Thermally Stable Porous Hydrogen-Bonded Coordination Networks Displaying Dual Properties of Robustness and Dynamics upon Guest Uptake

Two series of microporous lanthanide coordination networks of the general formula, {[Ln(ntb)Cl-3]center dot xH(2)O}(n) (series 1: monoclinic C2/c, Ln=Sm and Tb; series 2: hexagonal P3(1)/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)Cl-3] coordination units are consolidated by N-H center dot center dot center dot Cl or C-H center dot center dot center dot 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)Cl-3] 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 H-2, 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 nonoclinic network shows a normal type I isotherm, whereas the hexagonal network displays dynamic Porous properties.