Heterometallic Aluminum Metal–Organic Frameworks

Abstract

From spinel gemstone (MgAl₂O₄) to layered double hydroxides, nature has long relied on combinations between charge-complementary metal ions such as divalent metal ions (M²⁺) and Al³⁺ to create diverse valuable materials. However, for metal–organic frameworks (MOFs), heterometallic combinations such as Mg–Al are conspicuously absent. Here, we report a breakthrough in the synthesis of heterometallic Al-MOFs containing M²⁺/Al³⁺ trimeric clusters (M = Mg, Mn, Co, Ni). The synergistic effect between M(II) chlorides and aluminum lactate plays a critical role in the cooperative crystallization of M²⁺ and Al³⁺ into pore-space-partitioned MOFs (partitioned acs topology) with fast crystallization kinetics (about 3 h). New M²⁺/Al³⁺ MOFs exhibit highly tunable porosity and extraordinarily high uptakes for CO₂ and small hydrocarbon molecules (112 cm³/g for CO₂, 176 cm³/g for C₂H₂, 156 cm³/g for C₂H₄, and 163 cm³/g for C₂H₆) at 298 K and 1 bar. The high uptake capacity coupled with high selectivity (up to 8.5 for C₂H₂/CO₂, 10.8 for C₂H₂/C₂H₄) gives rise to efficient separations of either C₂H₂/CO₂ or C₂H₂/C₂H₄ gas mixtures, as confirmed by experimental breakthrough experiments.