Comparison of crystal structures and magnetic properties of two Co(II) complexes containing different dicarboxylic acid ligands

Two novel cobalt(II) complexes, [Co(μ-succinato)(H₂O)₂(pyridine)₂]_n1 and {[Co₂(μ-H₂O)(μ-glutarato)₂(pyridine)₂]·pyridine}_n2 have been synthesized by a wet chemistry method. In complex 1, the Co(II) ions are linked through succinate ligands to created one-dimensional polymeric chain along the b-axis. Complex 2 consists of a polymeric chain of dinuclear Co(II) moieties in which two cobalt(II) ions are linked through a bridging water and two bridging carboxylate groups from two glutarate ligands. The glutarate ligands in complex 2 display two coordination modes, interbinuclear bridging and intrabinuclear bridging. All the bond angles of the alkyl chain in complex 2 are between 115.7° and 118.5°, supporting the gauche conformation. Free pyridine molecules were found in the cavities between the chains. Two strong intramolecular hydrogen bonds are observed between the coordinated water and the uncoordinated carboxylate oxygen atom in both complexes. Complex 2 is further stabilized by π–π stacking of pyridine molecules. Complex 1 is a paramagnet (C = 3.50(1) cm³ K mol and θ = −5.0(5) K) and complex 2 exhibits a broad maximum at 4 K due to weak coupling within the dimeric unit.     

pH and molar ratio dependent formation of monomeric,dimeric and tetrameric cobalt malate complexes

The reactions of cobalt(II) chloride with racemic malic acid (H₃mal = C₄H₆O₅) result in the isolation of monomeric, dimeric and tetrameric cobalt malato complexes: (NH₄)₂[Co(R-Hmal)(S-Hmal)] · 2H₂O (1), [Co₂(R-Hmal)(S-Hmal)(H₂O)₄]_n · 2nH₂O (2), K₄[Co₄(OH)₂(R-mal)₂(S-mal)₂(H₂O)₄] · 10H₂O (3) and trans-[Co(R-H₂mal)(S-H₂mal)(H₂O)₂] · 2H₂O (4). The formations of the malato complexes are dependent on the pH value, the molar ratio of the solutions, the reaction temperature and the counterions. In the water-soluble compound 1, the Co^II ion is octahedrally coordinated by two tridentate malates via their α-hydroxy, α-carboxy and β-carboxy groups. The malate ligands in 2 coordinate with the cobalt ion via their α-hydroxy and α-carboxy groups, while the β-carboxy group acts as a bridging ligand for the other two cobalt ions, forming a novel dimeric unit [Co₂(R-Hmal)(S-Hmal)(H₂O)₄], which further connects into a layered structure through links from the oxygen atoms of the β-carboxy groups. Complex 3 is a tetranuclear mixed-valence species. Both of the Co^II ions exist in trans-[Co(R-mal)(S-mal)(H₂O)₂] units, which are linked by a Co^III₂(OH)₂ unit with bridging α-alkoxy and β-carboxy groups. Compound 4 is the main product of reaction between cobalt chloride and excess malate under weakly acidic conditions.     

Mononuclear and binuclear lanthanide(III) complexes: syntheses,structural, photophysical and thermal properties

Six new Ln(III) complexes viz., [Gd(tptz)(SCN)₃(CH₃OH)₂OH₂]·CH₃OH (1), [Eu(tptz)(SCN)₃(CH₃OH)₂OH₂]·CH₃OH (2), [Tb(tptz)(SCN)₃(OH₂)₃]₄ (3), [Gd(tptz)(OBz)₂(μ-OBz)OH₂]₂·2H₂O (4), [OH₂(OBz)₂(tptz)Eu₁(μ-OBz)₂Eu₂(tptz)(OBz)₂OH₂]·CH₃OH·7H₂O (5), and {[Tb₁(tptz)(OBz)₂(μ-OBz)]₂·[Tb₂(tptz)(OBz)₃CH₃OH]₂}·2CH₃OH·4H₂O (6) (Ln = Gd, Eu, Tb; tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine; BzONa = sodium benzoate), have been synthesized and characterized by physicochemical methods including single-crystal X-ray crystallography. The X-ray studies demonstrate that 1–3 are mononuclear, whereas 4–6 are binuclear. The photophysical properties of 1–6 have been studied with ultraviolet absorption and emission spectral studies. Their thermal properties have been studied by thermogravimetric (TG) and derivative thermogravimetric analysis (DTG), demonstrating that the final product after decomposition was Ln₂O₃ for all these complexes.     

