Theoretical Studies On The Cooperativity Effects Between Beryllium Bond And Weak Interactions

Intermolecular interactions have become a hot topic because of their importantroles in many fields such as biological engineering, crystal engineering, materialscience, supramolecular self-assemblies and molecular recognition. This thesis hassummarized several common intermolecular interactions such as hydrogen bond (HB),π-π interaction, CH/π interaction, cation-π interaction in the introduction part. Two ormore weak interactions coexist in the same system, and mutually influence to eachother. These interactions determine the structure as well as function of the complex.Generally, we define this interplay between two or more weak interactions ascooperativity. Thus, study on this mutually influence between weak interactions,which refers to cooperativity, is of great significance for our comprehensiveunderstand on the structures and functions of the complicated molecular systems. Thisthesis selects the cooperativity between the beryllium bond and some other weakinteractions as the objects of study. We employ theoretical approach with highaccuracy to reveal the nature of the intermolecular interactions and the rule ofcooperativity.In this thesis, we take the beryllium-containing complexes formed by Be and Natom in pyridine ring or O atom in furane ring as a theoretical model and investigatethe cooperativity between beryllium bond and hydrogen bond, π-π, CH/π, cation-πand lone pair-π interactions theoretically. Considering the difference in the researchsystems, different methods were used for our calculation. The results are as follows:In the first part, small molecular model systems in which beryllium bond and π-π, CH/π, cation-π, or lone pair-π interactions coexist have been studied theoretically atthe MP2/6-31+G*，MP2/aug-cc-pVDZ，B97-D/6-311++G*and M06-2x/6-311++G*levels respectively. To analysis the magnitude and direction of cooperativity effects indetail, atom in molecular (AIM) theory and charge-transfer theory (Mulliken andMerz-Kollman (MK)) have been performance at the MP2theory with a large basis setof aug-cc-pVDZ. The results indicate that beryllium bonds formed by pyridine andBeH2，BeF2show stronger interaction energies. In these model systems, thecooperativity between beryllium bond and most of the weak interactions mentionedabove is positive, with the only exceptional case of that between beryllium bond andLi+-π interaction, which shows a negative cooperativity. The results of both AIM andcharge-transfer analyses also suggest that beryllium bond can enhance the strength ofthe π-π, CH/π, lone pair-π interactions and weaken the strength of cation-π interaction.In the second part, the cooperativity effects between beryllium bond andhydrogen bond in the large molecular model systems have been studied by means ofMP2method with6-31++G**basis set. We have analyzed the magnitude ofcooperativity effects and have adopted atom in molecular (AIM) theory,charge-transfer theory (Mulliken and Merz-Kollman (MK)) again. The results implythat the cooperativity in these systems is relatively weak, and even show an adverseimpact on the stability of the system. However, as for the molecules from BeH2toBeF2, the cooperativity energy tends to a negative value from a positive one,indicating the increased strength of cooperativity. In addition, as the ring becomeslonger, the dispersion energy increases and the cooperativity can be reinforced to acertain extent.