【作者】 赵强；

【导师】 冯大诚； 郝京诚；

【作者基本信息】 山东大学 ， 理论与计算化学， 2011， 博士

【摘要】 卤键是由卤原子(路易斯酸)与中性的或者带负电的路易斯碱之间形成的非共价相互作用。作为平行于氢键的一种分子间相互作用,卤键在分子识别、手性拆分、晶体工程和超分子组装等很多领域有着广泛的应用。另外在生命科学领域,卤键的重要性也初露端倪,这为基于结构的药物设计提供了新的思路。基于卤键与氢键的相似性,某一路易斯碱既可以作为卤键的电子给体,也可以作为氢键的电子给体。在具体的复合物中,这两种分子间相互作用存在竞争效应。在一个超分子中,可能同时卤键与氢键相互作用,这两种相互作用之间存在协同效应,即相互增加,或相互减弱,或有的增加,有的减弱。卤键R-X…Y(X为卤原子,Y为电子给体)形成过程中,R-X键的键长通常会发生变化,振动频率也会相应减小或增大。键缩短,频率增大的为蓝移卤键；而键伸长,频率减小的为红移卤键。取代基对卤键与氢键的强度有很大影响。一般来说,吸电子基使电子给体亲核能力减弱,使电子受体亲电能力增加,而给电子基使电子给体亲核能力增加,使电子受体亲电能力减弱。本论文对一些卤键与氢键复合物中两者的竞争效应和协同效应、蓝移卤键的化学本质以及取代基(主要为甲基和过渡金属元素)对卤键强度的影响进行了理论计算方面的研究。本论文的主要研究内容如下：1.在MP2/6-311++G(2d,2p)(其中碘采用赝势基组)水平下研究了次卤酸HOX(X=F,Cl,Br,I)与C6H6形成的氢键、卤键复合物。我们研究了次卤酸分子的静电势分布,分析了复合物的能量性质,并运用NBO与AIM分析了轨道相互作用、电荷转移以及键的拓扑性质。得出以下结果：(1)HOCl、HOBr、和HOI可以与C6H6形成氢键、卤键复合物,而HOF只能形成氢键复合物,这与HOX的静电势分布有关：HOF只有一个最大正静电势点,而其它次卤酸分子有两个。(2)卤键复合物的相互作用能顺序与次卤酸的静电势顺序一致,静电相互作用处于主导地位；氢键复合物的相互作用能顺序与次卤酸的静电势顺序相反,色散相互作用对体系起主要稳定作用。(3)氢键与卤键存在竞争效应,除HOI外,其它的复合物都是氢键比卤键更稳定。(4)NBO分析的结果表明,电子从C6H6转移到了HOX上,二阶稳定化能和电荷转移量的变化都符合相互作用能的变化规律。AIM分析的结果表明,此类氢键和卤键相互作用属于弱氢键、弱卤键,这与相互作用能的数值相吻合。2.用量子化学方法研究了XY…HNC…XY(X,Y=F,Cl,Br)形成的三元复合物中氢键和卤键的协同作用。分别计算了二元体系和三元体系中氢键和卤键的相互作用能以及协调能Ecoop,计算结果表明三元体系中的氢键和卤键相对于二元体系都所增强。我们分析了氢键和卤键相互作用能变化的绝对量和相对百分比,提出了两种加强氢键与卤键分子识别的思路：(1)引入的第二个卤键(或氢键)相互作用越大,原本的氢键(或卤键)得到的强化作用也就越强；(2)如果要加强一个氢键或卤键相互作用,那么最好引入一个比之强的卤键或氢键相互作用,而不要引入与之相当或比之弱的相互作用。我们分析了HNC分子的振动频率在形成复合物过程中的变化,发现N-H不对称伸缩频率蓝移,H-N-C对称伸缩频率红移。振动频率的变化量与相互作用能的变化一致。我们计算了复合物生成过程中体系偶极矩的变化,发现二元复合物和三元复合物的偶极矩较单体来说都有增加,并且三元复合物的增加量要比二元复合物大。我们对复合物的电子结构进行了AIM分析,计算了复合物BCP处电子密度的变化,发现三元复合物BCP处电子密度比二元复合物的大,这与相互作用能的分析相吻合。3.用量子化学的方法在MP2/aug-cc-pVDZ水平下研究了CFnH3-nCl(n=0～3)与H2O、H2S、NH3以及Br-等电子给体之间形成的卤键复合物。在这些复合物中,C-C1键较CFnH3-nCl单体都有所缩短。AIM分析的结果表明,C-C1键BCP处的电子密度值和Laplacian值都有所增加；NBO分析的结果表明,C-C1键的Wiberg键级增大。以上结果证实,C-C1键的键长减小对应着键的强度的加强。我们利用分子间超共轭、分子内超共轭与分子轨道重杂化的理论解释了C-C1键缩短的化学本质。我们定义了ΔAP,用来表征C-C1键轨道布局数变化的综合效应,并认为卤键复合物形成过程中C-C1键是否缩短主要由ΔAP和%AS决定。4.用量子化学的方法在MP2/6-311++G**水平下研究了MenH3-nY(Y=N,P; n=0,1,2,3)…XF(X=Cl,Br)的卤键复合物。首先,我们对比MenH2-nY(Y=O,S;n=0,1,2),从静电势和轨道能量两个方面讨论了甲基取代对电子给体性质的影响,解释了一些实验与理论计算结果。我们发现,由于MenH3-nY(Y=N,P;n=0, 1,2,3)…XF(X=Cl,Br)复合物中分子的变形特别大,造成了一些特殊的现象：P系列复合物的电荷转移量,偶极矩增加量以及双卤分子键长的增加量要比相应的N系列复合物大得多。如果考虑分子变形能对整体相互作用能的影响,除了NH3和PH3以外,其它P系列的复合物稳定性要比相应的N系列复合物大得多。这与我们得到的静电势与轨道能量差异性是不相符的。由此可见,MenH3-nY(Y=N, P;n=0,1,2,3)…XF(X=Cl,Br)的卤键复合物与O和S为电子给体的卤键复合物是有本质不同的,前者更接近于inner Mulliken complex,而后者更接近outer Mulliken complex.5.用量子化学的方法在MP2/6-311++G**研究了过渡金属Cu,Ag和Au取代卤代烷烃CH3X(X=F,Cl,Br)作为电子给体,与FCl分子之间的卤键相互作用。CH3X…ClF只有一种稳定结构：CH3X中的两个氢原子朝向FCI中的氯原子。CH2CuX…ClF和CH2AgX…ClF有两种稳定结构,而CH2AuX…ClF只有一种稳定结构。我们计算了这些复合物的相互作用能,发现过渡金属取代卤代烃中的氢原子对卤键有加强作用。我们对这些复合物进行了NBO分析和AIM分析。以上研究将有利于加深对卤键本质的理解,更好地认识卤键与氢键之间的竞争效应和协同效应,以及取代基对卤键强度的影响,给设计和合成新材料提供有用的信息。更多还原