Organic amines reduce trans-dichlorotetrakis(pyridine)cobalt(III) chloride to cobalt(II)

Summary The reaction of dichlorotetrakis(pyridine)cobalt(III) chloride. [CoCl₂(Py)₄]Cl, with alkyl- or arylamines in EtOH or i-PrOH yielded [CoCl₂(Py)₂] in all cases. This reduction of Co^III to Co^II takes place only in the presence of the amines. [CoCl₂(Py)₂] in EtOH is oxidized by Cl₂ gas and in the presence of pyridine gives [CoCl₂(Py)₄] ⁺, while in pyridine alone [CoCl₂(Py)₄] is formed.     

The modifications of copper work function by layer-by-layer deposition of [W(CN)8] – Co bimetallic nanolayers

In the reaction of K₄[W(CN)₈] · 2H₂O and Co²⁺(aq) cations on the polycrystalline or monocrystalline [3 1 1] copper using layer-by-layer deposition, a thin film of the coordination polymer {[{Co(H₂O)₂(μ-CN)₄}₂W] · 4H₂O}_n was formed. The work function of copper and deposited on it bi-layers depended on a number of layers and the concentrations of the deposited precursors. At high complex concentrations work function reached the plateau after several deposition processes, while at low concentrations oscillations in the work function were observed when K⁺ or Co²⁺ cations were present in the outside layer. The changes of the work function were also dependent on Co²⁺ salt used (CoCl₂ · 6H₂O or Co(NO₃)₂ · 6H₂O). This was interpreted in terms of a layer structure resulting from various coordination of external anions to cobalt cations.     

Unexpected Formation of a π‐Coordinate Schiff Base Cobalt(0) Complex

Both tetrakis(trimethylphosphine)cobalt(0) and methyltetrakis(trimethylphosphine)cobalt(I) react with 2‐(benzylideneamino)pyridine ( 1 ) exclusively giving a complex of composition (η²(N,C)‐2‐Py‐N=CH‐C₆H₅)Co(PMe₃)₃ ( 2 ), which is shown by single‐crystal X‐ray diffraction to constitute the first π‐coordinate imine cobalt(0) complex. The route of formation is proposed and discussed.     

Synthesis and characterization of zinc benzoate complexes through combined solid and solution phase reactions

A combined solid and solution phase methodology for the synthesis of a series of mononuclear and polynuclear zinc benzoate complexes is described. The substituent on the aromatic ring and the effect of solvent on deciding the composition of the complexes is presented. From the 4-substituted benzoic acids 4-methylbenzoic acid (ptolH), 4-nitrobenzoic acid (pnitrobenH) and 4-chlorobenzoic acid (pchlorbenH), the mononuclear complexes [Zn(ptol)₂(H₂O)₂], [Zn(pnitroben)₂(H₂O)(DMSO)₂] and [Zn(pchlorben)₂py)₂] (where DMSO = dimethylsulfoxide, py = pyridine) have been synthesized and structurally characterised. Zinc complexes from the reaction of zinc sulfate heptahydrate with 3-methylbenzoic acid (mtolH) and 2-methylbenzoic acid (otolH), the dinuclear complexes [Zn₂(μ²-mtol)₄(py)₂], [Zn₂(μ²-otol)₄(py)₂], pentanuclear complex [Zn₅(μ²-mtol)₆(mtol)₂(μ³-OH)₂ (py)₂] and tetranuclear complex [Zn₄(μ²-otol)₆(μ⁴-O) (DMSO)₂], have been prepared by varying the reaction conditions and the complexes have been structurally characterized.     

