Synthesis, structures and magnetic studies of hexanuclear lanthanide complexes: SMM behavior of the Dy analogue and MCE properties of the Gd analogue.

The synthesis, structure and magnetic properties of homometallic hexanuclear lanthanide complexes [Ln(HL)(tfa)(S)]·2NO· HO·MeOH (1, Ln = Gd, S = MeOH, = 0, = 0; 2, Ln = Tb, S = HO, = 2, = 2; 3, Ln = Dy, S = MeOH, = 0, = 2; 4, Ln = Er, S = MeOH, = 0, = 2). [(HL) = 6-((bis(2-hydroxyethyl)amino)-'-(2-hydroxybenzylidene)picolinohydrazide) (tfa = trifloroacetylacetone)] are reported. These hexanuclear assemblies are made up of two trinuclear triangular sub-units linked through the oxygen atoms of two phenoxide bridging groups in a corner sharing arrangement. Magnetic studies reveal that 1 displays a magnetocaloric effect with a maximum value of -Δ = 21.03 J kg K at = 3 K and under an applied field change Δ = 5 T. Complex 3 shows slow relaxation of magnetization even under zero applied field although a clear maximum in the ac susceptibility plots cannot be seen. However, under an optimal applied field of 0.2 T, clear maxima are observed in the out-of-phase ('') component of the ac susceptibility in the temperature range 3.5 K (2 kHz) to 10.5 K (10 kHz). The temperature dependence of the relaxation times could be fitted to the sum of Orbach, Raman and QTM relaxation processes affording the following parameters: = 3.4(9) × 10 s, = 94(2) K, = 16.43(1) K s, = 3.2(3) and = 0.0044(3) s. 4, under an applied magnetic field of 0.2 T, shows slow relaxation of magnetization through a thermally activated Orbach process with = 18.2(9) K and = 3.5(3) × 10 s.