A Heterometallic Porous Material for Hydrogen Adsorption

Two kinds of heterometallic complexes, {[Sm2(L)6Co2][Co(H2O)6]·3H2O}n (Sm−Co) and {[Sm2(L)6Zn3(H2O)6]·1.5H2O}n (Sm−Zn) (H2L = oxydiacetic acid), were synthesized under hydrothermal conditions. In Sm−Co, each L chelates to one Sm3+ center and bonds to two Co2+ ions in an anti-anti configuration. Sm and Co atoms are arrayed alternatively and connected by O−C−O bridges to form a cubic octahedral cage as the secondary building unit. Consequently, topological NaCl nets with high symmetry in the cubic space group Fd3̄c have been constructed. It is interesting to note that Sm−Co contains interesting 2-fold interpenetrating 3D hydrogen-bonding supramolecular networks while in Sm−Zn each L adopts a syn-syn configuration to link two Zn2+ ions. Carboxylate groups bridge adjacent Sm and Zn atoms to create two kinds of metallocycles, Sm2(COO)4Zn2 and Sm6(COO)12Zn6, to be further assembled into a highly ordered 3D nanotubular structure. Sm−Zn represents the largest porous material among the heterometallic coordination polymers and the first example in the investigation of hydrogen adsorption. Sm−Zn possesses hydrogen storage capacity of up to 1.19 wt % at 77 K and 0.54 wt % at 298 K, respectively.