7Li NMR chemical shift titration and theoretical DFT calculation studies: solvent and anion effects on second-order complexation of 12-crown-4 and 1-aza-12-crown-4 with lithium cation in several aprotic solvents.
7Li NMR chemical shift titration and theoretical DFT calculation studies: solvent and anion effects on second-order complexation of 12-crown-4 and 1-aza-12-crown-4 with lithium cation in several aprotic solvents.
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7Li NMR化学位移滴定和理论DFT计算研究：溶剂和阴离子对12-crown-4和1-aza-12-crown-4与锂阳离子在几种非质子溶剂中的二级络合的影响。
DOI：
10.1002/mrc.2542
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
Eyring,EdwardM
中科院分区：
文献类型：
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作者：
Masiker,MarilynC;Mayne,CharlesL;Boone,BrianJ;Orendt,AnitaM;Eyring,EdwardM
采用7 Li NMR滴定法测定了锂阳离子与12-冠-4在乙腈、碳酸丙烯酯以及碳酸丙烯酯和碳酸二甲酯二元混合物中的二级络合常数。使用的阴离子是高氯酸盐、六氟磷酸盐和三氟甲磺酸盐。类似地研究了第二配体1-氮杂-12-冠-4。在这些反应中，游离阳离子和络合阳离子之间的交换在NMR时间尺度上是快速的，导致单个锂峰，其是游离和结合物质的浓度加权平均值。溶剂效应表明1：1络合物在乙腈中比在碳酸丙烯酯或碳酸丙烯酯碳酸二甲酯混合物中稳定得多。给定溶剂的阴离子效应很小。自由配体和1：1和1：2（夹心）金属-配体络合物的优化几何形状通过混合密度泛函理论使用Gaussian 03软件包预测。结果进行了比较，文献值为1：1的稳定常数，发现这些系统中的几个微量热法，并被发现是在良好的协议。虽然微量热法只考虑了1：1络合物的形成，但7 Li NMR显示了1：1和1：2络合物都应考虑的证据。版权所有© 2009约翰威利父子有限公司。
7Li NMR titration was used to determine stepwise complexation constants for the second‐order complexation of lithium cation with 12‐crown‐4 in acetonitrile, propylene carbonate and a binary mixture of propylene carbonate and dimethyl carbonate. The anions used were perchlorate, hexaflurophosphate and trifluromethanesulfonate. A second ligand 1‐aza‐12‐crown‐4 was similarly investigated. The exchange between the free and complexed cation in these reactions is fast on an NMR timescale resulting in a single lithium peak which is a concentration‐weighted average of the free and bound species. Solvent effects show that the 1:1 complex is much more stable in acetonitrile than in propylene carbonate or in the propylene carbonate dimethyl carbonate mixture. Anion effects for a given solvent were small. Optimized geometries of the free ligands and the 1:1 and 1:2 (sandwich) metal–ligand complexes were predicted by hybrid‐density functional theory using the Gaussian 03 software package. Results were compared to literature values for 1:1 stability constants found by microcalorimetry for several of these systems and are found to be in good agreement. Although microcalorimetry only considered the formation of 1:1 complexes,7Li NMR shows evidence that both 1:1 and 1:2 complexes should be considered. Copyright © 2009 John Wiley & Sons, Ltd.