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The post-thermal treatment (PTT) method was applied for crystal transformation on the structure of zeolitic imidazolate frameworks (ZIFs) from 2D to 3D under solvent-free conditions. The investigation was performed based on bridging of the cobalt ions by the 2-methylimidazole linker to form the ZIF structure. Extensive characterization revealed that the reaction mechanism was a transformation in the solid crystal phase and resulted from the de-coordination of the framework and reformation of the crystalline structure. In addition, the PTT method opens the opportunity to simultaneously dope transition metals (Zn, Co, Fe, Ni, and Mn) in the framework during the transformation of ZIFs. The materials with doped metals showed enhanced properties and excellent performance for applications including gas adsorption, dye degradation, and the catalytic activity of CO2 fixation. [ABSTRACT FROM AUTHOR]

The development of high-performance and cost-effective bifunctional water splitting catalysts has enormous significance in the hydrogen production industry from water electrolysis. Herein, an in situ Co and N co-doping method was developed to improve the electrocatalytic performance of Ni3S2 catalysts. The Co–N-Ni3S2/NF is successfully synthesized for the first time by a one-step hydrothermal method, wherein nickel foam, thioacetamide and Co(NO3)2·6H2O are used as the nickel source, sulfur source, nitrogen source and cobalt source. Co–N-Ni3S2/NF exhibits excellent oxygen evolution reaction activity (an overpotential of 285 mV@50 mA cm−2) and hydrogen evolution reaction activity (an overpotential of 215 mV@10 mA cm−2) in 1 M KOH solution. The electrolytic cell displayed a low cell voltage of 1.50 V when the Co–N-Ni3S2/NF material was used as the bifunctional water splitting electrocatalyst, which is one of the best catalysts reported so far. Density functional theory calculations show that Co–N-Ni3S2/NF exhibits stronger water adsorption energy than those of N-Ni3S2/NF, Co-Ni3S2/NF and Ni3S2/NF. It is proved that the doping of Co and N can effectively regulate the electron cloud density of Ni, thus enhancing the electrochemical activity of Co–N-Ni3S2/NF. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of Fe, Co and Ni complexes supported by silylene ligands in the past ten years are summarized. Due to the decrease of the electron cloud density on the Si atom after coordination, the downfield shift of the 29Si chemical shift is accompanied by the coordination between the free silylene ligand and metal. The strong electron-donating ability of silylene makes the metal center more electron-rich, which is conducive to the oxidative addition reaction in the metal center. In some cases, the coordination ability of silylene is stronger than those of phosphine and carbene ligands. Therefore, silylene transition metal complexes have better catalytic activity. The further challenges in this field are to develop new polydentate silylene ligands, synthesize chelate silylene–phosphine and silylene–carbene ligands, and design new silylene transition metal complexes for more catalytic research. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of neutral quasilinear 3d-metal(I) complexes of chromium to cobalt of the type [KM(N(Dipp)SiMe3)2] (Dipp = 2,6-di-iso-propylphenyl) are reported. In solid state these metal(I) complexes either occur as isolated molecules (Co) or are part of a potassium ion linked 1D-coordination polymer (Cr–Fe). In solution the potassium cation is either ligated within the ligand sphere of the metal silylamide or is separated from the complex depending on the solvent. For iron, we showcase that it is possible to use sodium or lithium metal for the reduction of the metal(II) precursor. However, in these cases the resulting iron(I) complexes can only be isolated upon cation separation using an appropriate crown-ether. Further, the neutral metal(I) complexes are used to introduce NBu4+ as an organic cation in the case of cobalt and iron. The impact of the intramolecular cation complexation was further demonstrated upon reaction with diphenyl acetylene which leads to bond formation processes and redox disproportionation instead of η2-alkyne complex formation. [ABSTRACT FROM AUTHOR]

Interaction of the trilacunary 9-tungstosilicate [A-α-SiW9O34]10− with cobalt(II), nickel(II) and zinc(II) ions in pH 9 aqueous medium at room temperature led to the formation of the respective M4-containing heteropolytungstates [M4(OH)3(H2O)2(α-SiW10O36.5)2]13− (M = Co2+ (1), Ni2+ (2), and Zn2+ (3)). Polyanions 1–3 were characterized in the solid state by single-crystal XRD, FT-IR spectroscopy, and thermogravimetric and elemental analyses. Electrochemical studies showed that the Co2+ ions in 1 can be oxidized to Co3+ and the CVs of the WVI centers of the polyanions feature well-defined and chemically reversible reduction waves. Magnetic measurements on 1 and 2 showed paramagnetism with complex ferromagnetic and antiferromagnetic interactions. A model was presented for extracting the exchange constants for the magnetic exchange interaction. [ABSTRACT FROM AUTHOR]

