Channel-Assisted Proton Conduction Behavior in Hydroxyl-Rich Lanthanide-Based Magnetic Metal–Organic Frameworks

Abstract

Two new lanthanide-based 3D metal-organic frameworks (MOFs), {[Ln(L)(Ox)(HO)]·xHO} [Ln = Gd and x = 3 (1) and Dy and x = 1.5 (2); HL = mucic acid; OxH = oxalic acid] showing interesting magnetic properties and channel-mediated proton conduction behavior, are presented here. Single-crystal X-ray structure analysis shows that, in complex 1, the overall structure originates from the mucate-bridged gadolinium-based rectangular metallocycles. The packing view reveals the presence the two types of hydrophilic 1D channels filled with lattice water molecules, which are strongly hydrogen-bonded with coordinated water along the a and b axes, whereas for complex 2, the 3D framework originates from a carboxylate-bridged dysprosium-based criss-cross-type secondary building block. Magnetic studies reveal that 1 exhibits a significant magnetic entropy change (-ΔS) of 30.6 J kg K for ΔH= 7 T at 3 K. Our electronic structure calculations under the framework of density functional theory reveal that exchange interactions between Gd ions are weak and of the antiferromagnetic type. Complex 2 shows field-induced single-molecule-magnetic behavior. Impedance analysis shows that the proton conductivity of both complexes reaches up to the maximum value of 4.7 × 10 S cm for 1 and 9.06 × 10 S cm for 2 at high temperature (>75 °C) and relative humidity (RH; 95%). The Monte Carlo simulations confirm the exact location of the adsorbed water molecules in the framework after humidification (RH = 95%) for 1. Further, the results from computational simulation also reveal that the presence of a more dense arrangement of adsorbed water molecules through hydrogen bonding in a particular type of channel (along the a axis) contributes more to the proton migration compared to the other channel (along the b axis) in the framework.

Lanthanide‐Based Layer‐Type Two‐Dimensional Coordination Polymers Featuring Slow Magnetic Relaxation, Magnetocaloric Effect and Proton Conductivity

“…Conductivity increases with increasing temperature at 95 % RH (Table S10). Highest proton conductivity of all the compounds were 1.13×10 −6 S cm −1 for CP 1, 2.73×10 −3 S cm −1 for CP 2, 6.27×10 −6 S cm −1 for CP 3 at 80 °C under 95 % RH (Figures and S15) and comparable with the proton conducting coordination polymers (Table S11) –. The proton conductivity follows the order CP 1 <CP 3 <CP 2 .…”

“…It is worth mentioning that CP 2 shows few orders of magnitude higher proton conduction than CPs 1 and 3 (10 −3 S cm −1 vs. 10 −6 S cm −1 ). Variation of proton conductivity for lanthanide coordination polymers with different magnitude, 2 or 3 orders has been noticed. The direct connection between the conductivity and ionic radius of lanthanide ions can be seen .…”

A Highly Stable Two‐Dimensional Copper(II) Organic Framework for Proton Conduction and Ammonia Impedance Sensing

“…Thus, it leads to the optimized protonconductivity for 1 of 1.50 10 À3 Scm À1 .A sl isted in Ta ble 2, althought he optimized conductivity value is smaller than that of severalr ecent MOFs, [38][39][40][41] this value can be compared to that of some previousM OFs under similar tested conditions, [41][42][43][44][45][46] and is remarkably highert han that of four imidazole dicarboxylate-based Co II MOFs and other MOFs. [27,28,47] It is illustrated again that the structural advantage of MOF 1 is the a large amount of uncoordinated carboxylate units between the layers forprotontransfer.…”

Field Induced Slow Magnetic Relaxation in a Non Kramers Tb(III) Based Single Chain Magnet

“…The in-phase χ M ac susceptibility data show no frequency dependence between 2 K and 10 K as shown in Figure S3b in the Supporting Information. While the χ M (T) curves exhibit small frequency dependence, hinting at slow relaxation at lower temperature however no clear peak maxima is observed above 2K which is mainly due to the fast quantum tunnelling of magnetization [59,60] ( Figure S5a). We performed ac measurements on complex 1 at different fields in the range of 500 Oe to 3000 Oe and optimal dc field of 2000 Oe was selected because it invokes the slowest relaxation in the range of in the 2000-3000 Oe fields (see Figures S6-S9, Supporting Information).…”