Physical/Materials Chemistry Division, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India.
J Am Chem Soc. 2011 Nov 9;133(44):17950-8. doi: 10.1021/ja2078637. Epub 2011 Oct 13.
Four new homochiral metal-organic framework (MOF) isomers, Zn(l-L(Cl))(Cl)(2) (1), Zn(l-L(Br))(Br)(2) (2), Zn(d-L(Cl))(Cl)(2) (3), and Zn(d-L(Br))(Br)(2) (4) [L = 3-methyl-2-(pyridin-4-ylmethylamino)butanoic acid], have been synthesized by using a derivative of L-/D-valine and Zn(CH(3)COO)(2)·2H(2)O. A three-periodic lattice with a parallel 1D helical channel was formed along the crystallographic c-axis. Molecular rearrangement results in an unprecedented zeolitic unh-topology in 1-4. In each case, two lattice water molecules (one H-bonded to halogen atoms) form a secondary helical continuous water chain inside the molecular helix. MOFs 1 and 2 shows different water adsorption properties and hence different water affinity. The arrangement of water molecules inside the channel was monitored by variable-temperature single-crystal X-ray diffraction, which indicated that MOF 1 has a higher water holding capacity than MOF 2. In MOF 1, water escapes at 80 °C, while in 2 the same happens at a much lower temperature (∼40 °C). All the MOFs reported here shows reversible crystallization by readily reabsorbing moisture. In MOFs 1 and 2, the frameworks are stable after solvent removal, which is confirmed by a single-crystal to single-crystal transformation. MOFs 1 and 3 show high proton conductivity of 4.45 × 10(-5) and 4.42 × 10(-5) S cm(-1), respectively, while 2 and 4 shows zero proton conductivity. The above result is attributed to the fact that MOF 1 has a higher water holding capacity than MOF 2.
四种新的手性金属有机骨架（MOF）异构体，Zn(l-L(Cl))(Cl)(2)（1），Zn(l-L(Br))(Br)(2)（2），Zn(d-L(Cl))(Cl)(2)（3）和Zn(d-L(Br))(Br)(2)（4）[L = 3-甲基-2-（吡啶-4-基甲基氨基）丁酸]，通过使用 L-/D-缬氨酸和 Zn(CH(3)COO)(2)·2H(2)O 的衍生物合成。沿晶轴形成了一个具有平行的 1D 螺旋通道的三周期格子。分子重排导致在 1-4 中形成了前所未有的沸石 unh-topology。在每种情况下，两个晶格水分子（一个与卤素原子氢键结合）在分子螺旋内形成二级螺旋连续水链。MOFs 1 和 2 表现出不同的水吸附性能，因此具有不同的亲水性。通过变温单晶 X 射线衍射监测通道内水分子的排列，表明 MOF 1 比 MOF 2 具有更高的持水能力。在 MOF 1 中，水在 80°C 时逸出，而在 2 中，相同的情况发生在低得多的温度（约 40°C）。所有报告的 MOFs 通过易于重新吸收水分而显示出可逆结晶。在 MOFs 1 和 2 中，在除去溶剂后框架是稳定的，这通过单晶到单晶的转变得到证实。MOFs 1 和 3 分别显示出 4.45×10(-5)和 4.42×10(-5)S cm(-1)的高质子电导率，而 2 和 4 则显示出零质子电导率。上述结果归因于 MOF 1 比 MOF 2 具有更高的持水能力。
