High Proton Conduction for CPM-200 Achieved by Aliovalent-Predefinition of M3(μ3-O) Building Blocks and In Situ Encapsulation of Hydrated Metal Ions

Trinuclear M3(μ3-O) cluster-based MOFs, possessing superior chemical tolerance and modular adjustability, have recently exhibited impressive proton conductivity through proper functional modification and guest encapsulation. In order to clarify how accurate regulation of framework electrification via aliovalent metal substitution on conductive properties is, we screen and prepare a CPM-200 model system, including an In-ABTC-H2O with cationic [In3(μ3-O)(COO)6] cluster, a neutral [InMn2(μ3-OH)(COO)6]-based In/Mn-ABTC-H2O, two [Mn3(μ3-OH)(COO)6] anion-type Mn-ABTC-DMA and Mn(H2O)6@Mn-ABTC-H2O, which contain terminal coordinated DMA and H3O+ molecules, respectively. Accompanied by the gradual aliovalent substitution of Mn(II) for In(III) in [In3(μ3-O)(COO)6] unit, the original NO3– ion in In-ABTC-H2O can be replaced to give an unusual [Mn(H2O)6]2+ cation in Mn-ABTC-H2O for charge balance. The synergistic effect of protonated metal node, hydrated metal ion, and contracted pore volume endows a high conductivity value of Mn(H2O)6@Mn-ABTC-H2O up to 1.15 × 10–2 S/cm. Moreover, a conductive mechanism is visually exhibited by molecular dynamics (MD) simulation, suggesting Grotthuss-like migration in void spaces.