Cobalt-zeolite catalysts for the synthesis of hydrocarbons from CO and H2

Catalysts prepared by mechanical mixing of high-silica zeolite ZSM-5 with cobalt oxide Co₃O₄, basic cobaltous carbonate, and cobaltous carbonate were studied. The nature of the cobalt compound introduced into the mixture affects the catalytic and physicochemical properties of the catalyst. The presence of Co₃O₄ in the sample (introduced as oxide or obtained by thermal decomposition of the carbonate) is favorable to the formation of aromatic compounds from CO and H₂. The use of cobaltous carbonates for the preparation of catalysts results in development of the porous structure of the catalyst. During preparation of samples, the mechanical treatment partially destroys the zeolite framework of the support.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1070–1073, June, 1995.     

Reversible formation of binuclear complexes between pyridine-2-carboxylato(tetraethylenepentamine)cobalt(III) and nickel(II)/cobalt(II) in aqueous solution. Anomalous behaviour in the dissociation of binuclear complexes

The kinetics of the reversible formation of binuclear species between M(OH₂) ₆ ²⁺ (M = Ni^II and Co^II) and oxygen-bonded (tetren)Co(pycH)³⁺ (tetren = tetraethylenepentamine, pycH = N-protonated pyridine-2-carboxylate) have been investigated by stopped-flow spectrophotometry at 25°C, I = 0.3 mol dm^-3. Both the protonated (pyridine-N) and deprotonated forms of the Co^III complex were involved in the formation of the binuclear complex (tetren)Co(pyc)Co⁴⁺, whereas only the deprotonated form of the complex was involved in the formation of (tetren)Co(pyc)Ni⁴⁺. The rate date forthe formation of the binuclear complex are consistent with an Id mechanism. Interestingly, the dissociation of the binuclear Co^II complex (tetren)Co(pyc)Co⁴⁺ was acid-catalysed while that with Ni^II was acid-independent. A suitable explanation for this anomalous behaviour has been discussed.     

Decay of Ru(BPY)3 3+ in thin nafion layers catalyzed by Co(II)

Catalytic oxidation of water by Ru(bpy)₃ ³⁺ in the presence of Co²⁺ ions, well known in homogeneous solution, has been investigated in thin Nafion layers. Nafion layers on ITO electrodes were equilibrated with Ru(bpy)₃ ²⁺. Ru(bpy)₃ ³⁺ was produced by electrochemical oxidation after which the electrode was transferred into the reaction cell containing buffered Co²⁺ solution. The build up of Ru(bpy)₃ ²⁺ absorbance at 454 nm was followed spectrophotometrically. The reaction rate is proportional to [Ru(III)], [Co²⁺] and [HPO₄ ^2-]. We found no evidence for a pH effect in the range 6–8, and no inhibition by Ru(II). A limiting rate of formation of Ru(II) is observed at high Co²⁺ or phosphate ion concentrations. At high local concentration of the Ru complex in the Nafion layer (~ 0.5 M), two Ru(II) formation processes are observed, their rates differ by one order, but other features (effects of [Ru(III)], [Ru(II)], [Co²⁺], phosphate and pH) remain unchanged. These results are in contrast with homogeneous solution where the rate of build up of Ru(II) has been previously reported to be proportional to [Ru(III)], [Co²⁺] and [OH^-]², and inversely proportional to [Ru(II)]. A mechanism is proposed which accounts for these observations.     

Die Struktur der Hydrate von Co3[Co(CN)6]2 und Cd3[Co(CN)6]2

The crystal structures of Co₃[Co(CN)₆]₂, 12 H₂O (a, = 10.210 ± 0.005 Å) and Cd₃[Co(CN)₆]₂, 12 H₂O (a = 10.590 ± 0.005 Å) have been determined by X-ray powder methods. According to the measured density the unit cell contains 1 1/3 formula units with 4 Co²⁺ (Cd²⁺) in 4a, 2 2/3 Co³⁺ in 4b, 16 C and 16 N in 24e, 8 H₂O_I near 24e, (96k) and 8 H₂O_II near 8 _c (192 l). Structure factor calculations based on the space group O_h⁵ - F m 3 m lead to the following final values of the reliability index R: 0.038 (Co₃[Co(CN)₆]₂, 12 H₂O) and 0.037 (Cd₃[Co(CN)₆]₂, 12 H₂O). The interatomic distances for the cobaltous compound (in parentheses for the cadmium compound) are: Co³⁺-C: 1.88 Å (1.89); C-N: 1.15 Å (1.17); Co²⁺-N: 2.08 Å (2.24); Co²⁺-O_I: 2.10 Å (2.27); shortest O_I-H-O_II-bonds: 2.89 Å (2.82). Co³⁺ is octahedrally coordinated by six carbon atoms, the divalent metal ion by four nitrogen atoms and two water molecules. The two different metal ions are connected by M²⁺-N-C-Co³-bonds to a threedimensional network. The infrared and electronic spectra are shown to be in agreement with the results of the structure analyses of these compounds. The observed positions of the OH-stretching vibrations lead to a hydrogenbond-length of 2.8–2.95 Å.     

