CoII Complexes Research Articles

Electrometric Study on Nature and Stability of CoII, NiII and CuII Complexes with 5-Sulfosalicylic Acid in DMSO-Water Mixtures

Electrometric Study on Nature and Stability of CoII, NiII and CuII Complexes with 5-Sulfosalicylic Acid in DMSO-Water Mixtures

Design, synthesis, structural characterization, molecular docking, antibacterial, anticancer activities, and density functional theory calculations of novel MnII, CoII, NiII, and CuII complexes based on pyrazolone-sulfadiazine azo-dye ligand

This study was designed to prepare novel metal chelates obtained from 4-((3-methyl-5-oxo-1-phenyl-pyrazol-4-yl)diazenyl)-N-(pyrimidin-2-yl) benzenesulfon amide (MPSA). They are characterized through CHN-analysis, spectroscopic (1HNMR, FT-IR, UV–Vis), mass, and TG analysis. The FT-IR and UV–visible spectra were related to the computed results and showed good conformity. The mass spectra determined that the ligand's molecular weight and chelates matched well with the found m/z values. The optimization for the studied chelates indicated the formation of distorted octahedral geometry for the prepared chelates. The B3LYP/6–311G** level for the free ligand and the B3LYP/6–311G**-LANL2DZ functional level for the metal ions in chelates were used in density functional theory (DFT) calculations. The results showed that the DFT computations match those of the experimental ones. Using the B3LYP/6–31G(d,p) basis set, TD-DFT/PCM was applied to determine the electronic spectral transitions of the produced compounds. Also, B3LYP/6–31G(d,p) has been utilized to implement the vibrational wavenumbers, and the results are reliable with the innovative ones. The antimicrobial activities of the compounds were experimentally established against a subsection of G+ and G- bacteria. The anticancer activities of the ligand were examined against some cell lines. The MCF7 cell line had the highest activity and was subjected to the anticancer effect of the ligand and its chelates. The cytotoxicity on normal cells was estimated against normal HSF cell lines. The outcomes demonstrated that chelates enhanced their cytotoxic and anticancer properties. Molecular docking mechanisms were done to establish how the obtained substances attach to the breast cancer-targeted protein binding sites,

TMPA‐based Cavitary Cobalt (II) Funnel Complexes

AbstractThe synthesis of a series of mononuclear, dicationic CoII funnel complexes is reported herein. Three ligands Calix‐TMPAX present a calix[6]arene cone closed at its small rim by a tris(2‐pyridylmethyl)amine (TMPA) unit and differ by the nature of three cavity walls, anisole, phenol or quinone. The X‐ray diffraction structure of [CoII(MeCN)Calix‐TMPAOMe](ClO4)2 displays a trigonal bipyramidal geometry, with Co bound to all 4 nitrogen atoms of the TMPA cap, and to one MeCN guest molecule buried inside the calixarene cavity. All complexes were fully characterized in solution as high spin 5‐coordinate species using various techniques, including 1H NMR spectroscopy. For comparison purpose, an analogous CoII complex based on the TMPACH2OH ligand, devoid of a calixarene core, was synthetized. Its X‐ray structure shows a dicationic 7‐coordinate cobalt(II) center in the N4O3 environment provided by the ligand, leaving no space for exogenous ligand binding. This contrasts with the 5‐coordinate complexes obtained with the calix‐ligands that allow guest‐ligand binding and exchange. A brief overview of the coordination properties of the calix‐complexes, compared to those obtained with TMPA ligands, devoid of a cavity, highlights major differences in terms of complexation kinetics, geometry, coordination to the labile site, anion affinity, nuclearity, and stability.

Synthesis of Cobalt(III) Complexes Derived from Pyridoxal: Structural Cleavage Evaluations and In Silico Calculations for Biological Targets

This study sought to investigate the synthesis of eight complexes constituted by a cobalt(III) (CoIII) metallic center coordinated to two units of iminic ligands LnC (n = 1–4, L1C–L4C), which are derivatives of pyridoxal hydrochloride and anilines with thioether function containing one to four carbons. Depending on the source of the cobalt ion and the addition (or not) of a non-coordinating counterion, complexes with distinct structures may form, being categorized into two series: [CoIII(LnC)(L0C)] (n = 1–4, C1’–C4’) with a LnC ligand and a ligand that has a thiolate function which cleaves the C-S(thioether) bond (L0C) and [CoIII(LnC)2]PF6 (n = 1–4, C1–C4) with two similar units of the same LnC ligand. The occurrence (or not) of cleavage in the eight complexes was observed by elucidating the solid-state structures by single crystal X-ray diffraction. This exciting method allows the synthesis of CoIII complexes without cleaving the C-S bonds from the ligands, thereby not requiring an inert atmosphere in the reaction systems. The synthesized complexes were evaluated by in silico calculations on viable biological targets such as deoxyribonucleic acid, superoxide dismutase enzyme, human serum albumin, and the structural spike glycoprotein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with the receptor binding domain (RBD) in both up and down conformations without and in complex with the cellular receptor angiotensin-converting enzyme 2 (ACE2). Overall, in silico results suggested that all the inorganic complexes under study are potential anticancer/antiviral agents; however, C4 and C4’ are the best candidates for future in vitro assays.

