Central CoII Ion Research Articles

Field induced single ion magnet behavior in CoII complexes in a distorted square pyramidal geometry.

We report three CoII-based complexes with the general formula [CoII(L)(X)2] by changing the halide/pseudo-halide ions [X = NCSe (1SeCN); Cl (2Cl) and Br (3Br)]. The obtained τ5 and CShM values confirm a distorted square pyramidal geometry around the CoII ion in all these complexes. In these three complexes, the central CoII ion is situated above the basal plane of the square pyramidal geometry. The extent of distortion from the ideal SPY-5 geometry differs upon changing the coordinating halide/pseudo-halide ion in these complexes. This essentially results in the alteration of the anisotropic parameter D and hence impacts the magnetic properties in these complexes. This phenomenon has been corroborated with the aid of theoretical investigations. All these complexes display field-induced SIM behaviour with magnetic relaxation occurring through a combination of processes depending on the applied dc magnetic field values and dilution.

Bioinspired cobalt molecular electrocatalyst for water oxidation coupled with carbon dioxide reduction

AbstractTo mimic photosynthesis in green plants, it is a crucial challenge to drive water oxidation and CO2 reduction in one single system. In this study, we present a bioinspired trinuclear pyridinedicarboxylate cobalt complex (Et3NH)2[CoIII2CoII(OH2)(pda)5]·H2O (1) that is capable of homogeneously electrocatalytic water oxidation and CO2 reduction simultaneously. The designed mix‐valent cobalt complex is in a V‐configuration composed of two terminal CoIII ions and one central CoII ion coordinated with one water ligand, which is resemble to aqua ligation of the natural catalytic complex in oxygen‐evolving complex (OEC). The electrochemical results show that this trinuclear cobalt complex could electrocatalyze water oxidation under neutral condition at the potentials of 1.15 V and 2.00 V versus NHE, with the Faraday efficiency as high as about 96% and 82%, and the TOF of 2.22 and 10.20 s−1, respectively. Meanwhile, it also displays electrocatalytic activity for the reduction of CO2 to CO with the TOF of 0.93 s−1. The cobalt complex has good catalytic performance for the conversion of H2O and CO2 into O2 and CO, respectively, which may be mainly due to the key role of the flexible water ligand on the central CoII ion in the catalytic process. This work represents the first multinuclear cobalt complex for mimicking bio‐system to drive water oxidation coupled with carbon dioxide reduction simultaneously.

A cobalt(II) coordination polymer constructed with the 2-carboxy-phenoxyacetate linker showing a corrugated layer structure: synthesis, structure analysis and magnetic properties

Abstract A new binary CoII coordination polymer, [Co(2-cpa)2(H2O)] n (1) has been synthesized by a hydrothermal reaction of cobalt(II) acetate tetrahydrate and 2-carboxy-phenoxyacetic acid (2-H2cpa) in the presence of potassium hydroxide. Structural analysis revealed that the central CoII ion is in an octahedral geometry coordinated with one aqua and five oxygen atoms of three 2-carboxy-phenoxyacetate (2-cpa) ligands. The 2-cpa anions function as pentadentate double bridging chelate-μ 3 linkers binding neighboring CoII ions together, to form an unusual corrugated (4,4)-connected layer. Variable-temperature magnetic susceptibility data in the 2–300 K temperature range indicates a weak antiferromagnetic coupling between adjacent cobalt(II) ions.

Conductive Self-Assembled Monolayers of Paramagnetic {CoII } and { } Coordination Clusters on Gold Surfaces.

Two polynuclear cobalt(II,III) complexes, [Co5(N3)4(N-n-bda)4(bza·SMe)2] (1) and [Co6(N3)4(N-n-bda)2(bza·SMe)5(MeOH)4]Cl (2), where Hbza·SMe = 4-(methylthio)benzoic acid and N-n-H2bda = N-n-butyldiethanolamine, were synthesized and fully characterized by various techniques. Compound 1 exhibits an unusual, approximately C2-symmetric {CoII} core of two isosceles Co3 triangles with perpendicularly oriented planes, sharing a central, high-spin CoII ion residing in a distorted tetrahedral coordination environment. This central CoII ion is connected to four outer, octahedrally coordinated low-spin CoIII ions via oxo bridges. Compound 2 comprises a semi-circular {} motif of four non-interacting high-spin CoII and two low-spin CoIII centers in octahedral coordination environments. Self-assembled monolayers (SAMs) of 1 and 2 were physisorbed on template-stripped gold surfaces contacted by an eutectic gallium-indium (EGaIn) tip. The acquired current density-voltage (I-V) data revealed that the cobalt-based SAMs are more electrically robust than those of the previously reported dinuclear {CuIILnIII} complexes with Ln = Gd, Tb, Dy, or Y (Schmitz et al., 2018a). In addition, between 170 and 220°C, the neutral, mixed-valence compound 1 undergoes a redox modification, yielding a {Co5}-based coordination cluster (1-A) with five non-interacting, high-spin octahedral CoII centers as indicated by SQUID magnetometry analysis in combination with X-ray photoelectron spectroscopy and infrared spectroscopy. Solvothermal treatment of 1 results in a high-nuclearity coordination cluster, [Co10(N3)2(N-n-bda)6(bza·SMe)6] (3), containing 10 virtually non-interacting high-spin CoII centers.

