Crystal structures are a source of information on geometries of species

that form networks in solids, in addition to providing information on the

nature of interactions that occur between them. Hydrogen bonding is one

of the most important interactions responsible for the arrangements of

molecules and ions in crystals. For this reason, this special issue collects

new, interesting, and important findings and ideas on the role of the

hydrogen bond in crystals.

The contributions of this issue may be classified into three groups: the

first concerns new crystal structures where interesting arrangements of

species are described; the second group considers crystal structures and

their observed phenomena; and the last group is strongly related to a

discussion on theoretical results, where often hydrogen bond interactions

are compared with other interactions (halogen bond, pnicogen bond,

carbon bond, etc.).

Despite the fact that the last group of articles concerns the results of

calculations, it is strongly associated with experiment since the results are

compared with experimental observations. Besides other interesting

phenomena, the hydrogen bond interactions are well described in the

theoretical work.