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Abstract
The structure and bonding of radium (Ra) is poorly understood because of challenges arising from its radioactivity and scarcity. Herein, we report the first synthesis and characterization of a molecular Ra2+ compound in the solid state by single crystal X-ray diffraction, using dibenzo-30-crown-10 (DB30C10) and 226Ra. Our study reveals an 11-coordinate Ra2+ structure arising from the 10 donor atoms of DB30C10 and a bound water molecule, whereas identical crystallization conditions with barium (Ba2+) yielded a 10-coordinate “Pac-Man” structure lacking water. The Ra—Owater bond distance is significantly longer than would be predicted from the ionic radius of Ra2+. Collectively, these findings support greater water lability in Ra2+ complexes and demonstrate that Ra2+ chemistry cannot always be predicted using Ba2+. Our results will be valuable in guiding both the design of new chelators and future characterization efforts for this underexplored metal ion.
