Disklike Hepta- and Tridecanuclear Cobalt Clusters. Synthesis, Structures, Magnetic Properties, and DFT Calculations

Peroxidase-like oxidative activity of cobalt-based 1D coordination polymer; experimental and theoretical investigations

CONTEXT

The present work describes the synthesis, structural characterization, and catalytic activity of a Co(II)-based one-dimensional coordination polymer (CP1). To validate the chemotherapeutic potential of CP1, in vitro DNA binding assessment was carried out by employing multispectroscopic techniques. Moreover, the catalytic activity of CP1 was also ascertained during the oxidative conversion of o-phenylenediamine (OPD) to diaminophenazine (DAP) under aerobic conditions.

METHODS

The molecular structure of CP1 was solved with the olex2.solve structure solution program using charge flipping and refined with the olex2.refine refinement package by using Gauss-Newton minimization. The DFT studies were performed by utilizing ORCA Program Version 4.1.1 to calculate the electronic and chemical properties of CP1 by calculating the HOMO-LUMO energy gap. All calculations were carried out at B3LYP hybrid functional using def2-TZVP as the basis set. Contour plots of various FMOs were visualized by using Avogadro software. Hirshfeld surface analysis was carried out by Crystal explorer Program 17.5.27 to examine the various non-covalent interactions which are crucial for the stability of crystal lattice. In addition, molecular docking studies of CP1 with DNA were performed by using AutoDock Vina software and AutoDock tools (version 1.5.6). Discovery studio 3.5 Client 2020 was used for visualization of the docked pose and binding interactions of CP1 with ct-DNA.

Switching of easy-axis to easy-plane anisotropy in cobalt(ii) complexes

In situ microcalorimetry monitored assembly and coligand induced switching of the magnetic anisotropy sign have been observed in a β-diketonate-Co(ii) system.

Structural characterization and magnetic property studies of a mixed-valence {CoIIICo} complex with a μ4-oxo tetrahedral {Co} motif

We have synthesized and structurally characterized a new mixed valence pentanuclear Co complex, bearing a rare μ4-O-tetrahedral CoII4 unit, by employing a pyridine-like Schiff base ligand. We have performed DC magnetic susceptibility and magnetization measurements over polycrystalline samples and chemical quantum computations in order to understand the exchange interaction pattern within Co(ii) sites and ground state magnetic anisotropy. This new complex shows an overall antiferromagnetic exchange interaction whose strength strongly depends on the local symmetry of Co(ii) sites. Also, local ion magnetic anisotropy reveals a strongly axial behaviour with the lowest Kramers doublet (KD) at each Co(ii) ion sufficiently isolated from excited states at low temperatures. Two Co(ii) sites show tetrahedral symmetry and the spin only formalism including axial zero-field splitting (ZFS) term properly described them; on the other hand, the other two Co(ii) sites have distorted octahedral and square base pyramidal coordination spheres, and a strong orbital contribution leads to a failure of the spin only formalism. A model of four Seff = 1/2 exchange interacting sites is necessary in order to account for low temperature magnetization behaviour. In view of the strongly anisotropic KD states, the exchange interactions are forced to be modelled as anisotropic ones. Overall, experimental data and quantum chemical computations are in good agreement, supporting the proposed model for magnetic behaviour.

Synthesis, structure and phenoxazinone synthase-like activity of three unprecedented alternating CoII–CoIII 1D chains

Three new one-dimensional Co^II/Co^III chains have been synthesized using N-salicylidene-l-alanine/N-salicylidene-l-phenylalanine and 2,2′-bipyridine/1,10-phenanthroline. All three complexes exhibit phenoxazinone synthase-like activity.

Solvent-induced single-crystal-to-single-crystal transformation and tunable magnetic properties of 1D azido-Cu(ii) chains with a carboxylate bridge

The solvent effect leads to structural transformation and tunable magnetism of chain-like azido-copper coordination polymers.

Cobalt complexes of the chelating dicarboxylate ligand "esp": a paddlewheel-type dimer and a heptanuclear coordination cluster

The coordination chemistry of Co(ii) with the chelating dicarboxylate ligand esp (esp = α,α,α',α'-tetramethyl-1,3-benzenedipropionate) is explored. We report here the bimetallic paddlewheel-type dimer, Co2(esp)2(EtOH)2 (1), and a bowl-shaped, heptanuclear coordination cluster, Co7(OH)4(Hesp)2(esp)4(MeCN)2·4MeCN (2). Crystal structures of both complexes are reported as well as their magnetic properties, which indicate antiferromagnetic interactions among the Co(ii) ions.