Oligomerisation of ethylene to linear α-olefins by tetrahedral cobalt(II) precursors stabilised by benzo[b]thiophen-2-yl-substituted (imino)pyridine ligands

On activation by MAO, 2-(imino)pyridine cobalt dichlorides bearing a benzo[b]thiophen-2-yl substituent in the 6-position of the pyridine ring oligomerise ethylene to α-olefins with turn-over-frequencies as high as 1.5 × 10⁶ mol of C₂H₄ converted (mol of Co × h)⁻¹ and productivities as high as 3769 kg of oligomers (mol of Co × h × bar)⁻¹. Aldimine precursors are more active than ketimine analogues, yet ketimines give higher molecular weight oligomers.     

Synthesis,structure and physical properties of trinuclear M3tdt3(PEt3)3 (M = Fe,Co) clusters containing metal–metal bonds

Trinuclear M₃tdt₃(PEt₃)₃ (M = Fe^II for I, Co^II for II) clusters have been synthesized from the reaction between M(PEt₃)₂Cl₂ and Na₂tdt (tdt = toluene-3,4-dithiolate) in MeCN. Both complexes have been characterized by elemental analyses, FT-IR, UV–Vis, FAB-MS, ¹H NMR and cyclic voltammetry. Structures of Fe₃tdt₃(PEt₃)₃ (I) and Co₃tdt₃(PEt₃)₃ (II) were determined by single crystal X-ray crystallography. The Fe₃ triangular core of the 48-electron complex I, with an isosceles triangular geometry, showed very short Fe–Fe distances of 2.4014(13) and 2.4750(12) Å, which are comparable to the extensive M–M frameworks found in the FeMo-cofactor in nitrogenase. The isostructural Co₃tdt₃(PEt₃)₃ (II), with an analogous Co₃ coordination geometry, showed short Co–Co distances of 2.4442(9) and 2.5551(10) Å. The slightly longer M–M distances in complex II were explained by a total valence electron counting argument. Cyclic voltammetry of Fe₃tdt₃(PEt₃)₃ (I) showed robust reduction waves compared to Co₃tdt₃(PEt₃)₃ (II). Temperature-dependent effective magnetic moment measurements of I and II showed both clusters behave similarly and the magnetic property of the M₃ equilateral triangle core with extensive metal–metal interactions was characterized as degenerate frustration.     

Electron spin resonance studies of the anaerobic and aerobic photolysis of alkylcobaloximes

Aerobic and anaerobic photolysis of methyl(pyridine)cobaloxime, benzyl(pyridine)cobaloxime and analogous compounds in CHCl₃ results only in an electron transfer reaction from an equatorial ligand producing photo-reduction of Co^III to Co^II, the complex retaining its axial ligands.If after the anaerobic photolysis of benzyl(pyridine)cobaloxime the oxygen is introduced without any further photolysis we obtain an ESR spectrum of nitroxide, arising from the attack of a benzyl radical on the dimethylglyoxime equatorial ligand.For the other complexes, homolytic cleavage of the CoC bond occurs and in the presence of oxygen gives rise to the superoxide cobalt complex adduct Py(Co^IIIO₂^?.During photolysis of methyl(pyridine)cobaloxime in isopropanol homolytic cleavage of the CoC bond occurs in preference to electron transfer reaction from the equatorial ligands.The anaerobic photolysis of benzyl(pyridine)cobaloxime in isopropanol or in water at 113–133 K results in an electron transfer reaction. However, at 170 K we observe the formation of the Co^II complex arising from CoC bond cleavage.A mechanism for photo-induced insertion of oxygen in the CoC bond is proposed.     

