Structure and magnetism of mono-, di-, and trinuclear benzoato cobalt(II) complexes

Metamagnetism in a coordination polymer built of trimeric cobalt units and melamine

A coordination polymer of linear trimeric cobalt units and melamine has been synthesized. The magnetic isotherms of violet coloured crystals as long as 400 μm show a field-induced transition in an external field of about 2 T at temperatures approximately below 2 K. It is addressed that by assuming the coexistent positive and negative exchange between the nearest-neighbour spins in the linear trimer, this metamagnetism can be interpreted as a transition from antiferromagnetic to ferromagnetic exchange within each trimeric spin cluster. Although weak inter-cluster or inter-chain exchange to yield a long-range magnetic order is another possible and often attributed origin of metamagnetism in low-dimensional spin systems, this study demonstrates the significance of the exchange flip within each cluster in clustered spin networks.

Pillared cobalt metal-organic frameworks act as chromatic polarizers

The ease with which molecular building blocks can be ordered in metal-organic frameworks is an invaluable asset for many potential applications. In this work, we exploit this inherent order to produce chromatic polarizers based on visible-light linear dichroism via cobalt paddlewheel chromophores.

Synthesis, structural determination, in vitro and in silico biological evaluation of divalent or trivalent cobalt complexes with indomethacin

The interaction of cobalt chloride with the non-steroidal anti-inflammatory drug indomethacin (Hindo) led to the formation of the polymeric complex [Co(indo-O)2(H2O)2(μ-Cl)]n·n(MeOH·H2O) bearing one chlorido bridge between the cobalt atoms. The presence of the nitrogen-donor co-ligands 2,2'-bipyridine (bipy), 2,2'-bipyridylamine (bipyam), 1,10-phenanthroline (phen) or 1H-imidazole (Himi) resulted in the isolation of complexes [Co2(μ-indo-O,O')2(indo-O)2(bipy)2(μ-H2O)]·3.3MeOH, [Co(indo-O,O')2(bipyam)]·0.9MeOH·0.2H2O, [Co(indo-O,O')2(phen)] (4) and [Co(indo-O)2(Himi)2] (5), respectively, where the indomethacin ligands were coordinated in diverse manners. The study of the affinity of the complexes for calf-thymus DNA revealed their intercalation between the DNA-bases. The binding of the complexes to albumins was also examined and the corresponding binding constants and binding subdomain were determined. The free radical scavenging activity of the compounds was evaluated towards 1,1-diphenyl-picrylhydrazyl and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid). Molecular modeling calculations may usually provide a molecular basis for the understanding of both the impairment of DNA by its binding with the studied complexes and the ability of these compounds to transportation through serum albumin proteins. This study can provide information for the elucidation of the mechanism of action of the compounds in a molecular level.

Exchange coupled Co(ii) based layered and porous metal-organic frameworks: structural diversity, gas adsorption, and magnetic properties

Four new Co(ii) based metal-organic frameworks (MOFs) ({[Co3(L)(TDCA)3(DMF)2]n·2nCH3CN}) (1), ({[Co3(L)2(BDCA)3]n·2nCH3CN}) (2), {[Co2(L)2(CA)2]n·4nCH3CN} (3) and {[Co2(L)(OBBA)2]n·3nCH3CN} (4) are synthesized, where L is [4'-(4-methoxyphenyl)-4,2':6',4''-terpyridine], a V-shaped flexible neutral spacer, and the four dicarboxylates are TDCA = thiophene 2,5-dicarboxylic acid, BDCA = benzene 1,4-dicarboxylic acid, CA = (1R,3S)-(+)-camphoric acid and OBBA = 4,4'-oxybisbenzoic acid. Structural analysis reveals that 1 and 2 are two dimensional (2D) layered structures having interesting sql and hxl topologies respectively with trinuclear SBUs (secondary building units). Compound 3 has a 3D structure, whereas 4 has a 2-fold interpenetrated 3D packing structure with a paddlewheel dinuclear SBU and both have pcu topology. Magnetic investigation revealed that 1, 3 and 4 show dominant antiferromagnetic behavior, while 2 shows ferromagnetic interaction at very low temperature. Interestingly 4 shows a sharp decrease in the χMT value from room temperature and this may be because of the direct Co(ii)Co(ii) interaction. Gas sorption studies reveal that 1, 2 and 3 show surface areas of 11.8 m2 g-1, 8.3 m2 g-1 and 28.5 m2 g-1 respectively and better adsorption behavior for CO2 over CH4, whereas 4 is nonporous in nature due to its 2-fold interpenetrated structure.

