Heterometallic Hexanuclear [Cu 2 Ln 4 ] Complexes Showing Zero-field SMM Behaviour and Magnetocaloric Effect.

Three heterometallic hexanuclear 3d-4f complexes bearing the formula [Cu 2 (L) 2 Ln 4 (L) 4 (o-van) 2 ] [L=2-((E)-((2-hydroxyphenyl)imino]methyl)phenol; o-van=ortho-vanillin] (Ln III =Gd III (1), Dy III (2), and Tb III (3)) have been synthesized and characterized. DC magnetic susceptibility measurements reveal overall antiferromagnetic interactions in 1 and 3, whereas co-existence of ferro- as well as antiferromagnetic interactions were observed in 2. The magnetocaloric effect has been observed for 1 with an entropy change (-ΔS m ) of 22.3 J kg -1  K -1 at 3 K and 7 T. Zero-field single molecule magnet (SMM) behaviour has been observed for 2, where Raman relaxation and quantum tunneling of magnetization (QTM) played a role in magnetization relaxation. The Cu-O-Ln angle well explains the magnetic exchange coupling occurring in the complexes. BS-DFT calculation for the complexes provides an estimate of the exchange interactions between the paramagnetic centres. Ab initio calculations performed for complex 2 established a good correlation to the experimental relaxation dynamics.