Cobalt Complexes Research Articles

Crystal structure and magnetic properties of iron(II) and cobalt(II) complexes containing tridentate pyridine-tetrazolate ligand: a study by X-ray diffraction and X-ray absorption spectroscopy

Crystal structure and magnetic properties of iron(II) and cobalt(II) complexes containing tridentate pyridine-tetrazolate ligand: a study by X-ray diffraction and X-ray absorption spectroscopy

Infrared Ion Spectroscopic Characterization of the Gaseous [Co(15-crown-5)(H2O)]2+ Complex.

We report fingerprint infrared multiple-photon dissociation spectra of the gaseous monohydrated coordination complex of cobalt(II) and the macrocycle 1,4,7,10,13-pentaoxacyclopentadecane (or 15-crown-5), [Co(15-crown-5)(H2O)]2+. The metal-ligand complexes are generated using electrospray ionization, and their IR action spectra are recorded in a quadrupole ion trap mass spectrometer using the free-electron laser FELIX. The electronic structure and chelation motif are derived from spectral comparison with computed vibrational spectra obtained at the density functional theory level. We focus here on the gas-phase structure, addressing the question of doublet versus quartet spin multiplicity and the chelation geometry. We conclude that the gas-phase complex adopts a quartet spin state, excluding contributions of doublet species, and that the chelation geometry is pseudo-octahedral with the six oxygen centers of 15-crown-5 and H2O coordinated to the metal ion. We also address the possible presence of higher-energy conformers based on the IR spectral evidence and calculated thermodynamics.

Cobalt-Catalyzed Enantioselective Hydrogenation of Diaryl Ketones with Ferrocene-Based Secondary Phosphine Oxide Ligands.

A new class of cobalt catalytic system for asymmetric hydrogenation of ketones was herein reported, involving the development of novel ferrocene-based secondary phosphine oxide ligands. An unusual P-O bidentate coordination pattern with cobalt was confirmed by an X-ray diffraction study. The bichelating tetrahedral cobalt(II) complexes afforded high reactivities (up to 99% yield) and good to excellent enantioselectivities (up to 92% ee) in the AH of various ortho-substituted diaryl ketones. In addition, the diferrocenyl cobalt complex was characterized with intriguing UV-vis absorption and electrochemical properties.

Modulating Photoinduced Electron Transfer between Photosensitive MOF and Co(II) Proton Reduction Sites forBoosting Photocatalytic Hydrogen Production.

Photocatalytic hydrogen production viawater splitting is the subject of intense research. Photoinduced electron transfer (PET) between a photosensitizer (PS) and a proton reduction catalyst is a prerequisite step and crucial to affecting hydrogen production efficiency. Herein, three photoactive metal-organic framework (MOF) systems having two different PET processes where PS and Co(II) centers are either covalently bonded or coexisting to drive photocatalytic H2 production arebuilt. Compared to these two intramolecular PET systems including CoII -Zn-PDTP prepared from the post-synthetic metalation toward uncoordinated pyridine N sites of Zn-PDTP and sole cobalt-based MOF Co-PDTP, the CoII (bpy)3 @Zn-PDTP system impregnated by molecular cocatalyst possessing intermolecular PET process achieves the highest H2 evolution rate of 116.8mmol g-1 h-1 over a period of 10h, about 7.5 and 9.3 times compared to CoII -Zn-PDTP and Co-PDTP in visible-light-driven H2 evolution, respectively. Further studies reveal that the enhanced photoactivity in CoII (bpy)3 @Zn-PDTP canbe ascribed to the high charge-separation efficiency of Zn-PDTP and the synergistic intermolecular interaction between Zn-PDTP and cobalt complexes. The present work demonstrates that the rational design of PET process between MOFs and catalytic metal sites can be a viable strategy for the development of highly efficient photocatalysts with enhanced photocatalytic activities.

Compositionally Controlled Electron Transfer in Metallo-Organics.

