Proton-Induced Spin State Switching in an FeIII Complex

Reversible proton-induced spin state switching of an Fe^III complex in solution is observed at room temperature. A reversible magnetic response was detected in the complex, [Fe^III(sal₂323)]ClO₄ ( 1 ), using Evans’ method ¹H NMR spectroscopy which indicated cumulative switching from low-spin to high-spin upon addition of one and two equivalents of acid. Infrared spectroscopy suggests a coordination-induced spin state switching (CISSS) effect, whereby protonation displaces the metal-phenoxo donors. The analogous complex, [Fe^III(4-NEt₂-sal₂323)]ClO₄ ( 2 ), with a diethylamino group on the ligand, was used to combine the magnetic change with a colorimetric response. Comparison of the protonation responses of 1 and 2 reveals that the magnetic switching is caused by perturbation of the immediate coordination sphere of the complex. These complexes constitute a new class of analyte sensor which operate by magneto-modulation, and in the case of 2 , also yield a colorimetric response.     

[(bdp)FeBr]: Structural Determination of a Polymorphic Iron Chelate with an Open‐Chain Tetrapyrrolic Ligand

Bromido‐(3,3′,4,4′,8,8′,9,9′‐octaethyl‐2,2′‐bidipyrrinato)iron(III) crystallizes in two different polymorphs, space groups and C2/c, with Z = 2 and 8, respectively, and slightly different densities. The Fe‐N and Fe‐Br bond lengths vary significantly with the polymorph indicating the presence of intermediate spin (S = 3/2) species admixed with different amounts of high spin (S = 5/2) iron(III) compounds in the triclinic resp. monoclinic form.     

Organosulfonate-Modulated Spin-Crossover Behavior in Three Halogen-Functionalized Cobalt(II) Complexes

We present here the syntheses, crystal structures, and spin crossover (SCO) properties of a series of halogen-functionalized cobalt(II) complexes, [Co(Brphtpy)₂](OTf)₂ ⋅ DMF ⋅ 2H₂O ( 1 ), [Co(Brphtpy)₂](HBS)₂ ⋅ H₂O ( 2 ), [Co(Brphtpy)₂](MQ)₂ ⋅ 2MeCN ⋅ 3H₂O ( 3 ) ( Brphtpy =4′–(4-Bromophenyl)–2,2′:6′,2′′-terpyridine; OTf⁻=trifluoromethanesulfonate; HBS⁻=hydroxybenzenesulfonate dihydrate; MQ⁻=methyl orange). Variable-temperature single-crystal X-ray analyses revealed mononuclear compounds of 1 – 3 consisted of [Co(Brphtpy)₂]²⁺ SCO active units and organosulfonate anions and no structural phase transformation happened in measured high-low temperature. The packing structures of these complexes were tuned by varying organosulfonates. However, no notable supramolecular interactions can be found, in turn leading to gradual, incomplete, and non-hysteretic SCO behaviors. Interestingly, the SCO behaviors of these three complexes were significantly modified after the removal of lattice solvents. Combined structural and magnetic investigations revealed the non-cooperative supramolecular packing structures, guest internal pressure, and the small structural distortions of the SCO units should be responsible for the worse SCO properties of 1 – 3 . The foregoing results show that to achieve high-performance Co²⁺ SCO, both the weak interactions, internal pressure, and structural distortion should be considered during the design and construction of SCO complexes.     

Strong Antiferromagnetic Exchange Interactions in Cobalt(II) Complexes with 2-Pyridyl Substituted Nitronyl Nitroxide Ligand

Three new complexes, [Co(hfac)₂(NIToPy)] (1), [CoCl₂(NIToPy)₂] (2), and [Co(NIToPy)₃](ClO₄)₂ (3), with NIToPy = 2-(2-Pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-oxy-3-oxide, and hfac = hexafluoroacetylacetonate, have been synthesized. The compound 3 crystallized in the monoclinic space group P2₁, with two molecules in a unit cell of dimensions a = 10.565(4) Å, b = 14.714(9) Å, c = 14.596(7) Å, and β = 107.10(4)°. The temperature-dependent magnetic susceptibility measurements (4.2 K-300 K) for the complexes demonstrated strong antiferromagnetic exchange interaction between cobalt(II) ion and NIToPy radical spins with J = ?140.1 cm^?1 for 1, J = ?94.2 cm^?1 for 2, and J = ?161.8 cm^?1 for 3, respectively. The magneto-structural correlation in these complexes has been discussed.     