Substituted pyrazines were successfully used to prepare two new coordination polymers of formulas {[Co(dca)2(NH2pyz)2]·H2O}n (1) and [Co3(dca)6(HOpyz)5(H2O)2]n (2) [dca = dicyanamide, NH2pyz = 2-aminopyrazine and HOpyz = 2-hydroxypyrazine] whose structures were determined by single-crystal X-ray crystallography. The structure of 1 consists of a two-dimensional rhombus grid of cobalt(II) ions where the dca ligand adopts the μ1,5 bridging mode with trans-positioned monodentate NH2pyz molecules completing the six-coordination around each metal ion. Compound 2 exhibits a stair-like two-dimensional structure where the intralayer connections are performed by the dca and HOpyz groups exhibiting μ1,5 and bis-monodentate coordination modes, respectively. The values of the cobalt–cobalt separation through the dca bridges are 8.2107(3) (1) and 8.4746(4) and 8.5249(4) Å (2) whereas the value through the hydroxypyrazine is 7.2052(6) Å (2). Solid-state direct-current magnetic susceptibility analyses in the temperature range of 1.9–300 K for 1 and 2 reveal the occurrence of magnetically isolated high-spin cobalt(II) ions with a significant contribution to the magnetic moment (1 and 2), D = +95.4 (1) and +76.5 cm−1 (2) and the antiferromagnetically coupled pairs of cobalt(II) centres through the bis-monodentate 2-hydroxypyrazine, J = −0.3 cm−1 (2). Both compounds exhibit frequency dependence of the out-of-phase alternating current (ac) magnetic susceptibility (χ′′M) under non-zero applied dc fields, a feature which is characteristic of single-ion magnet behaviour (SIM). Q-band EPR studies on the polycrystalline samples of 1 and 2 at low temperatures confirm the positive sign of D and reveal the occurrence of a strong asymmetry in the g-tensors. Theoretical calculations by CASSCF/NEVPT2 support these results. An analysis of the dynamic behaviour of 1 and 2 suggests that the relaxation of the magnetization occurs in the ground state under applied fields through two Orbach processes possibly bound to low-lying vibrational modes in the high temperature range, and to the slowing down of the fast interconversion between the two contributions of the ground Kramers doublet at lower temperatures induced by the applied dc field. [ABSTRACT FROM AUTHOR]

In sharp contrast with the standard [2 + 2 + 2] cycloaddition reaction of diyne/ene, cobalt-mediated cycloadditions with γ-alkylidenebutenolide led to unprecedented cobalt(III) polycyclic complexes. A plausible mechanism supported by a computational study based on an unusual fragmentation of the butenolide moiety was postulated to account for this original reaction. [ABSTRACT FROM AUTHOR]

Three mononuclear six-coordinate Co(ii)-pseudohalide complexes [Co(L)X2] with two N-donor pseudohalido coligands occupying the cis-positions (X = NCS− (1), NCSe− (2) or N(CN)2− (3)), and a five-coordinate complex [Co(L)(NCO)][B(C6H5)4] (4) [L = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane (12-TMC)] have been prepared and structurally characterized. Easy-plane magnetic anisotropy for 1–3 and easy-axis anisotropy for 4 were revealed via the analyses of the direct-current magnetic data, high-frequency and -field EPR (HFEPR) spectra and ab initio theoretical calculations. They display slow magnetic relaxations under an external applied dc field. Typically, two slow relaxation processes were found in 1 and 2 while only one relaxation process occurs in 3 and 4. The Raman-like mechanism is found to be dominant in the studied temperature range in 1. For 2–4, the Raman process is dominant in the low temperature region, while the Orbach mechanism dominates in the high temperature range. [ABSTRACT FROM AUTHOR]

The reactions of a three-coordinate cobalt(i) complex [(IAdMes)(PPh3)CoCl] (1) (IAdMes = 1-mesityl-3-adamantyl-4,5-dimethylimidazol-2-ylidene) with LiCH3, LiCH2SiMe3 and NaCp gave ligand-based C(sp3)–H bond activation products [(IAd′Mes)Co(η6-C6H5PPh2)] (2), [(IAdMes′)(PPh3)Co(CH2SiMe3)] (4) and [(IAd′Mes)Co(η5-Cp)] (5), respectively (IAd′Mes and IAdMes′ denote adamantyl- and mesityl-cyclometallated N-heterocyclic carbene (NHC) ligands, respectively). All the cobalt–NHC complexes have been characterized by various spectroscopic methods, and their structures have been established by single-crystal X-ray diffraction studies. These cyclometallation reactions are among the rare examples of C(sp3)–H bond activation reactions observed in structurally well-defined low-valent cobalt complexes. Different cyclometallated NHC ligands ([IAd′Mes]1−versus [IAdMes′]1−) and different oxidation states of the metal center (cobalt(i) versus cobalt(ii)) in the resultant cobalt complexes hint at different mechanisms for these cobalt-mediated C(sp3)–H bond activation reactions. [ABSTRACT FROM AUTHOR]