We demonstrate here the assembly of a nanolayer of electrochromic iron complexes on the top of composite layers of cobalt and ruthenium complexes. Depending on the ratio of the latter two complexes, we can tailor materials that show different electron transport pathways, redox activities, and color transitions. No redox activity of the top layer, consisting of iron complexes, is observable when the relative amount of the ruthenium complexes is low in the underlying composite layer because of the insulating properties of the isostructural cobalt complexes. Increasing the amount of ruthenium complexes opens an electron transport channel, resulting in charge storage in both the cobalt and iron complexes. The trapped charges can be chemically released by redox-active ferrocyanide complexes at the film-water interface.

Cobalt(III)-py2en systems as potential carriers of β-ketoester-based ligands

Two cobalt(III) complexes containing different β-ketoesters, namely [CoIII(L1)(py2en)](ClO4)2·H2O (1) and [CoIII(L2)(py2en)](ClO4)2 (2) (py2en = N,N′-bis(pyridin-2-ylmethyl)ethylenediamine; L1− = methylacetoacetate; L2− = ethyl 4-chloroacetoacetate) have been prepared and investigated as prototypes of bioreductive prodrugs. The presence of β-ketoester and py2en ligands in 1 and 2, as well as the perchlorate counterions, was supported by IR spectroscopy and CHN elemental analysis. The composition molecular structure of both complexes was confirmed by NMR spectroscopy and ESI mass spectrometry. Structural information was also obtained for 2via X-ray diffraction analysis. The redox properties indicate that 1 and 2 are suitable for reduction under biological conditions. Investigation of DNA-interacting suggest that 1 and 2 bind DNA via electrostatic forces. Both complexes may be employed as possible platforms for the delivery of biologically active compounds, since their reaction with ascorbic acid in PBS at pH 6.2 and 7.4 at 37°C results in the release of the β-ketoester ligands upon Co(III)/Co(II) reduction.

A Novel Synthesis of iso-nicotinamide ligand and its cobalt complex

The complex of cobalt(II) with iso-nicotinamide (intmd) was synthesized at a 1:1 mole ratio of metal to ligand. The complex formula obtained is [Co(intmd)2(H2O)2]Cl2.nH2O (n = 0 or 1). The Co(II)-intmd complex was characterized by UV-Vis Spectrophotometer, Atomic Absorption Spectrophotometry (AAS), Differential Thermal Analyzer (DTA), Conductivity meter, Fourier-transform Infrared Spectroscopy (FTIR), Magnetic Susceptibility Balance (MSB), and Powder X-Ray Diffraction. Thermal analysis showed the complex contained several hydrates. The electrical conductivity of the complex in aquades is 1:1, the complex is electrolyte. The infrared spectrum shows that C=O and -NH2 from intmd are coordinated with metal ion. The electronic spectra show two peaks indicating the transitions 4T1g(F) → 4T1g(P) (ν3) and 4T1g(F) → 4A2g(F) (ν2). The complex is paramagnetic with μeff = 5.31-5.44 BM. It is suggested that the Co(II)-intmd complex has an octahedral geometry and an orthorhombic crystal system.

In vitro biological activity of cobalt(II) complexes with salicylaldimine ligands in microbial and cancer cells.

Background: More studiesusing cobalt complexes as drugs areneeded. Results: The drug action oftwo cobalt salicylaldimines was determined. The complexes and amphotericin B (20mg/ml) inhibited Candida albicans at 9-15 and 21mm. This concentration of both ligands inhibited Staphylococcus aureus at 10mm and one ligand inhibited Escherichia coli at 9mm, but the complexes and ampicillin inhibited four bacteria at 9-20 and 21-26mm. The ligands were inactive against cancer and normal cells, but the complexes and doxorubicin provided IC50valuesof 28.18-54.19 and 9.66μM against MCF-7 cells and 15.76-20.49 and 36.42μM against BHK cells. Conclusion: The ligands' activity was much improved by complexation, although they remained substandard.

