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Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
Published on: March 20, 2017
Pentagonal Bipyramidal First-Row Transition Metal Complexes with Macrocyclic Ligand Containing Two Pyridine-N-Oxide
Bohuslav Drahoš1, Ivan Šalitroš2, Radovan Herchel1
1Department of Inorganic Chemistry, Faculty of Science, Palacký University Olomouc, 17. Listopadu 12, Olomouc CZ-77146, Czech Republic.
Abstract:
A heptadentate 15-membered pyridine-based macrocyclic ligand containing two pyridine-N-oxide pendant arms (L4 = 3,12-bis((pyridine-1-oxide-2-yl)methyl)-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]octadeca-1(18),14,16-triene) was synthesized together with its first-row transition metal complexes with the general formula [M(L4)](ClO4)2·1DMF (MII = Mn (1), Fe (2), Co (3), and Ni (4); DMF = N,N'-dimethylformamide), which were thoroughly investigated. According to the obtained X-ray crystal structures, all complexes possess axially compressed pentagonal bipyramidal geometry with a coordination number of 7 for 1-3 or 5 + 2 for Ni(II) complex 4 with a large Jahn-Teller distortion. Fe(II), Co(II), and Ni(II) complexes 2, 3, and 4 show pronounced magnetic anisotropy (D = 4.47, 30.10, -7.58 cm-1, respectively). The magnetic properties of the studied complexes were supported by theoretical calculations, which corresponded very well to the experimental data for magnetic anisotropy. Furthermore, complex 3 showed a field-induced single-molecule magnet behavior described best by the combination of direct (DHm = 145 K-1s-1) and Raman (C = 0.58 K-ns-1 for n = 5.76) relaxation processes. Magneto-structural correlation for Fe(II)/Co(II)/Ni(II) complexes with L4 and previously studied structurally similar ligands revealed a significant impact of the coordination ability of the functional group in pendant arms on the final magnetic anisotropy (π-acceptors appear to be more suitable).
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