Kinetics of thermal decomposition of Co3O4 powder and single crystals

Kinetics of thermal decomposition in vacuum of Co₃O₄ powder as well as single crystals has been investigated. Discrepancies with the results of previous authors have been discussed. Decomposition of Co₃O₄ proceeds through formation of a compact layer of CoO and hence diffusion is the rate-limiting factor. The experimental curves α(t) be described for 0.05 < α < 0.85 using a modified Ginstling-Brounshtein equation: 1 ? 2α/3 ? (1 ? α)^2/3 = ktⁿ where the activation energy varies with the degree of decomposition.     

Optimal Geometrical Configuration of Cobalt Cations in Spinel Oxides to Promote Oxygen Evolution Reaction

MgCo₂O₄, CoCr₂O₄, and Co₂TiO₄ were selected, where only Co³⁺ in the center of octahedron (Oh), Co²⁺ in the center of tetrahedron (Td), and Co²⁺ in the center of Oh, can be active sites for the oxygen evolution reaction (OER). Co³⁺(Oh) sites are the best geometrical configuration for OER. Co²⁺(Oh) sites exhibit better activity than Co²⁺(Td). Calculations demonstrate the conversion of O* into OOH* is the rate‐determining step for Co³⁺(Oh) and Co²⁺(Td). For Co²⁺(Oh), it is thermodynamically favorable for the formation of OOH* but difficult for the desorption of O₂. Co³⁺(Oh) needs to increase the lowest Gibbs free energy over Co²⁺(Oh) and Co²⁺(Td), which contributes to the best activity. The coexistence of Co³⁺(Oh) and Co²⁺(Td) in Co₃O₄ can promote the formation of OOH* and decrease the free‐energy barrier. This work screens out the optimal geometrical configuration of cobalt cations for OER and gives a valuable principle to design efficient electrocatalysts.     

The formation of a new mixed cobalt rhodium carbonyl from Co2(CO)8 and Rh4(CO)12: Infrared spectroscopic characterization under carbon monoxide pressure

The formation of a new compound, the most characteristic IR absorption bands of which appear at 2007 cm^-1 and 1956 cm^-1, has been in the reaction between Co₂(CO)₈ and Rh₄(CO)₁₂ under carbon monoxide pressure in a hydrocarbon medium. The same compound is also formed either by the reaction of Co₂(CO)₈ with [Rh(CO)₂Cl]₂ or by the reaction of Co₃Rh(CO)₁₂ with carbon monoxide. The new complex has not been isolated in a pure state, but the formula CoRh(CO)₇ is proposed on the basis of the stoichiometry of its formation and its physico-chemical properties. Equilibrium constants and thermo-dynamic parameters for the reaction 2 Co₂(CO)₈ + Rh₄(CO)₁₂  4 CoRh(CO)₇ have been estimated. Possible structures for the new complex are discussed on the basis of its IR spectrum.     

Structural and thermal properties of Co-Cu-Fe hydrotalcite-like compounds

The structural properties and thermal decomposition processes of Co-Cu-Fe ternary hydrotalcites (HT) have been studied through X-ray diffraction, thermogravimetric measurements, Fourier-transform infrared and Mössbauer spectroscopies. Due to the strong Jahn-Teller effect, the Cu-Fe layered system is stabilized only in the presence of Co²⁺. At low Co²⁺ contents, additional phases are segregated in the solids. X-ray patterns show the presence of Cu(OH)₂ and CuO. The decomposition process was investigated by in situ X-ray, in situ Mössbauer and FTIR experiments. By increasing the temperature from 25 °C up to 180 °C we observed that the structural disorder increases. This effect has been likely attributed to the Co²⁺→Co³⁺ oxidation since thermal decomposition was carried out under static air atmosphere. Part of the Co³⁺ cations could migrate to the interlayer region, thus forming a metastable compound that still has a layered structure. Collapse of the layered structure was observed at about 200 °C. By further increasing the temperature the system becomes more crystalline and the formation of Co₃O₄ is observed in the X-ray patterns. In Cu-rich HT, some of the carbonate anions are released at temperatures higher than 550 °C and this phenomenon is attributed to the formation of a carbonate-rich phase. The specific surface area data present its highest values in the temperature range where the collapse of the layered structure takes place.     

