4.8 nm Concave {M72} (M=Co, Ni, Fe) metal-organic polyhedra capped by 18 calixarenes

Three 4.8 nm isostructural {M72} (M=CoII for CIAC-128, NiII for CIAC-129, FeII for CIAC-130) metal-organic polyhedra (MOPs) are constructed by eighteen M4-p-tert-butylthiacalix[4]arene (M4-TC4A) units bridged via sixteen four-connected 5,5′-(1H-1,2,4-triazole-3,5-diyl) diisophthalic acid (H4TADIPA) linkers. These MOPs are featured with a rarely reported concave coordination cage, which can be simplified as a squeezed double-decker hexagonal prism pressed from the top and bottom hexagonal faces. Furthermore, CIAC-128, CIAC-129 and CIAC-130 are the highest nuclearity discrete clusters of Co, Ni and Fe reported so far. CIAC-128 has higher separation selectivity of C3H8 than CH4 under ambient conditions, and also exhibits separation selectivity for C2H6/CH4, C2H2/CH4, and C2H4/CH4. In addition, CIAC-128 can provide the cavity for the confined synthesis of noble metal nanoclusters such as Pd nanoclusters and the resulting Pd@CIAC-128 hybrids show higher electrocatalytic activity than commercial Pt/C towards hydrogen evolution reaction (HER).