mol x L(-1) NaCl) and in neutral conditions, is a promising catalyst as compared to other first-row transition metal complexes which generally function at more negative potentials and/or at lower pH. More than 100 turnovers can be achieved during controlled-potential electrolysis without detectable degradation of the catalyst. Cyclic voltammograms simulation is consistent with a heterolytic catalytic mechanism and allowed us to extract related kinetic parameters. Introduction of an electron-donating (electron-withdrawing) substituent in the axial pyridine ligand significantly increases (decreases) the rate constant of the catalytic cycle determining step. This effect linearly correlates with the Hammet coefficients of the introduced substituents. The influence of the equatorial glyoxime ligand was also investigated and the capability of the stabilized BF2-bridged species [Co(dmgBF2)2(OH2)2] for electrocatalyzed hydrogen evolution confirmed.     

The satellite-shaped Co-15 Polyoxotungstate, [Co6(H2O)30{Co9Cl2(OH)3(H2O)9(beta-SiW8O31)3}]5-

The 15-cobalt-substituted polyoxotungstate [Co(6)(H(2)O)(30){Co(9)Cl(2)(OH)(3)(H(2)O)(9)(beta-SiW(8)O(31))(3)}](5-) (1) has been characterized by single-crystal XRD, elemental analysis, IR, electrochemistry, magnetic measurements, and EPR. Single-crystal X-ray analysis was carried out on Na(5)[Co(6)(H(2)O)(30){Co(9)Cl(2)(OH)(3)(H(2)O)(9)(beta-SiW(8)O(31))(3)}].37H(2)O, which crystallizes in the hexagonal system, space group P6(3)/m, with a = 19.8754(17) A, b = 19.8754(17) A, c = 22.344(4) A, alpha= 90 degrees, beta = 90 degrees, gamma = 120 degrees, and Z = 2. The trimeric polyanion 1 has a core of nine Co(II) ions encapsulated by three unprecedented (beta-SiW(8)O(31)) fragments and two Cl(-) ligands. This central assembly {Co(9)Cl(2)(OH)(3)(H(2)O)(9)(beta-SiW(8)O(31))(3)}(17-) is surrounded by six antenna-like Co(II)(H(2)O)(5) groups resulting in the satellite-like structure 1. Synthesis of 1 is accomplished in a simple one-pot procedure by interaction of Co(II) ions with [gamma-SiW(10)O(36)](8-) in aqueous, acidic NaCl medium (pH 5.4). Polyanion 1 was studied by cyclic voltammetry as a function of pH. The current intensity of its Co(II) centers was compared with that of free Co(II) in solution. Our results suggest that 1 keeps its integrity in solution. Magnetic susceptibility results show the presence of both antiferro- and ferromagnetic coupling within the (Co(II))(9) core. A fully anisotropic Ising model has been employed to describe the exchange-coupling and yields g = 2.42 +/- 0.01, J(1) = 17.0 +/- 1.5 cm(-1), and J(2) = -13 +/- 1 cm(-(1). Variable frequency EPR studies reveal an anisotropic Kramer's doublet.     

First raw transition metal complexes of salicylidene and 2-hydroxy-1-naphthylidene-N-cyanoacetohydrazone

Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes of salicylidene-N-cyano-acetohydrazone H2L1 and 2-hydroxy-l-naphthylidene-N-cyanoacetohydrazone H2L2 have been prepared in ethanolic solution and characterized by analytical, spectral, magnetic susceptibility, molar conductivity and TGA measurements. The analytical data show that all the complexes derived from H2L1 and H2L2 are formed in molar ratios 1M:2L, except the complexes of Mn(II), Co(II) and Cu(II) acetates of H2L2 and the complexes of Mn(II), Co(II) and Ni(II) acetates and CuCl2 of H2L1 are formed in 1:1 molar ratios. The conductance data show that all metal complexes are non-electrolytes. Electronic absorption spectra and magnetic susceptibility measurements proved that the prepared complexes have octahedral configuration except [Co(HL2)OAc] which has tetrahedral structure. The ligand field parameters were calculated for the Co(II) and Ni(II) complexes and the data show that the covalent character of the metal ligand sigma-bond is low. The ESR parameters of the Cu(II) complexes at room temperature were calculated. Thermal TGA for some solid complexes are reported.     