Hierarchical Hollow Co9S8 Microspheres: Solvothermal Synthesis,Magnetic, Electrochemical,and Electrocatalytic Properties

A simple solvothermal route in a binary solution of triethylenetetramine (TETA) and deionized water (DIW) has been used to synthesize hierarchical hollow Co₉S₈ microspheres with high surface area (80.38 m² g^?1). An appropriate volume ratio of TETA:DIW has been found to be essential for the formation of hollow Co₉S₈ microspheres. The magnetic study indicated that the Co₉S₈ hollow microspheres are paramagnetic at high temperature and antiferromagnetic at low temperature. The oxygen reduction reaction experiments demonstrated that the onset potential of the Co₉S₈ sample is 0.88 V, which is comparable to the value predicted for Co₉S₈ (0.74 V) from the theoretical simulation. The discharge capability of Co₉S₈ hollow microspheres as cathode materials for lithium ion batteries and their electrocatalytic activity for the oxygen reduction reaction (ORR) have been studied.     

Cobalt(II)-8-mercaptoquinolines complexing in cobalt(II) hexacyanoferrate(II) gelatin-immobilized matrix materials

Complexing processes between Co^II and 8-mercaptoquinoline, or its various alkyl- and aryl-substituted derivatives, in contact with Co₂[Fe(CN)₆]-gelatin-immobilized matrix materials, with aqueous solutions of corresponding ligands, have been studied. When R² = Me or Ph, formation of Co^II chelates having a 1:2 metal ion/singly deprotonated ligand is observed, whereas when R² = H, formation of Co^III chelates having metal ion/singly deprotonated ligand 1:3 ratios occur.     

UV-sensitized nanomaterial semiconductor catalytic reduction of Co<Superscript>III</Superscript>(N–N)<Subscript>3</Subscript><Superscript>3+</Superscript>/nm-TiO<Subscript>2</Subscript> and Co:TiO<Subscript>2</Subscript> formation: SEM-EDX and HRTEM analyses

Interfacial electron transfer induced by 254 nm light at nanomaterial (nm) titanium dioxide/Co^III(N–N)₃ ³⁺ interface in binary mixed solvent media such as water/methanol (or 1,4-dioxane) has been probed. The distinct photo reduction of cobalt(III) complexes, Co^III(N–N)₃ ³⁺; (N–N)=(NH₃)₂, en (1,2-diamino ethane), pn (1,2-diamino propane), tn (1,3-diamino propane), and bn (1,4-diamino butane), by excited nm-TiO₂ particles: Co^III + nm-TiO₂ + hν → TiO₂ (h⁺;e⁻) + Co^III → nm-TiO₂ (h) + Co^II is solvent controlled. The electron transfer from the conduction band of TiO₂ (e⁻, CB) onto the metal centre of the complex consists of (i) electron transport from CB into surface-adsorbed species A: Co^III(N–N)₃ ³⁺ (ii) solution phase species B: Co^III(N–N)₃ ³⁺ _(sol.), accumulated at the surface of the nanoparticle. In addition, UV irradiation of Co^III(N–N)₃ ³⁺ stimulates generation of \textCo_\textaq^\textII {\text{Co}}_{\text{aq}}^{\text{II}} ion, due to charge transfer transition, in solution phase. After UV irradiation, cobalt-implanted nm-TiO₂ separated as gray ultrafine particles, which were isolated. Photo efficiency of the formation of Co^II ion was estimated and the cobalt implanted nanomaterial crystals isolated from the photolyte solutions were subjected to SEM-EDX, X-ray mapping, and HRTEM-SAED analyses. Solvent medium was found to contribute in both the formation of Co^II ion and interstitial insertion of cobalt into the lattice of nm-TiO₂.     