Trapping of a Pseudotetrahedral CoIIO4 Core in Mixed-Valence Mixed-Geometry [Co5] Coordination Aggregates: Synthetic Marvel, Structures, and Magnetism.

A systematic one-step one-pot multicomponent reaction of Co(ClO4)2·6H2O, H3L (2,6-bis((2-(2-hydroxyethylamino)ethylimino)methyl)-4-methylphenol), and readily available carboxylate salts (RCO2Na; R = CH3, C2H5) resulted in the two structurally novel coordination aggregates [CoIICoIII4L2(μ1,3-O2CCH3)2(μ-OH)2](ClO4)4·4H2O (1) and [CoIICoIII4L2(μ1,3-O2CC2H5)2(μ-OH)(μ-OMe)](ClO4)4·5H2O (2). At room temperature, reactions of H3L in MeOH with cobalt(II) perchlorate salts led to coassembly of initially formed ligand-bound {CoII2} fragments following aerial oxidation of metal centers and bridging by in situ generated hydroxido/alkoxido groups and added carboxylate anions. Available alkoxido arms of the initially formed {L(μ1,3-O2CCH3)(μ-OH/OMe)Co2}+ fragments were utilized to trap a central CoII ion during the formation of [Co5] aggregates. In the solid state, both complexes have been characterized by X-ray crystallography, variable-temperature magnetic measurements, and theoretical studies. Both 1 and 2 show field-induced slow magnetic relaxation that arises from the single pseudo- T d CoII ion present. The structural distortion leads to an easy-axis magnetic anisotropy ( D = -31.31 cm-1 for 1 and -21.88 cm-1 for 2) and a small but non-negligible transverse component ( E/ D = 0.11 for 1 and 0.08 for 2). The theoretical studies also reveal how the O-Co-O bond angles and the interplanar angles control D and E values in 1 and 2. The presence of two diamagnetic {Co2(μ-L)} hosts controls the distortion of the central {CoO4} unit, highlighting a strategy to control single-ion magnetic anisotropy by trapping single ions within a diamagnetic coordination environment.

Fine‐Tuning of Linear Hexa‐Cobalt and Defective Penta‐­Cobalt Metal‐String Complexes

AbstractThe ligand, 2, 7‐bis(α‐5‐phenylpyrazinamino)‐1, 8‐naphthyridine (H2bphpzany), was synthesized by the reaction of 2, 7‐dichloro‐1, 8‐naphthyridine with 2‐amino‐5‐phenylpyrazine in the presence of potassium tert‐butoxide under palladium(0)‐catalyzed conditions. Linear defective penta‐cobalt metal‐string complex [Co5(bphpzany)4(NCS)2] (1) and hexa‐cobalt Co611+ complex [Co6(bphpzany)4(NCS)2](PF6) (2) each containing four bphpzany2– ligands were synthesized, and their structure was determined using single‐crystal X‐ray diffraction. The structure of complex 1 consists of two lantern‐type dinuclear Co2 fragments at the terminal positions and one rare octacoordinated cobalt at the center forming a linear [Co2···Co···Co2] chain. The magnetic susceptibility measurement of 1 shows a quartet ground state with a significant spin‐orbital contribution of the central CoII ion. Complex 2 consists of a linear Co611+ configuration wrapped by four bphpzany2– ligands and its magnetic susceptibility measurement reveals a two‐stages magnetic behavior with spin‐states of S = 1/2 at 2 K, and S = 3/2 at 300 K. The cyclic voltammograms display three redox waves at E1/2 = +0.97, E1/2 = +0.71 and E1/2 = –1.02 V for 1, and four waves at E1/2 = +1.32, E1/2 = +0.99, E1/2 = +0.64, and E1/2 = –0.14 V for 2, respectively. The values of single‐molecular resistance for 1 and 2 are 15.5 (±4.84) and 16.1 (±10.4) MΩ, respectively.

