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3D isomorphous lanthanide coordination polymers displaying magnetic refrigeration, slow magnetic relaxation and tunable proton conduction

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Abstract

Four new isostructural lanthanide-based three-dimensional (3D) coordination polymers (CPs), {[Ln4(OH)4(L)2(H2O)8]·4.6H2O·1.4CH3CN}n (Ln3+ = Gd3+ (1), Dy3+ (2), Ho3+ (3) and Er3+ (4)), have been constructed using a sulfonate–carboxylate-based ligand (Na2H2L = disodium-2,2′-disulfonate-4,4′-oxydibenzoic acid) and the corresponding lanthanide metal(III) nitrates. All the CPs 1–4 contain [Ln43-OH)4]8+ cubane-like cores interconnected through L4− ligands to give rise to 3D coordination frameworks with 1D hydrophilic channels along the crystallographic c direction. From the topological perspective, the underlying 3D nets of the CPs can be classified as a 3,6,6-c net with an undocumented topology. Magnetic studies display that CP 1 exhibits a magnetocaloric effect with a significant magnetic entropy change (−ΔSm) = 34.6 J kg−1 K−1 for ΔH = 7 T at 3 K. CP 2 shows field-induced slow magnetic relaxation properties with energy barrier (Ueff/kB) = 30.40 K and relaxation time (τ0) = 2.47 × 10−7 s. Theoretical calculations have been performed to corroborate the magnetic exchange coupling constant value for CP 1 and to obtain a deeper understanding of the field-induced slow magnetic relaxation behavior of CP 2. Impedance analyses display high values of proton conductivity which reach 2.02 × 10−6, 2.96 × 10−6, 4.56 × 10−3 and 6.59 × 10−3 S cm−1 for CPs 1–4, respectively at high temperature (>75 °C) and 95% relative humidity (RH) in the order CP 1 < CP 2 < CP 3 < CP 4. Notably, the proton conductivities for CPs 3 and 4 are a few orders of magnitude higher than those of CPs 1 and 2 (10−3 S cm−1 vs. 10−6 S cm−1), and the conductivity increases periodically following the decreasing order of ionic radius (Gd3+ > Dy3+ > Ho3+ > Er3+). This demonstrates the effective employment of the lanthanide contraction strategy to tune proton conductivity while preserving proton-conducting pathways.

Graphical abstract: 3D isomorphous lanthanide coordination polymers displaying magnetic refrigeration, slow magnetic relaxation and tunable proton conduction

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Publication details

The article was received on 28 Aug 2018, accepted on 01 Oct 2018 and first published on 02 Oct 2018


Article type: Paper
DOI: 10.1039/C8DT03498B
Citation: Dalton Trans., 2018, Advance Article
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    3D isomorphous lanthanide coordination polymers displaying magnetic refrigeration, slow magnetic relaxation and tunable proton conduction

    S. P. Bera, A. Mondal, S. Roy, B. Dey, A. Santra and S. Konar, Dalton Trans., 2018, Advance Article , DOI: 10.1039/C8DT03498B

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