Existence of Intermolecular Bonds in Crystals

One of the problems sometimes found when working with intermolecular interactions is establishing whether or not they are bonds (see, for instance, the arguments used in Refs. [27, 34, 35]). As we will show in this section, the problem arises when one uses indirect criteria to establish the presence of bonds, many of them based on empirical trends. 

Over the years, instead of these direct criteria, it has been very common to use some indirect criteria that have been taken as evidence of the presence of intermolecular bonds. Hereafter we summarize some of the most popular ones, to allow the reader to evaluate their strong and weak points  

Each complex is identified by the REFCODE of the crystal where the complex is found, sometimes followed by a number, different complexes are found within the same crystal. 

REFCODE r(H---0) Ed Eer Epol Ect Edisp Etot Type EmP2 

---