This study evaluates the effect of equimolar substitution of manganese by cobalt or nickel in hexacyanoferrate (HCF) open frameworks as electrode materials for Na-ion batteries. As the stability of Mn–N bonds is crucial to obtain long term stability and cyclability of manganese (Mn–HCF), the samples were analyzed thoroughly using several spectroscopic and structural methods. The XPS and infrared experiments reveal that the charge density around Fe is modulated by the presence of Co or Ni, which is associated with their high polarizing power, leading to decreased cell distortion as revealed by XRD. The Rietveld refinement demonstrated that the octahedra built by 3d metals and the cyanide nitrogen were distorted with the axial bond distances being larger than the equatorial distances. This octahedral distortion promotes the spin behavior of 3/2 for Mn2+ confirmed by magnetic experiments; the arising of this spin state is attributed to d orbital splitting determined by UV-Vis experiments. Therefore, the changes upon Mn substitution are related to the modification of the covalent character of Mn–N bonds, modulated by the effect of the Ni and Co polarizing power. All these properties improve the electrochemical stability of the Ni or Co substituted materials as Na-ion batteries, leading to higher capacity retention even at higher C-rates (5C) and good capacity recovery, in comparison with those obtained for Mn–HCF. [ABSTRACT FROM AUTHOR]

The coordination chemistry of Co(ii) with the chelating dicarboxylate ligand esp (esp = α,α,α′,α′-tetramethyl-1,3-benzenedipropionate) is explored. We report here the bimetallic paddlewheel-type dimer, Co2(esp)2(EtOH)2 (1), and a bowl-shaped, heptanuclear coordination cluster, Co7(OH)4(Hesp)2(esp)4(MeCN)2·4MeCN (2). Crystal structures of both complexes are reported as well as their magnetic properties, which indicate antiferromagnetic interactions among the Co(ii) ions. [ABSTRACT FROM AUTHOR]

The back cover of the periodical's January 2017 issue is presented.

A distorted octahedral CoII complex is reported with homoscorpionate ligands. This complex comprised a field-induced single-molecule magnet, showing two slow relaxation processes under a low dc field (＜800 Oe) and only one process under a high dc field (≥800 Oe), which was an unusually discovery for 3d metal ions. On the basis of the ac magnetic data, we show for the first time that one of the slow relaxation processes in the low dc field originates from intermolecular dipolar interactions. Interestingly, the Raman process is predominant in the spin reversal relaxation process. The origin of the behaviours of the complex was elucidated by ab initio calculations. [ABSTRACT FROM AUTHOR]

The reactions of two variants of ENENES ligands, E(CH2)2NH(CH)2SR, where E = 4-morpholinyl, R = Ph (a), Bn (b) with MCl2 (M = Mn, Fe, Co, Ni and Cu) in coordinating solvents (MeCN, EtOH) affords isolable complexes, whose magnetic susceptibility measurements suggest paramagnetism and a high-spin formulation. X-Ray diffraction studies of available crystals show that the ligand coordinates to the metal in either a bidentate κ2[N,N′] or tridentate κ3[N,N′,S] fashion, depending on the nature of ligand and/or identity of the metal atom. In the case of a less basic SPh moiety, a bidentate coordination mode was identified for harder metals (Mn, Fe), whereas a tridentate coordination mode was identified in the case of a more basic SBn moiety with softer metals (Ni, Cu). In the intermediate case of Co, ligands a and b coordinate viaκ2[N,N′] and κ3[N,N′,S] coordination modes, which can be conveniently predicted by DFT calculations. For the softest metal (Cu), ligand a coordinates in a κ3[N,N′,S] fashion. [ABSTRACT FROM AUTHOR]

A series of cobalt(ii) complexes of a highly electron-withdrawing amido ligand, [N(C6F5)(C6H3Pri2-2,6)]− (L), were synthesized and structurally characterized. Mononuclear [CoL(Cl)(TMEDA)] (3) and heterobimetallic [CoL2(μ-Cl)Li(THF)3] (4) were obtained by direct metathetical reactions of anhydrous CoCl2 with one molar equivalent of [LiL(TMEDA)] (1) (TMEDA = Me2NCH2CH2NMe2) and [LiL(THF)3] (2), respectively. Complex 3 underwent facile ligand substitution reactions with LiMe and NaN3, yielding the corresponding mixed-ligand complexes [CoL(X)(TMEDA)] (X = Me 5, N36). Treatment of 3 with NaOMe led to the heterobimetallic complex [CoL2(μ-OMe)Na(TMEDA)] (7). The solid-state structures of complexes 1–7 were established by X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

The crystal and magnetic structures of brownmillerite-like Sr2Co1.2Ga0.8O5 with a stable Co3+ oxidation state at both octahedral and tetrahedral sites are refined using neutron powder diffraction data collected at 2 K (S.G. Icmm, a = 5.6148(6) Å, b = 15.702(2) Å, c = 5.4543(6) Å; Rwp = 0.0339, Rp = 0.0443, χ2 = 0.775). The very large tetragonal distortion of CoO6 octahedra (1.9591(4) Å for Co–Oeq and 2.257(6) Å for Co–Oax) could be beneficial for the stabilization of the long-sought intermediate-spin state of Co3+ in perovskite-type oxides. However, the large magnetic moment of octahedral Co3+ (3.82(7)μB) indicates the conventional high-spin state of Co3+ ions, which is further supported by the results of a combined theoretical and experimental soft X-ray absorption spectroscopy study at the Co-L2,3 edges on Sr2Co1.2Ga0.8O5. A high-spin ground state of Co3+ in Sr2Co1.2Ga0.8O5 resulted in much lower in comparison with a LaCoO3 linear thermal expansion coefficient of 13.1 ppm K−1 (298–1073 K) determined from high-temperature X-ray powder diffraction data collected in air. [ABSTRACT FROM AUTHOR]

