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Field-Assisted Slow Magnetic Relaxation in a Six-Coordinate Co(II)–Co(III) Complex with Large Negative Anisotropy
journal contribution
posted on 2017-05-26, 20:09 authored by Elena A. Buvaylo, Vladimir N. Kokozay, Olga Yu. Vassilyeva, Brian W. Skelton, Andrew Ozarowski, Ján Titiš, Beáta Vranovičová, Roman BočaThe
reaction of Co(CH3COO)2·4H2O
with the Schiff base ligand LH4 derived from o-vanillin and tris(hydroxymethyl)aminomethane produces the dinuclear
mixed-valence complex [CoIICoIII(LH2)2(CH3COO)(H2O)](H2O)3 (1), which has been investigated using IR spectroscopy,
X-ray crystallography, temperature-dependent magnetic susceptibility,
magnetization, HFEPR spectroscopy, and ac susceptibility measurements
at various frequencies, temperatures, and external magnetic fields.
The structure of 1 consists of neutral molecules in which
two cobalt ions with distorted octahedral geometries, CoIIO6 and CoIIIN2O4, are
bridged by two deprotonated −CH2O– groups of the two LH22– ligands. 1 completes a series with Cl, Br, NO3, and NCS
anions published before by different authors. Low-temperature HFEPR
measurements reveal that the ground electronic state of the Co(II)
center in 1 is a highly anisotropic Kramers doublet;
the effective g values of 7.18, 2.97, and 1.96 are
frequency-independent over the frequency ranges 200–630, 200–406,
and 200–300 GHz for the highest, intermediate, and lowest geff values, respectively. The two lower values
were not seen at higher frequencies because the magnetic field was
not high enough. Temperature-dependent magnetic susceptibility and
field-dependent magnetization data confirm high magnetic anisotropy
of the easy axis type. Complex 1 behaves as a single-ion
magnet under a small applied external field and demonstrates two relaxation
modes that strongly depend on the applied static dc field. The observation
of multiple relaxation pathways clearly distinguishes 1 from the Cl and Br analogues.
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Co II O 6axis typeg valuesSchiff base ligand LH 4Low-temperature HFEPR measurementsrelaxation modesdinuclear mixed-valenceg eff valuesanisotropic Kramers doubletac susceptibility measurementsBr analoguessingle-ion magnetdc fieldComplex 1IR spectroscopyHFEPR spectroscopyNCS anionsCOOCHLH 2Co II Co IIIX-ray crystallographyoctahedral geometriesfrequencyfield-dependent magnetization dataCo III N 2 O 4relaxation pathwayscobalt ionsMagnetic Relaxation
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