Structural investigation, quantum chemical calculation, energy framework analysis and MIC studies of silver and cobalt complexes of 4-amino-N-(4, 6-dimethyl-2 pyrimidinyl) benzenesulfonamide in presence of secondary ligand

Silver and cobalt complexes of SMZ ligand (SMZ = 4-amino-N-(4, 6-dimethyl-2 pyrimidinyl) benzenesulfonamide) have been synthesized and characterized by elemental, FT-IR and 1H-NMR spectroscopy analysis. Due to the magnetic behaviour of the cobalt complex, it was characterized by EPR and magnetic susceptibility analysis. Single crystal X-ray diffraction (SC-XRD) study reveals the [Ag2(C12H14N4O2S)2(C6H7N), complex-1 crystallizes in orthorhombic space group Pbca, while [{Co(C12H13N4O2S)2(C5H5N)2}.(C5H5N)], complex-2 crystallizes in monoclinic space group C2/c. The SC-XRD analysis shows that silver in complex-1 is four-coordinate exhibiting distorted tetrahedral geometry, while cobalt in complex-2 is coordinated to six nitrogen’s leading to distorted octahedral geometry. Additionally, Hirshfeld surfaces and 2D fingerprint plots analysis shows that the H…H intermolecular contacts are the main contribution to the Hirshfeld surface area displaying values for complex-1 and complex-2 are 59.1% and 50% respectively (%H-H; complex 1 > Complex 2). In 3D energy frameworks analysis, complex-1, has shown the highest dispersion interaction energies than that of complex 2 [dispersion energy; -74.5 kJ mol-1 (complex-1) > -63.4 kJ mol-1 (complex-2)], Moreover, computational studies such as frontier molecular orbital (FMO), natural bond orbital (NBO) and Mulliken population analysis (MPA) were calculated using B3LYP method. Besides, The MIC data against panel of gram-positive and gram-negative organisms confirm that both the metal complexes of SMZ ligand possesses better inhibitory activities than that of SMZ ligand. The MIC data shows the silver complex exhibits comparatively better response towards the panel of the gram positive and gram negative bacteria. Furthermore, the molecular docking study agrees that the binding affinity of the complexes with 1BNA is higher than that of free SMZ ligand.

Antimicrobial activity of novel Cobalt(II) complexes with Schiff base derived from L-cysteine and 2-substituted benzaldehyde

Antimicrobial activity of novel Cobalt(II) complexes with Schiff base derived from L-cysteine and 2-substituted benzaldehyde

Cobalt (II), Nickel (II) and Palladium (II) complexes appended terpyridine‐based ligand: Synthesis, spectral characterization, anticancer activity and apoptosis investigation

Three new complexes containing 2‐thiophenylterpyridine (TP) ligand, namely, [Co(stpy)2]Cl2 (Co‐TP), [Ni(stpy)Cl2]2 (Ni‐TP) and [Pd(stpy)Cl]Cl (Pd‐TP) were synthesized and subsequently characterized employing various spectroscopic techniques including UV–Visible, IR, 1H NMR, EPR, and ESI‐MS analysis. ESI‐MS spectra suggested the complexes Co‐TP and Ni‐TP to be six coordinated with two ligand units and the complex Pd‐TP to be a four‐coordinated mononuclear square planar complex. The dimeric nature of the complex Ni‐TP (M2L2Cl4) was established by X‐ray diffraction analysis, which confirmed the bridging of two nickel centers by two chloride ions. The ligand and complexes were assessed for their cytotoxic behavior by using MTT colorimetric assay. The compounds TP, Co‐TP, Ni‐TP and Pd‐TP displayed significant antiproliferative activity on A549 (human lung carcinoma) and MM2 (human breast cancer) cell lines and had no toxic effect on human normal embryonic kidney cells (HEK 293). Further, the morphological changes associated with MM2 and A549 cells triggered by the tested compounds due to apoptosis have been validated with the help of AO‐EB and DAPI staining assays.