【Abstract】 Halogen bonding is the noncovalent intermolecular interaction between halogen atoms (lewis acids) and neutral or anionic Lewis bases. Most of the energetic and structural features found in the hydrogen-bonded complexes are reproduced in halogen-bonded complexes as well. By virtue of its strength selectivity, and directivity, halogen bonding has led to a number of applications in fields as diverse as molecualr recognition, enantiomer’s separation, crystal engineering, and supramolecular architectures. Particularly, the utilization of this specific interaction in the context of drug design is nowadays coming to light. Based on the similarity of the hydrogen bond and halogen bond, one Lewis base can supply electrons to the hydrogen atom or halogen atom, so competitive effect can be found between hydrogen bond and halogen bond. There may exist two or more intermolecular interactions in one complex, and these interactions influence each other:both become stronger, or weaker, or one be stronger and one be weaker. Surely this cooperativity can be found between hydrogen bond and halogen bond. In the formation of R-X…Y halogen-boned complex, the length of the R-X bond can be shortened or lengthened, with the vibrational frequency shift. The former can be called blue-shift halogen bond, and the latter is referred to as red-shift halogen bond. The substituent group plays a very important role in the halogen-boned complex. Generally speaking, electronwithdrawing group weakens the electrondonating ability of the Lewis base and enhances the positive electrostatic potential of the halogen atom; electrodonating group enhances the electrondonating ability of the Lewis base and weakens the positive electrostatic potential of the halogen atom. The thesis is of quantum chemical study on the competitive and cooperative effects between hydrogen bonds and halogen bonds, the chemical origin of the blue-shift halogen bonds, and the influence of the substituent group on the strength of the halogen bonds.The main research contents of this thesis are as follows:1. The H…πand X (X=F, Cl, Br, I)…πinteractions between hypohalous acids and benzene are investigated at the MP2/6-311++G(2d,2p) level. We investigated the molecular electrostatic potential of the hypohalous acids and the interaction energies of the complexes. NBO analysis and AIM analysis have been performed to study the orbital interaction, the charge transfer and the topological properties. The main conclusion are as follows:(1) HOCl、HOBr、and HOI can form hydrogen and halogen-bonded complexes with C6H6, but there is only hydrogen bonding interaction between HOF and C6H6. This can be attributed to the electrostatic potential of the hypohalous acids. HOF has only one positive sites and the other hypohalous acids have two. (2) The strength of the H…πinteractions is contradictory to the MEP sequence, which is dominated by the dispersion interaction; the strength of the X…πinteractions follows the MEP sequence, which is dominated by the electrostatic interaction. (3)There exists competition between hydrogen bonding and halogen bonding. The hydrogen bonding is stronger than the halogen bonding except the HOI…C6H6 complex. (4) There exists charger transfer from C6H6 to HOX, and BCPs can be found between hydrogen or halogen atoms and carbon atom.2. The cooperativity between hydrogen and halogen bond in the XY…HNC…XY (X, Y=F, Cl, Br) complexes have been studied at the MP2/aug-cc-pVTZ level. Two hydrogen-bonded dimers, five hydrogen-bonded dimers, and ten trimers were obtained. The hydrogen-and