Structure of the five-coordinate CoII complex (1H-imidazole){tris-[(1-benzyl-triazol-4-yl-κN3)meth-yl]amine-κN}cobalt(II) bis-(tetra-fluoro-borate).

The title compound, [Co(C3H4N2)(C30H30N10)](BF4)2, is a five-coordinate CoII complex based on the neutral ligands tris-[(1-benzyl-triazol-4-yl)meth-yl]amine (tbta) and imidazole. It exhibits a distorted trigonal bipyramidal geometry in which the equatorial positions are occupied by the three N-atom donors from the triazole rings of the tripodal tbta ligand. The apical amine N-atom donor of tbta and the N-atom donor of the imidazole ligand occupy the axial positions of the coordination sphere. Two tetra-fluoro-borate anions provide charge balance in the crystal.

A CoII-Hydroxide Complex That Converts Directly to a CoII-Acetamide during Catalytic Nitrile Hydration.

In exploring structural and functional mimics of nitrile hydratases, we report the synthesis of the pseudo-trigonal bipyramidal CoII complexes (K)[CoII(DMF)(LPh)] (1(DMF)), (NMe4)2[CoII(OAc)(LPh)] (1(OAc)), and (NMe4)2[CoII(OH)(LPh)] (1(OH)) (LPh = 2,2',2''-nitrilo-tris-(N-phenylacetamide; DMF = N,N-dimethylformamide; -OAc = acetate)). The complexes were characterized using NMR, FT-IR, ESI-MS, electronic absorption spectroscopy, and X-ray crystallography, showing the LPh ligand to bind in a tetradentate tripodal fashion alongside the respective ancillary donor. One of the complexes, 1(OH), is an unusual structural and functional mimic of the Co active site in Co nitrile hydratases. 1(OH) reacted with acetonitrile to yield the CoII-acetamide complex (NMe4)2[CoII(NHC(O)CH3)(LPh)], 2, which was also thoroughly characterized. In the presence of excess hydroxide, 1(OH) was found to catalyze quantitative conversion of the added hydroxide into acetamide. Despite the differences in Co oxidation state in nitrile hydratases and 1(OH) (CoIII versus CoII, respectively), 1(OH) was nonetheless an effective nitrile hydration catalyst, selectively producing acetamide over multiple turnovers.

Dynamic kinetic resolution of an azlactone catalyzed by octahedral chiral-at-metal cobalt(III) complexes under phase-transfer alcoholysis

A family of well-defined octahedral cationic chiral-at- cobalt(III) catalysts based on (R,R)-1,2-cyclohexanediamine and (R,R)-1,2-diphenylethylenediamine has been examined in the dynamic kinetic resolution of an azlactone derived from N-benzoyl-tert-leucine. The reactions catalyzed by 10 mol% of CoIII complexes in the presence of 1 M aqueous NaOH solution under phase-transfer alcoholysis afforded the corresponding benzyl ester of tert-leucine with up to 76% yield and up to 66% enantioselectivity (ee).

Electronic Structure of Three-Coordinate FeII and CoII β-Diketiminate Complexes.

The β-diketiminate supporting group, [ArNCRCHCRNAr]-, stabilizes low coordination number complexes. Four such complexes, where R = tert-butyl, Ar = 2,6-diisopropylphenyl, are studied: (nacnactBu)ML, where M = FeII, CoII and L = Cl, CH3. These are denoted FeCl, FeCH3, CoCl, and CoCH3 and have been previously reported and structurally characterized. The two FeII complexes (S = 2) have also been previously characterized by Mössbauer spectroscopy, but only indirect assessment of the ligand-field splitting and zero-field splitting (zfs) parameters was available. Here, EPR spectroscopy is used, both conventional field-domain for the CoII complexes (with S = 3/2) and frequency-domain, far-infrared magnetic resonance spectroscopy (FIRMS) for all four complexes. The CoII complexes were also studied by magnetometry. These studies allow accurate determination of the zfs parameters. The two FeII complexes are similar with nearly axial zfs and large magnitude zfs given by D = -37 ± 1 cm-1 for both. The two CoII complexes likewise exhibit large and nearly axial zfs, but surprisingly, CoCl has positive D = +55 cm-1 while CoCH3 has negative D = -49 cm-1. Theoretical methods were used to probe the electronic structures of the four complexes, which explain the experimental spectra and the zfs parameters.

