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Keywords:

  • coordination networks;
  • host–guest systems;
  • hydrogen bonds;
  • lanthanides

Abstract

Two series of microporous lanthanide coordination networks of the general formula, {[Ln(ntb)Cl3]x H2O}n (series 1: monoclinic C2/c, Ln=Sm and Tb; series 2: hexagonal P31/c, Ln=Sm and Eu; ntb=tris(benzimidazol-2-ylmethyl)amine, x=0–4) have been synthesized and characterized by IR, elemental analyses, thermal gravimetry, and single-crystal and powder X-ray diffraction methods. In both series, the monomeric [Ln(ntb)Cl3] coordination units are consolidated by N[BOND]H⋅⋅⋅Cl or C[BOND]H⋅⋅⋅Cl hydrogen bonds to sustain three-dimensional (3D) networks. However, the different modes of hydrogen bonding in the two series lead to crystallization of the same [Ln(ntb)Cl3] monomers in different forms (monoclinic vs. hexagonal), consequently giving rise to distinct porous structures. The resulting hydrogen-bonded coordination networks display high thermal stability and robustness in water removal/inclusion processes, which was confirmed by temperature-dependent single-crystal-to-single-crystal transformation measurements. Adsorption studies with H2, CO2, and MeOH have been carried out, and reveal distinct differences in adsorption behavior between the two forms. In the case of MeOH uptake, the monoclinic network shows a normal type I isotherm, whereas the hexagonal network displays dynamic porous properties.