The architecture of molecules

Molecular architecture may be said to have originated in 1874, when J. H. van't Hoff and J. A. le Bel independently formulated the brilliant postulate that the four valence bonds of the carbon atom are directed approximately toward the corners of a regular tetrahedron. It was extended into inorganic chemistry in 1893, when A. Werner suggested that in many inorganic complexes six atoms are arranged at the corners of a regular octahedron about a central atom, and that other geometrical structures are represented by other complexes. However, the present-day subject of molecular architecture, involving the precise discussion of the structure of molecules and crystals in terms of interatomic distances and bond angles, is a product of the last half century. It began in 1913, when W. H. Bragg and W. L. Bragg reported the determination of the arrangement of atoms of sodium and chlorine in the sodium chloride crystal and the evaluation of the distance between the centers of the atoms by the newly discovered method of analysis of the X-ray diffraction pattern. During the last 50 years the precise structures of thousands of crystals and molecules have been determined by the methods of X-ray diffraction, electron diffraction, and molecular spectroscopy, with the aid of other techniques, such as the determination of entropy values