The structure and bonding of radium (Ra) is poorly understood because of challenges arising from its scarcity and radioactivity. Here we report the synthesis of a molecular Ra²⁺ complex using ²²⁶Ra and the organic ligand dibenzo-30-crown-10, and its characterization in the solid state by single-crystal X-ray diffraction. The crystal structure of the Ra²⁺ complex shows an 11-coordinate arrangement comprising the 10 donor O atoms of dibenzo-30-crown-10 and that of a bound water molecule. Under identical crystallization conditions, barium (Ba²⁺) yielded a 10-coordinate ‘Pac-Man’-shaped structure lacking water. Furthermore, the bond distance between the Ra centre and the O atom of the coordinated water is substantially longer than would be predicted from the ionic radius of Ra²⁺ and by analogy with Ba²⁺, supporting greater water lability in Ra²⁺ complexes than in their Ba²⁺ counterparts. Barium often serves as a non-radioactive surrogate for radium, but our findings show that Ra²⁺ chemistry cannot always be predicted using Ba²⁺.