Abstract
The homoleptic mononuclear compound [Co(bpp-COOMe)2 ](ClO4 )2 (1) (bpp-COOMe=methyl 2,6-di(pyrazol-1-yl)pyridine-4-carboxylate) crystallizes in the monoclinic C2/c space group, and the cobalt(II) ion possesses a pseudo-octahedral environment given by the two mer-coordinated tridentate ligands. Direct-current magnetic data, single-crystal torque magnetometry, and EPR measurements disclosed the easy-axis nature of this cobalt(II) complex, which shows single-molecule magnet behavior when a static field is applied in alternating-current susceptibility measurements. Diamagnetic dilution in the zinc(II) analogue [Zn(bpp-COOMe)2 ](ClO4 )2 (2) afforded the derivative [Zn0.95 Co0.05 (bpp-COOMe)2 ](ClO4 )2 (3), which exhibits slow relaxation of magnetization even in zero field thanks to the reduction of dipolar interactions. Theoretical calculations confirmed the overall electronic structure and the magnetic scenario of the compound as drawn by experimental data, thus confirming the spin-phonon Raman relaxation mechanism, and a direct quantum tunneling in the ground state as the most plausible relaxation pathway in zero field.
Highlights
Single-Molecule Magnets (SMMs) can in principle be used for encoding binary information and for data processing, exploiting their magnetic bistability and inherent quantum behaviour.[1]
The ester group is coplanar with the pyridyl ring C and is involved in one of the two shortest intermolecular interactions with one pyrazolyl C–H group (at 161/295 K, C1(H1)∙∙∙O17 = 3.252/3.291 Å, C1–H1∙∙∙O17 = 147.6/148.9°, which leads to a Co∙∙∙Co distance of 9.642 (9.664) Å
We have here presented a detailed magnetic and spectroscopic characterization, both on powder and single crystals, of a pseudo-octahedral cobalt(II) complex, which we used as a test bench for different theoretical approaches, ranging from ab initio calculations to Ligand Field model and spin Hamiltonian
Summary
Single-Molecule Magnets (SMMs) can in principle be used for encoding binary information and for data processing, exploiting their magnetic bistability and inherent quantum behaviour.[1]. Few examples of zero-field SMMs based on mononuclear complexes of iron(I)[12] iron(III),[13] and cobalt(II) have been reported,[14,15,16,17,18,19,20,21,22,23,24,25] which all feature half-integer spin states (3/2 or 5/2). Individual cobalt(II) ions were found to exhibit zero-field SMM behaviour when embedded in tetrahedral,[14,15,16,17,20,22,24] trigonal prismatic[18,19,23] or linear[21] coordination environments, or in a solid state lattice.[25] In all these cases, the metal complexes possess a negative zero field splitting (zfs) parameter D, suggesting to look for other coordination environments suitable to enforce an easy axis magnetic anisotropy on the cobalt(II) ion
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