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

• Published in: Dalton transactions : an international journal of inorganic chemistry 2018-11, Vol.47 (43), p.1545-15415
• Main Authors: Bera, Siba Prasad, Mondal, Arpan, Roy, Subhadip, Dey, Bijoy, Santra, Atanu, Konar, Sanjit
• Format: Article
• Language: English
• Subjects: Conductivity; Coordination polymers; Crystallography; Cubane; Dysprosium; Erbium; Gadolinium; Holmium; Ligands; Magnetic induction; Magnetic properties; Magnetic relaxation; Polymers; Proton conduction; Protons; Refrigeration; Relative humidity; Relaxation time; Topology
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c8dt03498b

Four new isostructural lanthanide-based three-dimensional (3D) coordination polymers (CPs), {[Ln 4 (OH) 4 (L) 2 (H 2 O) 8 ]·4.6H 2 O·1.4CH 3 CN} n (Ln 3+ = Gd 3+ ( 1 ), Dy 3+ ( 2 ), Ho 3+ ( 3 ) and Er 3+ ( 4 )), have been constructed using a sulfonate-carboxylate-based ligand (Na 2 H 2 L = disodium-2,2′-disulfonate-4,4′-oxydibenzoic acid) and the corresponding lanthanide metal( iii ) nitrates. All the CPs 1-4 contain [Ln 4 (μ 3 -OH) 4 ] 8+ cubane-like cores interconnected through L 4− 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 (−Δ S m ) = 34.6 J kg −1 K −1 for Δ H = 7 T at 3 K. CP 2 shows field-induced slow magnetic relaxation properties with energy barrier ( U eff / k B ) = 30.40 K and relaxation time ( τ 0 ) = 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 (Gd 3+ > Dy 3+ > Ho 3+ > Er 3+ ). This demonstrates the effective employment of the lanthanide contraction strategy to tune proton conductivity while preserving proton-conducting pathways. Four lanthanide 3D coordination frameworks with 1D hydrophilic channels along the crystallographic c direction have been investigated for their proton conduction and magnetic properties.