Co 3 Gd 4 Cage as Magnetic Refrigerant and Co 3 Dy 3 Cage Showing Slow Relaxation of Magnetisation.

Two structurally dissimilar 3d-4f cages having the formulae [(Co III ) 3 Gd 4 (μ 3 -OH) 2 (CO 3 ) (O 2 C t Bu) 11 (teaH) 3 ]·5H 2 O ( 1 ) and [(Co III ) 3 Dy 3 (μ 3 -OH) 4 (O 2 C t Bu) 6 (teaH) 3 ]·(NO 3 ) 2 ·H 2 O ( 2 ) have been isolated under similar reaction conditions and stoichiometry of the reactants. The most important factor for structural diversity seems to be the incorporation of one μ 3 -carbonate anion in 1 and not in 2 . Co atoms are in a +3 oxidation state in both complexes, as shown by the Bond Valence Sum (BVS) calculations and bond lengths, and as further supported by magnetic measurements. Co 3 Gd 4 displays a significant magnetocaloric effect (-∆S m = 25.67 J kg -1 K -1 ), and Co 3 Dy 3 shows a single molecule magnet (SMM) behavior.