Pike Sarah J, Lavagnini Ennio, Varley Lisa M, Cook Joanne L, Hunter Christopher A
Department of Chemistry , University of Cambridge , Lensfield Road , Cambridge , CB2 1EW , UK . Email:
Department of Chemistry , University of Sheffield , Sheffield , S3 7HF , UK.
Chem Sci. 2019 May 16;10(23):5943-5951. doi: 10.1039/c9sc00721k. eCollection 2019 Jun 21.
UV/Vis absorption and NMR spectroscopy titrations have been used to investigate the formation of complexes between cations and neutral H-bond acceptors in organic solvents. Complexes formed by two different H-bond acceptors with fifteen different cations were studied in acetone and in acetonitrile. The effects of water and ion pairing with the counter-anion were found to be negligible in the two polar solvents employed for this study. The data were used to determine self-consistent H-bond donor parameters () for a series of organic and inorganic cations; guanidinium, primary, tertiary and quaternary ammonium, imidazolium, methylpyridinium, lithium, sodium, potassium, rubidium and caesium. The results demonstrate the transferability of parameters for cations between different solvents and different H-bond acceptor partners, allowing reliable prediction of cation recognition properties in different environments. Lithium and protonated nitrogen cations form the most stable complexes, but the parameter is only 5.0, which is similar to the neutral H-bond donor 3-trifluoromethyl,4-nitrophenol ( = 5.1). Quaternary ammonium is the weakest H-bond donor investigated with an value of 2.7, which is comparable to an alcohol. The parameters for alkali metal cations decrease down the group from 5.0 (Li) to 3.5 (Cs).
紫外/可见吸收光谱和核磁共振光谱滴定法已被用于研究有机溶剂中阳离子与中性氢键受体之间配合物的形成。在丙酮和乙腈中研究了由两种不同的氢键受体与十五种不同阳离子形成的配合物。在本研究使用的两种极性溶剂中，发现水和离子与抗衡阴离子的配对效应可忽略不计。这些数据用于确定一系列有机和无机阳离子（胍盐、伯铵、叔铵和季铵、咪唑鎓、甲基吡啶鎓、锂、钠、钾、铷和铯）的自洽氢键供体参数（）。结果表明，阳离子的参数在不同溶剂和不同氢键受体伙伴之间具有可转移性，从而能够可靠地预测不同环境中的阳离子识别特性。锂和质子化氮阳离子形成最稳定的配合物，但其参数仅为5.0，这与中性氢键供体3-三氟甲基-4-硝基苯酚（=5.1）相似。季铵是所研究的最弱的氢键供体，其值为2.7，与醇相当。碱金属阳离子的参数在该族中从5.0（锂）降至3.5（铯）。