Structure and Magnetic Property of a Cobalt(II) Complex Synthesized Through in situ Hydrothermal Reaction

A new cobalt(II) coordination polymer [Co(L₁)(bpy)(H₂O)] · H₂O ( 1 , H₂L₁ = 2‐sulfobenzoic acid and bpy = 4,4’‐bipyridine) was synthesized by in situ hydrothermal reaction. The single‐crystal X‐ray diffraction analysis shows that compound 1 belongs to monoclinic system with space group C2/c. The structure of compound 1 exhibits a 2D framework linked by ligand L₁ and 4,4’‐bpy, of which L1 was produced by in situ hydrothermal reaction of 2‐(pyridinyl‐4‐methylsulfanyl) benzoic acid. The 2D structure was future connected into a 3D framework through hydrogen bonds. The magnetic analysis indicates the presence of weakly antiferromagnetic interaction between adjacent Co²⁺.     

[CoII2L(NCS)2(SCN)2]: The First Cobalt Complex to Exhibit Both Exchange Coupling and Spin Crossover Effects

A spin crossover transition (350 K, μ_eff=3.15 μ_B per Co atom; 4.5 K, μ_eff=0.70 μ_B per Co atom) and weak antiferromagnetic exchange (2 J=−11.7 cm⁻¹) between the octahedral, doubly pyridazine bridged cobalt(II ) ions are features of the structurally characterized complex [Co^II₂L(NCS)₂(SCN)₂] (the ligand L is shown).     

Anisotropic Change in the Magnetic Susceptibility of a Dynamic Single Crystal of a Cobalt(II) Complex

Atypically anisotropic and large changes in magnetic susceptibility, along with a change in crystalline shape, were observed in a Co^II complex at near room temperature. This was achieved by combining oxalate molecules, acting as rotor, and a Co^II ion with unquenched orbital angular momentum. A thermally controlled 90° rotation of the oxalate counter anion triggered a symmetry‐breaking ferroelastic phase transition, accompanied by contraction–expansion behavior (ca. 4.5 %) along the long axis of a rod‐like single crystal. The molecular rotation induced a minute variation in the coordination geometry around the Co^II ion, resulting in an abrupt decrease and a remarkable increase in magnetic susceptibility along the direction perpendicular and parallel to the long axis of the crystal, respectively. Theoretical calculations suggested that such an unusual anisotropic change in magnetic susceptibility was due to a substantial reorientation of magnetic anisotropy induced by slight disruption in the ideal D ₃ coordination environment of the complex cation.     

Syntheses,Structures and Characterization of Cobalt(II) and Cobalt(III) Complexes with N-Benzylated Polyamines and a Terminal Azido Ligand

Mononuclear cobalt(II) and cobalt(III) complexes, [Co(trenb)(N₃)]Cl (1) and [Co(dienb)(N₃)₂(OAc)] (2) (trenb = tris[2-(benzylamino)ethyl]amine, dienb = 1,9-diphenyl-2,5,8-triazanonane) were synthesized and characterized by elemental analyses, IR and electronic spectra. Their crystal structures were also determined by X-ray diffraction analyses. In Complex 1, cobalt(II) is five-coordinate trigonal bipyramidal with one azido nitrogen atom and four nitrogen donors of the tripodal ligand; the chloride interacts weakly with one of the secondary amino groups of trenb via a hydrogen bond. In Complex 2, cobalt(III) is in a distorted octahedral coordination environment, consisting of three nitrogen atoms of the amine ligand, two azide nitrogen atoms and an oxygen atom of the acetate ion; a six-membered ring involving the hydrogen bond may stabilize the complex, which maintains its solid geometry in DMF as indicated by the electronic spectrum.     

Cobalt(II) Complex with a Tridentate N Donor Ligand: Synthesis,Crystal Structure,Antioxidation, and DNA Binding Studies

A heptacoordinated mononuclear cobalt(II) complex of tridentate bis(N‐ethylbenzimidazol‐2‐ylmethyl)aniline (Etbba) formulated as [Co(Etbba)(pic)₂] · (MeCN) (pic = picrate), was synthesized and characterized by elemental analysis, electric conductivity measurements, as well as IR and UV/Vis spectroscopy. The crystal structure of the cobalt(II) complex was determined by single‐crystal X‐ray diffraction. The study shows the metal atom in a distorted monocapped octahedral arrangement that comprises two picrate molecules and one Etbba ligand molecule. The DNA‐binding properties of the cobalt(II) complex were investigated by electronic absorption and fluorescence spectroscopy, as well as viscosity measurements. The experimental results suggest that the cobalt(II) complex binds to DNA in an intercalating mode. In addition, the complex shows strong scavenging effects for hydroxyl radicals.     

