Heterometallic Aluminum Metal–Organic Frameworks

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.