Fluorine in crystal engineering--"the little atom that could".

In the last decade interactions of fluorine substituents in a variety of organic compounds have gained interest in life science and solid state materials. This review provides knowledge on fluorine interactions classified into phenyl-perfluorophenyl-, C-FH, FF and C-FpiF interactions. Except for phenyl-perfluorophenyl stacking featuring a stabilising energy of about 30 kJ.mol(-1), interactions involving fluorine are generally weak. Although, there is still no concise understanding of fluorine interactions, there are numerous examples showing the influence of weak synthons on chemical, physical and biological properties.