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Giant coercivity and high magnetic blocking temperatures for N23- radical-bridged dilanthanide complexes upon ligand dissociation.

ABSTRACT: Increasing the operating temperatures of single-molecule magnets-molecules that can retain magnetic polarization in the absence of an applied field-has potential implications toward information storage and computing, and may also inform the development of new bulk magnets. Progress toward these goals relies upon the development of synthetic chemistry enabling enhancement of the thermal barrier to reversal of the magnetic moment, while suppressing alternative relaxation processes. Herein, we show that pairing the axial magnetic anisotropy enforced by tetramethylcyclopentadienyl (CpMe4H) capping ligands with strong magnetic exchange coupling provided by an N23- radical bridging ligand results in a series of dilanthanide complexes exhibiting exceptionally large magnetic hysteresis loops that persist to high temperatures. Significantly, reducing the coordination number of the metal centers appears to increase axial magnetic anisotropy, giving rise to larger magnetic relaxation barriers and 100-s magnetic blocking temperatures of up to 20?K, as observed for the complex [K(crypt-222)][(CpMe4H2Tb)2(?-[Formula: see text])].

SUBMITTER: Demir S

PROVIDER: S-EPMC5732206 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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Giant coercivity and high magnetic blocking temperatures for N<sub>2</sub><sup>3-</sup> radical-bridged dilanthanide complexes upon ligand dissociation.

Demir Selvan S Gonzalez Miguel I MI Darago Lucy E LE Evans William J WJ Long Jeffrey R JR

Nature communications 20171215 1

Increasing the operating temperatures of single-molecule magnets-molecules that can retain magnetic polarization in the absence of an applied field-has potential implications toward information storage and computing, and may also inform the development of new bulk magnets. Progress toward these goals relies upon the development of synthetic chemistry enabling enhancement of the thermal barrier to reversal of the magnetic moment, while suppressing alternative relaxation processes. Herein, we show ...[more]

PMID: 29247236

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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

Giant coercivity and high magnetic blocking temperatures for N23- radical-bridged dilanthanide complexes upon ligand dissociation.

Publications

Giant coercivity and high magnetic blocking temperatures for N<sub>2</sub><sup>3-</sup> radical-bridged dilanthanide complexes upon ligand dissociation.

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