Systematic studies of hydrogen bonding
This thesis deals with wider application and implications of the hydrogen bond in crystal engineering studies and beyond; in addition, it also highlights the Cambridge Structural Database (CSD) as the potential knowledge-mine for inorganic chemists. The content of this thesis covers mainly three areas, viz, the role of hydrogen bonding in crystal engineering studies, the bridging between mainstream crystal engineering studies and solvates via hydrogen bond, and CSD studies on metal coordination spheres. Chapter 2 deals with crystal structure prediction through understanding the driving forces for forming supramolecular synthons and some rare supramolecular networks (Carbomndum III). With the help of a series of supraminols we attempt to identify the underlying reason for forming P-As networks. Chapter 3 covers the much debated topic of acceptor capabilities of organic halogens and consequently, how the so-called illusory hydrogen bond involving an organic halogen as an acceptor can explain a complex topic like synthon change-over, in a perfectly comprehensible manner. The aim of the Chapters 4 to 6 is to bring two separate fields, "crystal engineering" and "solvates" closer via a common root, like hydrogen bonding. The serendipitous host molecules are part of our crystal engineering studies, yet they form solvates due to less than optimum hydrogen bonding in their respective crystal structures. Alongside some usual solvates, in an unconventional way, different amines with varying steric, strain and donor hydrogen atoms were used. Different geometrical as well as crystallographical aspects and their explicit role in synthon selection has also been discussed. In Chapter 7, geometrical distortions of three-coordinate metal complexes in the crystal structures in the CSD have been analysed using symmetry modified Principal Component Analysis (PCA). Results shows that 90% of three coordinate species are accounted for by the five elements Cu, Ag, Hg, Au and Zn. Among the three major types of geometries, trigonal planar dominates the data sets, with smaller contribution for Y- and T-shaped structure. For Hg complexes, a possible reaction pathway for ligand addition reaction to two-coordinate linear complexes via T-shaped geometries leading to trigonal planar is discussed in detail. The background information and an overview of the experiments are discussed in the Introductory Chapter.