PH-Responsive Cobalt(II)-Coordinated Assembly Containing Quercetin for Antimicrobial Applications.

The development of novel drug delivery systems (DDSs) with promising antibacterial properties is essential for facing the emergency of increasing resistance to antimicrobial agents. The antibacterial features of quercetin and its metal complexes have been broadly investigated. However, several drawbacks affect their activity and effectiveness. In this work, we propose a DDS based on a pH-responsive cobalt(II)-coordinated assembly containing quercetin and polyacrylic acid. This system is suggested to trigger the release of the model drug in a pH-dependent mode by exploiting the localized acidic environment at the bacterial infection sites under anaerobic conditions. The delivery system has been designed by accurately examining the species and the multiple equilibria occurring in solution among the assembly components. The formation of cobalt(II) complexes with quercetin in the absence or presence of the pH-responsive polyacrylic acid was investigated in buffered aqueous solution at pH 7.4 using spectrophotometric (UV-Vis) and calorimetric (ITC) techniques. The determined binding affinities and thermodynamic parameters that resulted are essential for the development of a DDS with improved binding and release capabilities. Furthermore, the affinity of the polymer-cobalt(II) complex toward the model antimicrobial flavonoid was explored at the solid-liquid interface by quartz crystal microbalance (QCM-D) experiments, which provided marked evidence for drug loading and release under pH control.

A series of isomorphic cobalt(II), nickel(II) and zinc(II) complexes of mixed dithiophosphonate, 2,2-bipyridine and 1,10-phenanthroline ligands: Synthesis, structure, and theoretical calculations

Transition-metal complexes of dithiophosphonate ligands have attracted recent interest due to their involvement in several established and newly emerging applications. Herein, we report on the synthesis of six new complexes of Co(II), Ni(II), and Zn(II) and mixed dichalcogen (dithiophosphonate) and dipnictogen (2,2-bipyridine, and 1,10-phenanthroline) ligands: [Co{(S2P(4-C6H4OMe)(OCH(CH2CH3)2}2(C10H8N2)] 1, [Co{(S2P(4-C6H4OMe)(OCH2CH2CH2CH3)}2(C10H8N2)] 2, [Ni{S2P(4-C6H4OMe)(OCH3)}2(C12H8N2)] 3, [Ni{(S2P(4-C6H4OMe)(OCH(CH2CH3)2)}2(C12H8N2)] 4, [Zn{(S2P(4-C6H4OMe)(OCH3)}2 (C12H8N2)] 5 and [Zn{(S2P(4-C6H4OMe)(OCH2CH3)}2(C12H8N2)] 6. The complexes were characterized by solution 1H and 31P NMR spectroscopy, electrospray ionization mass spectrometry, elemental analysis, and FTIR. The crystal structures of 1, 3, 5, and 6 were established by single-crystal X-ray diffraction analysis. The four complexes are isomorphic and crystallize in the triclinic system, space group P-1, with Z = 2. Density functional theory (DFT) calculations of the electronic and structural properties of the complexes were carried out to estimate different quantum chemical properties. Crystallographic analysis showed that the Co(II) and Ni(II) metal centers in 1 and 3, respectively, adopted a distorted octahedral geometry, coordinating through the S (dithiophosphonate) and N (dipnictogen) donor atoms, while the Zn(II) center in 5 and 6 both adopted tetrahedral geometries. The obtained computational-based chemical parameters proved to be significant in evaluating the plausible reactivity and stability patterns of these complexes.

Cobalt-Catalyzed Enantioselective Cross-Electrophile Couplings: Stereoselective Syntheses of 5-7-Membered Azacycles.

Cobalt complexes of chiral pyrox ligands catalyzed enantioselective reductive couplings of nonconjugated iododienes with aryl iodides or alkenyl bromides. The reaction enabled stereoselective syntheses of 5-7-membered azacycles carrying quaternary stereocenters. Mechanistically, cross-electrophile selectivity originated from selective coupling of alkylcobalt(I) complexes generated after cyclization with aryl iodides.

