Halogen bonding once again plays a crucial role in this cluster, however, only isomer A contains a halogen bond along with an additional interaction. All of the higher energy isomers contain only one non-hydrogen bonding interaction. Similar to the (2, 1, 1) cluster, the (2, 2, 1) cluster exhibits almost equal bond lengths between what started as the iodine pentoxide and iodate constituents and the internal bond of what was the iodine pentoxide (bonds highlighted in green). These bond lengths are also slightly shorter than halogen bonds, but slightly longer than a typical I-O covalent bond, complicating the identification of the interaction taking place within the cluster. Once again isomer A has the fewest hydrogen bonds (six), whereas isomers B and C each have seven hydrogen bonds, and isomers D and E (SI Figure ) have eight. This further reinforces the preferential importance of halogen bonding/non-hydrogen bonding interactions in stabilizing these clusters over that provided by hydrogen bonding. The (2, 2, 1) cluster shows the extension of the O-I-O backbone through both halogen bond formation and an additional stronger interaction, further emphasizing the role of these intermolecular forces in the growth of this type of cluster into larger, more atmospherically relevant sizes.