Improvement of the Proton Conduction of Copper(II)-Mesoxalate Metal–Organic Frameworks by Strategic Selection of the Counterions

Abstract

Three copper(II)/mesoxalate-based MOFs with formulas (H 3 O)[Cu 9 (Hmesox) 6 (H 2 O) 6 Cl]·8H 2 O ( 1 ), (NH 2 Me 2 ) 0.4 (H 3 O) 0.6 [Cu 9 (Hmesox) 6 (H 2 O) 6 Cl]·8H 2 O ( 2 ), and (enH 2 ) 0.25 (enH) 1.5 [Cu 6 (Hmesox) 3 (mesox)(H 2 O) 6 Cl 0.5 ]Cl 0.5 ·5.25H 2 O ( 3 ) were synthesized (H 4 mesox = mesoxalic acid = 2,2-dihydroxypropanedioic acid, en = ethylenediamine). Essentially, all of the compounds display the same anionic network with a different arrangement of the cations, which have a remarkable effect on the proton conduction of the materials, ranging from 1.16 × 10 –4 S cm –1 for 1 to 1.87 × 10 –3 S cm –1 for 3 (at 80 °C and 95% RH). These compounds also display antiferromagnetic coupling among the copper(II) ions through both the carboxylate and alkoxido bridges. The values of the principal magnetic coupling constants were calculated by density functional theory (DFT), leading to congruent values that confirm the predominant antiferromagnetic nature of the interactions.

Enhanced Catalytic Activity of a Copper(II) Metal–Organic Framework Constructed via Semireversible Single-Crystal-to-Single-Crystal Dehydration

“…In 2′ and 2″ , the intermetallic distances are 3.476(8) and 3.482(11) Å, respectively. The shortest paddle-wheel Cu···Cu distance in the literature is commonly about 2.601(4) Å, and the longest is 4.730(1) Å . Therefore, these bond lengths are within normal statistical errors.…”

“…The shortest paddle-wheel Cu···Cu distance in the literature is commonly about 2.601(4) Å, 44 and the longest is 4.730(1) Å. 45 Therefore, these bond lengths are within normal statistical errors. In addition, the (∠O–Cu–O) bond angles vary from 77.99(19) to 168.06(12)° in 2′ and from 78.80(3) to 167.9(2)° in 2″ ( Tables S6–S7 ).…”

“…All of the water molecules in both 2′ and 2″, guest and coordinated, have been evacuated and the networks are now composed of four crystallographically unique Cu(II) centers 4) Å, 44 and the longest is 4.730(1) Å. 45 Therefore, these bond lengths are within normal statistical errors. In addition, the (∠O−Cu− O) bond angles vary from 77.99 (19) to 168.06 (12)°in 2′ and from 78.80(3) to 167.9(2)°in 2″ (Tables S6−S7).…”

Ligand-Functionalized MIL-68-type Indium(III) Metal–Organic Frameworks with Prominent Intrinsic Proton Conductivity

“…Additionally, their crystallinity features, coupled with the intervention of subsequent controllable factors, will optimize the proton transport channel and give people a deeper understanding of the proton conduction mechanism. Based on these advantages, researchers have achieved some impressive research results. − Given the various advantages of transition-metal-based MOFs, including plentiful reserves and low cost, much study has been conducted on proton conduction in such MOFs. − Furthermore, numerous investigations on the proton conductivity of lanthanide-based MOFs, which contain relatively rich rare-earth metals, have been published. − In contrast, the research of the proton conductivity of main-group-metal-based MOFs has primarily focused on those constructed from elements abundant in the earth’s crust, such as sodium, calcium, strontium, barium, and aluminum metal, − while the study of the proton conductivity of MOFs built by expensive and less abundant metals, such as indium, gallium, and thallium, has been extremely limited …”