The chemistry and history of oxocarbon materials is rich, both in terms of structure and their utility. Here, a thorough computational exploration of the K:CO phase diagram shows that six membered oxocarbon anions, rhodizonates, dominate the thermodynamic landscape. Rhodizonates possess a fascinating ability to hold different oxidation states, predicted to range from -2 in the semiconducting Fddd phase of K2C6O6 to -6 in the C2/m phase of K6C6O6, a likely record for small organic anions. Interactions in the semiconducting phases appear dominated by electrostatics, with ions packed in an alternating fashion so to maximize K-O interactions. In contrast, the predicted strongly metallic P6/mmm phase of K3C6O6 and P1 phase of K3.5C6O6 exhibit face-to-face stacking of rhodizonates. The structure of K3C6O6 is especially unusual, even unique, for several reasons. Particularly noteworthy is the equidistant stacking of highly charged, i.e., electrostatically repelling, anions. Metallic organic salts are rare, and equidistant π-stacking in them even more so.