CoII Complexes Research Articles

Field-induced single-ion magnet behavior in a hydrogen-bonded supramolecular cobalt(II) complex

Hydrogen-bonded supramolecular frameworks remain highly interesting for the development of novel porous materials. Herein a hydrogen-bonded supramolecular framework of a cobalt(II) complex, [Co(cpt)2(H2O)2] (Hcpt = 4-(p-carboxyphenyl)-1,2,4-triazole), was synthesized and structurally characterized. A single crystal X-ray diffraction (SC-XRD) study indicates that the monometallic Co2+ ion is located in a distorted octahedral geometry and the complex forms a two-dimensional supramolecular network stabilised by significant intermolecular N···H interactions. Variable-temperature PXRD and TGA analysis experiments revealed considerable thermal stability of the supramolecular framework of the CoII complex. Magnetic studies showed that the distorted octahedral Co2+ ion exhibits considerable easy-plane magnetic anisotropy with D = 22.3 cm−1, while field-induced single-ion magnet (SIM) behavior was evidenced at low temperature. The forgoing results further highlight that the hydrogen-bonded supramolecular framework could be used as a great platform for the development of molecular nanomagnets.

Photoinduced organometallic mediating radical polymerization of acrylates mediated by CoII complexes of non-symmetrical tetradentate Schiff-base ligands

Three new cobalt(II) complexes with non-symmetrically-substituted N2O2 tetradentate Schiff-base ligands, prepared from the 1:1:1 condensation of 3-etoxy-salicylaldehyde, salicylaldehyde and ethylenediamine (H2Etsal − 1), o-phenylenediamine (H2Phsal − 2) or 1,2-cis,trans-cyclohexyldiamine (H2Cysal − 3), were synthesized. The complexes 1–3 were characterized by UV–Vis, FTIR, and MALDI-TOF spectroscopy, elemental analysis, molar conductance, cyclic voltammetry, and computational methods. The CoII-Schiff-base complexes (1–3) were used as controlling agents for the polymerization of n-butyl acrylate (BA) photoinitiated by diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), according to an organometallic-mediated radical polymerization (OMRP) mechanism. Although, all complexes have presented good control ability, the polymerization mediated by complex 1 showed the best control over molecular weight (Mn matching with Mn,th) and dispersity (Ð < 1.50). Kinetic results and computational investigations support the activation/deactivation equilibrium, exerted by complexes 1–3, occurring by one face of the complexes via reversible termination (RT) mechanism.minim.

Antibacterial metal complexes of o‐sulfamoylbenzoic acid: Synthesis, characterization, and DFT study

Herein, antibacterial transition metal complexes of ML2 type having o‐sulfamoylbenzoic acid as ligand were synthesized from saccharin. All characterization techniques confirmed the syntheses of non‐ionic transition metal MnII (3), CoII (4), NiII (5), CuII (6), and ZnII (7) complexes, where mono‐anionic o‐sulfamoylbenzoic acid acts as a weak field ligand. The FT‐IR, elemental analysis, and magnetic susceptibility studies suggested octahedral and square pyramidal geometries depending on the nature of metal ions. Biological activity of these complexes was studied by using six bacterial strains. Interestingly, the bacterial strains Escherichia coli and Klebsiella aerogenes were inhibited to the maximum level by 6. Among aforementioned five complexes, 4 and 6 were found in crystalline form. Apart from experimental study, DFT study was also performed for entitled complexes at the M06/6‐311G(d,p) level. A comparative investigation was performed for geometrical parameters and vibrational analysis, and an agreement was obtained. Natural bonding orbital investigations expressed larger value of stabilization energy 21 kcal/mol for 3, 4, and 6 while 42 kcal/mol for 5 and 7. Furthermore, global reactivity findings also disclosed higher value of hardness (2.44–3.09 eV) for entitled chromophores, hence, showed more stability. Moreover, frontier molecular orbital (FMO) findings revealed a larger band gap (4.48–6.19 eV) with higher values of LUMO found for all complexes.