The low spin Co(II) fragment with homoleptic 1,10-phenanthroline ligands: synthesis, structures, DFT investigations, and magnetic properties

Two complexes {[Co(II)(phen)(3)][Co(III)(phen)(CN)(4)](2)}·phen·11H(2)O (1) and [Co(II)(μ-CN)(2)(Co(III))(2)(phen)(4)(CN)(6)]·C(2)H(5)OH·2H(2)O (2) were synthesized with identical starting materials but with a different order of addition. Their crystal structures, spectroscopic analysis, DFT calculations, and investigations of their magnetic properties are reported herein. The X-ray diffraction studies reveal that complex 1 mainly consists of discrete [Co(II)(phen)(3)](2+) cations and [Co(III)(phen)(CN)(4)](-) anions, while complex 2 is dominantly comprised of discrete neutral V-shaped trinuclear units [Co(II)(μ-CN)(2)(Co(III))(2)(phen)(4)(CN)(6)]. The first low-spin Co(II) fragment with homoleptic 1,10-phenanthroline ligands in 1 is observed at room temperature, owing to charge transfer from the neighboring anion via adventitious contacts and anion-π interactions. This is verified by structures, detailed theoretical analyses concerning frontier molecular orbital energy differences and Mulliken charge variations of the N atoms within the Co(II)N(6) sphere, and magnetism. Meanwhile, these kinds of supramolecular interactions are not found in complex 2, so it shows the ordinary magnetic behavior of the high-spin Co(II) ion. Our investigations highlight that for quantitative comprehension of spin-state energetic ordering in transition metal complexes, the supramolecular interactions must be taken into account in addition to classical ligand field theory. Moreover, we find that the [Co(II)(phen)(3)](2+) dication is sensitive to its surroundings in the solid state, which is beneficial for magnetic adjustment for the further synthesis of tunable molecular magnets and spin crossover systems.     

Mechanism of the cycloaddition of carbon dioxide and epoxides catalyzed by cobalt-substituted 12-tungstenphosphate

Co(II)-substituted α-Keggin-type 12-tungstenphosphate [(n-C(4)H(9))(4)N](4)H[PW(11)Co(H(2)O)O(39)]-(PW(11)Co) is synthesized and used as a single-component, solvent-free catalyst in the cycloaddition reaction of CO(2) and epoxides to form cyclic carbonates. The mechanism of the cycloaddition reaction is investigated using DFT calculations, which provides the first computational study of the catalytic cycle of polyoxometalate-catalyzed CO(2) coupling reactions. The reaction occurs through a single-electron transfer from the doublet Co(II) catalyst to the epoxide and forms a doublet Co(III)-carbon radical intermediate. Subsequent CO(2) addition forms the cyclic carbonate product. The existence of radical intermediates is supported by free-radical termination experiments. Finally, it is exhilarating to observe that the calculated overall reaction barrier (30.5 kcal mol(-1)) is in good agreement with the real reaction rate (83 h(-1)) determined in the present experiments (at 15 °C).     

Bisphosphonate metal complexes as selective inhibitors of Trypanosoma cruzi farnesyl diphosphate synthase

In the search for a pharmacological answer to treat Chagas disease, eight metal complexes with two bioactive bisphosphonates, alendronate (Ale) and pamidronate (Pam), were described. Complexes of the formula [M(2)(II)(Ale)(4)(H(2)O)(2)]·2H(2)O, with M = Cu, Co, Mn, Ni, and ([CuPam]·H(2)O)(n) as well as [M(II)(Pam)(2)(H(2)O)(2)]·3H(2)O, with M = Co, Mn and Ni, were synthesized and fully characterized. Crystal structure of [Cu(2)(II)(Ale)(4)(H(2)O)(2)]·2H(2)O, [Co(II)(Pam)(2)(H(2)O)(2)] and [Ni(II)(Pam)(2)(H(2)O)(2)] were solved by X-ray single crystal diffraction methods and the structures of [M(2)(II)(Ale)(4)(H(2)O)(2)]·2H(2)O complexes M = Co, Mn and Ni were studied by X-ray powder diffraction methods. All obtained complexes were active against the amastigote form of Trypanosoma cruzi (T. cruzi), etiological agent of Chagas disease. Most of them were more active than the corresponding free ligands showing no toxicity for mammalian cells. The main mechanism of the antiparasitic action of bisphosphonates, inhibition of parasitic farnesyl diphosphate synthase (TcFPPS), remains in the obtained metal complexes and an increase in the inhibiting enzyme levels was observed upon coordination. Observed enzymatic inhibition was selective for TcFPPS as the metal complexes showed no or little inhibition of human FPPS. Additionally, metal complexation might improve the bioavailability of the complexes through the hindrance of the phosphonate group's ionization at physiological pH and, eventually, through the ability of plasma proteins to work as complex transporters.     

