【作者】 王勇；

【导师】 李浩然；

【作者基本信息】 浙江大学 ， 化学工程与技术， 2007， 博士

【摘要】 作为一类完全由离子构成的介质，离子液体具有与传统分子介质不同的内部环境。微观结构决定性质，对离子液体这种离子介质中各物质的相互作用和运动规律的细致研究有助于获得一些有别于分子介质的规律与知识。本论文从研究离子液体的内部相互作用出发，进一步扩展到离子液体和各种环境分子间的相互作用，采用量子化学计算、分子动力学模拟和实验相结合的方法，从多方位、多角度来研究离子液体中的各种相互作用。论文首先采用密度泛函理论对离子液体中阴阳离子之间的相互作用进行了研究。我们将咪唑阳离子的周围划分为多个区域，对这些区域中阴阳离子间的相互作用分别进行了研究。研究表明，在咪唑环的周围存在着多个活性区域，在这些区域里，阴阳离子间能形成稳定的离子对结构。咪唑阳离子能同时和1个、2个或者3个卤素阴离子形成离子氢键作用，但是不能同时和3个以上的卤素阴离子形成离子氢键作用。为加深对离子液体中阴阳离子之间相互作用关系的理解，我们进一步采用NBO（Natural Bond Orbital）和AIM（Atom in Molecule）的方法，以1-乙基-3-甲基咪唑氯盐（[emim][Cl]）和1-乙基-3-甲基咪唑溴盐（[emim][Br]）离子液体为例，对阴阳离子间形成的离子氢键进行了更深入的分析。研究发现，轨道重叠和电子转移对离子对的稳定性有较大的贡献。NBO分析表明阴离子的孤对电子和C₂-H反键轨道之间的n→σ^*作用能提供较大的稳定化能，它对整个离子对的稳定性起到了非常关键的作用。微量水的存在对离子液体的物理化学性质及其催化性能有显著的影响。我们采用量子化学计算的方法研究了离子液体中阳离子、阴离子及离子对和水分子之间的相互作用。发现阴阳离子以及离子对均能够和水分子形成强的氢键作用。基于计算的结论我们提出了阴离子（X^-=Cl^-、Br^-或BF₄^-）和水分子（W）之间相互作用的四种模式：X^-…W、2X^-…W（X=Cl、Br）、BF₄^-…W及W…BF₄^-…W。计算发现疏水性的阴离子PF₆^-不能和水分子形成稳定的构型，这很好地体现了PF₆^-阴离子的疏水性。咪唑阳离子也能够和水分子之间形成强氢键作用，其氢键键能范围在50～100 kJ／mol之间。这可能是疏水性的PF₆^-盐离子液体表现出一定亲水性的原因之一。相关研究表明，离子液体能显著地提高许多化学反应的反应速率和选择性，但是离子液体在反应中的催化机理十分复杂，要建立一套完整的理论模型来研究离子液体催化反应的机理非常困难。因此，有必要对体系进行适当地简化，从不同的角度来探讨离子液体对反应可能存在的影响。我们以Diels-Alder反应为例，通过研究离子液体和丙烯酸甲酯之间的相互作用来探讨离子液体对Diels-Alder反应的催化机理。研究发现离子液体能够有效地降低丙烯酸甲酯的LUMO轨道的能量，从而降低环戊二烯和丙烯酸甲酯HOMO和LUMO轨道间的能差，进而有效地促进Diels-Alder反应。更深入地研究发现，阳离子的静电荷能够显著地降低丙烯酸甲酯的LUMO轨道能量，这很好地解释了文献报道所发现的实验现象，能为以后设计新型离子液体催化Diels-Alder反应提供理论指导。具有温室效应的CO₂气体和能产生酸雨的SO₂气体浓度的增加是21世纪人类面临的最重要的环境问题之一。离子液体是一种潜在的吸收CO₂和SO₂的载体，从分子层面上研究离子液体与CO₂和SO₂之间的作用模式，能为设计开发对CO₂和SO₂具有高吸收率的新型离子液体提供理论指导。因此，我们开发了对CO₂及SO₂有特殊吸收性能的胍类离子液体的力场，并对CO₂及SO₂和离子液体体系进行了模拟研究，发现阴离子是造成CO₂和SO₂在胍类离子液体中溶解差异的主要原因。通过对径向分布函数的统计和分析，发现离子液体的阴阳离子中所含的活泼基团（如-NH2、-OH等）对CO₂及SO₂的吸收有重要的帮助。这个结论启发我们设计合成了两种含-NH₂基团的离子液体，测定了CO₂气体在两种离子液体中的溶解性能，发现二乙烯三胺醋酸盐离子液体是吸收CO₂气体的良好溶剂。通过以上研究，本论文建立了用实验、理论和计算机模拟研究离子液体体系中各种相互作用关系的初步框架，总结了离子介质中各种相互作用和微观结构之间的一些内在联系，为进一步研究离子液体中的相互作用关系以及离子液体的分子设计打下了坚实的基础。更多还原

