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Issue 2, 2016
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Supramolecular aggregates of single-molecule magnets: exchange-biased quantum tunneling of magnetization in a rectangular [Mn3]4 tetramer

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Abstract

The syntheses and properties of four magnetically-supramolecular oligomers of triangular Mn3 units are reported: dimeric [Mn6O2(O2CMe)8(CH3OH)2(pdpd)2] (3) and [Mn6O2(O2CMe)8(py)2(pdpd)2](ClO4)2 (4), and tetrameric [Mn12O4(O2CR)12(pdpd)6](ClO4)4 (R = Me (5), tBu (6)). They were all obtained employing 3-phenyl-1,5-di(pyridin-2-yl)pentane-1,5-dione dioxime (pdpdH2), either in direct synthesis reactions involving oxidation of MnII salts or in metathesis reactions with the preformed complex [Mn3O(O2CMe)6(py)3](ClO4) (1); complex 6 was then obtained by carboxylate substitution on complex 5. Complexes 3 and 4 contain two [MnIII2MnII3-O)]6+ and [MnIII33-O)]7+ units, respectively, linked by two pdpd2− groups. Complexes 5 and 6 contain four [MnIII33-O)]7+ units linked by six pdpd2− groups into a rectangular tetramer [MnIII3]4. Solid-state dc magnetic susceptibility studies showed that the Mn3 subunits in 3 and 4 have a ground-state spin of S = 3/2 and S = 2, respectively, while the Mn3 subunits in 5 and 6 possess an S = 6 ground state. Complexes 5 and 6 exhibit frequency-dependent out-of-phase (χ′′M) ac susceptibility signals indicating 5 and 6 to be tetramers of Mn3 single-molecule magnets (SMMs). High-frequency EPR studies of a microcrystalline powder sample of 5·2CH2Cl2 provided precise spin Hamiltonian parameters of D = −0.33 cm−1, |E| = 0.03 cm−1, B04 = −8.0 × 10−5 cm−1, and g = 2.0. Magnetization vs. dc field sweeps on a single crystal of 5·xCH2Cl2 gave hysteresis loops below 1 K that exhibit exchange-biased quantum tunneling of magnetization (QTM) steps with a bias field of 0.19 T. Simulation of the loops determined that each Mn3 unit is exchange-coupled to the two neighbors linked to it by the pdpd2− linkers, with an antiferromagnetic inter-Mn3 exchange interaction of J/kB = −0.011 K (Ĥ = −2i·Ŝj convention). The work demonstrates a rational approach to synthesizing magnetically-supramolecular aggregates of SMMs as potential multi-qubit systems for quantum computing.

Graphical abstract: Supramolecular aggregates of single-molecule magnets: exchange-biased quantum tunneling of magnetization in a rectangular [Mn3]4 tetramer

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Supplementary files

Article information


Submitted
17 Jul 2015
Accepted
01 Nov 2015
First published
16 Nov 2015

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2016,7, 1156-1173
Article type
Edge Article
Author version available

Supramolecular aggregates of single-molecule magnets: exchange-biased quantum tunneling of magnetization in a rectangular [Mn3]4 tetramer

T. N. Nguyen, W. Wernsdorfer, M. Shiddiq, K. A. Abboud, S. Hill and G. Christou, Chem. Sci., 2016, 7, 1156
DOI: 10.1039/C5SC02599K

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