Photocontrolled reversible-deactivation radical polymerization of butyl acrylate mediated by Salen-type CoII complexes

Salen-type Co II complexes were applied in the photo-OMRP of BA and MA to synthetize a copolymer (poly[MA]– co -poly[BA]) under 390 and 400–800 nm LEDs. • Co II complexes with Schiff-base ligands were prepared. • The Co II complexes were applied in the photo-OMRP of butyl acrylate. • The photosystems proposed showed a living character being able to mediate the copolymerization of poly[MA]- b -[BA]. • Experimental and theoretical data suggest a majority reversible termination pathway for these photo-OMRP reactions. In this study, we synthesized the complex [Co(BuSalen)] using the novel tetradentate BuSalen ligand and analyzed its ability as a controlling agent for the photo-induced organometallic-mediated radical polymerization (photo-OMRP) of butyl acrylate (BA) using diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) as photo-initiator. BA polymerization with [Co(BuSalen)] reached significant control levels using the [BA]/[Co II ]/TPO molar ratio of 600/1/1. The [Co(Salen)] and [Co(Bu 2 Salen)] complexes were also obtained following literature methods aiming a comparison in the mediating ability in photo-OMRP. [Co(BuSalen)] and [Co(Bu 2 Salen)] showed better controlling ability, as observed in the copolymerization study (Đ= 2.64, 1.50, and 1.26 for complexes [Co(Salen)], [Co(BuSalen)] and [Co(Bu 2 Salen)], respectively). Kinetics studies and computational investigations support a reversible termination (RT) mechanism and a tailorable Co II complex reactivity mainly altered by Schiff-base steric factors. Calculated thermodynamic parameters agree with the controlling degree delivered by these complexes, since the polymerization control increases with increasing the ΔG values for the formation of dormant species.

Synthesis of Chiral Spirolactams via Sequential C−H Olefination/Asymmetric [4+1] Spirocyclization under a Simple CoII/Chiral Spiro Phosphoric Acid Binary System

AbstractAn unprecedented enantioselective synthesis of spiro‐γ‐lactams via a sequential C−H olefination/asymmetric [4+1] spirocyclization under a simple CoII/chiral spiro phosphoric acid (SPA) binary system is reported. A range of biologically important spiro‐γ‐lactams are obtained with high levels of enantioselectivity (up to 98 % ee). The concise, asymmetric synthesis of an aldose reductase inhibitor was successfully achieved. Notably, contrast to previous reports that relied on the use of cyclopentadienyl or its derivatives (achiral Cp*, CptBu, or chiral Cpx) ligated CoIII complexes requiring tedious steps to prepare, cheap and commercially available cobalt(II) acetate tetrahydrate was used as an efficient precatalyst.

Synthesis of Chiral Spirolactams via Sequential C-H Olefination/Asymmetric [4+1] Spirocyclization under a Simple CoII /Chiral Spiro Phosphoric Acid Binary System.

An unprecedented enantioselective synthesis of spiro-γ-lactams via a sequential C-H olefination/asymmetric [4+1] spirocyclization under a simple CoII /chiral spiro phosphoric acid (SPA) binary system is reported. A range of biologically important spiro-γ-lactams are obtained with high levels of enantioselectivity (up to 98 % ee). The concise, asymmetric synthesis of an aldose reductase inhibitor was successfully achieved. Notably, contrast to previous reports that relied on the use of cyclopentadienyl or its derivatives (achiral Cp*, CptBu , or chiral Cpx ) ligated CoIII complexes requiring tedious steps to prepare, cheap and commercially available cobalt(II) acetate tetrahydrate was used as an efficient precatalyst.

Heterometallic Coii-Lii carboxylate complexes with N-heterocyclic carbene, triphenylphosphine and pyridine: a comparative study of magnetic properties

Heterometallic Coii-Lii compounds with N-heterocyclic carbene 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), tri phenylphosphine (Ph3P) and pyridine (py), [Co2Li2(Piv)6(IMes)2] (Piv is the anion of pivalic acid), [Co2Li2(Piv)6(Ph3P)2] and [Co2Li2(Fur)6(py)2] (Fur is the anion of 2-furoic acid), respectively, have been prepared and structurally characterized by X-ray crystallography. Easy-plane magnetic anisotropy in Coii complexes with pseudo-tetrahedral cores CoO3X (X = C, P and N) was revealed by measuring the magnetic properties together with quantum-chemical calculations using the SA-CASSCF/NEVPT2 approach. The field-induced slow magnetic relaxation of the complexes was mainly attributed to the Raman and direct processes.