High Power Density of a Hydrogen Peroxide Fuel Cell Using Cobalt Chlorin Complex Supported on Carbon Nanotubes as a Noncorrosive Anode.

Hydrogen peroxide fuel cells (HPFCs) have attracted much attention due to their simple one-compartment structures and high availability under harsh conditions such as an anaerobic environment; however, catalysis improvement is strongly demanded for both anodes and cathodes in terms of activity and durability. Herein, we report the high catalytic activity of CoII chlorin [CoII(Ch)] for hydrogen peroxide (H2O2) oxidation with a low overpotential (0.21 V) compared to that of the CoII phthalocyanine and CoII porphyrin complexes, which have previously been reported as active anode catalysts. Linear sweep voltammograms and differential pulse voltammograms of the CoII complexes (CoIIL) and the corresponding ligands clearly showed that the CoIIIL species are the active species for H2O2 oxidation. Then, one-compartment HPFCs were constructed with CoII(Ch) supported on multiwalled carbon nanotubes (CNTs) as the anode together with FeII3[CoIII(CN)6]2 supported on CNTs as the cathode. The maximum power density of the HPFCs reached 151 μW cm-2 with an open circuit potential of 0.33 V when the coverage of CNT surfaces with CoII(Ch) exceeded ∼60% at the anode.

"Catch and release" of the CpN3 ligand using cobalt: dissociation, protonation, and C-H bond thermochemistry.

The coordination chemistry of an amine-rich CpN3 ligand has been explored with cobalt. We demonstrate that in the presence of NaCo(CO)4, the cationic precursor [CpN3]+ yields the complex CpN3CoI(CO)2. While 2e- oxidation generates new CoIII complexes such as [CpN3Co(NCMe)3]2+ and CpN3CoI2(CO), subsequent ligand loss is facile, generating free [CpN3]+ or the protonated dication [CpN3H]2+. We have structurally characterized both these ligand release products via single crystal X-ray diffraction and obtained thermochemical C-H bond strengths via experiment and density functional theory (DFT). Upon reversible 1e- reduction, the radical cation [CpN3H]˙+ has a weak C-H BDFE of 52 kcal mol-1 in acetonitrile. Mechanistic analysis shows that [CpN3H]˙+ undergoes radical-radical disproportionation in the absence of exogenous H-atom acceptors, which is supported by deuterium isotope labelling experiments. Structural comparison of these organic molecules shows a high degree of iminium-like electron delocalization over the C-N bonds connected to the central five-membered ring.

Exploring the effect of a pendent amine group poised over the secondary coordination sphere of a cobalt complex on the electrocatalytic hydrogen evolution reaction.

A CoIII complex (2) of a bispyridine-dioxime ligand (H2LNMe2) containing a tertiary amine group in the proximity of the Co center is synthesized and characterized. One of the oxime protons of the ligand is deprotonated, and the amine group remains protonated in the solid-state structure of the CoII complex (2a). The acid-base properties of 2 showed pKa values of 5.9, 8.4, and 9.6, which are assigned to the dissociation of two consecutive oxime protons and amine protons, respectively. The electrocatalytic proton reduction of 2 was investigated in an aqueous phosphate buffer solution (PBS), revealing a catalytic hydrogen evolution reaction (HER) at an Ecat/2 of -1.01 V vs. the SHE, with an overpotential of 673 mV and a kobs value of 2.6 × 103 s-1 at pH 7. For comparison, the HER of the Co complex (1) lacking the tert-amine group at the secondary sphere was investigated in PBS, which showed a kobs of 1.3 × 103 s-1 and an overpotential of 577 mV. At pH 4, however, 2 revealed a ∼3 times higher kobs value than 1, which suggests that the protonated amine group likely works as a proton relay site. Notably, no significant change in the reaction rate was observed at different pH values for 1, implying that oxime protons may not be involved in the intramolecular proton-coupled electron transfer reaction in the HER. The kobs values for Co complexes at pH 7.0 are significantly higher than those of the [Co(dmgH)2(pyridine)(Cl)] complex, implying that the primary coordination sphere around 1 or 2 enhances the HER and offers better catalyst stability in acidic buffer solutions.

