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Effect of coordination geometry on the magnetic properties of a series of Ln2 and Ln4 hydroxo clusters

Abstract

A series of isostructural tetranuclear complexes were isolated, represented by molecular formula of [Ln4(µ3-OH)4(L)4(µ2-piv)4(MeOH)4] (Ln = Gd 1, Dy 2 and Ho 3; LH = [1,3-Bis(o-methoxyphenyl)-propane-1,3-dione]). Under similar reaction conditions, by simply varying the co-ligand from pivalate to 2,6-Bis(hydroxymethyl)-p-cresol (LH3’) led us to the isolation of a dinuculear family of complexes with the general molecular formula of [Ln2(L)4(µ2-LH2ʹ)2].4DMF (Ln = Gd 4, Dy 5 and Ho 6). Direct current magnetic susceptibility data studies on polycrystalline sample of 1-3 reveals the existence of weak antiferromagnetic exchange interaction between the lanthanide ions as is evident from the spin Hamiltonian (SH) parameters (J1 = -0.055 cm-1 and g = 2.01) extracted by fitting the MT(T) data of 1. On the other hand, though complex 4 exhibits weak antiferromagnetic coupling (J1 = -0.048 cm-1 and g = 1.99) between the Gd(III) ions, the MT(T) data of complexes 5 and 6 unambiquously shows the presence of ferromagnetic interaction between Dy(III) and Tb(III) ions at lower temperature. Magnetization relaxation dynamics studies performed on 2 shows frequency dependent out-of-phase susceptibility signals without any maxima (with and without external magnetic field) indicates that the magnetization vector prefers an underbarrier relaxation mechanism rather than an Orbach process. In contrast, complex 5 shows slow magentization of relaxation with an effective energy barrier (Ueff) of 32.5 K with a pre-exponential factor (0) of 1.987 X 10-6 s. The significant change in magnetization relaxation behaviour of 5 (compared to 2) is attributed to the presence of ferromagnetic exchange with suitable square anti-prism (SAP) geometry around Dy(III) ion which is in conjunction with co-parallel arrangement of gz axis of both Dy(III) ions. Magnetocaloric effect (MCE) of complexes 1 and 4 were extracted from detailed magnetization measurement and the change in magnetic entropy (-ΔSm) of 1 and 4 found to 25.57 J Kg-1 K-1 and 12.93 J Kg-1 K-1 respectively at 3.0 K for ΔH = 70 kG.

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Publication details

The article was received on 16 Jan 2017, accepted on 06 Dec 2017 and first published on 07 Dec 2017


Article type: Paper
DOI: 10.1039/C7DT00172J
Citation: Dalton Trans., 2017, Accepted Manuscript
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    Effect of coordination geometry on the magnetic properties of a series of Ln2 and Ln4 hydroxo clusters

    B. Viswanathan, A. Rasamsetty, C. Das, E. C. Sañudo and M. Shanmugam, Dalton Trans., 2017, Accepted Manuscript , DOI: 10.1039/C7DT00172J

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