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Effect of Ligand Substitution around the DyIII on the SMM Properties of Dual-Luminescent Zn–Dy and Zn–Dy–Zn Complexes with Large Anisotropy Energy Barriers: A Combined Theoretical and Experimental Magnetostructural Study

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posted on 14.04.2016, 14:36 by Jean Pierre Costes, Silvia Titos-Padilla, Itziar Oyarzabal, Tulika Gupta, Carine Duhayon, Gopalan Rajaraman, Enrique Colacio
The new dinuclear ZnII–DyIII and trinuclear ZnII–DyIII-ZnII complexes of formula [(LZnBrDy­(ovan) (NO3)­(H2O)]­(H2O)·0.5­(MeOH) (1) and [(L1ZnBr)2Dy­(MeOH)2]­(ClO4) (3) (L and L1 are the dideprotonated forms of the N,N′-2,2-dimethylpropylenedi­(3-methoxysalicylideneiminato and 2-{(E)-[(3-{[(2E,3E)-3-(hydroxyimino)­butan-2-ylidene ]­amino}-2,2-dimethylpropyl)­imino]­methyl}-6-methoxyphenol Schiff base compartmental ligands, respectively) have been prepared and magnetostructurally characterized. The X-ray structure of 1 indicates that the DyIII ion exhibits a DyO9 coordination sphere, which is made from four O atoms coming from the compartmental ligand (two methoxy terminal groups and two phenoxido bridging groups connecting ZnII and DyIII ions), other four atoms belonging to the chelating nitrato and ovanillin ligands, and the last one coming to the coordinated water molecule. The structure of 3 shows the central DyIII ion surrounded by two L1Zn units, so that the DyIII and ZnII ions are linked by phenoxido/oximato bridging groups. The Dy ion is eight-coordinated by the six O atoms afforded by two L1 ligands and two O atoms coming from two methanol molecules. Alternating current (AC) dynamic magnetic measurements of 1, 3, and the previously reported dinuclear [LZnClDy­(thd)2] (2) complex (where thd = 2,2,6,6-tetramethyl-3,5-heptanedionato ligand) indicate single molecule magnet (SMM) behavior for all these complexes with large thermal energy barriers for the reversal of the magnetization and butterfly-shaped hysteresis loops at 2 K. Ab initio calculations on 13 show a pure Ising ground state for all of them, which induces almost completely suppressed quantum tunnelling magnetization (QTM), and thermally assisted quantum tunnelling magnetization (TA-QTM) relaxations via the first excited Kramers doublet, leading to large energy barriers, thus supporting the observation of SMM behavior. The comparison between the experimental and theoretical magnetostructural data for 13 has allowed us to draw some conclusions about the influence of ligand substitution around the DyIII on the SMM properties. Finally, these SMMs exhibit metal- and ligand-centered dual emissions in the visible region, and, therefore, they can be considered as magnetoluminescent bifunctional molecular materials.