Control of the geometry and anisotropy driven by the combination of steric and anion coordination effects in CoII complexes with N6-tripodal ligands: the impact of the size of the ligand on the magnetization relaxation time.

Four mononuclear CoII complexes of formula [Co(L)(SCN)2(CH3OH)0.5(H2O)0.5]·1.5H2O·0.75CH3OH (1), [Co(L1)Cl2]·H2O·2CH3CN (2), [Co(L1)(SCN)2]·1.5H2O·CH3OH (3) and [Co(L1)]ClO4·2CH3OH (4) were prepared from the N6-tripodal Schiff base ligands (S)P[N(Me)NC(H)2-Q]3 (L) and (S)P[N(Me)NC(H)1-ISOQ]3 (L1), where Q and ISOQ represent quinolyl and isoquinolyl moieties, respectively. In 1, the L ligand does not coordinate to the CoII ion in a tripodal manner but using a new N,N,S tridentate mode, which is due to the fact that the N6-tripodal coordination promotes a strong steric hindrance between the quinolyl moieties. However, L1 can coordinate to the CoII ions either in a tripodal manner using CoII salts with poorly coordinating anions to give 4 or in a bisbidentate fashion using CoII salt-containing medium to strongly coordinating anions to afford 2 and 3. In the case of L1, there is no steric hindrance between ISOQ moieties after coordination to the CoII ion. The CoII ion exhibits a distorted octahedral geometry for compounds 1-3, with the anions in cis positions for the former and in trans positions for the two latter compounds. Compound 4 shows an intermediate geometry between an octahedral and trigonal prism but closer to the latter one. DC magnetic properties, HFEPR and FIRMS measurements and ab initio calculations demonstrate that distorted octahedral complexes 1-3 exhibit easy-plane magnetic anisotropy (D > 0), whereas compound 4 shows large easy-axis magnetic anisotropy (D < 0). Comparative analysis of the magneto-structural data underlines the important role that is played not only by the coordination geometry but also the electronic effects in determining the anisotropy of the CoII ions. Compounds 2-3 show a field-induced slow relaxation of magnetization. Despite its large easy-axis magnetic anisotropy, compound 4 does not show significant slow relaxation (SMR) above 2 K under zero applied magnetic fields, but its magnetic dilution with ZnII triggers SMR at zero field. Finally, it is worth remarking that compounds 2-4 show smaller relaxation times than the analogous complexes with the tripodal ligand bearing in its arms pyridine instead of isoquinoline moieties, which is most likely due to the increase of the molecular size in the former one.

Metamagnetism and canted antiferromagnetic ordering in two monomeric CoII complexes with 1-(2-pyrimidyl)piperazine. Hirshfeld surface analysis and theoretical studies.

Here we present the magnetic properties of two cobalt complexes formulated as: [Co(SCN)2(L)2] (1) and (H2L)2[Co(SCN)4]·H2O (2) (L = 1-(2-pyrimidyl)piperazine). The two compounds contain isolated tetrahedral CoII complexes with important intermolecular interactions that lead to the presence of a canted antiferromagnetic order below 11.5 and 10.0 K, with coercive fields at 2 K of 38 and 68 mT, respectively. Theoretical calculations have been used to explain this behaviour. Hirshfeld surface analysis shows the presence of strong intermolecular interactions in both compounds. The crystal geometries were used for geometry optimization using the DFT method. From the topological properties, electrostatic potential maps and molecular orbital analysis, information about the noncovalent interaction and chemical reactivity was obtained.

Hydrogen atom abstraction as a synthetic route to a square planar CoII complex with a redox-active tetradentate PNNP ligand.

Redox-active ligands improve the reactivity of transition metal complexes by facilitating redox processes independent of the transition metal center. A tetradentate square planar (PNCH2CH2NP)CoII (1) complex was synthesized and the ethylene backbone was dehydrogenated through hydrogen atom abstraction to afford (PNCHCHNP)CoII (2), which now contains a redox-active ligand. The ligand backbone of 2 can be readily hydrogenated with H2 to regenerate 1. Reduction of 1 and 2 with KC8 in the presence of 18-crown-6 results in cobalt-based reductions to afford [(PNCH2CH2NP)CoI][K(18-crown-6)] (3) and [(PNCHCHNP)CoI][K(18-crown-6)] (4), respectively. Cyclic voltammetry revealed two reversible oxidation processes for 2, presumed to be ligand-based. Following treatment of 2 with one equivalent of FcPF6, the one-electron oxidation product {[(PNCHCHNP)CoII(THF)][PF6]}·THF (5) was obtained. Treating 5 with an additional equivalent of FcPF6 affords the two-electron oxidation product [(PNCHCHNP)CoII][PF6]2 (6). Addition of PMe3 to 5 produced [(PNCHCHNP)CoII(PMe3)][PF6] (7). A host of characterization methods including nuclear magnetic resonance (NMR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, cyclic voltammetry, magnetic susceptibility measurements using SQUID magnetometry, single-crystal X-ray diffraction, and density functional theory calculations were used to assign 5 and 6 as ligand-based oxidation products of 2.