A difunctional azido-cobalt(ii) coordination polymer exhibiting slow magnetic relaxation behaviour and high-energy characteristics with good thermostability and insensitivity

A novel one-dimensional azido-cobalt(ii) compound, [Co2(1-mbt)2(N3)4]n (1) (1-mbt = 1-((2-propyl-imidazol-1-yl)methyl)-benzo[1,2,3]triazole), was solvothermally synthesized. X-ray crystal structure analysis demonstrates that two crystallographically independent Co(ii) atoms in the asymmetrical unit of compound 1 exhibit a rectangular pyramid geometry. The 3D supermolecular network of 1 consists of well-isolated 1D metal chains in which the azido bridging ligands assume an unusual pattern of combination with the Co(ii) centre as the sign of [-EE-EO-EO-EO-]n. The various coordination modes of the azido anion are responsible for different magnetic exchanges between the adjacent Co(ii) ions. The end-to-end (EE) mode mediates the antiferromagnetic coupling, whereas the end-on (EO) manner contributes to the ferromagnetic interaction. Magneto-structural relationships are discussed with the aid of theoretical calculations which are employed to find the potential single-ion magnetic anisotropy and reproduce the observed magnetic coupling properly. Alternating current magnetic susceptibility measurements reveal that 1 features a typical behaviour of field-induced slow magnetic relaxation. Energetic characterization evidences that the resulting compound possesses satisfactory detonation properties, superior lack of sensitivity and thermostability owing to the high nitrogen content (N% = 40.10%) and a coherent intrachain configuration. The kinetic parameters of the exothermic processes for 1 are investigated by the Kissinger method and the Ozawa method. We note that 1 has potential application prospects as a new generation of environmentally friendly high-energy materials based on this nitrogen-rich and oxygen-free system. In addition, the compound is developed as a practical additive to promote the thermal decomposition of ammonium perchlorate (AP) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The finding in this work highlights an example of effective development of advanced magneto-energetic materials.

A family of 3d metal clusters based on N–N single bonds bridged quasi-linear trinuclear cores: the Mn analogue displaying single-molecule magnet behavior

The reactions of the diacylhydrazine ligands N,N′-bisalicyl-2,6-pyridine dicarbohydrazide (H₆sphz) and N,N′-bis(3-methoxysalicyl)-2,6-pyridine dicarbohydrazide (H₆msphz) with various 3d metal salts, afforded a series of coordination clusters, namely, [Mn^III₂Mn^II(sphz)(acac)₂(CH₃OH)₄] (1, acac⁻ = acetylacetone anions), [Ni^II₃(msphz)(Py)₄] (2, Py = pyridine), [Cu^II₆(sphz)₂(Py)₄] (3) and [Cu^II₆(msphz)₂(Py)₄]·2DMF·2H₂O (4). Cluster 1 and 2 are single ligand assembled quasi-linear trinuclear structures. Both 3 and 4 consist a pair of quasi-linear {Cu₃} cores, which are linked together by two crossed ligands. The adjacent 3d metal ions in all trinuclear cores of 1–4 are bridged by N–N single bonds of ligands, which convey ferromagnetic (FM) interactions between 3d metal centers of 1, and antiferromagnetic (AFM) interactions between those of 2–4. In particular, the FM interactions and linear arrangement of mixed-valence Mn centers in 1 result in a large spin ground states value (S_T) of 13/2, as well as single-molecule magnet (SMM) behavior of slow relaxation and hysteresis of magnetization.

A family of 3d metal clusters featuring N–N single bonds bridged quasi-linear trinuclear cores were designed and synthesized. The Mn analogue represents a very rare case of quasi-linear 3d SMM using N–N single bonds as magnetic coupling pathways.

New molecular heptanuclear cobalt phosphonates: synthesis, structures and magnetic properties

Synthesis, structures and magnetic properties (strong anisotropy, ferromagnetic and antiferromagnetic interactions) of novel {Co₇} homoleptic molecular cobalt phosphonates with a similar structure motif are described.

Wheel-type heterometallic ferromagnetic clusters: [Ni7−xMx(HL)6(μ3-OMe)4(μ3-OH)2]Cl2 (M = Zn, Co, Mn; x = 1, 3)

Wheel-type heptanuclear heterometallic clusters display metal ion dependent ferromagnetic properties and express single molecule magnet behavior based on the magnetic anisotropy.

Synthesis and magneto-structural studies on a new family of carbonato bridged 3d–4f complexes featuring a [CoII3LnIII3(CO3)] (Ln = La, Gd, Tb, Dy and Ho) core: slow magnetic relaxation displayed by the cobalt(ii)–dysprosium(iii) analogue

A new series of carbonato-bridged complexes containing a CoII3LnIII3 core have been synthesized.

Cages on a plane: a structural matrix for molecular ‘sheets’

A family of heterometallic Anderson-type ‘wheels’ of general formula [MIII2MII5(hmp)₁₂]⁴⁺ has been extended to include M^III = Cr, Al; M^II = Co, Ni, Fe, Mn, Cu and Zn, alongside the ‘extended’ [AlIII6CuII7(OH)₁₂(hmp)₁₂]⁸⁺.

Tetranuclear Ni(ii) and Co(ii) Schiff-base complexes with an M4O6 defective dicubane-like core: zero-field SMM behavior in the cobalt analogue

Two tetranuclear Ni₄ and Co₄ complexes were prepared and characterized. Their magnetic properties were thoroughly studied and it was revealed that the Co₄ compound behaves as a zero-field single-molecule magnet.

