An Ab Initio Study On The COCl₂…NH₃, COCl₂…H₂S And COCl₂…PH₃ Complexes

It is well known that the weak interactions play an important role in chemistry, physics,and particularly in the biodisciplines, since all life on earth may be viewed as a matter ofsupramolecular chemistry. These interactions greatly influence the structures and propertiesof molecular cluster systems. In recent years, much attention has been evinced to examinetheir roles on the structure and properties of molecular complexes, including biologicalmolecular recognition, crystal packing, cluster formation, and so on. Considered in terms ofenvironment, a lot of organic compounds including instability of Cl are used as the solventin industry. The improper treatment of these wastes may bring serious pollution to theatmosphere, soil and the groundwater. Various methods have been adopted to deal with thepollutant. However, the photooxidizing and photocatalysis of chlorine ethylene will producethe material of phosgene, which is more poisonous than the chlorine ethylene. The phosgeneCOCl2 belongs to the toxic asphyxiating gas, which has serious danger to the human body.Meanwhile, it is an important industrial chemical, and is widely used in the field of polymermaterials, agriculture chemical, spices and dyestuffs, etc. So it is necessary to carry furthertheoretical research on the system of COCl2…NH3, COCl2…H2S and COCl2…PH3 whichshow important meaning on reducing the pollution of phosgene and on the chemical industry.Among moist environment, the output of phosgene will be reduced. Amana et al. think thathydrolysis may be happen to phosgene, N.Tanaka et al. have utilized the computingtechnology from the beginning to study the system of COCl2…H2O. But can the phosgeneform the similar complex compound with other gas? Whether there are such complexeswhich are more stable than the COCl2…H2O compound?In this thesis, we carried the theoretical research on the structures and the properties ofthe phosgene-poisonous gases complexes COCl2…NH3, COCl2…H2S and COCl2…PH3,predicted the geometries of these complexes, obtained the stability order among differentisomers, and analyzed the types of weak interactions among these new complexes. Theresults obtained on new structures and intermolecular interactions may be valuable forimproving our understanding of the nature of weak intermolecular interaction, and offering atheoretical suggestion to reduce the pollution of phosgene. The main results of this thesis areas follows:By means of ab initio calculations at the MP2/6-31++G(d,p), MP2/6-311++G(d,p),MP2/aug-cc-pVDZ, MP2/aug-cc-pVTZ levels, the geometrical structures of theCOCl2…NH3, COCl2...H2S, and COCl2…PH3 complexes are optimized. Similarly, the abovefour basis sets had also been used by N. Tanaka etc. The results show that the bond lengths,bond angles and interaction energies obtained at the MP2/aug-cc-pVTZ level are close to thecorresponding experiment data. So in this thesis, the geometrical optimizations andfrequency calculations of above three systems are all performed at the MP2/aug-cc-pVTZlevel. The basis set superposition error(BSSE) is also calculated according to thecounterpoise(CP) method proposed by Boys and Bernardi. Four stable structures ofCOCl2…NH3 , two stable structures of COCl2…H2S and four stable structures ofCOCl2…PH3 have been found. The most stable geometries have been found by thefrequency analyses. It is found that the stable structures can be divided into two types. Incomplexes III, IV, VII, IX, X the monomer lie with N (S, P) … C contact. In complexes V,VI, VIII, XI, XII the monomer lie with almost linear N (S, P)…Cl-C contact. The stability ofthe type adopting the N (S, P)…C contact (III, IV;VII;IX, X) is higher than other types,indicating that the interaction of N (S , P)…C is stronger than that of N (S , P )…Cl. It canmake the system more stable to adopt the crossing type. The existence of the weak hydrogenbond has a little effect on the structures of these complexes. The interactions between N (S,P) and C are the main interaction between the two systems. The corrected interaction energyof ten complexes is -0.1482 ev, -0.1064 ev, -0.0558 ev, -0.0255 ev, -0.1054 ev, -0.0629 ev,-0.0923 ev, -0.0772 ev, -0.0598 ev, -0.0438 ev, respectively. The stability tendency of tencomplexes are III > IV >VII > IX > X > VIII > XI > V > XII > VI. The interaction energy ofcomplex III is the largest, so it is more stable than the COCl2…H2O system. This has offereda proper method to reduce phosgene pollution in theoretical research .