Slow Magnetic Relaxation in a Californium Complex.

We report the synthesis and characterization of the macrocyclic californium derivative Na[Cf(HO)(DOTA)] (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate), , which was studied in comparison to its dysprosium counterpart, Na[Dy(HO)(DOTA)], . Divergent spectroscopic and magnetic behaviors were observed between and . Based upon spectroscopic measurements, we propose that accessible 5f → 6d transitions (potentially operating in tandem with charge-transfer transitions) are the major contributors to the observed broadband photoluminescence in . Dc magnetic susceptibility data for revealed lower magnetic moments than those previously observed for and expected for an f free ion, which calculations suggest is the result of greater ligand field effects. Notably, displays slow magnetic relaxation on the time scale of ac susceptibility measurements, making it the first example of a californium-based single-molecule magnet. A side-by-side comparison of the ac susceptibility data reveals magnetic relaxation properties that widely differ between and . This divergent relaxation behavior is attributed mainly to the inherent difference in spin-orbit coupling between Dy and Cf.