The Impact of Anion‐Modulated Structural Variations on the Magnetic Coupling in Trinuclear Heterometallic CuII–CoII Complexes Derived from a Salen‐Type Schiff Base Ligand

AbstractThree new trinuclear heterometallic [(CuIIL)2CoIIX2] complexes [H2L = N,N′‐bis(salicylidene)‐1,3‐propanediamine and X = thiocyanate (1), benzoate (2), or azide (3)] have been synthesized by reacting the metalloligand [CuL] with Co(ClO4)2·6H2O and the NH4+ or Na+ salt of the corresponding anion in methanol. Structural characterization reveals that the central CoII ion is connected to two terminal metalloligands through μ1,1‐diphenoxido bridges in all three complexes. However, two monodentate thiocyanato ions, which are mutually cis coordinated to the Co atom in 1, generate a “bent” structure, whereas the trans‐coordinated syn–syn bridging benzoato (1κO:2κO′) and the end‐on bridging azido (μ1,1) coligands in 2 and 3, respectively, produce linear structures. The changes in the number and nature of the bridges with a shortening of the distances between the metal centers leads to a concomitant decrease of the average CuII–O–CoII bridging angle from 99.3(2) to 97.1(4) and 91.5(1)° for 1, 2 and 3, respectively. Variable‐temperature magnetic susceptibility measurements show the presence of a dominant antiferromagnetic coupling between the Cu–Co pairs in all three complexes. However, a steady decrease of the magnitude of the exchange coupling constant (JCu‐Co) is observed from –33.4 (for 1) to –11.4 (for 2) and –2.15 cm–1 (for 3). This trend suggests that larger Cu–O–Co angles are associated with stronger antiferromagnetic coupling.

Bis{2-[bis(3,5-dimethyl-1H-pyrazol-1-yl-κN 2)methyl]pyridine-κN}cobalt(II) dinitrate

The central CoII ion in the title complex, [Co(C16H19N5)2](NO3)2, is located on a twofold rotation axis and has a slightly distorted octa­hedral coordination sphere. It is bonded to six N atoms from two 2-[bis­(3,5-dimethyl-1H-pyrazol-1-yl)meth­yl]pyridine ligands. In the crystal, mol­ecules are linked by weak C—H⋯O inter­actions.

(Picolinato-κN,O)[tris(2-isopropyl-1H-imidazol-4-yl-κN)phosphane]cobalt(II) nitrate.

Single crystals of the title compound, [Co(C6H4NO2)(C18H27N6P)]NO3, were obtained from the reaction of nitrato[tris­(2-isopropyl­imidazol-4-yl)phosphane]cobalt(II) nitrate with picolinic acid in the presence of potassium tert-butoxide as base. The coordination polyhedron around the central CoII ion is about halfway between square-pyramidal and trigonal-bipyramidal geometry. In the structure, the nitrate counter-anion is connected by N—H⋯O hydrogen bonding to the complex cation. Additionally, the complex cations form one-dimensional chains along [010] by hydrogen bonding of the NH group of an imidazole ring to the picolinate group of a neighbouring complex cation.

Bis(1,5-diphenylcarbazonato)dimethanolcobalt(II)

The structure of the title compound, [Co(C13H11N4O)2(CH3OH)2], is a mononuclear six-coordinated octa­hedral cobalt(II) complex of C i mol­ecular symmetry. The CoII ion is coordinated by two N atoms and two O atoms from two 1,5-biphenyl­carbazide ligands, and two O atoms from two methanol molecules. Two diphenyl­carbazidate ligands and the central CoII ion form the basal plane, with the two methanol mol­ecules located in axial positions. The crystal packing is defined by bifurcated O—H⋯N hydrogen bonding and intra­molecular N—H⋯O inter­actions.