Synthesis of alkali-metal cobalt kambaldaite by precipitation method

Alkali-metal cobalt kambaldaite (alkali-metal cobalt carbonate hydroxide hydrate; ideal structure, M₂Co₈(CO₃)₆(OH)₆ · 6H₂O; M-CoKBL) was prepared by the addition of a cobalt nitrate solution into a solution containing a large excess of alkali-metal bicarbonate followed by aging at 50 °C for 2–3 h. Hydrated alkali-metal ions are present in the channels of the kambaldaite structure; therefore, we tried to ion-exchange the K-CoKBL sample with various metals. However, collapse of the kambaldaite structure took place easily because of low pH of the ion-exchange solution. The catalytic activity of Co₃O₄ obtained by the calcination of “ion-exchanged” K-CoKBL was dependent on the residual potassium content in the catalyst.     

Assembly of novel phenanthroline-based cobalt(II) coordination polymers by selecting dicarboxylate ligands with different spacer length: From 1-D chain to 3-D interpenetrated framework

Three novel Co^II coordination polymers [Co(Dpq)₂(1,4-NDC)_0.5] · (1,4-HNDC) (1), [Co(Dpq)(2,6-NDC)] (2), and [Co₂(Dpq)₂(BPEA)₄(H₂O)] · H₂O (3) have been obtained from hydrothermal reaction of cobalt nitrate with the mixed ligands dipyrido[3,2-d:2′,3′-f]quinoxaline (Dpq) and three dicarboxylate ligands with different spacer length [1,4-naphthalene-dicarboxylic acid (1,4-H₂NDC), 2,6-naphthalene-dicarboxylic acid (2,6-H₂NDC) and biphenylethene-4,4′-dicarboxylic acid (BPEA)]. All these complexes are fully structurally characterized by elemental analysis, IR, and single-crystal X-ray diffraction analysis. Single-crystal X-ray analysis reveal that complex 1 is infinite one-dimensional (1-D) chains bridged by 1,4-NDC ligands, which are extended into a two-dimensional (2-D) supramolecular network by π-π interactions between the Dpq molecules. Complex 2 is a distorted three-dimensional (3-D) PtS network constructed from infinite Co-O-C rod units. Complex 3 has a 5-fold interpenetrated 3-D structure with diamondoid topology based on dinuclear [Co₂(CO₂)₂(μ₂-OH₂)N₄O₂] units and BPEA molecules. The different structures of complexes 1-3 illustrate the influence of the length of dicarboxylate ligands on the self-assembly of polymeric coordination architectures. In addition, the thermal properties of complexes 1-3 and fluorescent properties of complexes 2 and 3 have been investigated in the solid state.     

Synthesis,DNA binding and antitumor activities of some novel polymer–cobalt(III) complexes containing 1,10-phenanthroline ligand

The novel water-soluble polymer–cobalt(III) complex samples, cis-[Co(phen)₂(BPEI)Cl]Cl₂ · 4H₂O (phen = 1,10-phenanthroline, BPEI = branched polyethyleneimine), with different amounts of cobalt complex content in the polymer chain, were prepared by ligand substitution method in water–ethanol medium and characterized by Infra-red, UV–Vis, ¹H NMR spectral and elemental analysis methods. The interaction of these polymer–cobalt(III)-phenanthroline complex samples with calf thymus DNA has been explored using electronic absorption spectroscopy, emission spectroscopy and gel electrophoresis techniques. The presence of multiple small size molecular binding sites, namely, the cobalt(III)–phenanthroline complex moieties, and free amino groups in a single big sized polymer molecule enhanced both the electrostatic and/or van der Waals interaction and partial intercalative bindings with calf thymus DNA. The antitumor activity of a sample of polymer–cobalt(III) complex was determined using HEp-2 cell line and different cell death indicator stains and MTT assay. Many of the cultured HEp-2 cells treated with this complex suffered loss of viability and death mostly through apoptosis as evidenced by the nuclear and cytoplasmic morphology.     

