Effect of Ligand Substitution around the Dy^III 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

The new dinuclear Zn^II–Dy^III and trinuclear Zn^II–Dy^III-Zn^II complexes of formula [(LZnBrDy­(ovan) (NO₃)­(H₂O)]­(H₂O)·0.5­(MeOH) (<b>1</b>) and [(L¹ZnBr)₂Dy­(MeOH)₂]­(ClO₄) (<b>3</b>) (L and L¹ are the dideprotonated forms of the <i>N</i>,<i>N</i>′-2,2-dimethylpropylenedi­(3-methoxysalicylideneiminato and 2-{(<i>E</i>)-[(3-{[(2<i>E</i>,3<i>E</i>)-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 <b>1</b> indicates that the Dy^III 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 Zn^II and Dy^III 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 <b>3</b> shows the central Dy^III ion surrounded by two L¹Zn units, so that the Dy^III and Zn^II 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 <b>1</b>, <b>3</b>, and the previously reported dinuclear [LZnClDy­(thd)₂] (<b>2</b>) 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. <i>Ab initio</i> calculations on <b>1</b>–<b>3</b> 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 <b>1</b>–<b>3</b> has allowed us to draw some conclusions about the influence of ligand substitution around the Dy^III 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