An in situ high-temperature single-crystal investigation of a dehydrated metal-organic framework compound and field-induced magnetization of one-dimensional metaloxygen chains
An in situ high-temperature single-crystal investigation of a dehydrated metal-organic framework compound and field-induced magnetization of one-dimensional metaloxygen chains
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DOI：
10.1002/anie.200501508
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发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Fjellvåg, H
中科院分区：
文献类型：
--
作者：
Dietzel, PDC;Morita, Y;Fjellvåg, H
6512 2005 Wiley-VCH Verlag GmbH & Co. KGaA，魏因海姆Angew. 2005，117，6512-6516中所述。其脱水形式的原位电子晶体X射线研究表明，最初与金属中心配位的水分子在溶剂消除过程中也被除去。然而，该框架保持稳定，与钴原子的配位环境从八面体到四方锥形的变化。合成的化合物反铁磁秩序低于8 K，但随后通过一个变磁相变显示场诱导铁磁有序。乙酸钴（II）与2，5-二羟基对苯二甲酸（C_8H_6O_6）在聚四氟乙烯内衬的高压釜中（50%填充量），在1108 ℃的自生压力下，在水和四氢呋喃（摩尔比2：1：556：165）的混合溶剂中反应，得到粉红色针状结晶物[Co_2（C_8H_2O_6）（H_2O）_2]·8H_2O（1）。元素分析的结果证实，即使在合成中使用溶剂混合物，通道也仅被水分子占据。晶体结构分析揭示了具有蜂窝拓扑结构的三维配位聚合物，其包含一维溶剂填充通道（图1a）。钴原子以扭曲的八面体方式与六个氧原子配位。五个氧原子是有机配体的一部分，其利用其所有氧原子与钴中心形成配位键。钴中心的第六个氧配体来自水分子。其中四个距离在2.03和2.06之间，而第五个距离是2.190（5）。水分子是反式的，它的钴氧键也是拉长的（2.158（7））。氢氧化物氧原子和羧酸根氧原子中的一个各自配位两个钴原子，而第二羧酸根氧原子仅配位一个钴原子。这种配位排列导致钴氧八面体通过顺式取向的边缘连接（图1b），使得钴原子形成平行于c轴的三重螺旋。骨架拓扑结构与最近描述的[Zn 2（C8 H2O 6）（dmf）2]·（H2O）2（dmf= N，N-二甲基甲酰胺）相同。[7]假设除去通道中的非配位溶剂分子后，空通道占晶胞总体积的49%，平均横截面通道尺寸为11.08 × 11.08 × 2。如果配位水也被除去，空体积增加到60%。不包括配位水的水分子和包括配位水的水分子分别占质量的29.2%和36.6%。我们发现，通过在干燥氩气流中加热至100 ℃，然后冷却并将水蒸气与惰性气体流混合，可以重复地使化合物1脱水和水合。室温下的干燥气流实际上足以在43小时内除去90%的水。在加热实验期间的重量损失的量表明，配位结合的水分子也被去除。事实上，这是通过在958 ℃下的原位单晶结构测定证实的，该测定显示三维框架在脱水后实际上保持完整。由于配位水分子的解离，钴中心仍处于四方锥配位环境中。
6512 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. 2005, 117, 6512–6516 containing metal–organic framework. The in situ singlecrystal X-ray investigation of its dehydrated form reveals that a water molecule originally coordinated to the metal center is removed as well in the course of the solvent elimination. However, the framework remains stable, with the coordination environment of the cobalt atom changing from octahedral to square pyramidal. The as-synthesized compound orders antiferromagnetically below 8 K, but it subsequently passes through a metamagnetic phase transition to display field-induced ferromagnetic ordering. The reaction of cobalt (ii) acetate and 2, 5-dihydroxyterephthalic acid (C8H6O6) in a mixture of water and tetrahydrofuran (molar ratio 2: 1: 556: 165) under autogenous pressure at 1108C in a Teflon-lined autoclave (50% filling level) yielded the pink-red, needle-shaped crystalline substance [Co2 (C8H2O6)(H2O) 2]· 8 H2O (1). The results of the elemental analysis confirm that the channels are occupied solely by water molecules even though a solvent mixture was used in the synthesis. The crystal structure analysis revealed a threedimensional coordination polymer with honeycomb topology that contains one-dimensional, solvent-filled channels (Figure1a). The cobalt atom is coordinated in a distorted octahedral fashion by six oxygen atoms. Five of the oxygen atoms are part of the organic ligand, which utilizes all of its oxygen atoms in coordinative bonds with the cobalt center. The sixth oxygen ligand at the cobalt center comes from a water molecule. Four of the CoÀO distances are in the range between 2.03 and 2.06, while the fifth CoÀO distance is 2.190 (5). The water molecule is trans to this bond, and its CoÀO bond is also elongated (2.158 (7)). The hydroxide oxygen atom and one of the carboxylate oxygen atoms coordinate two cobalt atoms each, while the second carboxylate oxygen coordinates only one cobalt atom. This coordination arrangement results in cobalt–oxygen octahedra that are linked by cis-oriented edges (Figure 1b) such that the cobalt atoms form a threefold helix parallel to the c axis. The framework topology is identical to that recently described for [Zn2 (C8H2O6)(dmf) 2]·(H2O) 2 (dmf= N, N-dimethylformamide).[7]After the hypothetical removal of the noncoordinating solvent molecules in the channels, the empty channels occupy 49% of the total volume of the unit cell, and the average cross-sectional channel dimensions are 11.08 11.08 2. The empty volume increases to 60% if the coordinating water is also removed. The water molecules excluding and including the coordinating water account for 29.2% and 36.6% of the mass, respectively. We found that it was possible to repeatedly dehydrate and hydrate compound 1 by heating to 1008C in a dry argon gas stream and then cooling down and admixing water vapor with the inert gas stream. A dry gas stream at room temperature actually suffices to remove 90% of the water within 43h. The amount of weight loss during the heating experiments indicates that the coordinatively bound water molecules are also removed. Indeed, this was confirmed by an in situ single-crystal structure determination at 958C which revealed that the three-dimensional framework actually remains intact upon dehydration. Because of the abscission of the coordinating water molecule, the cobalt center remains in a square-pyramidal coordination environ-