Synthesis,structures and magnetic properties of copper (II) and cobalt (II) complexes containing pyridyl-substituted nitronyl nitroxide and 3,5-dinitrobenzoate

Four new metal-radical complexes - [Cu(NIT3Py)₂(DTB)₂] 1, [Co(NIT3Py)₂(DTB)₂(CH₃OH)₂] 2, [Cu(NIT4Py)₂(DTB)₂(H₂O)₂] 3, [Co(NIT4Py)₂(DTB)₂(H₂O)₂] 4, (NIT3Py = 2-(3^′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide], NIT4Py = 2-(4^′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide], DTB = 3,5-dinitrobenzoic anion) have been synthesized by using transition metal ions, nitronyl nitroxide radicals as spin carriers, and incorporating 3,5-dinitrobenzoic acid (DTB) as a coligand.     

Structure and magnetism of mono-, di-, and trinuclear benzoato cobalt(II) complexes

Three cobalt(II) - benzoato (bz) complexes have been prepared and structurally characterized. In the mononuclear complex trans-[Co(bz)₂(H₂O)₂(nca)₂] the benzoato ligand is unidentate (nca = nicotinamide). The dinuclear complex [(μ₂-bz)₄{Co(qu)}₂] is a structural analog of the copper acetate (qu = quinoline) where four bidentate benzoato ligands link two cobalt(II) pentacoordinate centers. The trinuclear complex of the composition [Co₃(bz)₆(inca)₆] contains a central hexacoordinate {(bz)₂Co(inca)₂(bz)₂} unit in which the bidentate benzoato ligands held the central and peripheral cobalt(II) centers (inca = iso-nicotinamide); the peripheral hexacoordinate {(bz)Co(inca)₂<} units contain the terminal benzoato ligand in its bidentate function. The magnetic susceptibility data down to T = 2 K and the magnetization data up to B = 7 T reveal a considerable magnetic anisotropy due to the single-ion zero-field splitting.     

Synthesis and Magnetic Properties of Two New Cobalt Complexes Constructed by Semirigid V‐shaped 5‐(4‐Carboxyphenoxy)‐pyridine‐2‐carboxylic Acid

Two cobalt complexes, [Co₃(L)₂(CH₃OH)₂(μ₃‐OH)₂] ( 1 ) and [Co(L)(bpe)_0.5] · H₂O ( 2 ) [H₂L = 5‐(4‐carboxyphenoxy)‐pyridine‐2‐carboxylic acid; bpe = 1, 2‐bis(4‐pyridyl)ethylene] were synthesized and fully characterized by elemental analyses, IR spectroscopy, single‐crystal X‐ray diffraction, thermogravimetric analysis (TGA), and magnetic analysis. Complex 1 has a two‐dimensional (2D) structure with puckered Co–O–Co chains, and 2 displays a three‐dimensional (3D) network containing one‐dimensional rectangular channels with dimensions of 9.24 × 13.84 Å. In complex 1 , variable‐temperature magnetic susceptibility measurements indicate antiferromagnetic interactions between cobalt magnetic centers.     

Role of hydrogen peroxide in the synthesis of nitrogen heterocycle containing cobalt complexes

The reactions of Co(O₂CCH₃)₂·4H₂O with the sodium salt of p-toluene sulfonic acid (NapTS) and pyridine (py) or 4-methylpyridine (4mepy) in the presence of hydrogen peroxide in methanol led to the formation of [Co(py)₃(H₂O)₃](pTS)₂ or [Co(4mepy)₂(H₂O)₄](pTS)₂·MeOH, respectively. The coordination polymer [{Co(44′bpy)(H₂O)₄}(pTS)₂]_n (4,4′-bipyridine = 44′bpy) was obtained from the reaction of Co(O₂CCH₃)₂·4H₂O with 44′bpy in the presence of NapTS. The reaction of Co(O₂CCH₃)₂·4H₂O, 2,2′-bipyridine (22′bpy) and NapTS with hydrogen peroxide resulted in the formation of the dinuclear complex [Co₂(μ-OH)₂(μ-O₂CCH₃)(O₂CCH₃)₂(22′bpy)₂](pTS). Characterization of these complexes and the role of hydrogen peroxide in these reactions are discussed. Similar reactions with sodium sulfamate gave the mononuclear [Co(22′bpy)₂(O₂CCH₃)]NH₂SO₃·2H₂O complex and [Co₂(μ-OH)₂(μ-O₂CCH₃)(O₂CCH₃)₂(22′bpy)₂](NH₂SO₃).     