The syntheses of M(ii) (M = Mn, Fe, Co) complexes bearing the tris(5-cycloaminoazafulvene-2-methyl)amine (H3N(afaCy)3) ligand in its datively coordinated, tautomeric form is reported. The metal–azafulvene complexes [N(afaCy)3M](OTf)2 are generated in high yields, featuring a secondary coordination sphere composed of amino moieties from the ligand platform. To investigate the ability of the hydrogen bonding network to support hydrogen-bond accepting, coordinating anions, pseudohalide derivatives, [N(afaCy)3MX](OTf) (X = NCS−, NCO−, N3−) were synthesized by exposure of [N(afaCy)3M](OTf)2 to an equivalent of the corresponding salt, [(nBu)4N](X). Structural characterization of the products reveals two isomorphs of the desired species. One complex features a single hydrogen bonding interaction with the pseudohalide, while the second compound has two H-bonds from the secondary coordination sphere to the coordinated anion. These complexes showcase the structural and electron flexibility of the ligand platform, presenting a scaffold capable of accessing a different number of hydrogen bonds for stabilizing a given moiety. [ABSTRACT FROM AUTHOR]

The introduction of NaBPh4 into a methanolic solution of CoCl2·6H2O and 2-[(pyridine-2-ylimine)-methyl]phenol (Hpymp) afforded {[CoII3(pymp)4(MeOH)2][BPh4]2}·2MeOH (1) with a centro-symmetrically linear trinuclear structure. Magnetic analysis of 1 exhibited significant intracluster ferromagnetic exchange (2.4 cm−1) and slow relaxation of magnetization in both zero and non-zero static fields below 5 K, giving the first [CoII3] single molecule magnet with an effective energy barrier of 17.2(3) cm−1 under a 500 Oe dc field. [ABSTRACT FROM AUTHOR]

A water-soluble glucose-functionalized cobalt(iii) complex [CoIII(dmgH)2(py-glucose)Cl] is active and stable for electrocatalytic hydrogen production in neutral aqueous solution. [ABSTRACT FROM AUTHOR]

Eight cobalt and nickel clusters with the formulae [Co4(μ4-O)(MBT)5(μ2-Piv)] (1), [Ni3(MBT)2(L1)2(OCH3)2] (2), [Ni4(μ3-S)(µ3-S2)(MBT)2(L2)] (3), [Ni4(L3)4] (4), [Ni6(μ4-S)3(MBT)6]·(C2H5OH)2 (5), H[Co4(μ4-O)(HMBI)6]·(NO3)(TEA)0.5(CH3OH)2(H2O) (6), [Ni2(HMBI)4]·(CH3OH)2 (7), and [Ni5(MBI)2(HMBI)4(OCH3)2]·(CH3OH)3(H2O)2 (8) (HPiv = pivalic acid, HL1 = 2-disulfanylbenzo[d]thiazole, H2L2 = (Z)-2-((2-mercaptophenyl)imino)benzo[d]thiazole-3(2H)-thiol, H2L3 = (Z)-2-(benzo[d]thiazol-2(3H)-ylideneamino)benzenethiol, TEA = triethylamine) have been solvothermally prepared via assembling distinct metal resource and thiol-containing ligands 2-mercaptobenzothiazole (HMBT)/2-mercaptobenzimidazole (H2MBI). Complexes 1 and 6 are tetrahedral cobalt clusters. Complex 2 features linear arrangement of nickel ions. Complexes 3 and 4 are tetranuclear nickel clusters with the butterfly and square shape, respectively. Complex 5 displays a trigonal prism geometry. Complexes 7 and 8 exhibit paddle-wheel and trigonal bipyramidal geometry, respectively. The starting ligand HMBT undergoes in situ ligand transformation in the formation of the nickel clusters, and the new generated inorganic ligands (S2- and S22-) and organic ligands (HL1, H2L2 and H2L3) were captured within the metallic cores. Magnetic studies indicate that complexes 1 and 6 show dominating antiferromagnetic couplings and that spin frustration exists in 6. [ABSTRACT FROM AUTHOR]

Aryl-bromine bonds are successfully cleaved by cobalt(II) porphyrins in basic media to give Co(por)Ar (por = porphyrin) in good yields. Mechanistic studies suggested that the aryl-bromine bond is cleaved through a halogen atom transfer mechanism, which is different from the aryl-halogen bond cleavage mechanism with other group 9 metalloporphyrins. [ABSTRACT FROM AUTHOR]

