HX与H_2O分子间氢键理论研究

Theory study of hydrogen bond between HX and H_2O

在B3LYP/6-311++G^(**)水平上对H_2O与HX(F,C1,Br,I)分子间形成的(H_2O)_2HX和H_2O(HX)_2六元环氢键复合物的构型进行了全优化,频率计算表明,所有构型中O(2)—H(1),O(6)—H(5)及X(6)—H(5)的伸缩振动频率均发生红移,而对于X(4)—H(3)的伸缩振动频率在(H_2O)_2HF、(H_2O)_2HCl、H_2O(HF)_2体系中发生红移,在(H_2O)_2HBr、(H_2O)_2HI、H_2O(HCl)_2、H_2O(HBr)_2、H_2O(HI)_2体系中发生蓝移.在MP2/6-311++G^(**)水平上计算了体系的相互作用能,得到F、Cl、Br所形成的复合物其总相互作用能均为负值,而I形成的复合物其总相互作用能为正值.采用SCRF(PCM)方法研究了体系的溶剂化效应,结果表明溶剂化效应使复合物更稳定.自然键轨道(NBO))分析表明,复合物分子中的直接超共轭作用,导致了复合物中O(2)—H(1)、O(6)—H(5)及X(6)—H(5)键有所拉长,同时增加了复合物的稳定性.综合分析得到八种复合物的稳定性顺序为:H_2O(HF)_2>(H_2O)_2HF>(H_2O)_2HCl>(H_2O)_2HBr>H_2O(HCl)_2>H_2O(HBr)_2>(H_2O)_2HI>H_2O(HI)_2.

The six-membered ring hydrogen-bonded between HzO and HX（X= F, Cl, Br, I） have been fully optimized by means of B3LYP/6-31l＋＋G＊＊. The stretching vibrational frequencies of the O（2）-- H（1） ,O（6）--H（5） and X（6）--H（5） bonds in all the eight complexes are red-shifted. The stretching vibrational frequencies of X（4）--H（3） in （H2O）zHF.（H2O）zHC1 and H2O（HF）2 complexes are redshifted obviously, while they are blue-shifted in （H2O）2 HBr 、 （H2 O）2 HI 、 H2O （HCl）2 、H2 O （HBr） 2 and H2O（HI）2 complexes. The hydrogen bond interaction energy were calculated with basis set superpositon error （BSSE） correction in the MP2/6-311＋＋G＊＊. The calculated total interaction energies for （H2O）2HX and H2O（HX）2（X= F, CI, Br） complexes are positive. However, they are negative for （H2O）2HI and H2O（HI）2 complexes. The complexes in water solution have been investigated at the B3LYP/6-311＋＋G＊＊ with SCRF （PCM） method, and the results show that the energy of each compound is lower than that in the gas phase. The solvent effects enhance the stability of complexes to a large extent. Natural bond orbital（NBO） theory analysis show that the stability of these complexes has been enhanced because of intermolecular hyperconjugation. The hyperconjugative interaction effect leads to the elongation of O（2）--H（1） ,O（6）--H（5） and X（6）--H（5） bonds. The energetic order for these complexes is ： H2O（HF）2〉（H2O）2HF〉（H2O）2HCl〉（H2O）2HBr〉H2O（HCl）2〉H2O（HBr）2〉（H2O）2HI〉H2O（HI）2.