Plasma‐Engraved Co3O4 Nanosheets with Oxygen Vacancies and High Surface Area for the Oxygen Evolution Reaction

Co₃O₄, which is of mixed valences Co²⁺ and Co³⁺, has been extensively investigated as an efficient electrocatalyst for the oxygen evolution reaction (OER). The proper control of Co²⁺/Co³⁺ ratio in Co₃O₄ could lead to modifications on its electronic and thus catalytic properties. Herein, we designed an efficient Co₃O₄‐based OER electrocatalyst by a plasma‐engraving strategy, which not only produced higher surface area, but also generated oxygen vacancies on Co₃O₄ surface with more Co²⁺ formed. The increased surface area ensures the Co₃O₄ has more sites for OER, and generated oxygen vacancies on Co₃O₄ surface improve the electronic conductivity and create more active defects for OER. Compared to pristine Co₃O₄, the engraved Co₃O₄ exhibits a much higher current density and a lower onset potential. The specific activity of the plasma‐engraved Co₃O₄ nanosheets (0.055 mA cm^?2_BET at 1.6 V) is 10 times higher than that of pristine Co₃O₄, which is contributed by the surface oxygen vacancies.     

Synthesis of Co2+-doped Fe2O3 photocatalyst for degradation of pararosaniline dye

In this paper, x (=2, 5, 7 and 10mol%) Co²⁺-doped Fe₂O₃ (xCo:Fe₂O₃) nanoparticles with enhanced photocatalytic activity have been reported. xCo:Fe₂O₃ nanoparticles were successfully prepared by co-precipitation followed thermal decomposition method. The structural, optical and morphological properties of the prepared samples were studied by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), diffuse reflectance (DR) UV–visible absorption spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The obtained results revealed that Co²⁺ ions were well doped within the lattices of Fe₂O₃. Also, Co²⁺ ions suppress the formation of the most stable α- Fe₂O₃ and stabilize less stable γ-Fe₂O₃ at 450 °C. The photocatalytic activity of xCo:Fe₂O₃ was examined by using pararosaniline (PR) dye. It was found that photocatalytic degradation of PR depends on dopant concentration (Co²⁺ ions). Relatively, the highest photocatalytic activity was observed for 5%Co:Fe₂O₃ nanoparticles. The plausible photocatalytic degradation pathway of PR at xCo:Fe₂O₃ surface has also been proposed.     

Temperature- and pressure-dependent kinetico-mechanistic studies on the formation of mixed-valence {(tetraamine)CoIIINCFeII(CN)5}− units

The reduction of Co^III in the tetraamine-encapsulating ligand complex [Co^III{(μ-ET)(Me₂)cyclen}(H₂O)₂]³⁺ by [Fe^II(CN)₆]^4? has been studied kinetico-mechanistically at different pH, temperatures, and pressures. The process agrees with the expected outer-sphere redox mechanism, with the value of the encounter-complex equilibrium constant large enough to allow for kinetic determination of the first-order electron transfer reaction rate constant. The value of the encounter-complex equilibrium constant, K_pre-eq, is not only dependent on the charge of the redox partners, but also on the establishment of an important network of hydrogen bonds. These can also explain the differences obtained in the activation volumes determined for the diaqua and bis-hydroxo complexes. Neither the leaching of Co^II nor the presence of [Fe^III(CN)₆]^3? is observed in the final reaction medium, which indicates that a fast sequence involving substitution on the transient Co^II complex followed by a fast inner-sphere electron transfer takes place. This sort of mechanism has already been established for encapsulating pentaamine ligand complexes, but this is the first example of such a sequential reaction occurring on a tetradentate ligand complex. Preliminary UV–Vis and electrochemical characterization experiments have been conducted on the final reaction mixtures, suggesting the formation of a stable cyanide-bridged Co^III/Fe^II mixed-valence complex of the same type reported in the literature for encapsulating {Co^III(N)₅} skeletons.     

