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Structural and Electronic Dependence of the Single-Molecule-Magnet Behavior of Dysprosium(III) Complexes

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posted on 03.03.2014 by Victoria E. Campbell, Hélène Bolvin, Eric Rivière, Regis Guillot, Wolfgang Wernsdorfer, Talal Mallah
We investigate and compare the magnetic properties of two isostructural DyIII-containing complexes. The DyIII ions are chelated by hexadentate ligands and possess two apical bidendate nitrate anions. In dysprosium­(III) N,N′-bis­(imine-2-yl)­methylene-1,8-diamino-3,6-dioxaoctane (1), the ligand’s donor atoms are two alkoxo, two pyridine, and two imine nitrogen atoms. Dysprosium­(III) N,N′-bis­(amine-2-yl)­methylene-1,8-diamino-3,6-dioxaoctane (2) is identical with 1 except for one modification: the two imine groups have been replaced by amine groups. This change has a minute effect on the structure and a larger effect the magnetic behavior. The two complexes possess slow relaxation of the magnetization in the presence of an applied field of 1000 Oe but with a larger barrier for reorientation of the magnetization for 1 (Ueff/kB = 50 K) than for 2 (Ueff/kB = 34 K). First-principles calculations using the spin–orbit complete active-space self-consistent-field method were performed and allowed to fit the experimental magnetization data. The calculations gave the energy spectrum of the 2J + 1 sublevels issued from the J = 15/2 free-ion ground state. The lowest-lying sublevels were found to have a large contribution of MJ = ±15/2 for 1, while for 2, MJ = ±13/2 was dominant. The observed differences were attributed to a synergistic effect between the electron density of the ligand and the small structural changes provoked by a slight alteration of the coordination environment. It was observed that the stronger ligand field (imine) resulted in complex 1 with a larger energy barrier for reorientation of the magnetization than 2.

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