Synthesis, structural characterizations and spectroscopic properties of binuclear CoIII complex and its Schiff ligand as a chemosensor for fuorescent recognition of ZnII

Binuclear CoIII complex [Co2(L)3(DMF)3] containing a Schiff ligand H2L was synthesized and analyzed by elemental analysis, single crystal X-ray crystallography, FT-IR, UV–Vis absorption spectroscopy, Hirshfeld surface analysis and DFT calculation. The CoIII complex was a 3:2 ((L)2− : CoIII) binuclear structure. The spatial configuration of central CoIII ions was six-coordinated slightly twisted octahedron. The 3D supramolecular network structure was linked by intermolecular hydrogen bonds, CH···π and π···π stacking interactions. The Schiff ligand H2L exhibits weak luminescence, but this weak fluorescence is turned on after coordination with the ZnII ion. Furthermore, H2L could as an “OFF-ON” chemosensor for fluorescent recognition of ZnII.

High Spin Cobalt Complexes Supported by a Trigonal Tris(Phosphinimide) Ligand.

Terminal, π-basic moieties occupy a prominent position in the stabilization of unusual or reactive inorganic species. The electron-releasing, π-basic properties of phosphinimides (PN) have been employed to stabilize electron-deficient early transition metals and lanthanides. In principle, a ligand field comprised of terminal PN groups should enable access to high-valent states of late first row transition metals. Herein, we report a new class of multidentate phosphinimide ligands to logically explore this hypothesis. Access to such ligands is made possible by a new procedure for the electrophilic amination of rigid, sterically encumbering, multidentate phosphines. Such frameworks facilitate terminal PN coordination to cobalt as demonstrated by the synthesis of a trinuclear CoII3 complex and a homoleptic, three-coordinate CoIII complex. Interestingly, the CoIII complex exhibits an exceedingly rare S = 2 ground state. Combined XRD, magnetic susceptibility, and DFT studies highlight that terminally bound PNs engage in strong dπ-pπ interactions that present a weak ligand field appropriate to stabilize high-spin states of late transition metals.

Investigation of spectroscopic, thermal, and biological properties of FeII, CoII, ZnII, and RuII complexes derived from azo dye ligand

In this study, the novel azo dye FeII, CoII, ZnII, and RuII complexes with an azo dye ligand (L: (E)-4-((4-methoxyphenyl)diazenyl)-3-methyl-1H-pyrazol-5-amine) were synthesized. The structures of the complexes were characterized by FT-IR, elemental analysis, UV-Vis, mass spectra (FeII and CoII), NMR spectra (only diamagnetic ZnII and RuII), thermogravimetric and differential thermal analysis (TGA-DTA). All of the newly synthesized compounds were tested for their biochemical properties, including enzyme inhibitory and antioxidant activities. According to the in vitro ABTS, DPPH, CUPRAC, and FRAP antioxidant methods, the ligand and its metal complexes showed close antioxidant activities to the standards (BHA, BHT, ascorbic acid, and α-tocopherol). Enzyme inhibitions of the metal complexes were investigated against glutathione S-transferase (GST), acetylcholinesterase (AChE), and butyrylcholinesterase (BChE) enzymes. The best inhibition values (Ki) were observed for Ru(II) complex against GST (14.36 ± 2.16 µM), AChE (16.86 ± 2.74 µM), and BChE (14.12 ± 2.04 µM).

Cobalt-Catalyzed Chemo- and Enantioselective Hydrogenation of Conjugated Enynes.

Asymmetric hydrogenation is one of the most powerful methods for the preparation of single enantiomer compounds. However, the chemo- and enantioselective hydrogenation of the relatively inert unsaturated group in substrates possessing multiple unsaturated bonds remains a challenge. We herein report a protocol for the highly chemo- and enantioselective hydrogenation of conjugated enynes while keeping the alkynyl bond intact. Mechanism studies indicate that the accompanying Zn2+ generated from zinc reduction of the CoII complex plays a critical role to initiate a plausible CoI /CoIII catalytic cycle. This approach allows for the highly efficient generation of chiral propargylamines (up to 99.9 % ee and 2000 S/C) and further useful chemical transformations.

