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Huge Deuterated Effect on Permittivity in a Metal–Organic Framework



Colorless block crystals of MOF (metal-organic framework) 1 and 2 were prepared in respective yields of 65 and 60 % by thermal treatment of HQA (HQA=6-methoxyl-(8S,9R)-cinchonan-9-ol-3-carboxylic acid) with ZnBr2 in either H2O or D2O and 2-butanol at 70 °C for 1–2 days. The MOFs 1 and 2 are isostructural, one-dimensional chains in which the local coordination geometry around the Zn center can be best described as a slightly distorted tetrahedron defined by two bromine atoms, one nitrogen atom of quinoline from HQA, and an oxygen atom of carboxylate from HQA. The nitrogen atom of the quinuclidine of HQA is protonated in a zwitterionic form. The MOFs 1 and 2 crystallize in a polar point group (C2, space group P21) which belongs to ferroelectric active compounds. MOFs 1 and 2 display both ferroelectric behavior and large dielectric constants. Interestingly, at low frequency range the dielectric response to water can achieve an approximate increase of more than 600 %. Crystal parameters: 1: C20H28Br2NO7Zn, M=619.62, monoclinic, P21, a=9.5711(8), b=12.0486(10), c=11.1972(9) Å, α=γ=90, β=98.4(2)°, V=1277.39(18) Å3, Z=2, ρcald=1.611 mg m−3, R1=0.0499, wR2=0.0982, μ=4.126 mm−1, S=1.015, Flack value=0.032(13); 2: C20H22D6Br2NO7Zn, M=625.66, monoclinic, P21, a=9.5650(9), b=12.0392(11), c=11.1973(10) Å, α=γ=90, β=98.44(2)°, V=1275.5(2) Å3, Z=2, ρcald=1.629 mg m−3, R1=0.0543, wR2=0.1072, μ=4.133 mm−1, S=1.056, Flack value=0.025(17).