Temperature-controlled chiral and achiral copper tetrazolate metal-organic frameworks: Syntheses, structures, and I _2 adsorption

摘要

Four tetrazole-based three-dimensional (3D) metal- organic frameworks (MOFs), {[Cu ~II(btz)]·0.5H _2O} _n (1), [Cu ~II(btz)]n (1'), {[Cu ~II(btz)]·0.5I _2} _n (1'·0.5I _2), and [Cu ~IICu I _2(btz) _2] _n (2) [H _2btz = 1,5-bis(5-tetrazolo)-3-oxapentane)], have been successfully obtained and characterized by crystallography. Compound 1 features a chiral porous framework. The bulk crystallization of 1 is composed of enantiomers 1a (P4 _1) and 1b (P4 _3), which has been demonstrated by the crystal structure analyses of nine crystals of 1 randomly selected. The Cotton effect displayed in the solid-state circular dichroism spectrum of 1 is therefore attributed to enantiomeric excess rather than enantiopurity. The completely dehydrated phase of 1, that is, 1', can adsorb 0.5 I _2 molecule per formula unit to yield compound 1'·0.5I _2, which has been supported by single-crystal X-ray diffraction, elemental analysis, and thermogravimetric analysis. The locations of I _2 in the pores were unambiguously determined, and the interactions between I _2 molecules and the pore structures were investigated. Compound 2 crystallizes in an achiral C2/c space group. Interestingly, the formations of chiral 1 and achiral 2 significantly depend on the reaction temperature. Between 80 and 140 °C, we got compound 1 as the only product. At 150 °C, both 1 and 2 were in coexistence in the final product. From 160 to 180 °C, only compound 2 was obtained. More interestingly, treatment of the crystals of 1 or the mixture of 1 and 2 obtained at 150 °C in their mother liquor at 170 °C yielded the crystals of 2 in a single phase.