A new highly selective and sensitive colorimetric chemosensor 1 for Co2+ was developed. The receptor 1 sensed Co2+ by changing its color from yellow to orange in aqueous solution. Moreover, 1 could be used as a practical, visible colorimetric test kit for Co2+. [ABSTRACT FROM AUTHOR]

Two pentacobalt(II) EMACs were synthesized. A pyrazine-modulated tripyridyldiamine resulted in an EMAC with fully delocalized Co-Co bonds along molecules. From a pyrazine- and naphthyridine-containing ligand, a defective cobalt linear EMAC with an 8-coordinated cobalt(II) in the center was obtained for the first time. An electrochemistry study on the defective pentacobalt chain compound showed redox peaks at E1/2 = -1.00, +0.76, and +0.98 V (versus EAg/AgCl), indicating that it is quite stable and very resistant to both oxidation and reduction. Research on magnetism revealed that the fully delocalized Co EMAC is a spin mixture, and the defective cobalt EMAC showed a high-spin mononuclear cobalt(II) behaviour with a magnetic moment of 2.63µB per molecule at room temperature. Measurement on molecular electric conductance by STM bj showed a single-molecular resistance of 15.4 (±3.1) MO for defective and 12.3 (±2.6) MΩ for delocalized pentacobalt complexes. [ABSTRACT FROM AUTHOR]

A series of cobalt salen complexes, where salen represents an N2O2 bis-Schiff-base bis-phenolate framework, are prepared, characterised and investigated for reversible-termination organometallic mediated radical polymerisation (RT-OMRP). The salen ligands contain a cyclohexane diimine bridge and systematically altered para-substituted phenoxide moieties as a method to examine the electronic impact of the ligand on complex structure and reactivity. The complexes are characterised by single crystal X-ray diffraction, cyclic voltammetry, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy and computational methods. Structural studies all support a tailorable metal centre reactivity altered by the electron-donating ability of the salen ligand. RT-OMRP of styrene, methyl methacrylate and vinyl acetate is reported and suggests that cobalt-carbon bond strength varies with the ligand substitution. Competing β-hydrogen abstraction affords long-chain olefin-terminated polymer chains and well controlled vinyl acetate polymerisations, contrasting with the lower temperature associative exchange mechanism of degenerative transfer OMRP. [ABSTRACT FROM AUTHOR]

Pentacobalt EMACs [Co5(μ5-dpzpda)4X2] (X = Cl−(1), NCS−(2)) with fine-tuning of the supporting ligand based on the tripyridyldiamine ligand, N,N′-di(pyrazin-2-yl)pyridine-2,6-diamine (H2dpzpda), and their reduced form (Ph4P)[Co5(μ5-dpzpda)4X2] (X = Cl−(3), NCS−(4)) were first synthesized and structurally characterized. The structures of 1–4showed direct Co–Co bonds with Co–Co distances in the range 2.2385(7)–2.2888(15) , and valence electrons delocalized through the whole metal chain with distances of longer than 9.06 . The distances of the inner Co–Co bonds and the Co–axial ligands became longer after reduction, whereas no significant change was observed in the distances of the outer Co–Co bonds and Co–N (supporting ligand) bonds, which was consistent with the MO analysis. Electrochemical studies on both 1and 2showed one reversible oxidation and one reversible reduction at E1/2= +0.82 and −0.05 V for 1, and at E1/2= +0.89 and +0.02 V for 2, respectively. The redox reactions of the thiocyanate complex 4happened at higher potentials than the chloride complex 3. A magnetism study of 1–4revealed anomalous magnetic behaviour similar to that of heptacobalt EMACs, and a deviation from the Curie–Weiss law was observed. The χMTvalue at 300 K is 0.84 and 1.16 emu K mol−1for 1and 2, respectively, suggesting spin-equilibrium or a spin-admixture between doublet and quartet states arising from the Boltzmann distribution over different energy levels. Similar results were obtained for 3and 4, showing intermediate χMTvalues between a diamagnetic and a triplet state of 0.15–0.96 emu K mol−1in the temperature range 5–300 K. The structural and magnetic results were interpreted through an EHMO study. [ABSTRACT FROM AUTHOR]

DNA damage was investigated in the presence of sulfite, dissolved oxygen and cobalt(ii) complexes with glycylglycylhistidine, glycylhistidyllysine, glycylglycyltyrosylarginine and tetraglycine. These studies indicated that only Co(ii) complexed with glycylglycylhistidine (GGH) induced DNA strand breaks at low sulfite concentrations (1–80 μM) via strong oxidants formed in the reaction. In the presence of the other complexes, some damage occurred only in the presence of high sulfite concentrations (0.1–2.0 mM) after incubation for 4 h. In the presence of GGH, Co(ii) and dissolved O2, DNA damage must involve a reactive high-valent cobalt complex. The damaging effect was increased by adding S(iv), due to the oxysulfur radicals formed as intermediates in S(iv) autoxidation catalyzed by the complex. SO3˙−, HO˙ and H˙ radicals were detected by EPR-spin trapping experiments with DMPO (5,5-dimethyl-1-pyrroline N-oxide). The results indicate that Co(ii) binds O2 in the presence of GGH, and leads to the formation of a DMPO–HO˙ adduct without first forming free superoxide or hydroxyl radical, supporting the participation of a reactive high-valent cobalt complex. [ABSTRACT FROM AUTHOR]

