Dinuclear Iron(III) and Cobalt(III) Complexes Featuring a Biradical Bridge: Their Molecular Structures and Magnetic, Spectroscopic, and Redox Properties

Crossover from Antiferromagnetic to Ferromagnetic Exchange Coupling in a New Family of Bis-(μ-phenoxido)dicopper(II) Complexes: A Comprehensive Magneto-Structural Correlation by Experimental and Theoretical Study

Five neutral bis(μ-phenoxido)dicopper(II) complexes, [Cu₂(L^Me,Me,Me)₂] (1), [Cu₂(L^Me,Me,Et)₂]·CH₂Cl₂ (2), [Cu₂(L ^{i-Pr,i-Pr,i-Pr})₂]·2H₂O (3), [Cu₂(L ^t-Bu,Me,i-Pr)₂] (4), and [Cu₂(L ^{t-Bu,t-Bu,i-Pr})₂]·H₂O (5) have been synthesized and characterized by single-crystal X-ray diffraction analyses, magnetic studies, and density functional theory (DFT) calculations, in which the ligands [H₂L^Me,Me,Me = N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-N',N'-dimethylethylene-1,2-diamine, H₂L^Me,Me,Et = N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-N',N'-dimethylethylene-1,2-diamine, H₂L ^{i-Pr,i-Pr,i-Pr} = N,N-bis(2-hydroxy-3,5-diisopropylbenzyl)-N',N'-diisopropylethylene-1,2-diamine, H₂L ^t-Bu,Me,i-Pr = N,N-bis(2-hydroxy-3-tert-butyl-5-methylbenzyl)-N',N'-diisopropylethylene-1,2-diamine, and H₂L ^{t-Bu,t-Bu,i-Pr} = N,N-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-N',N'-diisopropylethylene-1,2-diamine] contain the same [O,N,N,O]-donor atoms combination but differ in substituents at phenol rings and at an amino nitrogen atom. The effect of these remote substituents on the nature of exchange coupling interactions (ferromagnetic vs antiferromagnetic) between the copper(II) ions has been investigated. The average Cu-O-Cu angle, Cu-O-Cu-O torsion angle, and Cu···Cu separation in 1-5 are varied systematically by these remote ligand substituents in the range 98.6-83.3°, 26.0-46.5°, and 2.982-2.633 Å, respectively. As a result, the intramolecular spin-spin coupling in these complexes are changing gradually from a strong antiferromagnetic (J = -395 cm^-1, where Ĥ = -JŜ ₁ Ŝ ₂) to a moderate ferromagnetic (J = +53.2 cm^-1) regime. The crossover angle at which the magnetic interaction changes from antiferromagnetic to ferromagnetic (J = 0) is determined to be ca. 87° for this series of dicopper(II) complexes. DFT calculations support the experimentally determined crossover angle and disclose various magneto-structural correlations in the series 1-5.

Syntheses, structures, and magnetic properties of mixed-ligand complexes based on 3,6-bis(benzimidazol-1-yl)pyridazine

Six new metal-organic coordination polymers (CPs) [Ni(L)(2,5-TDC)(H2O)] n (1), [Ni(L)(1,3-BDC)(H2O)] n (2), [Ni(L)(1,4-BDC)(H2O)] n (3), [Mn(L)(2,5-TDC)(H2O)] n (4), [Mn(L)(2,6-PYDC)(H2O)] n (5) and [Mn(L)(1,4-NDC)] n (6) were achieved by reactions of the corresponding metal salt with mixed organic ligands (L = 3,6-bis(benzimidazol-1-yl)pyridazine, 2,5-H2TDC = thiophene-2,5-dicarboxylic acid, 1,3-H2BDC = isophthalic acid, 1,4-H2BDC = terephthalic acid, 2,6-H2PYDC = pyridine-2,6-dicarboxylic acid, 1,4-H2NDC = naphthalene-1,4-dicarboxylic acid) under solvothermal condition. CPs 1-6 were characterized by single-crystal X-ray diffraction, IR, TG, XRD and elemental analyses. Their structures range from the intricate 3D CPs 1, 3, 4 and 6 to the 2D coordination polymer 2 and the infinite 1D chain 5. The CPs 1-4 and 6 underlying networks were classified from the topological viewpoint, disclosing the distinct sql (in 1), pcu (in 3 and 6), new topology (in 2), and dia (in 4) topological nets. Moreover, analysis of thermal stability shows that they had good thermal stability. Finally, magnetic properties of CPs 1-6 have been studied, the results showed that complex 2 had ferromagnetic coupling and complexes 1, 3-6 were antiferromagnetic.

Rare azido and hydroxido bridged tetranuclear Co(ii) complexes of a polynucleating Mannich base ligand with a defect dicubane core: structures, magnetism and phenoxazinone synthase like activity

Triply azido/hydroxido bridged defect dicubane tetranuclear Co(ii) complexes of a Mannich base ligand show ferromagnetic/antiferromagnetic coupling and phenoxazinone synthase like activity.