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Heterometallic Zn3Ln3 ensembles containing (μ6-CO3) ligand and triangular disposition of Ln3+ ions: Analysis of single-molecule toroic (SMT) and single-molecule magnet (SMM) behavior

Heterometallic Zn3Ln3 ensembles containing (μ6-CO3) ligand and triangular disposition of Ln3+ ions: Analysis of single-molecule toroic (SMT) and single-molecule magnet (SMM) behavior
Heterometallic Zn3Ln3 ensembles containing (μ6-CO3) ligand and triangular disposition of Ln3+ ions: Analysis of single-molecule toroic (SMT) and single-molecule magnet (SMM) behavior
Two new heterometallic Zn3Ln3 (Ln3+=Dy, Tb) complexes, with a double triangular topology of the metal ions, have been assembled from the polytopic Mannich base ligand 6,6′-{[2-(dimethylamino)ethylazanediyl]bis(methylene)}bis(2-methoxy-4-methylphenol) (H2L) with the aid of an in situ generated carbonate ligand from atmospheric CO2 fixation. Theoretical calculations indicate axial ground states for the Ln3+ ions in these complexes, with their local magnetic moments being almost coplanar and tangential to the Ln3+ atoms that define the equilateral triangle. Therefore, they can be considered as single-molecule toroics (SMTs) with almost zero total magnetic moment. Micro-SQUID measurements on the Dy3+ counterpart show hysteresis loops below 3 K that have an S-shape, with large coercive fields opening upon cooling. This behavior is typical of a single molecule magnet (SMM) with very slow zero-field relaxation. At around ±0.35 T, the loops have a broad step, which is due to a direct relaxation process and corresponds to an acceleration of the relaxation of the magnetization, also observed at this magnetic field from ac susceptibility measurements. Simulations suggest that the broad step corresponds to two level avoidance of crossing points where the spin chiral Kramers doublet meets excited states of the coupled manifold, whose position is defined by exchange and dipole interactions. The Tb3+ counterpart does not exhibit SMM behavior, which is due to the fact that the degeneracy of the ground state of the exchange coupled system is lifted at zero field, thus favoring quantum tunneling of magnetization (QTM).
0947-6539
16621-16636
Goura, Joydeb
a1e753c8-74fe-45b0-842e-02a880a1b4d6
Colacio, Enrique
f4595033-9a6f-4437-8994-f800de084eac
Herrera, Juan Manuel
7b8359f0-c591-41db-af4f-a01f4eff6c1f
Suturina, Elizaveta A.
24dd007d-949a-4852-99d1-ea42b00103ef
Kuprov, Ilya
bb07f28a-5038-4524-8146-e3fc8344c065
Lan, Yanhua
aa86fb5d-3619-48aa-bd5e-04eba8eaddfe
Wernsdorfer, Wolfgang
9c041513-34d5-475f-9197-1e910260fc10
Chandrasekhar, Vadapalli
85d32ddd-480c-4905-b07e-c826fb94b463
Goura, Joydeb
a1e753c8-74fe-45b0-842e-02a880a1b4d6
Colacio, Enrique
f4595033-9a6f-4437-8994-f800de084eac
Herrera, Juan Manuel
7b8359f0-c591-41db-af4f-a01f4eff6c1f
Suturina, Elizaveta A.
24dd007d-949a-4852-99d1-ea42b00103ef
Kuprov, Ilya
bb07f28a-5038-4524-8146-e3fc8344c065
Lan, Yanhua
aa86fb5d-3619-48aa-bd5e-04eba8eaddfe
Wernsdorfer, Wolfgang
9c041513-34d5-475f-9197-1e910260fc10
Chandrasekhar, Vadapalli
85d32ddd-480c-4905-b07e-c826fb94b463

Goura, Joydeb, Colacio, Enrique, Herrera, Juan Manuel, Suturina, Elizaveta A., Kuprov, Ilya, Lan, Yanhua, Wernsdorfer, Wolfgang and Chandrasekhar, Vadapalli (2017) Heterometallic Zn3Ln3 ensembles containing (μ6-CO3) ligand and triangular disposition of Ln3+ ions: Analysis of single-molecule toroic (SMT) and single-molecule magnet (SMM) behavior. Chemistry - A European Journal, 23 (65), 16621-16636. (doi:10.1002/chem.201703842).

Record type: Article

Abstract

Two new heterometallic Zn3Ln3 (Ln3+=Dy, Tb) complexes, with a double triangular topology of the metal ions, have been assembled from the polytopic Mannich base ligand 6,6′-{[2-(dimethylamino)ethylazanediyl]bis(methylene)}bis(2-methoxy-4-methylphenol) (H2L) with the aid of an in situ generated carbonate ligand from atmospheric CO2 fixation. Theoretical calculations indicate axial ground states for the Ln3+ ions in these complexes, with their local magnetic moments being almost coplanar and tangential to the Ln3+ atoms that define the equilateral triangle. Therefore, they can be considered as single-molecule toroics (SMTs) with almost zero total magnetic moment. Micro-SQUID measurements on the Dy3+ counterpart show hysteresis loops below 3 K that have an S-shape, with large coercive fields opening upon cooling. This behavior is typical of a single molecule magnet (SMM) with very slow zero-field relaxation. At around ±0.35 T, the loops have a broad step, which is due to a direct relaxation process and corresponds to an acceleration of the relaxation of the magnetization, also observed at this magnetic field from ac susceptibility measurements. Simulations suggest that the broad step corresponds to two level avoidance of crossing points where the spin chiral Kramers doublet meets excited states of the coupled manifold, whose position is defined by exchange and dipole interactions. The Tb3+ counterpart does not exhibit SMM behavior, which is due to the fact that the degeneracy of the ground state of the exchange coupled system is lifted at zero field, thus favoring quantum tunneling of magnetization (QTM).

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Zn3Ln3_Manuscript_16_08_17 - Accepted Manuscript
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Accepted/In Press date: 16 August 2017
e-pub ahead of print date: 25 October 2017
Published date: 21 November 2017

Identifiers

Local EPrints ID: 416348
URI: https://eprints.soton.ac.uk/id/eprint/416348
ISSN: 0947-6539
PURE UUID: 20daa777-0b86-43c2-87d9-7bca86eae25d
ORCID for Ilya Kuprov: ORCID iD orcid.org/0000-0003-0430-2682

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Date deposited: 13 Dec 2017 17:30
Last modified: 17 Sep 2019 04:34

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