THE HYDROGEN-BOND AND CRYSTAL ENGINEERING

The hydrogen bond, particularly between ions, is much stronger than commonly acknowledged, and the number of recognized hydrogen-bond donors (such as C-H) and acceptors (such as aromatic pi-clouds) is rapidly expanding. We present here an overview of the hydrogen bond, and show how hydrogen-bond patterns in the solid state can be classified using a topological analysis. We conclude by illustrating the use of the hydrogen bond as a synthetic vector for crystal engineering, and consider the problems of polymorphism (a matter of immense current interest, given the multi-billion dollar law suit of Glaxo versus Novopharm, which has polymorphism as its cynosure).