Bifunctional Zn^IILn^III Dinuclear Complexes Combining Field Induced SMM Behavior and Luminescence: Enhanced NIR Lanthanide Emission by 9‑Anthracene Carboxylate Bridging Ligands

There were new dinuclear Zn^II–Ln^III complexes of general formulas [Zn­(μ-L)­(μ-OAc)­Ln­(NO₃)₂] (Ln^III = Tb (<b>1</b>), Dy (<b>2</b>), Er (<b>3</b>), and Yb (<b>4</b>)), [Zn­(μ-L)­(μ-NO₃)­Er­(NO₃)₂] (<b>5</b>), [Zn­(H₂O)­(μ-L)­Nd­(NO₃)₃]·2CH₃OH (<b>6</b>), [Zn­(μ-L)­(μ-9-An)­Ln­(NO₃)₂]·2CH₃CN (Ln^III = Tb (<b>7</b>), Dy (<b>8</b>), Er (<b>9</b>), Yb­(<b>10</b>)), [Zn­(μ-L)­(μ-9-An)­Yb­(9-An)­(NO₃)₃]·3CH₃CN (<b>11</b>), [Zn­(μ-L)­(μ-9-An)­Nd­(9-An)­(NO₃)₃]·2CH₃CN·3H₂O (<b>12</b>), and [Zn­(μ-L)­(μ-9-An)­Nd­(CH₃OH)₂(NO₃)]­ClO₄·2CH₃OH (<b>13</b>) prepared from the reaction of the compartmental ligand <i>N,N</i>′<i>,N</i>″-trimethyl-<i>N,N</i>″-bis­(2-hydroxy-3-methoxy-5-methylbenzyl)­diethylenetriamine (H₂L), with ZnX₂·<i>n</i>H₂O (X = NO₃^– or OAc^–) salts, Ln­(NO₃)₃·<i>n</i>H₂O, and, in some instances, 9-anthracenecarboxylate anion (9-An). In all these complexes, the Zn^II ions invariably occupy the internal N₃O₂ site whereas the Ln^III ions show preference for the O₄ external site, giving rise to a Zn­(μ-diphenoxo)­Ln bridging fragment. Depending on the Zn^II salt and solvent used in the reaction, a third bridge can connect the Zn^II and Ln^III metal ions, giving rise to triple-bridged diphenoxoacetate in complexes <b>1</b>–<b>4</b>, diphenoxonitrate in complex <b>5</b>, and diphenoxo­(9-anthracenecarboxylate) in complexes <b>8</b>–<b>13</b>. Dy^III and Er^III complexes <b>2</b>, <b>8</b> and <b>3</b>, <b>5</b>, respectively, exhibit field induced single molecule magnet (SMM) behavior, with <i>U</i>_eff values ranging from 11.7 (3) to 41(2) K. Additionally, the solid-state photophysical properties of these complexes are presented showing that ligand L^2‑ is able to sensitize Tb^III- and Dy^III-based luminescence in the visible region through an energy transfer process (antenna effect). The efficiency of this process is much lower when NIR emitters such as Er^III, Nd^III, and Yb^III are considered. When the luminophore 9-anthracene carboxylate is incorporated into these complexes, the NIR luminescence is enhanced which proves the efficiency of this bridging ligand to act as antenna group. Complexes <b>2</b>, <b>3</b>, <b>5</b>, and <b>8</b> can be considered as dual materials as they combine SMM behavior and luminescent properties