New complexes of nickel(ii), copper(ii), and cobalt(ii) derived from bidentate coordinating heteroscorpionate ligands, (4-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane, (L4c) and (3-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane, (L3c) have been synthesized and characterized by X-ray diffraction, IR, elemental analysis and UV-vis spectroscopy. By adjusting the reaction conditions the coordination modes of the ligands can be controlled. Solid-state interactions utilizing the strong hydrogen bonding capabilities of protonated and uncoordinated carboxylate groups can be the result of these changed reaction conditions. Finally the different orientation of the carboxylate groups in the ligands L3c and L4c also affect the overall coordination modes and the nature of the solid-state interactions in these systems. [ABSTRACT FROM AUTHOR]

A doping of 5 wt% CoCl2 considerably decreases the dehydrogenation temperature of a mixture of LiNH2 and LiBH4. More that 8 wt% of hydrogen can be released at ca. 155 °C. X-Ray absorption near edge structure (XANES) spectroscopy indicated the formation of metallic Co after ball milling CoCl2 with LiNH2 and LiBH4. Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements revealed that Co particles have poor crystallinity and are finely dispersed in the sample, which could lead to a high catalytic efficiency. [ABSTRACT FROM AUTHOR]

Three new volatile cobalt amidinate compounds were prepared: Co(tBuNC(R)NEt)2, R = Me, Et and n-Bu. They were characterized by elemental analysis, 1H NMR, X-ray structure analysis, melting point, vapor pressure, vaporization rate, thermal stability and chemical reactivity. They were found to evaporate cleanly without decomposition. Two of them are liquids at room temperature, allowing for more convenient preparation, handling and purification by distillation. They are highly reactive compounds that have been found to be suitable precursors for vapor deposition of cobalt metal, cobalt nitride and cobalt oxide. A new synthetic method allows for the facile and inexpensive preparation of large quantities of these compounds. [ABSTRACT FROM AUTHOR]

Thin films of iron cobalt oxides with spinel-type structure are made by the atomic layer deposition (ALD) technique using Fe(thd)3 (Hthd = 2,2,6,6-tetramethylheptane-3,5-dione), Co(thd)2, and ozone as precursors. Pulse parameters for ALD-type growth are established and such growth can be achieved at deposition temperatures between 185 and 310 °C. Films have been deposited on amorphous soda-lime glass and single-crystalline substrates of Si(100), MgO(100), and α-Al2O3(001) which all provide crystalline films, but with various orientations and crystallite sizes. Application of an external magnetic field during the film growth does not influence film growth characteristics (growth rate, crystallinity, topography etc.). Magnetization data are reported for phase-pure films of spinel-type structure with composition Fe2CoO4. [ABSTRACT FROM AUTHOR]

Anaerobic reaction of Co(O2CMe)2·4H2O with the thioether-containing acyclic pyrazine amide hexadentate ligand 1,4-bis[o-(pyrazine-2-carboxamidophenyl)]-1,4-dithiobutane (H2L1) (–CH2CH2– spacer between the two pyrazine amide tridentate coordination units) furnishes [CoII(L1)]·MeOH (1a) having CoN2(pyrazine)N′2(amide)S2(thioether) coordination. It exhibits an eight-line EPR spectrum, attesting to a low-spin (S = 1/2) state of CoII. A similar reaction in air, however, furnishes [CoIII(L3a)(L3b)]·2MeOH (2a) (S = 0), resulting from a C–S bond cleavage reaction triggered by an acetate ion as a base, having CoN2(pyrazine)N′2(amide)S(thioether)S′(thiolate) coordination. On the other hand, the reaction of Co(O2CMe)2·4H2O with 1,4-bis[o-(pyrazine-2-carboxamidophenyl)]-1,5-dithiopentane (H2L2) (–CH2CH2CH2– spacer between the two pyrazine amide tridentate coordination units) in air affords a cobalt(ii) complex [CoII(L2)]·MeOH (1b·MeOH) (S = 1/2); its structurally characterized variety has the composition 1b·C6H6. Interestingly, 1b·MeOH undergoes facile metal-centred oxidation by aerial O2–H2O2–[Fe(η5-C5H5)2][PF6], which led to the isolation of the corresponding cobalt(iii) complex [CoIII(L2)][ClO4] (2b). When treated with methanolic KOH, 2b affords a low-spin (S = 0) organocobalt(iii) complex [CoIII((L2′)] (3). Structures of all complexes, except 1a, have been authenticated by X-ray crystallography. A five-membered chelate-ring forming ligand L1(2–) effects C–S bond cleavage and a six-membered chelate-ring forming ligand L2(2–) gives rise to Co–C bond formation, in cobalt(iii)-coordinated thioether functions due to α C–H bond activation by the base. A rationale has been provided for the observed difference in the reactivity properties. The spectroscopic properties of the complexes have also been investigated. Cyclic voltammetry experiments in MeCN–CH2Cl2 reveal facile metal-centred reversible-to-quasireversible CoIV–CoIII (or a ligand-centred redox process; 2a), CoIII–CoII (1a, 1b·MeOH, 2a, 2b and 3), CoII–CoI (1a, 1b·MeOH, 2a and 2b), and CoI–Co0 (1a, 1b·MeOH and 2b) redox processes. [ABSTRACT FROM AUTHOR]