Controlling the symmetry of hexamonodentate 3d-transition metal complexes through symmetry propagation from high-symmetry Ti-Mo and Zr-Mo clusters via hydrogen-bonding interactions.

The symmetry of one of the simplest hexamonodentate complexes, [M(H2O)6]2+ (M = Fe, Co, Ni, and Zn), was controlled by tuning interactions in the second coordination sphere. Highly symmetric Ti-Mo or Zr-Mo cluster cations acted as symmetry templates, imposing a crystallographic trigonal coordination geometry in the hexamonodentate complexes through intermolecular hydrogen-bonding interactions. Magnetic measurements revealed that the ideal trigonal symmetry results in weak spin-orbit coupling for high-spin FeII complexes, despite the T-term ground state in the octahedral geometry. In contrast, high-spin CoII analogues with the T-term ground state exhibited strong spin-orbit coupling. DFT studies supported that a d6 FeII ion in the D3 symmetry has a 5A1 ground state while a d7 CoII in the same symmetry has a 4E ground state. Single-ion magnet behavior was observed in the CoII complexes. These results demonstrate that incorporating a diamagnetic, highly symmetric cluster enables precise symmetry control in single-ion magnets containing only monodentate ligands.

Insight into the conformational selectivity of cobalt(iii) complexes with a tetradentate salen-type Schiff base ligand and their biorelevant catalysis: a combined experimental and theoretical study

A series of mononuclear CoIII complexes showing conformational selectivity (stepped vs. umbrella) and biomimetic catalytic activities are reported.

Single-ion magnetism in novel Btp-based cobalt complexes of different charge

By deprotonating Btp-derived ligands, precise control over counterions in the outer-coordination sphere is achieved in both neutral and charged anisotropic CoII complexes exhibiting field-induced single-ion magnetism.

Synthesis, Spectroscopy and Structural Elucidation of Two new CoII and NiII Complexes of Pyrazole Derived Heterocyclic Schiff base ligand as Potential Anticancer and Photocatalytic Agents

Synthesis, Spectroscopy and Structural Elucidation of Two new CoII and NiII Complexes of Pyrazole Derived Heterocyclic Schiff base ligand as Potential Anticancer and Photocatalytic Agents

Alkyl Chains Modulated Magnetization Dynamics of Mononuclear Trigonal Prismatic CoII Complexes.

Four benzeneboron-capped mononuclear CoII complexes with different alkyl substitutions on the fourth position of phenylboronic acid were obtained. The CoII ions are all wrapped by the pocket-like ligands and located in trigonal prismatic coordination geometries. Alternating-current magnetic susceptibility measurements reveal that they show different magnetization dynamics, such as distinct relaxation rates at the same temperature, the faster QTM rates for the ethyl and propyl substituted complexes, as well as different relaxation processes. Magneto-structural correlation study reveals that the various deviations of coordination geometry of CoII ion, diverse crystal packings and possible different vibration modes of substituents caused by modifying alkyl chains are the key factors affecting the magnetization dynamics. This work demonstrates that the alkyl chains even locating far away from the metal center can have a large impact on the magnetic behavior of the CoII complex with a very rigid coordination geometry, offering a new perspective towards transition metal based single-molecule magnets.

Structural evolution and zero-field SMM behaviour in ferromagnetically-coupled disk-type Co7 clusters bearing exclusively end-on azido bridges

Concise chemistry leads to a family of heptanuclear CoII-clusters, [Co7(N3)12(CH3CN)12] [Y2(NO3)4(piv)4]·2CH3CN (DC1) (pivH = pivalic acid), [Co7(N3)12(CH3CN)10(NO3)0.4 (Cl)1.6]·4CH3CN (DC2) and [Co7(N3)12(CH3CN)10(NO3)2]·4CH3CN (DC3), in which the metal ions are exclusively bridged by end-on azido ligands to stabilize a beautiful disk-like topology. The resulting clusters exhibit interesting structural transformations and thermodynamically-distinct steady states verified by theoretical calculations. Magnetic studies reveal the first observation of zero-field SMM behaviour in disk-like heptanuclear CoII complexes.