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Tuning of Exchange Coupling and Switchable Magnetization Dynamics by Displacing the Bridging Ligands Observed in Two Dimeric Manganese(III) Compounds.

ABSTRACT: Two Mn(III)-based dimers, [Mn₂(bpad)₂(CH₃O)₄]_n (1) and [Mn₂(bpad)₂(pa)₂]_n·2H₂O (2) (Hbpad?=?N³-benzoylpyridine-2-carboxamidrazone, H₂pa?=?phthalic acid), have been assembled from a tridentate Schiff-base chelator and various anionic coligands. Noteworthily, compound 1 could be identified as a reaction precursor to transform to 2 in the presence of phthalic acid, resulting in a rarely structural conversion process in which the bridges between intradimer Mn(III) ions alter from methanol oxygen atom with ?₂-O mode in 1 (Mn Mn distance of 3.046?Å) to syn-anti carboxylate in 2 (Mn Mn distance of 4.043?Å), while the Mn(III) centers retain hexa-coordinated geometries with independently distorted octahedrons in two compounds. The dc magnetic determinations reveal that ferromagnetic coupling between two metal centers with J?=?1.31?cm^-1 exists in 1, whereas 2 displays weak antiferromagnetic interactions with the coupling constant J of -0.56?cm^-1. Frequency-dependent ac susceptibilities in the absence of dc field for 1 suggest slow relaxation of the magnetization with an energy barrier of 13.9?K, signifying that 1 features single-molecule magnet (SMM) behavior. This work presents a rational strategy to fine-tune the magnetic interactions and further magnetization dynamics of the Mn(III)-containing dinuclear units through small structural variations driven by the ingenious chemistry.

SUBMITTER: Liu XY

PROVIDER: S-EPMC5359551 | biostudies-literature | 2017 Mar

REPOSITORIES: biostudies-literature

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Tuning of Exchange Coupling and Switchable Magnetization Dynamics by Displacing the Bridging Ligands Observed in Two Dimeric Manganese(III) Compounds.

Liu Xiang-Yu XY Cen Pei-Pei PP Wu Li-Zhou LZ Li Fei-Fei FF Song Wei-Ming WM Xie Gang G Chen San-Ping SP

Scientific reports 20170321

Two Mn(III)-based dimers, [Mn2(bpad)2(CH3O)4]n (1) and [Mn2(bpad)2(pa)2]n·2H2O (2) (Hbpad = N3-benzoylpyridine-2-carboxamidrazone, H2pa = phthalic acid), have been assembled from a tridentate Schiff-base chelator and various anionic coligands. Noteworthily, compound 1 could be identified as a reaction precursor to transform to 2 in the presence of phthalic acid, res ...[more]