First report on N,N′-diisoalkylisonicotinamide 1D coordination network containing linear trinuclear [Co3L4Cl6] units with mixed CoII(Td)–CoII(Oh)–CoII(Td) geometries: structure and magnetic properties

Reaction of anhydrous CoCl(2) with N,N'-diisopropylisonicotinamide (L) has yielded a coordination polymer containing linear trinuclear [Co(3)L(4)Cl(6)] units with a rare, mixed Co(T(d))-Co(O(h))-Co(T(d)) assembly (compound 1). The central Co(II) ion, of each trinuclear entity, exhibits a distorted octahedral geometry, with two ligand molecules coordinating through their carbonyl oxygen atoms along with two bridging Cl(-) ions and two pyridine N atoms from the neighboring molecules. Also, in each unit, two outer Co(II) ions display distorted tetrahedral geometry, coordinating to one ligand molecule through the pyridine N atom and to three Cl(-) ions (one of them bridged to the central Co(II) and the two acting as a terminal ligands). The magnetic properties of this compound were investigated in the temperature range of 2.0 to 300.0 K. Owing to the complexity of the system and the weak interactions among trinuclear aggregates, the magnetic response has been analyzed using a model which considers these units as isolated systems. In addition, magnetic data has been examined in two separated blocks, above and below 50 K, applying programs VPMAG FORTRAN and MAGPACK-fit, respectively. This way, only the most significant effects at each interval of temperature were considered: spin-orbit coupling of the Co(O(h)), at high temperatures and zero-field splitting parameters of the Co(T(d)) at the low. Spin-spin magnetic interaction has been taken into account for the whole range of temperatures. As a result, the analysis of the magnetic data shows that, within every trinuclear unit, the central position matches well with a high-spin Co(II) (S = 3/2) and also reveals weak ferromagnetic interactions between the Co(O(h)) and the two terminal Co(T(d)) ions (J = +0.34 cm(-1)).

Crystal Structures and Solution Behavior of Paramagnetic, Trinuclear, Mixed‐Valent Cobalt Complexes with Salen‐Type Ligands

AbstractNew trinuclear mixed‐valent CoIII‐CoII‐CoIII complexes with salen‐type ligands have been synthesized and characterized both in the solid state and in solution. These complexescomprise a central CoCl2 unit connecting two [RCo(4,4′,7,7′tmsalen)] fragments with chlorides acting as bridging ligands between the metals, while the central CoII ion completes its octahedral coordination through the salen oxygen donors. Complex 1 (R = CH2Cl), which has cis Cl ligands at the central CoII ion, has approximate C2 symmetry, whereas the centrosymmetric complex 2 (R = CF3CH2) contains trans Cl ligands (C2h symmetry). Complexes 1 and 2 are paramagnetic with magnetic moments of 4.7 and 4.4 μB, respectively, which indicate the presence of a high‐spin CoII center in the molecule. The 1H NMR spectra, which spread over a range of nearly 190 ppm, are consistent with the presence of both cis and trans isomers in solution (with cis being the prevailing species), and indicate that exchange is slow on the NMR time‐scale. Isotropically shifted 1H NMR signals have been fully assigned by comparison with those of appropriately substituted complexes and by T1 measurements and 2D exchange experiments (EXSY). The K constant for the trans [rlarr2] cis equilibrium, as evaluated from the 1H NMR signal intensity ratio at various temperatures, has allowed us to estimate, at least qualitatively, the thermodynamic parameters ΔH° and ΔS°.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Redox Chemistry of Tetrakis[5,6‐di(2‐pyridyl)‐2,3‐pyrazino]porphyrazinatocobalt(II): Isolation and Characterization of Solid Pure CoI, CoII, and CoIII Complexes

AbstractSalt‐like hydrated complexes of formulae Na[Py8TPyzPzCo] and [Py8TPyzPzCo](SbCl6) containing CoI and CoIII, respectively, and the neutral CoII–bis(dimethyl sulfoxide) (DMSO) adduct [Py8TPyzPzCo(DMSO)2], bearing additional clathrated DMSO molecules, have been prepared and characterized {Py8TPyzPz = tetrakis[5,6‐di(2‐pyridyl)‐2,3‐pyrazino]porphyrazinato dianion}. The sodium CoI salt, the anion of which, [Py8TPyzPzCo]1–, had previously been identified by electrochemical solution studies, represents the first example of a CoI derivative of a tetrapyrrolic macrocyclic chromophore prepared as a solid pure material. Solutions of Na[Py8TPyzPzCo] in DMSO, under defined experimental conditions, allow the slow formation (months) of crystals of its corresponding CoII complex of formula [Py8TPyzPzCo(DMSO)2]·6 DMSO. The structure of the adduct, elucidated by single‐crystal X‐ray analysis, shows the central CoII ion surrounded by the four pyrrole N atoms of the porphyrazine macrocycle and two O atoms of the axially bonded DMSO molecules. Oxidation of the basic starting material [Py8TPyzPzCo] with phenoxathiin hexachloroantimonate (phenox‐SbCl6) led to the formation of the CoIII complex [Py8TPyzPzCo](SbCl6). Full characterization of the title CoI, CoII, and CoIII species has been accomplished by solution studies and from IR, UV/Vis, EPR and X‐ray crystallography data.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Dichloridobis[2-(2-chloroethyl)-1,2,3,4-tetrahydropyrazino[1,2-a]benzimidazole-κN]cobalt(II)

