Ternary complexes formed between calcium, the oxochromium(V) ion and N-acetylneuraminic (sialic) acid (naH₆) of the form, Ca(II)–oxoCr(V)–naH₆, have electronic structures and equilibrium distributions distinct from the binary oxoCr(V)–naH₆ analogues, as illustrated by electron paramagnetic resonance (EPR) spectroscopy.