Slow Magnetic Relaxation in a Co(III)–Co(II)–Co(III) Mixed-Valence Complex with Negative Anisotropy

Abstract

An air-stable trinuclear mixed-valence complex [Co II Co III 2 L 2 (py) 4 ]• 2H 2 O (1) bearing a magnetic core [Co II N 4 ] has been synthesized using 1,3-bis(5methylpyrazole-3-formylamine) propane (H 4 L) as a ligand, which was investigated by single-crystal X-ray diffraction, magnetic measurements, and theoretical study. Due to the tetrahedral geometry of the central Co(II) ion, this complex possesses a negative and large zero-field splitting D, exhibiting field-assisted slow relaxation of magnetization with an effective energy barrier of 36.1 cm −1 . Ab initio CASSCF calculations confirm the easy-axis magnetic anisotropy of complex 1, agreeing with the experimental results. The foregoing result constitutes the first example of a trinuclear Co(III)−Co(II)−Co(III) single-molecule magnet containing a tetrahedral Co(II) center.

Cobalt(ii) coordination polymers with single-ion magnet property

“…16 Subsequently, there has been a significant shift towards designing and constructing mononuclear SMMs, termed as single-ion magnets (SIMs), as they are liable to design and synthesize compared to their polynuclear counterparts, while also exhibiting larger magnetic anisotropy. 17–20 Over the past decade, a variety of 3d SIMs, including Cr 2+ , Fe 1+/2+/3+ , Co 1+/2+ , Ni 1+/2+ , Mn 3+ , Cu 2+ , and Re 3+/4+ ions, have been reported, 21–50 with Co( ii ) SIMs being particularly common and prominent in this group due to high air stability and significant magnetic anisotropy resulting from both orbital and spin contributions to the magnetic moment. 51 To date, numerous two- to eight-coordinated Co( ii ) SIMs with diverse structures, including linear, tetrahedral, square antiprism, pyramidal, square pyramidal, trigonal prismatic, octahedral, pentagonal bipyramidal geometries, have been successfully synthesized and characterized.…”