The Interaction of C60, C70, and C60(CN)2 radical anions with cobalt(II) tetraphenylporphyrin in solid multicomponent complexes

A method for the synthesis of the multicomponent ionic complexes: [Cr(I)(C(6)H(6))(2) (.+)][Co(II)(tpp)(fullerene)(-)].C(6)H(4)Cl(2), comprising bis(benzene)chromium (Cr(C(6)H(6))(2)), cobalt(II) tetraphenylporphyrin (Co(II)(tpp)), fullerenes (C(60), C(60)(CN)(2), and C(70)), and o-dichlorobenzene (C(6)H(4)Cl(2)) has been developed. The monoanionic state of the fullerenes has been proved by optical absorption spectra in the UV/vis/NIR and IR ranges. The crystal structures of the ionic [[Cr(I)(C(6)H(6))(2)](.+)](1.7)[[Co(II)(tpp)(C(60))](2)](1.7-). 3.3 C(6)H(4)Cl(2) and [[Cr(I)(C(6)H(6))(2)] (.+)](2)[Co(II)(tpp)[C(60)(CN)(2)]](-)[C(60)(CN)(2) (.-)]).3 C(6)H(4)Cl(2) are presented. The essentially shortened Co.C(fullerene) bond lengths of 2.28-2.32 A in these complexes indicate the formation of sigma-bonded [Co(II)(tpp)][fullerene](-) anions, which are diamagnetic. All the ionic complexes are semiconductors with room temperature conductivity of 2 x 10(-3)-4 x 10(-6) S cm(-1), and their magnetic susceptibilities show Curie-Weiss behavior. The neutral complexes of Co(II)(tpp) with C(60), C(60)(CN)(2), C(70), and Cr(0)(C(6)H(6))(2), as well as the crystal structures of [Co(II)(tpp)](C(60)).2.5 C(6)H(4)Cl(2), [Co(II)(tpp)](C(70)). 1.3 CHCl(3).0.2 C(6)H(6), and [Cr(0)(C(6)H(6))(2)][Co(II)(tpp)] are discussed. In contrast to the ionic complexes, the neutral ones have essentially longer Co.C(fullerene) bond lengths of 2.69-2.75 A.     

Isolation of four new CoII/CoIII and NiII complexes with a pentadentate Schiff base ligand: syntheses, structural descriptions and magnetic studies

In this paper we report the temperature and pH dependent syntheses and systematic characterization of four new Co(II)/Co(III) and Ni(II) complexes with a pentadentate Schiff base ligand H(3)L obtained by condensing 1,3,-diaminopropan-2-ol with 2-hydroxyacetophenone in 1:2 molar ratio. The room temperature syntheses involving Co(II) and Ni(II) nitrates and the ligand H(3)L lead to the isolation of the dinuclear species [Co(2)L(2)(H(2)O)] (1), and the mononuclear complex [Ni(LH)] (3), respectively, whereas refluxing at basic pH leads to the tetranuclear complexes, [Co(II)(2)Co(III)(2)L(2)(μ(3)-OMe)(2)(NO(3))(H(2)O)(2)]NO(3)·2(H(2)O) (2), and [Ni(4)L(2)(μ(3)-OMe)(2)(H(2)O)(2)]·2H(2)O (4). 1 is found to be a simple mono alkoxo-bridged Co(III) dinuclear species, whereas 2 and 4 are both rhomb-like tetrameric complexes with double oxo bridges and μ(3)-methoxo bridges, derived from the methanol solvent, in an open dicubane arrangement. Moreover 2 shows six coordinate ordered Co(II) and Co(III) ions and 4 has both six- and five-coordinate Ni(II) centers. Compound 3 is assigned a tentative mononuclear structure based on IR, UV-Vis spectroscopic, (1)H-NMR and ESI mass study results and is supposed to have one Ni(II) center coordinated with a ligand fragment in square planar geometry. The variable temperature magnetic susceptibility study for 2 and 4 is performed which indicate for both 2 and 4 the presence of intracluster dominant ferromagnetic interactions.     