Heterobimetallic complexes as oxygen donor bidentate ligands: synthesis of early-late trinuclear complexes

The early-late heterometallic complexes [TiCp^∗((OCH₂)₂Py)(μ-O)M(COD)] (M = Rh, Ir) behave as four-electron donor ligands yielding the polynuclear cationic complexes [TiCp^∗(OCH₂)₂ Py(μ-O){M(COD)}₂]OTf (M = Rh (1), Ir (2)). The molecular structure of complex 1 has been established through an X-ray diffraction study.     

A unique tridecanuclear Co(II) cluster with derivatised salicylaldoxime ligands: Structure,electrospray ionization mass spectrometry analysis and preliminary magnetic studies

A unique [Co₁₃(mosao)₈(Hmosao)₆]·(ClO₄)₄·3DMF·MeOH·3H₂O (1, H₂mosao = 3-methoxysalicylaldoxime) supercluster has been synthesized by a method of solvothermal reaction. The [Co₁₃(μ₂-O)₈(μ₃-O)₆(μ₂-O–N)₂(μ₃-O–N)₈]⁴⁺ core is highly conjugated butterfly-like disc, which can be considered as fourteen distorted defective cubes sharing the neighboring faces one another. The electrospray ionization mass spectrometry (ESI-MS) analysis of 1 strongly suggests that Co₁₃ cluster also exists in solution and maintains a conformation similar to that in the crystal structure, indicating that the significant stability of 1 in solution. Magnetic measurements of 1 reveal antiferromagnetic behaviors resulting from the cooperative magnetic coupling through multiplicate monoatomic oxygen and –N–O– exchange bridges and the odd number of spins result in relatively effective noncompensated moments at very low temperature.     

Photocytotoxic and anaerobic DNA cleavage activity of binuclear 3,3′-dithiodipropionic acid cobalt(II) complexes having phenanthroline bases

Dicobalt(II) complexes [{(B)Co^II}₂(μ-dtdp)₂] (1–3) of 3,3′-dithiodipropionic acid (dtdp) and phenanthroline bases (B), viz. 1,10-phenanthroline (phen in 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq in 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 3), have been prepared, characterized and their photo-induced anaerobic DNA cleavage activity studied. The elemental analysis and mass spectral data suggest binuclear formulation of the complexes. The redox inactive complexes have magnetically non-interacting dicobalt(II) core showing magnetic moment of ∼3.9 μ_B per cobalt(II) center. The complexes show good binding propensity to calf thymus DNA giving K_b values within 4.3 × 10⁵–4.0 × 10⁶ M⁻¹. Thermal melting and viscosity data predict DNA groove binding and/or partial intercalative nature of the complexes. The complexes show significant anaerobic DNA cleavage activity in green light under argon atmosphere possibly involving radical species generated from the disulfide moiety in a type-I pathway. The DNA cleavage reaction under aerobic medium in green light is found to involve hydroxyl radical species. The dppz complex 3 exhibits significant photocytotoxicity in HeLa cervical cancer cells with an IC₅₀ value of 2.3 μM in UV-A light of 365 nm, while it is essentially non-toxic in dark giving an IC₅₀ value of >200 μM. A significant reduction of the dark toxicity of the organic dppz base (IC₅₀ = 8.3 μM in dark) is observed on binding to the cobalt(II) center while essentially retaining its photocytotoxicity in UV-A light (IC₅₀ = 0.4 μM).