An IUPAC task group has recently published their recommendations for the definition for the hydrogen bond.
“The hydrogen bond is an attractive interaction between a hydrogen atom from a molecule or a molecular fragment X–H in which X is more electronegative than H, and an atom or a group of atoms in the same or a different molecule, in which there is evidence of bond formation.”
The recommendations continue with a list of experimental and theoretical criteria that can be used as evidence for the presence of the hydrogen bond, and finish with characteristics that are typical of hydrogen bonded systems.
For more information on the task group and to view the provisional recommendation see the IUPAC report.
Follow the links below to read two Dalton Transactions articles with a focus on bonding: