The three lowest energy calculations (in Figure ) exhibit the same number of hydrogen bonds between the cluster constituents, unlike the higher energy calculations of the smaller halogen bonded clusters previously discussed. Another dissimilarity between the (2, 1, 1) cluster and the smaller clusters of this class emerges, where we see what appears to be equal bond lengths between the central iodine and two neighboring oxygens, as well as identical bond lengths of the central oxygens to the outer iodine molecules in isomer A. These bond lengths are shorter than the previously explored halogen bond lengths and therefore suggest that a stronger interaction than a halogen bond might be forming. However, we will discuss this interaction in more detail in the upcoming sections. Irrespective of the classification of this interaction, it results in the continuation of the O-I-O backbone, and emphasizes the importance of the ammonium hydrogen-bonded scaffold in facilitating an optimal orientation of I 2 O 5 and IO - 3 for an interaction to take place.