Two multifunctional Dy(iii)-based metal–organic frameworks exhibiting proton conduction, magnetic properties and second-harmonic generation

Abstract

The construction of multifunctional metal–organic frameworks (MOFs) has attracted considerable attention. Two novel Dy-MOFs namely [Dy₂(TPTC-2OMe)_1.5(H₂O)₄·H₂O]_n (1) and {[Dy₂(TPTC-2OMe)(H₂TPTC-2OMe)(H₂O)₂]·2H₂O}_n (2) were obtained by a solvothermal method using 2′,5′-dimethoxy-[1,1′:4′,1′′-terphenyl]-4,4′′-dicarboxylic acid (H₄TPTC-2OMe) as the ligand. Structure analysis demonstrates that both MOFs 1 and 2 displayed three-dimensional framework structures, in which MOF 1 was with Dy(III) metal chains as nodes, while MOF 2 was with Dy₂ binuclear metal clusters as nodes. Interestingly, MOFs 1 and 2 exhibited high thermal and chemistry stabilities and presented relatively high proton conductivity (σ) values of 1.69 × 10⁻⁴ S cm⁻¹ and 3.52 × 10⁻⁶ S cm⁻¹ at 50 °C and 98% RH. Although there exist a large number of coordinated or free H₂O molecules in both structures, it is easier to form an ordered hydrogen-bonding network between the coordinated H₂O molecules in the structure of MOFs, resulting in a more excellent proton conductivity of MOF 1. Moreover, MOF 1 exhibited field-induced single-molecule magnet (SMM) behavior with energy barriers (U_eff) of 37.22 K (τ₀ = 9.27 × 10⁻⁸ s). Furthermore, MOF 1 exhibits obvious second-order nonlinear optical properties. This research provides guidance for the design of novelty multifunctional MOF materials.