Non-covalent interactions in Crystals and Heterocycles of Sulphur and Selenium
Hydrogen bonding plays a very important role in the fields of both chemistry and biology. Conventionally it is represented as D-H---A, where D is the donor atom, A is the acceptor atom and H is the hydrogen atom. It has been studied for quite a long period of time, however the inaccuracy in locating hydrogen atoms in the X-ray crystallographic structural data posed as a significant setback in its analysis initially. The recent advancements in X-ray crystallography and Neutron Diffraction, have helped in locating the hydrogen atom accurately. The availability of a database for crystals via the CSD software has made the study of Hydrogen bonding in crystals easy and reliable. Previous work on hydrogen bond radii have not considered S-H groups in crystals. In this work we have investigated hydrogen bonding with sulphur using X-ray crystallographic database to find the hydrogen bond radius of various atoms involved in such contacts using the CSD software. The original criterion for hydrogen bond distance to be considered as the sum of the van der Waals radii of the atoms involved has been proved to be unreliable through the previous works in this field. It is hoped that the availability of hydrogen bond radii for all groups involved in hydrogen bonding would lead to a more appropriate criterion in identifying hydrogen bond in various circumstances. Another form of a weak non-covalent interaction is the σ-hole bonding. This concept was first proposed in context of halogens as an explanation for the non-covalent interactions between covalently bond halogen atoms and negative sites on other molecules. It has further been expanded to the chalcogen and pnictogen groups. In this project we have also worked with heterocycles of sulphur and selenium from the chalcogen group and have investigated the non-covalent interactions in their complexes with water. A detailed computational analysis was conducted for these complexes using the GAUSSIAN software to analyse the different structures formed using certain specific basis sets. AIM analysis was performed in order to study the non-covalent interactions between the molecules in the complexes.