Metal-ion-dependent,Solvent-mediated Structural Transformation and Simultaneous Partial Transmetalation of an srs Framework into Desulfurization-efficient Co-Cu-HKUST-1

[Co₂(BTC)(Cl)(DMA)₃] ( 1 ) (BTC^3– = benzene-1,3,5-tricarboxylate, DMA = N,N-dimethylacetamide) obtained from the reaction between Co²⁺ and H₃BTC in DMA features a three-dimensional srs framework built of 3-connected {Co₂(COO)₃} as secondary building units and BTC^3– as spacers. When exposed to DMA solution of Cu(NO₃)₂, 1 was progressively transformed into the first heterometallic Co-Cu-HKUST-1 ([Co_0.14Cu_2.86(BTC)₂]) ( 2 ) of such kind via unusually solvent-mediated structural transformation and simultaneous partial transmetalation. While the mechanism for such conversion is proposed based on systematic studies, 2 was revealed to be an equally efficient desulfurization adsorbent as the homometallic Cu-HKUST-1 in removing thiophene (0.142 mmol S per gram of adsorbent). However, when exposed to Zn(NO₃)₂ solution in DMA for longer time, 1 retained its framework with limited metal-ion exchange, resulting in the formation of [Co_1.93Zn_0.07(BTC)(Cl)(DMA)₃] ( 3 ). Possible reasons responsible for the formation of 2 and 3 through different routes could be due to the less solubility and more thermodynamic stability of 2 in comparison with those of 1 , and the different coordination geometries which Co²⁺, Zn²⁺ and Cu²⁺ prefer.     

A new octahedral cobalt(III) complex of (1,8)- bis (2-hydroxybenzamido)-3,6-diazaoctane incorporating phenolate-amide-amine coordination: synthesis, X-ray crystal structure, ligand substitution and redox activity with sulfur(IV) and l -ascorbic acid

The octahedral complex, [Co^III(HL)]·9H₂O (H₄L = (1,8)-bis(2-hydroxybenzamido)-3,6-diazaoctane) incorporating bis carboxamido-N-, bis sec-NH, phenolate, and phenol coordination has been synthesized and characterized by analytical, NMR (¹H, ¹³C), e.s.i.-Mass, UV–vis, i.r., and Raman spectroscopy. The formation of the complex has also been confirmed by its single crystal X-ray structure. The cyclic voltammetry of the sample in DMF ([TEAP] = 0.1 mol dm⁻³, TEAP = tetraethylammonium perchlorate) displayed irreversible redox processes, [Co^III(HL)] → [Co^IV(HL)]⁺ and [Co^III(HL)] → [Co^II(HL)]⁻ at 0.41 and −1.09 V (versus SCE), respectively. A slow and H⁺ mediated isomerisation was observed for the protonated complex, [Co^III(H₂L)]⁺ (pK = 3.5, 25 °C, I = 0.5 mol dm⁻³). H₂Asc was an efficient reductant for the complex and the reaction involved outer sphere mechanism; the propensity of different species for intra molecular reduction followed the sequence: [{[Co^III(HL)],(H₂Asc)}–H]⁻ <<< {[Co^III(H₂L)],(H₂Asc)}⁺ < {[Co^III(HL)],(H₂Asc)}. A low value (ca. 3.7 × 10⁻¹⁰ dm³ mol⁻¹ s⁻¹, 25 °C, I = 0.5 mol dm⁻³) for the self exchange rate constant of the couple [Co^III(HL)]/[Co^II(HL)]⁻ indicated that the ligand HL³⁻ with amido (N-) donor offers substantial stability to the Co^III state. HSO₃⁻ and [Co^III(HL)] formed an outer sphere complex {[Co^III(HL)],(HSO₃⁻)}, which was slowly transformed to an inner sphere S-bonded sulfito complex, [Co^III(H₂L)(HSO₃)] and the latter was inert to reduction by external sulfite but underwent intramolecular S^IV → Co^III electron transfer very slowly. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Kinetics of oxidation of glutathione by an octahedral cobalt(III) complex with phenolate–amide–amine coordination

The reduction of the octahedral cobalt(III) complex Co^III(HL)·9H₂O, H₄L = 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane by glutathione (GSH) has been studied by conventional spectrophotometry at 25.0 ≤ t/°C ≤ 45.0, 0.02 ≤ [H⁺]/mol dm^?3 ≤ 0.20 and I = 0.3 mol dm^?3 (NaClO₄). The reaction is biphasic. The fast initial phase is attributed to the H⁺-induced formation of the mixed ligand complex, [Co^III(H₂L)GSH]⁺, for which the rate-limiting step is the chelate ring opening via Co^III–NH (amide–N) bond cleavage of the protonated species, [Co^III(H₂L)]⁺. Outer-sphere association equilibria between GSH/GSH₂ ⁺ and [Co^III(H₂L)]⁺ substantially retard the ring opening process and consequently the mixed ligand complex formation. This is then followed by a slow phase involving reduction of [Co^III(H₂L)GSH]⁺ by both GSH and GSH₂ ⁺. The final products are the corresponding Co(II) complex and the oxidized form of GSH, GS–SG. The kinetic data and activation parameters for the redox process are interpreted in terms of an outer-sphere electron transfer mechanism.     

