Synthesis, structure, magnetic properties and kinetics of formation of a cluster containing a {Cu₃(μ₃-OH)} core supported by a triazole-based ligand

<p>The trinuclear copper complex, [Cu₃(μ₃-OH)(CTMB)₃(NO₃)₂(CH₃CN)₂]·5CH₃CN·H₂O (<b>1</b>) {CTMB = cyclohexotriazole-3-(4-methoxybenzamide)}, has been prepared by mixing Cu(NO₃)₂·2.5H₂O and CHMBH {CHMBH = N,N′-cyclohexane-1,2-diylidene-bis(4-methoxybenzoylhydrazide)} in acetonitrile under ambient conditions. Compound <b>1</b> was characterized by IR and UV–visible spectroscopies as well as elemental analyses. X-ray crystallography shows that the cluster contains a {Cu₃(μ₃-OH)} core supported by three triazole-based Schiff base ligands. Each Cu is bound to the 2-N of one triazole ring and the 1-N of another. However, the coordination sphere of each Cu is different, one is five-coordinate and the other two are six-coordinate and bridged by a NO₃ group. The six-coordinate sites are different, one has a terminal NO₃ and the other a MeCN ligand. Magnetic measurements revealed the presence of isotropic and antisymmetric exchange between the copper(II) centers. The data were analyzed using the Hamiltonian containing isotropic exchange for an isosceles triangle together with antisymmetric exchange: <i>H</i> = –<i>J</i>₁(<i>S</i>₁<i>S</i>₂ + <i>S</i>₂<i>S</i>₃)−<i>J</i>₂<i>S</i>₁<i>S</i>₃ + <i>G</i>[<i>S</i>₁ × <i>S</i>₂ + <i>S</i>₂ × <i>S</i>₃ + <i>S</i>₃ × <i>S</i>₁]. Compound <b>1</b> exhibits strong antiferromagnetic coupling with <i>J</i>₁ = −180 and <i>J</i>₂ = −118 cm⁻¹ and antisymmetric exchange with <i>G</i>_z = 15 cm⁻¹. Stopped flow spectrophotometric studies show that the formation of <b>1</b> occurs in three distinct phases and the kinetics of each phase has been determined.</p

A Spin-Frustrated Trinuclear Copper Complex Based on Triaminoguanidine with an Energetically Well-Separated Degenerate Ground State

We present the synthesis and crystal structure of the trinuclear copper complex [Cu₃(saltag)­(bpy)₃]­ClO₄·3DMF [H₅saltag = tris­(2-hydroxybenzylidene)­triaminoguanidine; bpy = 2,2′-bipyridine]. The complex crystallizes in the trigonal space group <i>R</i>3̅, with all copper ions being crystallographically equivalent. Analysis of the temperature dependence of the magnetic susceptibility shows that the triaminoguanidine ligand mediates very strong antiferromagnetic interactions (<i>J</i>_CuCu = −324 cm^–1). Detailed analysis of the magnetic susceptibility and magnetization data as well as X-band electron spin resonance spectra, all recorded on both powdered samples and single crystals, show indications of neither antisymmetric exchange nor symmetry lowering, thus indicating only a very small splitting of the degenerate <i>S</i> = ¹/₂ ground state. These findings are corroborated by density functional theory calculations, which explain both the strong isotropic and negligible antisymmetric exchange interactions

Anionic Dinuclear Oxidovanadium(IV) Complexes with Azo Functionalized Tridentate Ligands and μ‑Ethoxido Bridge Leading to an Unsymmetric Twisted Arrangement: Synthesis, X‑ray Structure, Magnetic Properties, and Cytotoxicity

The synthesis of ethoxido-bridged dinuclear oxidovanadium­(IV) complexes of the general formula (HNEt₃)­[(VOL^1–3)₂(μ-OEt)] (<b>1</b>–<b>3</b>) with the azo dyes 2-(2′-carboxy-5′-X-phenylazo)-4-methylphenol (H₂L¹, X = H; H₂L², X = NO₂) and 2-(2′-carboxy-5′-Br-phenylazo)-2-naphthol (H₂L³) as ligands is reported. The ligands differ in the substituents at the phenyl ring to probe their influence on the redox behavior, biological activity, and magnetochemistry of the complexes, for which the results are presented and discussed. All synthesized ligands and vanadium­(IV) complexes have been characterized by various physicochemical techniques, namely, elemental analysis, electrospray ionization mass spectrometry, spectroscopic methods (UV/vis and IR), and cyclic voltammetry. X-ray crystallography of <b>1</b> and <b>3</b> revealed the presence of a twisted arrangement of the edged-shared bridging core unit. In agreement with the distorted nature of the twisted core, antiferromagnetic exchange interactions were observed between the vanadium­(IV) centers of the dinuclear complexes with a superexchange mechanism operative. These results have been verified by DFT calculations. The complexes were also screened for their <i>in vitro</i> cytotoxicity against HeLa and HT-29 cancer cell lines. The results indicated that all the synthesized vanadium­(IV) complexes (<b>1</b>–<b>3</b>) were cytotoxic in nature and were specific to a particular cell type. Complex <b>1</b> was found to be the most potent against HeLa cells (IC₅₀ value 1.92 μM)

Light-Induced Spin Crossover in an Fe(II) Low-Spin Complex Enabled by Surface Adsorption

Understanding and controlling the spin-crossover properties of molecular complexes can be of particular interest for potential applications in molecular spintronics. Using near-edge X-ray absorption fine structure spectroscopy, we investigated these properties for a new vacuum-evaporable Fe­(II) complex, namely [Fe­(pypyr­(CF₃)₂)₂(phen)] (pypyr = 2-(2′-pyridyl)­pyrrolide, phen = 1,10-phenanthroline). We find that the spin-transition temperature, well above room temperature for the bulk compound, is drastically lowered for molecules arranged in thin films. Furthermore, while within the experimentally accessible temperature range (2 K < <i>T</i> < 410 K) the bulk material shows indication of neither light-induced excited spin-state trapping nor soft X-ray-induced excited spin-state trapping, these effects are observed for molecules within thin films up to temperatures around 100 K. Thus, by arranging the molecules into thin films, a nominal low-spin complex is effectively transformed into a spin-crossover complex