New salicylaldoximato-borate ligands resulting from anion hydrolysis and their respective copper and iron complexes

Computational studies of the magneto-structural correlations in a manganese dimer with Jahn-Teller distortions

Inspired by the crystal structure of a Mn^III dinuclear complex we obtained featuring both Jahn-Teller (JT) elongation and compression distortions, we have modelled a series of complex cations based on the disordered crystal formulation; [Mn₂(L1)₂(μ₂-OH)₂)⁴⁺ (1), [Mn₂(L1)(L2)(μ₂-OH)₂)⁴⁺ (2), [Mn₂(L2)(L1)(μ₂-OH)₂)⁴⁺ (3), and [Mn₂(L2)₂(μ₂-OH)₂)⁴⁺ (4) (where L1 = (1E,1'E)-5-tert-butyl-3-(((4-(((5-tert-butyl-2-hydroxy-3-((E)-(hydroxyimino)methyl)benzyl)(methyl)amino)methyl)benzyl)(methyl)amino)methyl)-2-hydroxybenzaldehyde and L2 = 3,3'-(1,4-phenylenebis(methylene))bis(methylazanediyl)bis(methylene)bis(5-tert-butyl-2-hydroxybenzaldehyde)) with different geometries to investigate the effects of the distortions on the magnetic coupling parameter. All computationally modelled dimers had a ferromagnetic interaction between the Mn^III centres, with greater magnetic coupling calculated for complexes with both JT elongation and compression present. The ferromagnetic contribution to the J coupling was ascribed to the orthogonality of the singly occupied magnetic orbitals along with the cross-interaction between the unfilled Mn1(d_x²-y²) and singly occupied Mn2(d_x²-y²) orbitals. Constrained calculations showed that reducing the extent of the compression at Mn2 results in a concomitant increase in the dihedral angle between the JT axes, thereby reducing the relative magnitude of the magnetic coupling between Mn^III centres.

Synthesis and Characterization of Symmetrically versus Unsymmetrically Proton-Bridged Hexa-Iron Clusters

Syntheses and magnetic and structural characterization of hexa-iron complexes of derivatized salicylaldoximes are discussed. Complexation of Fe(BF₄)₂·6H₂O with each ligand (H₂ L1 and H₄ L2) in a methanolic-pyridine solution resulted in hexa-iron compounds (C1 and C2, respectively), which each contain two near-parallel metal triangles of [Fe₃-μ₃-O], linked by six fluoride bridges and stabilized by a hydrogen-bonded proton between the μ₃-O groups. Within each metal triangle of C2, Fe(III) ions are connected via the amine "straps" of (H₄ L2-2H). Variable-temperature magnetic susceptibility and Mössbauer data of C1 and C2 indicate the presence of dominant antiferromagnetic interactions between the high-spin (S = 5/2) Fe(III) centers. For C1, two quadrupole doublets are observed at room temperature and 5 K, consistent with structural data from which discrete but disordered [Fe₃-μ₃-O] and [Fe₃-μ₃-OH] species were inferred. For C2, a single sharp quadrupole doublet with splitting intermediate between those determined for C1 was observed, consistent with the symmetric [Fe₃-μ₃-O···H···μ₃-O-Fe₃] species inferred crystallographically from the very short μ₃-O···μ₃-O separation. The differences in the physical properties of the complexes, as seen in the Mössbauer, X-ray, and magnetic data, are attributed to the conformational flexibility imparted by the nature of the linkages between the closely related ligands.