Anhydrous and hydrated [Co(en)₂CO₃]X salts as predictive guides for crystallization behavior in other systems

The premise leading to this investigation was based on the following: if a class of compounds has desirable crystallization behavior(s), can one translate that information to related species whose behavior is not yet established, but which may be valuable scientifically and/or commercially? We explored that premise, and below present our results. Thus, since we noted that [CoN₄(oxalato)]⁺ (N₄ = di- or multi-dentate amine ligands) frequently crystallize in Sohncke space groups, sometimes with more than one molecule in the asymmetric unit, we decided to investigate the effect of replacing the oxalato ligand with a simple relative (carbonato) to determine if this held true. For that purpose, we examined a number of [Co(en)₂carbonato]⁺ salts with various counter-anions and found that, as in the oxalato series, there were essentially two categories: anhydrous ones and hydrated ones, and that there were, indeed, some interesting common features in their crystallization modes, including important, identifiable hydrogen bonding interactions which are described below.