Key Laboratory of Macromolecular Science of Shaanxi Province, Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering , Shaanxi Normal University , Xi'an , Shaanxi 710062 , China.
Department of Chemistry and Chemical Engineering, Laboratory of New Energy and New Function Materials, Key Laboratory of Analytical Technology and Detection , Yan'an University , Yan'an , Shaanxi 716000 , China.
Inorg Chem. 2018 Nov 19;57(22):14280-14289. doi: 10.1021/acs.inorgchem.8b02312. Epub 2018 Nov 5.
During the formation of magnesium-organic frameworks, the coordination sphere of magnesium tends to be partially occupied by O-containing solvent molecules such as amides, which will dramatically decrease the symmetry of Mg-organic frameworks and thus lead to low stability. It is noted that up to now, most reported Mg-metal-organic frameworks (MOFs) (>80%) crystallize in the space groups whose symmetry is lower than that of a tetragonal system. In this work, we demonstrate that acetate (Ac) may act as modulator to eliminate the influence of amide solvent and improve the symmetry of Mg-organic frameworks. Two novel Mg-MOFs, namely, {[(CH)NH][Mg(BTB)(Ac)(HO)]} (SNNU-35, HBTB = 4',4'',4'''-benzene-1,3,5-tribenzoic acid) and {[(CH)NH][Mg(FDA)(Ac)]} (SNNU-36, HFDA = 2,5-furandicarboxylic acid) were successfully designed, which crystallize in rhombohedral R-3 and tetragonal I4 /mmm space groups, respectively. Four independent BTB ligands link three unique Mg cations and generate superlarge [MgBTB] nanocages, which interlock each other by strong π···π stacking to give a two-fold interpenetrating architecture of SNNU-35. On the other hand, carboxylate and acetate groups chelate Mg atoms to form one-dimensional chains, which are extended by FDA to produce the rod-packing framework of SNNU-36. Two microporous Mg-MOFs both exhibit notable CO and H uptakes. HBTB and HFDA ligands both have emission features, and Mg ions usually can enhance the fluorescent intensity, which lead to a strong solid-state luminescence emission property of SNNU-35 and -36. Importantly, two Mg-MOFs both show fast and quantative sensing performance for nitrocompounds. Among three selected models of substrate, SNNU-35 and -36 can eliminate the interference of nitromethane (NM) and exhibit high sensitivity to nitrobenzene (NB) and o-nitrotoluene (2-NT) with large k values (>10 M). Especially, the fluorescence quenching efficiency of NB (5000 ppm) and 2-NT (8000 ppm) can reach 96.3% and 89.5% and 85.0% and 83.7% for SNNU-35 and -36, respectively. This work offers not only an effective route to improve the symmetry of magnesium-organic frameworks but also two potential fluorescence sensors for nitroaromatic compounds.
在镁有机骨架的形成过程中，镁的配位球倾向于被酰胺等含氧溶剂分子部分占据，这将显著降低镁有机骨架的对称性，从而导致其稳定性降低。值得注意的是，到目前为止，大多数报道的镁金属有机骨架（MOFs）（>80%）在对称性低于四方晶系的空间群中结晶。在这项工作中，我们证明了乙酸盐（Ac）可以作为调节剂，消除酰胺溶剂的影响，提高镁有机骨架的对称性。我们成功设计了两种新型的 Mg-MOFs，即 {[(CH)NH][Mg(BTB)(Ac)(HO)]} （SNNU-35，HBTB = 4'，4''，4''' - 苯 -1,3,5-三苯甲酸）和 {[(CH)NH][Mg(FDA)(Ac)]} （SNNU-36，HFDA = 2,5-呋喃二甲酸），它们分别结晶在三方 R-3 和四方 I4 / mmm 空间群中。四个独立的 BTB 配体连接三个独特的 Mg 阳离子，生成超大的[MgBTB]纳米笼，通过强π···π堆积相互扣合，形成 SNNU-35 的双互穿结构。另一方面，羧酸盐和乙酸盐基团螯合 Mg 原子形成一维链，FDA 将其扩展形成 SNNU-36 的棒状堆积骨架。两种微孔 Mg-MOFs均表现出显著的 CO 和 H 吸附性能。HBTB 和 HFDA 配体均具有发射特征，而 Mg 离子通常可以增强荧光强度，导致 SNNU-35 和 -36 具有强烈的固态发光发射特性。重要的是，两种 Mg-MOFs 对硝基化合物均具有快速和定量的传感性能。在三种选定的底物模型中，SNNU-35 和 -36 可以消除硝基甲烷（NM）的干扰，并对硝基苯（NB）和邻硝基甲苯（2-NT）表现出高灵敏度，k 值较大（>10 M）。特别是，NB（5000 ppm）和 2-NT（8000 ppm）对 SNNU-35 和 -36 的荧光猝灭效率分别可达 96.3%和 89.5%和 85.0%和 83.7%。这项工作不仅提供了一种有效提高镁有机骨架对称性的途径，而且还提供了两种用于检测硝基芳香族化合物的潜在荧光传感器。
