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首页> 外文期刊>Crystal growth & design >Control of the crystallization process and structure dimensionality of Mg-benzene-1,3,5-tricarboxylates by tuning solvent composition
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Control of the crystallization process and structure dimensionality of Mg-benzene-1,3,5-tricarboxylates by tuning solvent composition

机译：通过调节溶剂组成控制Mg-苯-1,3,5-三羧酸镁盐的结晶过程和结构尺寸

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摘要

Four new magnesium 1,3,5-benzenetricarboxylate metal-organic framework materials (NICS-n; n = 3-6) were synthesized solvothermally in the presence of solvents with different EtOH/H_2O ratios. We showed that the crystallization process of the Mg-1,3,5-benzentricarboxylate system strongly depends on the solvent composition, and that dimensionality of their structures can be tuned by changing the EtOH/water ratios in the reaction mixture. The presence of only water as a solvent yields the zero-dimensional molecular structure of Mg(H_2BTC)_2(H_2O)_4 (NICS-3). One-dimensional (1D) chainlike Mg_3(BTC)_2(H _2O)_(12) (NICS-4) and two-dimensional (2D) layered Mg _2(BTC)(OH)(H_2O)_4·2H_2O (NICS-5) structures were crystallized from EtOH/H_2O mixtures with molar ratios of 0.3 and 0.4-0.7, respectively. The crystallization in pure ethanol yields Mg_3(BTC)_2 material (NICS-6) with three-dimensional structure. Nuclear magnetic resonance investigations indicated that bulkier clusters of Mg species are formed in ethanol-rich solutions, even in the absence of the BTC ligand, and that the starting precursors formed with the reaction of Mg species and the BTC ligand at room temperature does not represent the final structures obtained by solvothermal reactions. NICS-4 and NICS-5 are formed from similar starting precursors but slightly different EtOH/H_2O ratios causing the crystallization to go in two different directions. Systematic investigation of phase formation using different EtOH/H_2O ratios, times, and temperatures of the synthesis along with the computational DFT studies confirmed that the 2D NICS-5 structure represents a thermodynamically more stable phase than 1D chainlike NICS-4. We showed that solvothermal reaction between Mg-precursors and the BTC ligand in EtOH/water mixture represents a complex and sensitive thermodynamic process.
机译：在具有不同EtOH / H_2O比的溶剂存在下，溶剂热合成了四种新型的1,3,5-苯三甲酸镁金属有机骨架材料（NICS-n; n = 3-6）。我们表明，Mg-1,3,5-苯三羧酸酯体系的结晶过程在很大程度上取决于溶剂的组成，并且可以通过改变反应混合物中EtOH /水的比例来调整其结构尺寸。仅水作为溶剂的存在会产生Mg（H_2BTC）_2（H_2O）_4（NICS-3）的零维分子结构。一维（1D）链状Mg_3（BTC）_2（H _2O）_（12）（NICS-4）和二维（2D）层状Mg _2（BTC）（OH）（H_2O）_4·2H_2O（NICS- 5）从EtOH / H_2O混合物中分别以0.3和0.4-0.7的摩尔比结晶结构。在纯乙醇中结晶产生具有三维结构的Mg_3（BTC）_2材料（NICS-6）。核磁共振研究表明，即使在没有BTC配体的情况下，即使在没有BTC配体的情况下，在富含乙醇的溶液中仍会形成较大的Mg团簇，并且在室温下由Mg物种与BTC配体反应形成的起始前体并不代表通过溶剂热反应获得的最终结构。 NICS-4和NICS-5由相似的起始前体形成，但EtOH / H_2O的比例略有不同，导致结晶沿两个不同的方向进行。使用不同的EtOH / H_2O比率，合成时间和合成温度对系统的相形成进行系统研究，并通过计算DFT研究证实，与1D链状NICS-4相比，2D NICS-5结构在热力学上更稳定。我们表明，EtOH /水混合物中Mg前体与BTC配体之间的溶剂热反应代表了复杂而敏感的热力学过程。

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