High-valance molybdenum doped Co3O4 nanowires: Origin of the superior activity for 5-hydroxymethyl-furfural oxidation

Co₃O₄ has been widely explored in electrocatalytic 5-hydroxymethyl-furfural (HMF) oxidation. However, the poor intrinsic ability has seriously limited its electrochemical ability. Heteroatom-doping is an efficient method to enhance the electrocatalytic ability of catalyst by regulating electronic structure. Herein, we have modulated the electronic structure of Co₃O₄ by high valance Mo⁶⁺-doping. With the introduction of Mo⁶⁺, the content of Co²⁺ was increased and metal-oxygen bond was strength. Electrochemical results suggested that the electrocatalytic ability of Co₃O₄ towards HMF oxidation has been dramatically improved and reaction kinetics has been fasten. Theoretical calculations demonstrated that the surrounding cobalt sites after Mo⁶⁺-doping with assembled electron has a strong adsorption ability towards HMF molecule leading to more favourable oxidation of HMF. Post characterizations demonstrated pristine Co₃O₄ structure was kept after electrolysis cycles and CoOOH active species were formed. This work provides a valuable reference for developing efficient heteroatom-doped electrocatalysts for HMF oxidation.     

Kinetic and mechanistic studies of oxidation of amine-N-polycarboxylates complexes of cobalt(II) by periodate ions in aqueous medium

The kinetics and mechanism of interaction of periodate ion with [Co^IIL(H₂O)]^2-n [L = trimethylenediaminetetraaceticacid (TMDTA)] and ethylene glycol bis(2-aminoethyl ether) N,N,N’,N’-tetraaceticacid (EGTA) have been studied spectrophotometrically by following an increase in absorbance at λ_max = 550 nm in acetate buffer medium as a function of pH, ionic strength, temperature, various concentration of periodate and [Co^IIL(H₂O)]^2-n under pseudo-first order conditions. The experimental observations have revealed that the intermediates having sufficiently high half life are produced during the course of both the reactions which finally get converted into a corresponding [Co^IIIL(H₂O)]^3-n complexes as a final reaction product. The reaction is found to obey the general rate law Rate = (k₂ [IO₄ ^?] + k₃ [IO₄ ^?]²) [Co^IIL(H₂O)]^2-n. This rate law is consistent with a four step mechanistic scheme (vide supra) where electron transfer proceeds through an inner sphere complex formation. The value of rate constant k₂ is independent of pH over the entire pH range which suggest that unprotonated form of [Co^IIL(H₂O)]^2-n is the only predominant species. The value of k₂ is invariant to ionic strength variation in both the systems. The value of k₃ is also found to be almost invariant to ionic strength in case of [Co^IITMDTA(H₂O)]^2?-[IO₄]^? system but it decreases considerably in case of [Co^IIEGTA(H₂O)]^2?-[IO₄]^? system with the corresponding decrease in ionic strength. The activation parameters have been computed and given in support of proposed mechanistic scheme.     

Synthesis,characterization, and crystal structure of cobalt(II) complex with 2-oximino-3-thiosemicarbazone-2,3-butanedione

The reaction of cobalt(II) chloride with the tridentate ligand 2-oximino-3-thiosemicarbazone-2,3-butanedione [Hotsb (1)] leads to the formation of the novel six-coordinated complex [Co(otsb)₂]·2H₂O (2). This complex has been synthesized and characterized by X-ray crystallography, spectroscopic and cyclic voltammetric measurements. The ligand Hotsb (1) obtained by the condensation of 2,3-butanedione monoxime and thiosemicarbazide is used for the preparation of complex 2. The Hotsb (1) crystallizes into a monoclinic lattice with space group P2₁/c. The crystal structure of 2 shows a distorted mer-octahedral geometry in which the ligands are coordinated as uninegatively charged tridentate chelating agents via the hydrazine nitrogen atoms, the azomethine nitrogen atoms, and the thiolate sulfur atoms. The cyclic voltammogram of 2 undergoes two irreversible one-electron waves corresponding to Co^II/Co^III and Co^II/Co^I processes.