PMID: 28322305

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Project description:PURPOSE:An extended phase graph framework (EPG-X) for modeling systems with exchange or magnetization transfer (MT) is proposed. THEORY:EPG-X models coupled two-compartment systems by describing each compartment with separate phase graphs that exchange during evolution periods. There are two variants: EPG-X(BM) for systems governed by the Bloch-McConnell equations, and EPG-X(MT) for the pulsed MT formalism. For the MT case, the "bound" protons have no transverse components, so their phase graph consists of only longitudinal states. METHODS:The EPG-X model was validated against steady-state solutions and isochromat-based simulation of gradient-echo sequences. Three additional test cases were investigated: (i) MT effects in multislice turbo spin-echo; (ii) variable flip angle gradient-echo imaging of the type used for MR fingerprinting; and (iii) water exchange in multi-echo spin-echo T2 relaxometry. RESULTS:EPG-X was validated successfully against isochromat based transient simulations and known steady-state solutions. EPG-X(MT) simulations matched in-vivo measurements of signal attenuation in white matter in multislice turbo spin-echo images. Magnetic resonance fingerprinting-style experiments with a bovine serum albumin (MT) phantom showed that the data were not consistent with a single-pool model, but EPG-X(MT) could be used to fit the data well. The EPG-X(BM) simulations of multi-echo spin-echo T2 relaxometry suggest that exchange could lead to an underestimation of the myelin-water fraction. CONCLUSIONS:The EPG-X framework can be used for modeling both steady-state and transient signal response of systems exhibiting exchange or MT. This may be particularly beneficial for relaxometry approaches that rely on characterizing transient rather than steady-state sequences. Magn Reson Med 80:767-779, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Project description:The syntheses and crystal structures for the compounds tetra-μ-aqua--tetra-kis-{2-[aza-nid-yl-ene(oxido)meth-yl]phenolato}tetra-kis-(μ2-3-hy-droxy-benzoato)dys-pro-s-ium(III)-tetra-manganese(III)sodium(I) N,N-di-methyl-acetamide deca-solvate, [DyMn4Na(C7H5O3)4(C7H4NO2)4(H2O)4]·10C4H9NO or [DyIIINa(4-OHben)4{12-MCMn(III)N(shi)-4}(H2O)4]·10DMA, 1, and tetra-μ-aqua--tetra-kis-{2-[aza-nid-yl-ene(oxido)meth-yl]phenolato}tetra-kis-(μ2-3-hy-droxy-benzoato)dys-pros-ium(III)tetra-manganese(III)sodium(I) N,N-di-methylformamide tetra-solvate, [DyMn4Na(C7H5O3)4(C7H4NO2)4(H2O)4]·4C3H7NO or [DyIIINa(3-OHben)4{12-MCMn(III)N(shi)-4}(H2O)4]·4DMF, 2, and where MC is metallacrown, shi3- is salicyl-hydroximate, 3-OHben is 3-hy-droxy-benzoate, DMA is N,N-di-methyl-acetamide, 4-OHben is 4-hy-droxy-benzoate, and DMF is N,N-di-methyl-formamide, are reported. For both 1 and 2, the macrocyclic metallacrown consists of an [MnIII-N-O] ring repeat unit, and the domed metallacrown captures two ions in the central cavity: a DyIII ion on the convex side of the metallacrown and an Na+ ion the concave side. The MnIII ions are six-coordinate with an elongated tetra-gonally distorted octa-hedral geometry. Both the DyIII and Na+ ions are eight-coordinate. The DyIII ions possess a square-anti-prismatic geometry, while the Na+ ions have a distorted biaugmented trigonal-prismatic geometry. Four 3-hy-droxy-benzoate or 4-hy-droxy-benzoate ligands bridge each MnIII ion to the central DyIII ion. For 1, whole-mol-ecule disorder is observed for the main mol-ecule, excluding only the DyIII and Na+ ions, and the occupancy ratio refined to 0.8018 (14):0.1982 (14). Three DMA mol-ecules were refined as disordered with two in general positions by an approximate 180° rotation and the third disordered twice by general disorder as well as by an exact 180° rotation about a twofold axis that bis-ects it. The occupancy ratios refined to 0.496 (8):0.504 (8), 0.608 (9):0.392 (9), and 2×0.275 (7):2×0.225 (7), respectively. For 2, segments of the metallacrown are disordered including the DyIII ion, one of the Mn ions, two of the Mn-bound 4-hy-droxy-benzoate ligands, the Mn-bridging salicyl-hydroximate ligand, and portions of the remaining three shi3- ligands. The occupancy ratio for the metallacrown disorder refined to 0.849 (9):0.151 (9). Two DMF solvent mol-ecules are also disordered, each over two orientations. The disorder ratios refined to 0.64 (3):0.36 (3) and to 0.51 (2):0.49 (2), respectively. For 2, the crystal under investigation was refined as a non-merohedric twin by a 90° rotation around the real a axis [twin ratio 0.9182 (8):0.0818 (8)].

Dataset Information

Tuning of Exchange Coupling and Switchable Magnetization Dynamics by Displacing the Bridging Ligands Observed in Two Dimeric Manganese(III) Compounds.

Publications

Tuning of Exchange Coupling and Switchable Magnetization Dynamics by Displacing the Bridging Ligands Observed in Two Dimeric Manganese(III) Compounds.

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