Reductive functionalization of CO2 under mild reaction conditions for the catalytic synthesis of N-formamides by Mannich base based Cobalt (III) complex

Reductive functionalization of carbon dioxide is an important approach which not only reduces CO2 concentration but also functionalized it for the formation of value added chemicals. In this perspective, a hexadentate mononuclear cobalt (III) complex [CoIIIL] of Mannich base ligand (H4L) was synthesized and structurally characterized by single crystal X-ray diffraction. The electronic spectra of the complex showed two bands at 448 and 561 nm corresponds to the LMCT and d-d transitions respectively. The derived inexpensive [CoIIIL] complex was very much effective as catalyst in carbon dioxide functionalization reaction. The catalytic synthesis of mono selective N-formamide product from amines was produced through diagonal transformation of carbon dioxide in presence of polymethylhydrosiloxane (PMHS) as reducing agent and [CoIIIL] complex as catalyst. The effects of various reaction parameters were examined. Broad range of substrates (aromatic as well as aliphatic amines) smoothly produced good percentage of respective N-formamides product (72–94%) under mild reaction condition utilizing 1 atmospheric CO2. The high TON (1540–2000) and TOF value (192.5–400.0 h−1) for the catalytic reactions strongly depicted the productive nature of the [CoIII(L)] catalyst. The probable mechanestics studies clearly reveals that the [CoIIIL] complex activated the Si−H bond of PMHS to react with carbon dioxide in order to form the silyl formates intermediate for activation of N–H bonds in amines, thus leading to the excellent performance of the catalytic reaction.

Coordinatively Unsaturated Metallates of Cobalt(II), Nickel(II), and Zinc(II) Guarded by a Rigid and Narrow Void.

Both natural enzymatic systems and synthetic porous material catalysts utilize well-defined and uniform channels to dictate reaction selectivities on the basis of size or shape. Mimicry of this design element in homogeneous systems is generally difficult owing to the flexibility inherent in most small molecular species. Herein, we report the synthesis of a tripodal ligand scaffold that orients a narrow and rigid cavity atop accessible metal coordination space. The permanent void is formed through a macrocyclization reaction whereby the 3,5-dihydroxyphenyl arms are covalently linked through methylene bridges. Deprotonative metallation leads to anionic and coordinatively unsaturated complexes of divalent cobalt, nickel, and zinc. An analogous series of trigonal monopyramidal complexes bearing a nonmacrocyclized variant of the tripodal ligand are also reported. Physical characterization of the coordination complexes has been carried out using multiple spectroscopic techniques (NMR, EPR, and UV-vis), cyclic voltammetry, and X-ray diffraction. Complexes of the macrocyclized [LOCH2O]3- ligand retain a rigid cavity upon metallation, with this cavity guarding the entrance to the open axial coordination site. Through a combination of spectroscopic and computational studies, it is shown that acetonitrile entry into the void is sterically precluded, disrupting anticipated coordination at the intracavity site.

Structurally Rigid (8-(Arylimino)-5,6,7-trihydroquinolin-2-yl)-methyl Acetate Cobalt Complex Catalysts for Isoprene Polymerization with High Activity and cis-1,4 Selectivity

A series of cobalt complexes bearing (8-(arylimino)-5,6,7-trihydroquinolin-2-yl)methyl acetate ligand framework were prepared using a one-pot synthesis method. These complexes were then extensively investigated for their catalytic performance in isoprene polymerization. In addition to the complexes being characterized via FT-IR spectrum and elemental analysis, the molecular structure of Co1 and Co5 was determined via X-ray diffraction analysis. The analysis revealed a chloride-bridged centrosymmetric binuclear species in which each cobalt center exhibited a distorted square pyramidal geometry. Among the prepared complexes, Co1 demonstrated the highest catalytic activity of 1.37 × 105 g (mol of Co)−1(h)−1, achieving complete monomer conversion and resultant polyisoprene showed high molecular weight (Mn ≥ 2.6 × 105 g/mol). All of the complexes showed preference for the cis-1,4 configuration ranging from 65% to 72%, while the 3,4 monomer insertion units constituted between 27% and 34% of the polymer structure. Moreover, extensive investigations were conducted to assess the impact of reaction parameters and ligand properties on the catalytic activities and microstructural characteristics of the resulting polymer.

