氯铝酸离子液体酸性的红外光谱探针和量子化学研究

文章采用吡啶探针红外光谱、吡啶递增吸附实验研究和量子化学理论计算相结合的方法深入研究了氯铝酸离子液体的酸性及氯铝酸离子液体Lewis酸位Al₂Cl-₇与吡啶吸附之间的相互作用机理。通过实验和理论计算研究发现，Al₂Cl-₇,AlCl-₄阴离子具有吸电性，能够吸引吡啶环上的孤对电子产生吸附作用，具有Lewis酸性，它们分别呈现吡啶探针红外光谱Lewis酸特征峰；通过红外光谱特征峰峰位、键长及电荷分布分析表明Al₂Cl-₇的酸性强于AlCl-₄；氯铝酸离子液体Lewis酸位Al₂Cl-₇与吡啶吸附的机理为：当吡啶含量小时，仅存在Py-Al₂Cl-₇吸附；当吡啶量增加到一定程度时，Py-Al₂Cl-₇配位络合物中的AlCl-₄容易与吡啶发生吸附解离为Py-AlCl-₄配位络合物和Py-AlCl₃配位络合物，导致离子液体吡啶递增吸附红外特征峰发生变化。

Studies on IR Spectroscopy and Quantum Chemical Calculation of Chloroaluminate Ionic Liquids Acidity

The acidity of chloroaluminate ionic liquids and the interaction mechanism of Lewis acid site Al2Cl-7 of chloroaluminate ionic liquid and pyridine were experimentally investigated by IR characterization by using pyridine as molecular probe and increasing pyridine adsorption,and theoretically confirmed by quantum chemical calculations at density functional theory(DFT) and ab initio levels.It was found that the anions,Al2Cl-7 and AlCl-4,which could withdraw lone pair electrons of pyridine,were characteristic of Lewis acid.Therefore,they displayed pyridine coordinated to Lewis acidic site using pyridine as probe.The acidity of Al2Cl-7 was found stronger than that of AlCl-4 by analyzing IR absorption frequency,bond length and charge distribution.The mechanism of forming and evolvement of the Lewis acid site Al2Cl-7 of chloroaluminate ionic liquid was proposed.When the amount of pyridine is small,only the adsorption state of Py-Al2Cl-7 exists.The highly Lewis acidic adsorption state of Py-Al2Cl-7 complex was converted into Py-AlCl-4 complex and Py-AlCl3 complex with increasing pyridine contents,leading to the changes in IR absorption spectra.