The crystal and molecular structure of pyridine picrate

Abstract

The X-ray diffraction analysis of the crystal structure of pyridine picrate forms the subject matter of the thesis. The structure has been solved in projections by using a combined strategy of optical-transform approach and Fourier methods. Computer facility was not readily available. The major part of the computational work involved in this work has been done using desk calculator. The optical-transform techniques were freely used to cut down computational work as far as possible. In the chapter one, the basic principles of optical-transform methods have been described. The collection of physical and X-ray data of pyridine picrate and placement of Fobs values on absolute scale constitute the subject matter of chapter two. The third chapter is devoted mainly to procedures adopted for determination of the approximate structure. The unitary structure factors have been derived. The applications of the optical-transform and Fourier-transform principles in deriving shape and position of the molecule is discussed in this chapter. The chapter four, deals with the refinement of (010) projection. The application of the process of optical phase determination in the initial stages of refinement has been discussed. Further refinement of the (010) projection by difference syntheses and methods of least-squares has been described in chapter five. The necessity of extinction correction for a few reflexions has been pointed out. An attempt has also been made to locate the hydrogen atoms. Derivation of approximate structure of the (100) projection and its subsequent refinement have been dealt with in the chapter six. Final atomic co-ordinates, calculations of bond lengths and bond angles, intermolecular distances, and assessment of accuracy of atomic co-ordinates, bond lengths and bond angles, are presented in chapter seven. The geometry of the molecule is discussed.