An octanuclear Schiff-base complex with a Na2Ni6 core: structure, magnetism and DFT calculations

An octanuclear complex with a Na₂Ni₆ core was prepared and characterized. Its magnetic properties were thoroughly studied by experimental and theoretical methods.

Self-assembly, structures, magnetic properties and solution behaviors of six mixed-valence cobalt clusters

Six novel mixed-valence cobalt clusters with flexible {Co^II_xCo^III_y} cores have been constructed via in situ synthesis and stepwise synthesis routes. Their solution behaviors and possible assembly evolutions were detected by HRESI-MS. All of them also show interesting magnetic behaviours.

A disc-like Co7 cluster with a solvent dependent catecholase activity

Herein, we report the first example of a new Co₇ disc-like cluster with a solvent dependent catecholase activity characterized by spectral, X-ray and magnetic studies.

Different magnetic responses observed in Co, Co and Co-based MOFs

Four magnetic MOFs with anisotropic Co(II) ions, {[Co5(H2O)2(μ3-OH)2(atz)2(stp)2]·1.5H2O}n (1), {[Co5(H2O)2(μ3-OH)2(trz)2(stp)2]·1.3H2O}n (2), {[Co5(H2O)6(μ3-OH)2(trz)2(stp)2]·2.5CH3OH}n (3) and {[Co3(H2O)4(Hdatrz)2(stp)2]·3H2O}n (4) (stp(3-) = 2-sulfoterephthalate, trz(-) = 1,2,4-triazolate, atz(-) = 3-amino-1,2,4-triazolate and Hdatrz = 3,5-diamino-1,2,4-triazole) were solvothermally isolated by varying the substituent groups appended on the N-heterocyclic triazole and structurally and magnetically characterized. Structural analyses indicate that the former two complexes are crystallographically isostructural, exhibiting pillared-layer frameworks with mixed triazolyl and carboxylate extended Co + Co layers supported by rigid stp(3-) connectors. Complex 3 is built from butterfly-shaped Co cluster-based layers, which are interconnected with single cobalt(ii) octahedra by ditopic stp(3-) bridges. By contrast, complex 4 consists of linear {Co3(μ-N1,N4-Hdatrz)2} subunits, which are extended by 3-connected stp(3-) linkers into a stable 3D framework. Magnetically, 1 exhibits ferromagnetic ordering below 2.7 K due to the well-organized alignment of the non-compensated resultant moment from octahedra and tetrahedral cobalt(ii) carriers, while 3 is in a non-zero paramagnetic state above 2.0 K resulting from the coexistence of intermetallic ferromagnetic and antiferromagnetic interactions. The magnetic competition between weak inter-subunit antiferromagnetic interactions and the external magnetic field makes 4 behave as a field-induced metamagnet with a critical field of 27.5 kOe. These interesting magnetostructural results suggest that the anisotropy of the moment carrier and the interlayer/intersubunit separations significantly dominate the magnetic responses in extended MOFs, providing an informative platform for the further development of interesting magnetic materials, both of academic and industrial interest.

Hexagonal Co6 and zigzag Co4 cluster based magnetic MOFs with a pcu net for selective catalysis

Two magnetic MOFs with a pcu net, constructed by using hexagonal Co₆ rings and zigzag Co₄ clusters, respectively are reported. Furthermore, activated 1 exhibits an excellent catalytic selectivity in the allylic oxidation reaction of cyclohexene to form an α,β-unsaturated ketone.

Competitive coordination aggregation for V-shaped [Co3] and disc-like [Co7] complexes: synthesis, magnetic properties and catechol oxidase activity

The synthetic procedures, magnetic properties and catecholase-like activity of a V-shaped [CoII3L₄] and planar disc-like [CoII7L₆] complexes have been discussed.

Magnetism behaviours dominated by the interplay of magnetic anisotropy and exchange coupling in local CoII7 discs

Structure and magnetism of two CoII7 disc-based layers were reported. An asymmetric CoII7 core in the (4,4) layer exhibited single-molecule magnetic behavior. A highly symmetric C_2h CoII7 disc in the (3,6) sheet showed ferromagnetic exchange.

A cyclic dodecanuclear cobalt cluster based on a derivative of the rhodamine 6G dye with unusual magnetization

A novel cyclic dodecanuclear cluster [Co^II₁₂(L)₆(OH)₆(Ac)₆]·2DMF (1) decorated by a rhodamine 6G derivative (H₂L) presents dominant intracluster antiferromagnetic interactions with S-shaped M vs. H plots.

Triazolate-based 3D frameworks and a 2D layer with centrosymmetric CuII7, CuII5, CuII4 clusters and tunable interlayer/interchain compactness: hydrothermal syntheses, crystal structures and magnetic properties

A 2D layer and three 3D frameworks with different interchain/interlayer compactness and spin ground-states were reported.