| In this work, a systematic theoretical investigation on a series of dimeric complexes formed between electron donor and acceptor has been carried out by employing correlated ab initio methods. The main results are divided into three parts:Part one, first-principle calculations at different levels of theory have been carried out to investigate a series of complexes formed between iodo-perfluorobenzene and several heteroatomic rings. Such model systems are selected to mimic halogen bonding interactions experimentally found within supramolecular architectures. In all cases, the predicted intermolecular distances are significantly shorter than the sums of van der Waals radii of I and N (O or S) atoms and the interactions appear to be highly directional. Halogen bonding energies, calculated at the MP2/lanl2dz level, are substantial, ranging from-2.50 to-7.53 kcal/mol. Given the strength as well as the directionality comparable to hydrogen bonds, these synthons should be of general use in many fields of chemistry and drug design. Finally, in order to gain more insights into the nature of such interactions, we have employed the natural bond orbital and atoms in molecules analyses on the studied systems, which show a considerable magnitude of charge transfer, significant orbital interaction, and distinct bond critical points between the two interacting atoms.Part two, a systematic theoretical investigation on a series of dimeric complexes formed between MH2 and HX has been carried out by employing correlated ab initio methods. It is shown that besides dihydrogen bonds, there also exists novel noncovalent X…H interactions between the two molecules, which has similar characteristics to traditional halogen bonds. Upon complexation, the H-X bonds tend to elongate in all cases, concomitant with red-shifts of H-X stretching frequencies. X…H interaction energies in the studied systems are predicted to be in a range from-1.72 to-9.12 kJ/mol, which are much weaker than corresponding dihydrogen bonds. The major stabilization source of dihydrogen and halogen bonds arises from the electrostatic force, while charge transfer force plays a minor role in the formation of the complexes. AIM analyses further confirm the presence of X…H interactions in these systems, and the electron density at bond critical points appear a good description of the strength of these interactions.Part three, we have investigated the weak S…O bonding, which is specific noncovalent interaction, plays crucial roles in fields as diverse as molecular recognition, crystal engineering, and biological systems. This paper presents an ab initio investigation of a series of dimeric complexes formed between formaldehyde and several sulfur-containing molecules as electron accepters. The bond-length change, interaction energy, topological property of the electron density, and charge transfer of these S…O bonds have been systematically investigated. Moreover, a comprehensive search for nonbonded S…O interactions in proteins was also performed. It was found that the O atom shows a strong intrinsic tendency to approach S from the backside of the R-S bond (in theσs* direction); the S atom tends to approach the O atom either from the orientation of the lone pair of O (in the no direction) or from the vertical direction (in theπo direction). Besides, the linearity of this interaction was also reproduced by the statistical study. As suggested by the results presented in this work, S…O contacts may control protein structures to some extent and the unique directional properties of S…O interactions could be applied in the context of drug design. |