halogen-bonded interaction energies in the trimers are larger than those in the dimers, indicating both the hydrogen bonding and the halogen bonding are enhanced. The binary halogen bonding plays the most important role in the ternary system. The hydrogen bonding influences the magnitude of the halogen bonding interaction much more than the hydrogen bonding in the trimers with respect to the dimers. Our calculations are consistent with the conclusion that the stronger noncovalent interaction has a bigger effect on the weaker one. The variation of the vibrational frequency in the HNC molecule has been considered. The NH antisymmetry vibration frequency has a blue shift, whereas the symmetry vibration frequency has a red shift. A dipole moment enhancement is observed in the formation of the trimers. The variation of the topological properties at BCP have been obtained using the AIM method, which is consistent with the results of the interaction energy analysis.3. We calculated a series of halogen-bonded complexes at the MP2/aug-cc-pVDZ level. The halogen bond donor is CFnH3-nCl, and the halogen bond acceptors are NH3, H2O, H2S, and Br-. Ten stable halogen-bonded complexes were obtained and the C-Cl bond length was contracted in all of these complexes. We carried out AIM and NBO analysis under the MP2/aug-cc-pVDZ optimized structures. The contracted C-Cl bond implies the enhancement of the bond strength. The variation of the electron density at the bond critical point of C-Cl bond correlates well with△r(C-Cl). A balance among intra-and inter-hyperconjugation and rehybridization determined the contracted C-Cl bond.4. We investigated the MenH3.nY(Y=N, P; n=0,1,2,3)…XF(X=Cl, Br) halogen-bonded complexes at the MP2/6-311++G** level. We discussed the electrondonating ability of 0, S, N, P from two aspects:molecular electrostatic potential and the orbital energies of the lone pairs, and some corresponding results can be explained. Compared with the 0 and S series, the halogen-bonded complexes containing N and P are very different. Very large amount of charge transfer and increment of dipole moment have been obtained in our calculations. The F-X bond length in the MenH3-nP…XF(X=Cl, Br) complex is larger than the corresponding MenH3-nN…XF(X=Cl, Br) complex. Deformation energy must be added to correct the interaction energy in order to obtain the regular intermolecular strength.5. We investigated the enhancing effect of halogen bonding induced by the transition metal Cu, Ag, and Au in the M-CH2-X…CIF (M=Cu, Ag, Au; X=F, Cl, Br) complexes. We obtained two optimized Cu-CH2-X…CIF and Ag-CH2-X…ClF structues, and only one Au-CH2-X…CIF structure. The comparison of the interaction energy between these complexes and the CH3X…CIF complex indicates that the substitution of the transition metal enhances the strength of the halogen bonding. The NBO results indicates that there exists an interaction between the lone pairs of the halogen atom and the antibonding orbital of the F-Cl and C-M bond. AIM analysis have been carried out to disclose the nature of these noncovalent interactions.更多还原