A Porous Framework Polymer Based on a Zinc(II) 4,4‘-Bipyridine-2,6,2‘,6‘-tetracarboxylate: Synthesis, Structure, and “Zeolite-Like” Behaviors

The robust metal−organic framework compound {[Zn2(L)]·4H2O}∞ I has been synthesized by
hydrothermal reaction of ZnCl2 and 4,4‘-bipyridine-2,6,2‘,6‘-tetracarboxylic acid (H4L). Compound I crystallizes
in a chiral space group, P42212, with the chirality generated by the helical chains of hydrogen-bonded
guest water molecules rather than by the coordination framework. Removal of guest water molecules from
the crystal affords the porous material, [Zn2(L)]∞ (II), which has very high thermal stability and is chemically
inert. The N2 isotherm of II at 77 K suggests a uniform porous structure with a BET surface area of 312.7
m2/g and a remarkably strong interaction with N2 molecules (βE0 = 29.6 kJ mol-1). II also exhibits significant
gas storage capacities of 1.08 wt % for H2 at 4 bar and 77 K and 3.14 wt % (44.0 cm3/g, 67 v/v) for
methane at 9 Bar at 298 K. The adsorption behavior of II toward organic solvent vapors has also been
studied, and isotherms reveal that for different solvent vapors adsorption is dominated by two types of
processes, absorbate−absorbate or absorbate−absorbent interactions. The adsorption and desorption
kinetic processes in II are determined mainly by the molecular size of the guest species and their interaction
with the host.

通过氯化锌（ZnCl₂）与4,4'-联吡啶-2,6,2',6'-四羧酸（H₄L）的水热反应，成功合成了稳定的金属有机框架（Metal-Organic Framework, MOF）化合物{[Zn₂(L)]·4H₂O}ₙ I。化合物I以手性空间群P42212结晶，其手性源于氢键结合的客体水分子螺旋链，而非配位骨架本身。脱去晶体中的客体水分子后，得到多孔材料[Zn₂(L)]ₙ（II），该材料具备极高的热稳定性与化学惰性。77 K下测得的II的氮气吸附等温线表明，其具有均一的多孔结构，BET比表面积为312.7 m²/g，且与氮气分子存在极强的相互作用（βE₀=29.6 kJ·mol⁻¹）。在储气量方面，II同样表现优异：77 K、4 bar条件下对氢气的吸附量可达1.08 wt%；298 K、9 bar条件下对甲烷的吸附量可达3.14 wt%（折合44.0 cm³/g，即67 v/v）。本研究还考察了II对有机溶剂蒸气的吸附行为，吸附等温线结果显示，针对不同溶剂蒸气的吸附过程主要由两类相互作用主导，即吸附质-吸附质相互作用与吸附质-吸附剂相互作用。II中的吸附与脱附动力学过程，主要由客体物种的分子尺寸及其与主体框架的相互作用所决定。