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Exchange coupling and single molecule magnetism in redox-active tetraoxolene-bridged dilanthanide complexes.

ABSTRACT: Tetraoxolene radical-bridged lanthanide SMM systems were prepared for the first time by reduction of the respective neutral compounds. Magnetic measurements reveal the profound influence of the radical center on magnetic behavior. Strong magnetic couplings are revealed in the radical species, which switch on SMM behavior under zero applied field for DyIII and TbIII compounds. HFEPR spectra unravel the contributions of the magnetic coupling and the magnetic anisotropy. For GdIII this results in much more accurate magnetic coupling parameters with respect to bulk magnetic measurements.

SUBMITTER: Zhang P

PROVIDER: S-EPMC5885778 | biostudies-literature | 2018 Feb

REPOSITORIES: biostudies-literature

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Exchange coupling and single molecule magnetism in redox-active tetraoxolene-bridged dilanthanide complexes.

Zhang Peng P Perfetti Mauro M Kern Michal M Hallmen Philipp P PP Ungur Liviu L Lenz Samuel S Ringenberg Mark R MR Frey Wolfgang W Stoll Hermann H Rauhut Guntram G van Slageren Joris J

Chemical science 20171208 5

Tetraoxolene radical-bridged lanthanide SMM systems were prepared for the first time by reduction of the respective neutral compounds. Magnetic measurements reveal the profound influence of the radical center on magnetic behavior. Strong magnetic couplings are revealed in the radical species, which switch on SMM behavior under zero applied field for Dy<sup>III</sup> and Tb<sup>III</sup> compounds. HFEPR spectra unravel the contributions of the magnetic coupling and the magnetic anisotropy. For G ...[more]

PMID: 29675167

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Project description:The ability of tetraazalene radical bridging ligands to mediate exceptionally strong magnetic exchange coupling across a range of transition metal complexes is demonstrated. The redox-active bridging ligand N,N',N'',N'''-tetra(2-methylphenyl)-2,5-diamino-1,4-diiminobenzoquinone (NMePhLH2) was metalated to give the series of dinuclear complexes [(TPyA)2M2(NMePhL2-)]2+ (TPyA = tris(2-pyridylmethyl)amine, M = MnII, FeII, CoII). Variable-temperature dc magnetic susceptibility data for these complexes reveal the presence of weak superexchange interactions between metal centers, and fits to the data provide coupling constants of J = -1.64(1) and -2.16(2) cm-1 for M = MnII and FeII, respectively. One-electron reduction of the complexes affords the reduced analogues [(TPyA)2M2(NMePhL3-˙)]+. Following a slightly different synthetic procedure, the related complex [(TPyA)2CrIII2(NMePhL3-˙)]3+ was obtained. X-ray diffraction, cyclic voltammetry, and Mössbauer spectroscopy indicate the presence of radical NMePhL3-˙ bridging ligands in these complexes. Variable-temperature dc magnetic susceptibility data of the radical-bridged species reveal the presence of strong magnetic interactions between metal centers and ligand radicals, with simulations to data providing exchange constants of J = -626(7), -157(7), -307(9), and -396(16) cm-1 for M = CrIII, MnII, FeII, and CoII, respectively. Moreover, the strength of magnetic exchange in the radical-bridged complexes increases linearly with decreasing M-L bond distance in the oxidized analogues. Finally, ac magnetic susceptibility measurements reveal that [(TPyA)2Fe2(NMePhL3-˙)]+ behaves as a single-molecule magnet with a relaxation barrier of Ueff = 52(1) cm-1. These results highlight the ability of redox-active tetraazalene bridging ligands to enable dramatic enhancement of magnetic exchange coupling upon redox chemistry and provide a rare opportunity to examine metal-radical coupling trends across a transmetallic series of complexes.

Dataset Information

Exchange coupling and single molecule magnetism in redox-active tetraoxolene-bridged dilanthanide complexes.

Publications

Exchange coupling and single molecule magnetism in redox-active tetraoxolene-bridged dilanthanide complexes.

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