The solvothermal reaction of cobalt(ii) acetate with p-tert-butylcalix[8]arene (calix) and triethylamine affords the compound (Et3NH)2 [CoII2(calix)2] (1·2Et3NH) that shows a hydrogen bond bridged dinuclear complex [CoII2(calix)2]2− (1) with cobalt(ii) ions in a tetrahedral geometry. The compound crystallises in the monoclinic, space group P21/n with cell parameters a = 14.89(1) Å, b = 20.90(2) Å, c = 30.87(4) Å, β = 102.57(7)°, V = 9376(16) Å3, Z = 2. The magnetic studies together with ab initio calculations are evidence of an important role of the geometry of the second coordination sphere of carbon and hydrogen atoms around the CoO4 core in quantifying the zero field splitting on cobalt sites. This results in strong magnetic anisotropies with a negative axial component on the cobalt fragments. [ABSTRACT FROM AUTHOR]

Cobalt(ii) complexes of the type [CoCl2(P,N)], where P,N represents a heterobidentate phosphino- or phosphinito-oxazoline-type ligand, have been synthesised and characterised by infrared spectroscopy and elemental analysis. Their molecular structures were established by single-crystal X-ray diffraction in the solid state. Whereas the phosphino-oxazoline complex [CoCl2{Ph2PCH2oxMe2}] (Ph2PCH2oxMe2 = 2-[(diphenylphosphanyl)-methyl]-4,4-dimethyl-4,5-dihydro-oxazole) (8) and the phosphinito-oxazoline complexes [CoCl2{Ph2POCH2oxMe2}] (Ph2POCH2oxMe2 = 1-[4,4-dimethyl-2{1-oxy(diphenylphosphino)-1-methyl}]-4,5-dihydro-oxazole) (9) and [CoCl2{Ph2POCMe2oxMe2}] (Ph2POCMe2oxMe2 = 1-[4,4-dimethyl-2- [1-oxy(diphenylphosphino)-1-methylethyl]]-4,5-dihydrooxazole) (10) are mononuclear, the phosphino-oxazoline complexes [CoCl2{μ-i-Pr2PCH2ox}]2 (i-Pr2PCH2ox = 2-[(diisopropyl-phosphanyl)-methyl]-4,5-dihydro-oxazole) (6) and [CoCl2{µ-Ph2PCH2ox}]2 (Ph2PCH2ox = 2-[(diphenyl-phosphanyl)-methyl]-4,5-dihydro-oxazole) (7) are dinuclear compounds and contain two bridging phosphino-oxazoline ligands which form a 10-membered ring. In the course of this work, the zwitterionic complex [CoCl3{Ph2PCH2C(O)OCH2CMe2NH3] (11) was obtained and characterised by X-ray diffraction in which the oxazoline ring has been opened. Air-oxidation of the phosphine function of the mononuclear P,N chelate complex 8 yielded the blue N,O-bridged, centrosymmetric dinuclear complex [┌CoCl2{μ-OPPh2CH2C=NCMe2CH2O}]2 (12) which contains a 12-membered ring. All these complexes are paramagnetic and their magnetic moments in solution were measured by the Evans method. Complexes 6–10 were evaluated in the catalytic oligomerisation of ethylene with AlEtCl2 or methylaluminoxane (MAO) as cocatalysts and provided moderate activities. In the presence of AlEtCl2 (6–14 equiv.), the selectivities for ethylene dimers were higher than 92% and complex 8 showed the highest turnover frequency with 14 equiv. of AlEtCl2. When MAO was used as cocatalyst, the catalytic activities were similar to those with AlEtCl2 but significant amounts of C6–C12 oligomers were produced. [ABSTRACT FROM AUTHOR]

The potential for cobalt(iii) complexes in medicine, as chaperones of bioactive ligands, and to target tumours through bioreductive activation, has been examined over the past 20 years. Despite this, chemical properties such as reduction potential and carrier ligands required for optimal tumour targeting and drug delivery have not been optimised. Here we review the chemistry of cobalt(iii) drug design, and recent developments in the understanding of the cellular fate of these drugs. [ABSTRACT FROM AUTHOR]

