Heterometallic Hexanuclear [Cu2 Ln4 ] Complexes Showing Zero-field SMM Behaviour and Magnetocaloric Effect
Arindam Gupta1, Sandhya Kapurwan1, Siba Prasad Bera1
1Department of Chemistry, Indian Institute of Science Education and Research Bhopal Bhopal By-pass road, Bhauri, Madhya Pradesh, 462066, India.
Abstract:
Three heterometallic hexanuclear 3d-4f complexes bearing the formula [Cu2 (L)2 Ln4 (L)4 (o-van)2 ] [L=2-((E)-((2-hydroxyphenyl)imino]methyl)phenol; o-van=ortho-vanillin] (LnIII =GdIII (1), DyIII (2), and TbIII (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 (-ΔSm ) 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.
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