Cobalt‐Catalyzed Chemo‐ and Enantioselective Hydrogenation of Conjugated Enynes

AbstractAsymmetric hydrogenation is one of the most powerful methods for the preparation of single enantiomer compounds. However, the chemo‐ and enantioselective hydrogenation of the relatively inert unsaturated group in substrates possessing multiple unsaturated bonds remains a challenge. We herein report a protocol for the highly chemo‐ and enantioselective hydrogenation of conjugated enynes while keeping the alkynyl bond intact. Mechanism studies indicate that the accompanying Zn2+ generated from zinc reduction of the CoII complex plays a critical role to initiate a plausible CoI/CoIII catalytic cycle. This approach allows for the highly efficient generation of chiral propargylamines (up to 99.9 % ee and 2000 S/C) and further useful chemical transformations.

Rotaxane CoII Complexes as Field-Induced Single-Ion Magnets.

Mechanically chelating ligands have untapped potential for the engineering of metal ion properties. Here we demonstrate this principle in the context of CoII‐based single‐ion magnets. Using multi‐frequency EPR, susceptibility and magnetization measurements we found that these complexes show some of the highest zero field splittings reported for five‐coordinate CoII complexes to date. The predictable coordination behaviour of the interlocked ligands allowed the magnetic properties of their CoII complexes to be evaluated computationally a priori and our combined experimental and theoretical approach enabled us to rationalize the observed trends. The predictable magnetic behaviour of the rotaxane CoII complexes demonstrates that interlocked ligands offer a new strategy to design metal complexes with interesting functionality.

Rotaxane CoII Complexes as Field‐Induced Single‐Ion Magnets

AbstractMechanically chelating ligands have untapped potential for the engineering of metal ion properties. Here we demonstrate this principle in the context of CoII‐based single‐ion magnets. Using multi‐frequency EPR, susceptibility and magnetization measurements we found that these complexes show some of the highest zero field splittings reported for five‐coordinate CoII complexes to date. The predictable coordination behaviour of the interlocked ligands allowed the magnetic properties of their CoII complexes to be evaluated computationally a priori and our combined experimental and theoretical approach enabled us to rationalize the observed trends. The predictable magnetic behaviour of the rotaxane CoII complexes demonstrates that interlocked ligands offer a new strategy to design metal complexes with interesting functionality.

Versatility of coordination modes of N’-(pyridin-2-ylmethylene)picolinoylhydrazidate in the mononuclear cobalt(III) and polynuclear cobalt(II) complexes

Molecular and crystal structures of the mononuclear cobalt(III) complexes bearing N’-(pyridin-2-ylmethylene)picolinoylhydrazidate (Lpy–), [Co(Lpy)3] (1) and [Co(Lpy)2]BF4 (2a and 2b), as well as those of the Lpy-bridged CoIII2CoII trinuclear and CoII4 tetranuclear complexes, [Co3(Lpy)4(H2O)2](BF4)4 (3) and [Co4(Lpy)4Cl2(CH3CN)2](BF4)2 (4), were determined by the single-crystal X-ray diffraction method, which revealed a variety of coordination and bridging modes of the multidentate Lpy– ligand. The protonated free hydrazone, HLpy, exists as an E-form (in regard to the imine configuration) in the solid state and in solution. In the mononuclear CoIII complexes, the hydrazonate anion (Lpy–) coordinates to a CoIII center in three different coordination modes: a bidentate κ2N1,N2 mode with the E-form (in 1) and two kinds of tridentate modes with the respective configuration, Z-κ3N1,N2,N4 and E-κ3O,N3,N4, in 2a and 2b. The former tridentate mode was sterically favored in the CoIII complexes, resulting in the five- and six-membered chelate rings, with a conversion of the imine configuration during the complexation. Complex 2a could also serve as a complex ligand toward a CoII ion with the κ2O,N3 mode, forming the CoIII–CoII–CoIII trinuclear complex (3). In the novel tetranuclear CoII complex (4), the E-Lpy– hydrazonates bridged two CoII ions in two different modes: μ-κ2O,N1:κ3O,N3,N4 and μ-κ2N1,N2:κ3O,N3,N4, where all chelate coordinations formed a five-membered ring with the CoII ion.

Stimulation of Redox-Induced Electron Transfer by Interligand Hydrogen Bonding in a Cobalt Complex with Redox-Active Guanidine Ligand.