In the title compound, [CoCl2(C12H14ClN3)2], the central CoII ion lies on a twofold rotation axis and adopts a distorted tetra­hedral coordination geometry defined by two N atoms from two 2-(2-chloro­ethyl)-1,2,3,4-tetra­hydro­pyrazino[1,2-a]benzimidazole ligands and two chloride anions. The Cl atom located in the side chain of the ligand is involved in inter­molecular C—H⋯Cl hydrogen bonding, which links neutral complex units into a one-dimensional right-handed helical chain running along a crystallographic 41 axis. Such hydrogen-bonded helical chains are connected to each other to form a homochiral three-dimensional supra­molecular network. One C atom of the 2-chloro­ethyl chain is disordered over two positions, with site-occupancy factors of 0.52 and 0.48.

Inclusion Complexes for Use in Room‐Temperature Gas‐Sensor Design

AbstractThe inclusion complex [{Co(bpy)(H2O)4}·(fcds)]n (1), which has been constructed using the guest molecule ferrocene‐1,1′‐disulfonate (fcds), the bridging ligand 4,4′‐bipyridine (bpy) and d7 Co2+, contains an infinite zigzag chain formed by the central CoII ion and the bridging bpy ligand. Guest fcds molecules lie between two adjacent zigzag chains. The highly conjugated structure of complex 1 means that it can be used as a metal‐organic semiconductor, and it also shows a high response to liquefied petroleum gas (LPG) and ethanol/petroleum ether (EP) at room temperature. The inclusion complexes [{Co(bpp)2(H2O)2}·(fcds)·4H2O]n [2; bpp = 1,3‐bis(4‐pyridyl)propane] and [{Zn(bpy)(H2O)4}·(fcds)]n (3), on the other hand, cannot be employed as room‐temperature gas sensors because they are insulators. The electrical resistivity of inclusion complex [{Ni(bpy)(H2O)4}·(fcds)]n (4) is 621 MΩ, whereas that of [{Co(bpy)(H2O)4}SO4·(4‐abaH)2·3H2O]n (5) (4‐abaH = 4‐aminobenzoic acid) is only 137 MΩ. This means that the semi‐conducting properties of such inclusion complexes depend on both the conjugated structure and the central metal ions. Furthermore, conjugated inclusion complexes with an odd number of electrons could be useful for the design of highly selective room‐temperature gas sensors.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Tetraaquabis(4,6-dioxidopyrimidin-1-ium-κ3N)cobalt(II)

In the title complex, [Co(C4H3N2O2)2(H2O)4], the central CoII ion is located at an inversion centre and is coordinated by two N atoms from 4,6-dihydroxy­pyrimidine ligands and four O atoms from water mol­ecules in an approximately octa­hedral geometry. This discrete structure is further extended into a three-dimensional supramolecular structure via weak hydrogen bonds.

A linear trinuclear CoII–CoII–CoIIcomplex with μ-acetate bridges: di-μ-acetato-bis[μ-N,N′-bis(salicylidene)-1,4-butanediaminato]tricobalt(II)

The title linear trinuclear complex, di-μ-acetato-1:2κ2O,O′;2:3κ2O,O′-bis{2,2′-[1,4-butane­diyl­bis­(nitrilo­methyl­idyne)]­diphenolato}-1:2κ6O,N,N,O′:O,O′;2,3κ6O,O′:O,N,N,O′-tricobalt(II), [Co3(C18H18N2O2)2(C2H3O2)2], was prepared by the reaction of the tetradentate Schiff base ligand bis­(salicyl­idene)-1,4-di­amino­butane and Co(CH3COO)2·2H2O in a methanol solution. The central CoII ion, which is located on an inversion center, has a distorted octahedral coordination involving four bridging O atoms from two Schiff base ligands in the equatorial plane and one O atom from each bridging acetate group in the axial positions. The coordination around the terminal CoII ion is irregular square pyramidal, with two O and two N atoms of the ligand in the basal plane and one O atom from an acetate group in the apical position. The acetate bridges linking the central and terminal CoII ions are mutually trans. The closest Co⋯Co separation is 3.125 (4) Å.