Crystals of a cobalt(ii) 3-amino-1,2,4-triazolate; Co2Cl(C2N4H3)3, 1 can be formed from a hydrothermal synthesis. X-Ray crystallography shows an extended 3-dimensional network structure within a hexagonal space group with a = 9.9655(7) and c = 7.7523(7) Å. The data reveal an orientational disorder to the ligand. Structural considerations suggest that the ligand orientation is strongly correlated in 1-dimension, but the nature and length scale of the 2-dimensional order is not obvious. The structure is discussed in terms of three key structural models, two of which are crystallographically ordered, while the third is disordered in 2-dimensions. The effect of ligand orientation on the network topology has profound effects on the expected magnetic behaviour, with the two fully ordered models having either antiferromagnetic or ferrimagnetically ordered ground states. The magnetism of 1 is complex. It shows an antiferromagnetically coupled paramagnetic phase above ∼5.3 K. Below ∼4.5 K we see a ferrimagnetically ordered state (Hcoer = 50 Oe, Mrem = 1830 Oe cm3 mol−1, Msat = 3450 Oe cm3 mol−1 at 2 K). In the intermediate temperature range 4.5 to 5.3 K we see unusual behaviour with evidence of rapid, low-energy relaxation of the magnetisation. The unusual relationship between the structure and the magnetism of 1 is discussed in detail. [ABSTRACT FROM AUTHOR]

Four potential tetradentate ligands of formulae 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)ethane (H4L1, 1), 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)propane (H4L2, 2), 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)benzene (H4L3, 3) and 1,8-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)naphthalene (H4L4, 4) have been prepared and the crystal structures of three of them (1, 3 and 4) determined by single crystal X-ray diffraction. The investigation of their complexing ability toward Co(ii) afforded the compounds of formulae [CoIII(L3)NaI(H2O)2] (5), [CoIII(Ln)LiI(H2O)2] with n = 1 (6), 2 (7) and 3 (8) and [CoII(L4)LiI2] (9). Complexes 5–8 are square planar Co(iii) species, as corroborated by the crystal structure of 5. In this compound, two amide-nitrogen and two phenolate-oxygen atoms of a fully deprotonated (L3)4− anion build a slightly distorted square planar surrounding around the cobalt atom, the Co–N distances [1.858(3) and 1.861(3) Å] being somewhat longer than the Co–O ones [1.798(3) and 1.801(3) Å]. Magnetic and 1H NMR data at room temperature for 6–8 support the occurrence of an intermediate S = 1 low-lying state for the Co(iii) center which is stabilized by the strong donating ability of the fully deprotonated bis-amidate ligands. In the case of the compound with the naphthalene derivative (9), the analytical and spectroscopic data suggest the occurrence of a low spin Co(ii) complex. The weakening of the ligand field strength of the tetradentate bis-amidate ligand in the naphthalene derivative (5–6–5 ring-membered fused chelate) when compared to the situation in complexes 5–8 (5–5–5 ring-membered fused chelate) would account for this feature. [ABSTRACT FROM AUTHOR]

Polymeric networks, {[Co(dpyo)(ox)]}n (1), {[Co(dpyo)(fum)(H2O)2]}n (2) and {[Co(dpyo)(tp)(H2O)2]·[Co(H2O)6]·(tp)·(H2O)}n (3) [ox = oxalate dianion, fum = fumarate dianion, tp = terephthalate dianion and dpyo = 4,4′-dipyridyl N,N′-dioxide] have been synthesized and characterized by single crystal X-ray diffraction analyses. The structural determination reveals 1 and 2 are covalent bonded 2D networks of 4,4 topology and of these, complex 2 undergoes a H-bonding scheme resulting in a 3D supramolecular architecture. Complex 3 is a 1D coordination polymer built up by almost collinear hexacoordinated Co(ii), doubly bridged by a tp carboxylate group and a dpyo oxygen, which in combination with lattice [Co(H2O)6]2+, tp and water molecules shows an unprecedented 3D supramolecular network through H-bonding. In the polymer the dpyo shows novel µ-4,4 bridging mode towards the cobalt ion. Low temperature magnetic interaction reveals antiferromagnetic coupling in all of the complexes. [ABSTRACT FROM AUTHOR]

Vibrational absorption (VA) and vibrational circular dichroism (VCD) spectroscopy was applied in the analysis of vibrational and low lying electronic transitions of a triplet ground state cobalt(iii) coordination compound. The spectroscopic measurements were performed on the tetrabutylammonium salt of (6S,7S)-1,3,5,8,10,12-hexaaza-2,4,9,11-tetraoxo-6,7-diphenyl-dodecanato(4-)cobaltate(iii) in DMSO solution and in potassium bromide pellets. The chiral anion exhibits an unusual geometry for cobalt(iii), being four-coordinate, planar, and paramagnetic with an intermediate spin state. The spectroscopic results were compared to measurements performed on the free ligand and to theoretical calculations using density functional theory (B3LYP/TZVP). The results of the VCD analysis of the coordination compound identified an electronic, dipole-forbidden, magnetic dipole-allowed low-lying d–d transition located in the mid infrared, as well as several amide stretch transitions located in the fingerprint region (1800–1100 cm−1), in both the liquid and solid phase. VCD signals were found to be 5–10 times higher than expected, indicating enhancement of the vibrational CD signals, caused by coupling of the vibrational transitions with the close-lying electronic transition. [ABSTRACT FROM AUTHOR]