Octahedrally coordinated cobalt(II) complexes with a redox‐active bisguanidine ligand and acac co‐ligands were synthesized and their redox chemistry analysed in detail. The N−H functions in a bisguanidine ligand with partially alkylated guanidino groups form N−H⋅⋅⋅O hydrogen bonds with the acac co‐ligands, thereby massively influencing the redox chemistry. For all complexes, the first one‐electron oxidation is metal‐centred, leading to CoIII complexes with neutral bisguanidine ligand units. Further one‐electron oxidation is ligand‐centred in the case of Co–bisguanidine complexes with fully alkylated guanidino groups, giving CoIII complexes with radical monocationic bisguanidine ligands. On the other hand, the hydrogen‐bond strengthening upon oxidation of the Co–bisguanidine complex with partially alkylated guanidino groups initiates metal reduction (CoIII→CoII) and two‐electron oxidation of the guanidine ligand, providing the first example for the stimulation of redox‐induced electron transfer by interligand hydrogen bonding.

Synthesis, characterization and biological properties of binuclear complexes of CuII, NiII and CoII with 3,4-diphenyl-5-(2-hydroxyphenyl)-1,2,5-triazapenta- 2,4-diene (DHTP

Synthesis, characterization and biological properties of binuclear complexes of CuII, NiII and CoII with 3,4-diphenyl-5-(2-hydroxyphenyl)-1,2,5-triazapenta- 2,4-diene (DHTP

A Mixed Valence CoIICoIII2 Field-Supported Single Molecule Magnet: Solvent-Dependent Structural Variation.

One-pot reaction of the Schiff base N,N’-ethylene bis(salicylaldimine) (H2L), CoCl2.6H2O, and [Ph2SnCl2] in acetone produces the mixed valence CoIICoIII2 compound [CoIICoIII2(μ-L)2(Ph)2(μ-Cl)2]·(CH3)2CO·H2O (1). Our recent study already revealed that the same reaction mixtures in methanol or ethanol produced a heterometallic SnIVCoIII (2) or monometallic CoIII complex (3), respectively. Comparison of these organometallic systems shows that the 2,1-intermetallic Ph shift occurs in any of those solvents, but their relevant structural features (mononuclear, dinuclear-heterometallic, and trinuclear mixed valence) are solvent dependent. Geometrical structural rotation is also discussed among the related organometallic CoIICoIII2 systems. The AC magnetic susceptibility measurements indicate that 1 is a single molecule magnet (SMM), exhibiting a field-induced slow magnetic relaxation with two modes. The relaxation time for the low-frequency channel is as slow as τ~0.6 s at T = 2.0 K and BDC = 1.0 T.

The synthesis and characterization of the octahedral CoIII complex of a pyrrolopyrrolizine derivative formed with dicyanovinylene-bis-(meso-aryl)dipyrrin.

A low spin state and diamagnetic CoIII complex 1 possessing pyrrolopyrrolizine ligands formed with dicyanovinylene-bis-(meso-aryl)dipyrrin was synthesized via the thermally activated metalation with CoCl2 and isolated via column chromatography. The nuclear magnetic resonance of complex 1 revealed diamagnetism, thereby confirming the structure of the octahedral CoIII-complex of strong-field ligands. The resulting molecular structure of 1 was elucidated by the X-ray diffraction analysis. An arrangement of two pyrrolizine-ligands for the metal chelation was found in the AB–BA order, which was distinct from the case observed during the formation of bis-NiII-expanded porphyrinoids.

DNA Binding and DNA Cleavage Activities of Newly Synthesized Co

Two water soluble complexes with CoII and CuII ions were synthesized using a novel β-cyclodextrin based azo-functionalized Schiff base as a ligand. The Schiff base and its metal complexes were characterized by different physico-chemical and spectroscopic methods. From the analyses of the experimental data, distorted octahedral geometry has been assigned for both the metal complexes. The binding interactions between the metal complexes and DNA were investigated by means of a thermal denaturation study and viscosity measurements as well as by electronic absorption and fluorescence spectroscopy. The DNA cleavage efficacy of the metal complexes was also studied by agarose gel electrophoresis using pBR DNA. These studies revealed that both the metal complexes followed an intercalative mode of binding to calf thymus (CT)-DNA and also effectively cleaved the supercoiled pBR DNA. The CoII complex, however, more efficiently cleaved CT-DNA than the CuII complex as much as the experimental results are concerned.