Phase separation in liquid crystalline mesophases of [Co(H2O)6]X2:P65 Systems (X = NO3-, Cl-, or ClO4-)

Transition-metal aqua complex salts [M(H2O)6]X2 (where M is Mn(II), Co(II), Ni(II), Zn(II), or Cd(II) and X is NO3-, Cl-, or ClO4-) can be dissolved in triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymers (Pluronics, such as P65) to form homogeneous liquid crystalline (LC) mesophases. However, the [Co(H2O)6]X2:P65 LC mesophases slowly undergo phase separation into a disordered ion-free phase and an ordered ion-rich LC mesophase. The phase separation also takes place in the two-salt systems [Co(H2O)6](NO3):[Co(H2O)6](ClO4)2:P65 in which the ion-free disordered domains separate out from the initially ordered homogeneous mesophase. The phase separation results in a physical mixture of a hexagonal nitrate-rich and cubic perchlorate-rich LC and disordered ion-free domains in the mixed salt systems. The driving force in the phase separation in the [Co(H2O)6]X2:P65 system is Co(II)-catalyzed aerobic oxidation of P65 into ester and/or other oxidation products. The separation of ions in the [Co(H2O)6](NO3)2:[Co(H2O)6](ClO4)2:P65 system is related to the mesostructures of the two-salt systems that are different, hexagonal in the [Co(H2O)6](NO3)2:P65 system and cubic in the [Co(H2O)6](ClO4)2:P65 system. There is no visible phase separation in the other transition-metal salt:P65 systems. The phase separation in the [Co(H2O)6]X2:P65 systems can also be eliminated by keeping the mesophase under a N2 atmosphere.     

Study on the mechanism and applications of the fluorescence reactions among cobalt (II), H(2)O(2) and two new derivatives of 8-sulfonamidoquinoline

The fluorescence intensities of the reaction systems of Co(II) with two new 8-sulfonamidoquinoline derivatives, 5-(4-Chlorophenylazo)-8-(benzenesulfonamido)-quinoline (CPBSQ), which was firstly synthesized and characterized, and 5-(3-fluo-4-chlorophenylazo)-8-(benzenesulfonamido)quinoline (FCPBSQ), could be enhanced by H(2)O(2). The mechanism and analytical characters of these reactions in the presence of H(2)O(2) were investigated in this paper. CPBSQ and FCPBSQ reacted with Co(II) in the presence of H(2)O(2) and in the basic medium forming a chelate, which exhibited an intensive fluorescence in ultraviolet region. The fluorescence intensities were proportional to the concentration of Co(II) over the range of 0.1-100 and 0.5-200 mug/l with the detection limits of 0.05 and 0.10 mug/l for the CPBSQ and FCPBSQ systems, respectively. A lot of metal ions included Cu(II) and Ni(II) did not interfere the determinations for both the systems. The methods, which are high sensitive and more selective, have been successfully applied to the determination of trace amount of cobalt in environmental and biological samples.     

Photolytic and thermal properties of a new series of intramolecular bridged alkyl cobaloxime complexes

The photolytic kinetic properties of a new series of intramolecular bridged alkyl cobaloxime complexes Br(O-C(3)H(6)-(dmgH))(dmgH))Co(III)(2), [H(2)O(O-C(3)H(6)-(dmg))(dmgH(2))]Co(III)[ClO(4)(3), ]Py(O-C(3)H(6)-(dmg))(dmgH(2))[Co(III)]ClO(4)(4), [Bzm(O-C(3)H(6)-(dmg))(dmgH(2))]Co(III)[ClO(4)(5) and ]Im(O-C(3)H(6)-(dmg))(dmgH(2))[Co(III)]ClO(4)(6) and their precursor aqua-(3-bromopropyl)cobaloximes (1) were investigated by UV-Vis spectroscopy. The products of photolytic solutions were characterized by both ESI-MS and (1)H-NMR techniques. Our results revealed a carbon-center radical that is produced from Co-C bond cleavage under photolysis might be linked to the equatorial ligand and thus retained in the proximity of Co(II)-complex. The thermo-gravimetric analysis of complex 2 gives the same conclusion.     

Structural diversity in metal complexes with a dinucleating ligand containing carboxyamidopyridyl groups

The synthesis of a (carboxyamido)pyridinepyrazolate (H(5)bppap) dinucleating ligand is described. Bimetallic iron and cobalt complexes of H(5)bppap ([M(II)(2)H(2)bppap](+)) showed structural differences in both their primary and secondary coordination spheres. The binding of small molecules into the preorganized ligand cavity is verified by the hydration of [Fe(II)(2)H(2)bppap](+) and [Co(II)(2)H(2)bppap](+), leading to the formation of complexes [{Co(II)(OH)}Co(II)H(3)bppap](+) and [{Fe(II)(OH)}Fe(II)H(3)bppap](+), in which one of the metal centers has a terminal hydroxo ligand.