Clathrochelate Complexes Containing Axial Cymantrene and Tromancenium Moieties.

New clathrochelate complexes of manganese, iron and cobalt containing peripheral organometallic manganese moieties cymantrene or tromancenium were synthesized via self-assembly from di/tri-topic dioximes, metal templates and cymantrene/tromancenium boronic acid pinacol esters. These air-stable, highly colored, oligometallic complexes are composed of various combinations of MnIFeIIMnI, MnICoIIMnI, MnIMnIIMnIIMnI and MnICoIICoIIMnI metal assemblies with corresponding complicated magnetic and electrochemical properties. Full spectroscopic and structural characterization by 1H/11B/13C NMR, HRMS, IR, UV-vis, single crystal XRD and CV (cyclic voltammetry) is provided. Tetrametallic complexes containing tromanceniumyl substituents with two CoII or MnII central metals exhibit promising anticancer properties against different tumor cell lines.

Photocatalytic Activity and Thermal Stability of Hybrid Metal-Polymer-Coordinated Complexes Derived from Gallic Acid and Ethylenediamine.

Three new hybrid metal-polymer-coordinated complexes (MPCs) of copper(II), cobalt(II), and nickel(II) ions with an organic polymer derived from gallic acid and ethylenediamine (GAEtH) were synthesized. The structures of GAEtH and MPCs were characterized with FT-IR, ultraviolet (UV)-Vis, 1H and 13C NMR spectroscopy, and elemental and thermogravimetric analysis. The results reveal that the organic polymer GAEtH exhibits an infinite one-dimensional chain structure, while the hybrid MPCs have a double chain structure, with the two chains joined by metal ions. The thermodynamic and kinetic parameters of the thermal degradation stages were determined by the Coats Redfern method, and the photocatalytic behaviors of the MPCs were investigated through the decomposition of methyl orange dye under UV irradiation.

Controlling Intramolecular and Intermolecular Electronic Coupling of Radical Ligands in a Series of Cobaltoviologen Complexes.

Controlling electronic coupling between multiple redox sites is of interest for tuning the electronic properties of molecules and materials. While classic mixed-valence (MV) systems are highly tunable, e.g., via the organic bridges connecting the redox sites, metal-bridged MV systems are difficult to control because the electronics of the metal cannot usually be altered independently of redox-active moieties embedded in its ligands. Herein, this limitation was overcome by varying the donor strengths of ancillary ligands in a series of cobalt complexes without directly perturbing the electronics of viologen-like redox sites bridged by the cobalt ions. The cobaltoviologens [1X-Co]n+ feature four 4-X-pyridyl donor groups (X = CO2Me, Cl, H, Me, OMe, NMe2) that provide gradual electronic tuning of the bridging CoII centers, while a related complex [2-Co]n+ with NHC donors supports exclusively CoIII states even upon reduction of the viologen units. Electrochemistry and IVCT band analysis indicate that the MV states of these complexes have electronic structures ranging from fully localized ([2-Co]4+; Robin-Day Class I) to fully delocalized ([1CO2Me-Co]3+; Class III) descriptions, demonstrating unprecedented control over electronic coupling without changing the identity of the redox sites or bridging metal. Additionally, single-crystal XRD characterization of the homovalent complexes [1H-Co]2+ and [1H-Zn]2+ revealed radical-pairing interactions between the viologen ligands of adjacent complexes, representing a type of through-space electronic coupling commonly observed for organic viologen radicals but never before seen in metalloviologens. The extended solid-state packing of these complexes produces 3D networks of radical π-stacking interactions that impart unexpected mechanical flexibility to these crystals.