Paramagnetic One-Dimensional Chain Complex Consisting of Three Kinds of Metallic Species Showing Magnetic Interaction through Metal-Metal Bonds

A heterometallic and paramagnetic one-dimensional (1-D) chain (3) aligned as -Rh(+2)-Rh(+2)-Pt(+2)-Co(+2)-Pt(+2)- with direct metal-metal bonds was obtained by HOMO-LUMO interactions at the σ* (d_z²) orbital between two kinds of complexes. The 1-D chains in 3 have relatively straight backbones because the raw material complexes, [Rh₂(O₂CCH₃)₄] and [Pt₂Co(piam)₄(NH₃)₄], are connected and stacked in a face-to-face fashion, where Co---Co are separated by about 13.3 Å with four different metals. Physical measurements revealed that 3 has a band gap between the σ-type conduction and valence bands, where d-orbitals of the Co ion with three unpaired electrons are laid among them. The magnetic behavior of 3 was investigated and found to be consistent with a complex interaction involving both zero-field splitting and Pauli paramagnetism attributed to band formation superimposed on relatively strong exchange coupling (zJ = -22.2 cm^-1) between two high-spin Co(+2) ions separated by the diamagnetic Pt-Rh-Rh-Pt.

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.

Structural and magnetic properties of Co(II) complexes with tridentate ONO pincer-type ligands

Pincer type ligand 2,6-pyridinedimethanol was used as a useful tool in the preparation of the Co(II) pseudoctahedral complex together with 3,5-dinitrobenzoate counteranion. New complex of the composition [Co(pydm)2](3,5-dnbz)2(pydm = 2,6-pyridinedimethanol, and 3,5-dnbz = 3,5-dinitrobenzoate anion) has been prepared and characterized. Its XRD structure revealed pseudooctahedral {CoN2O4} chromophore around the cobalt atom with Co-N distances significantly shorter (Co-Nav = 2.038 Ǻ) in comparison to the Co-O ones (Co-Oav = 2.142 Ǻ), which was probably the reason of its relatively high zero-field splitting parameter (D/hc = 43.6 cm-1). Positive value of the D parameter causes slow relaxation process typical for Co(II) SMM behavior. The 3,5-dinitrobenzoate counteranions are strongly bonded to the [Co(pydm)2] cation via rather strong hydrogen bonds (O∙∙∙Oav = 2.568 Ǻ) forming “quasi molecular” units. Solid state structure allowed different π-π stacking interactions of neighboring “molecular” unit aromatic rings probally leading to observation of the additional relaxation mode.

Synthesis, crystal structure and magnetic properties of diaquabis(2,6-diamino-7H-purin-1-ium-κN9)bis(4,4'-oxydibenzoato-κO)cobalt(II) dihydrate

The title mononuclear Co^II complex, [Co(C₅H₇N₆)₂(C₁₄H₈O₅)₂(H₂O)₂]·2H₂O, has been synthesized and its crystal structure determined by X-ray diffraction. The complex crystallizes in the triclinic space group P-1, with one formula unit per cell (Z = 1 and Z' = 1/2). It consists of a mononuclear unit with the Co^II ion on an inversion centre coordinated by two 2,6-diamino-7H-purin-1-ium cations, two 4,4'-oxydibenzoate anions (in a nonbridging κO-monodentate coordination mode, which is less common for the anion in its Co^II complexes) and two water molecules, defining an octahedral environment around the metal atom. There is a rich assortment of nonbonding interactions, among which a strong N⁺-H...O^- bridge, with a short N...O distance of 2.5272 (18) Å, stands out, with the H atom ostensibly displaced away from its expected position at the donor side, towards the acceptor. The complex molecules assemble into a three-dimensional hydrogen-bonded network. A variable-temperature magnetic study between 2 and 300 K reveals an orbital contribution to the magnetic moment and a weak antiferromagnetic interaction between Co^II centres as the temperature decreases. The model leads to the following values: A (crystal field strength) = 1.81, λ (spin-orbit coupling) = -59.9 cm^-1, g (Landé factor) = 2.58 and zJ (exchange coupling) = -0.5 cm^-1.