A Breast Cancer Stem Active Cobalt(III)-Cyclam Complex Containing Flufenamic Acid with Immunogenic Potential

The cytotoxic and immunogenic-activating properties of a cobalt(III)-cyclam complex bearing the non-steroidal anti-inflammatory drug, flufenamic acid is reported within the context of anti-cancer stem cell (CSC) drug discovery. The cobalt(III)-cyclam complex 1 displays sub-micromolar potency towards breast CSCs grown in monolayers, 24-fold and 31-fold greater than salinomycin (an established anti-breast CSC agent) and cisplatin (an anticancer metallopharmaceutical), respectively. Strikingly, the cobalt(III)-cyclam complex 1 is 69-fold and 50-fold more potent than salinomycin and cisplatin towards three-dimensionally cultured breast CSC mammospheres. Mechanistic studies reveal that 1 induces DNA damage, inhibits cyclooxygenase-2 expression, and prompts caspase-dependent apoptosis. Breast CSCs treated with 1 exhibit damage-associated molecular patterns characteristic of immunogenic cell death and are phagocytosed by macrophages. As far as we are aware, 1 is the first cobalt complex of any oxidation state or geometry to display both cytotoxic and immunogenic-activating effects on breast CSCs.     

Synthesis,Structure, and Magnetic Properties of a Dinuclear Antiferromagnetically Coupled Cobalt Complex

A new dinuclear cobalt(II) compound,[(TPA*)Co^II(DHBQ^2–)Co^II(TPA*)]²⁺ ( 1 ²⁺) {TPA* =tris[(3, 5‐dimethyl‐pyrazol‐l‐yl)methyl] amine, DHBQ = deprotonated 2, 5‐dihydroxy‐1, 4‐benzoquinone}, was prepared and structurally and magnetically characterized. X‐ray crystallography revealed the centrosymmetric dinuclear divalent cobalt ions bridged by DHBQ^2– unit. The cobalt ions in the title compound have a distorted octahedral arrangement by coordination with four nitrogens of a TPA* and two oxygens of a bridging DHBQ unit. Due to the interdimer offset face‐to‐face π–π stacking in the crystallographic ac plane, the complex shows extended 2D supramolecular structure. Magnetic experiments showed the cobalt‐based dinuclear compound exhibits antiferromagnetic interactions with g = 2.35 and J/k_B = –2.76 K, respectively.     

Synthesis of a New Cobalt (II) Complex and its Interaction with DNA

The interaction of metal complexes with DNA has been widely studied by differentmethods such as spectrophotometry, light scattering technique, fluorometry1-3. Manycomplexes such as Co(phen)2 ,Co(en)2 ,Fe(EDTA)2- etc.4,5 have been synthesized and 3+ 3+their effect on DNA has been studied in order to further explain the mechanism of genemutation, anti-cancer or cancer-induced reason and DNA targeted drugs. In this paper,a new cobalt complex was synth…     

The gem-Diol Form of (py)2CO as a Ligand in Cobalt(II) Carboxylate Clusters: A Cubane Complex and a Novel Nonanuclear Species with a Vertex-Sharing Double Square Pyramidal Structure

A vertex-sharing double square pyramid of cobalt(II ) ions (see picture) is present in the nonanuclear complex 1 , obtained by treating cobalt acetate with 0.5 equivalents of (py₂)CO. The corresponding 1:1 reaction gave 2 , which has a central core with a cubane structure. py=pyridine.     

Mononuclear High-spin Octahedral Cobalt(II) Complex with Positive Axial Magnetic Anisotropy: Synthesis,Crystal Structure,and DFT Studies

This article outlines the magnetic features of a new six–coordinate high-spin cobalt(II) complex cis-[Co^II(tmphen)₂(NCS)₂] ( 1 ) achieved via the reactions of cobalt(II) thiocyanate with 3,4,7,8-tetramethyl-1,10-phenanthroline. The complex 1 was thoroughly characterized by different analytical and spectroscopic techniques and further confirmed by single X-ray crystal diffraction pattern. Complex 1 is a neutral molecule and adopt highly distorted six-coordinate CoN₆ octahedral coordination sphere surrounded by two thiocyanate N atoms in cis locations and the equatorial plane is occupied by two imine N atoms from the two tmphen ligand while the remaining two imine N atoms reside in the axial positions. Magnetic susceptibility data of complex 1 revealed that the χ_ΜT values decrease significantly to a value of 1.49 cm³ · K · mol^–1 at 2.0 K on decreasing temperatures below 100 K, mainly ascribed to the significant spin–orbit coupling (SOC) of six-coordinate Co^II ions. Furthermore, a field-dependence measurement was performed at 2 K, which shows a positive curvature up to 27 kOe, while it becomes linear up to 2.01 Nμ_B, which authenticated the fact that only the lowest Kramers doublet of ground state is appreciably populated.