Lanthanide(III) Hexanuclear Circular Helicates: Slow Magnetic Relaxation, Toroidal Arrangement of Magnetic Moments, and Magnetocaloric Effects

Four hexanuclear circular helicates, {[Dy6L6(DMF)(12)]center dot 6CF(3)SO(3)center dot 12DMF}(2) (1Dy), {[Gd6L6(DMF)(12)]center dot 6CF(3)SO(3)center dot 12DMF}(2) (1Gd), [Dy6L6(DMF)(10)(H2O)(2)]center dot 6ClO(4)center dot 4H(2)O center dot 10DMF (2Dy), and [Gd6L6(DMF)(12)]center dot 6ClO(4)center dot 2H(2)O center dot 10DMF (2Gd), where DMF = N,N-dimethylformamide, were synthesized by employing a glutaratedihydrazide-bridged bis(3-methoxysalicylaldehyde) ligand (H2L) and characterized structurally and magnetically. Direct-current magnetic susceptibility studies indicated predominant weak antiferromagnetic exchange interactions among gadolinium analogues, which were quantified using the PHI software, giving J = -0.003 cm(-1) with g = 2.00 for 1Gd and J = -0.001 cm(-1) with g = 2.02 for 2Gd. Alternating current magnetic susceptibility measurements indicated that complexes 1Dy and 2Dy show slow relaxation of magnetization behavior, further supported by theoretical calculations that also highlighted the toroidal arrangement of the magnetic moments.