【Abstract】 As a kind of new ionic solvents, the ionic liquids （ILs） have different internal environment compared with the tranditional molecular solvents. A systematic study of the interaction in the ILs might lead to a better understanding of their structure-activity relationship. In the present work, quantum chemical calculations, molecular dynamics are combined to investigate the interactions in the ILs.The interaction between the anion and the cation in the ILs was firstly focused on using the density functional theory （DFT）. Forty structures of different ion pairs were optimized and geometrical parameters of them have been discussed in details. Anions have been gradually placed in different regions around imidazolium cation and the interaction energies between the anion and the cation have been calculated. Theoretical results indicate that there are four active regions in the vicinity of the imidazolium cations, in these regions, the imidazolium cations and the halide anions formed stable ion pairs. Imidazolium cations can interact with one, two or three but no more than three nearest halide anions by forming hydrogen bond. The halide ions are situated in hydrogen bond positions rather than at random.In order to obtain deeper insight on the interaction between the cation and the anion, the natural bond orbital （NBO） and atom in molecular （AIM） were used to study the ion hydrogens in the ion pairs. Based on the calculation results, a better understanding of the origin of the interaction between the imidazolium cations and the anions. The nature of the ion hydrogens are mainly electrostatic, however, the charge transfer and orbital interaction can contribute significantly, thereby making the interaction partly covalent. In addition, the NBO analysis demonstrated that the stabilization energy isdue to the n→σ^* C-H orbital interaction.The presence of water could affect the activity of the ILs dramatically and it is often presented as a contaminant in hydrophilic as well as in hydrophobic ILs, significantly affecting their physical properties. Quantum chemical calculations have been used to investigate the interaction between the water molecules and ILs based on the imidazolium cation with different anions: [Cl^-], [Br^-], [BF₄^-], and [PF₆^-]. The predicted geometries, interaction energies implied that the water molecules interact with the Cl^-, Br^-, BF₄^- anions to form X^-…W （X=Cl or Br, W=H₂O）, 2X^-…2W, BF₄^-…W and W…BF₄^-…W complexes. The hydrophobic PF₆^- anion could not form stable complex with the water molecules at the DFT level. Further studies indicate that the cation could also form strong interaction with water molecules. The l-Ethyl-3-methylimidazolium cation （Emim⁺） has been used as a model cation to investigate the interaction between the water molecule and the cation. In addition, the interaction between the ion pairs and water were studied using the 1-ethyl-3-methylimidazolium chloride （[emim][Cl]） as a model ionic liquid. The strengths of the interactions in these categories follow the trend anion-W > cation-W > ion pair-W.The mechanism of how the ILs affect the Diels-Alder is an active area of ongoing research. A microscopic insight in the mechanism of the reaction via quantum chemical calculations was given, evidencing how the ILs affect the energy barrier and promot the reaction. The ILs can lower the dienophile LUMO and HOMO energies, bringing dienophile LUMO energy closer to the diene HOMO. The effect of the positive charge of the imidazolium cation was then estimated. It was surprised to find that the positive charge could decrease the LUMO_dienophile-HOMO_diene energy gap significantly. Based on these results, it could be predicted that the positive charge center of cation could affect the reaction significantly. These results provide opportunities in the design of future ILs catalytic systems for the organic reactions.The consuming of the CO₂ and the SO₂ has become a world-wide problem. The emerging of the ILs provides a new way for the absorption of the CO₂ and SO₂ gases. An all-atom force field is developed using a combination of density functional theory calculations and OPLS force field parameter values for the 1,1,3,3-Tetramethyl -guanidium Lactate （TMG） lactic acid （LAC） ionic liquid （TMGL）. Molecular dynamics simulations are then conducted to investigate the solubility of the SO₂ and CO₂ gases in the TMGL. The simulations show strong organization of SO₂ about the cation and the anion of the TMGL, but relatively weak organization of CO₂ about the cation and the anion of the TMGL, which well explained the selectivity of the TMGL toward the SO₂ and CO₂. Based on the calculations, it was found that the active groups such as the -NH2 and -OH has great effect on the absorbing of the SO₂ and CO₂, this inspired us to design two simple amine ILs which include the -NH₂ group. The experiment result demonstrates that the TECAc ionic liquid is a good solvent for CO₂.All in all, the chemical theory, computer simulations and experiment are combined to investigate the interaction relationship in the ILs. The frame of studing on interaction in ionic liquid is established to successfully reveal the structures and interactions in the systems. It could be expected that these methods are applicable to investigate more important phenomena in the ILs.更多还原