Solvato- and vapochromic exchange-coupled Dy2 single-molecule magnets achieved by attaching iron-cyanido metalloligands

Abstract

Lanthanide single-molecule magnets (Ln-SMMs) have attracted scientific attention due to their potential application in data storage and spintronics. On the other hand, stimuli-responsive molecular materials are considered for chemical sensors thanks to their solvato- and vapochromism. Aiming at advanced multifunctionality, the Ln-SMMs can be functionalized toward various physical properties, e.g., luminescence or ferroelectricity. We present an approach toward the conjunction of molecular nanomagnetism with solvatochromism in solution and vapochromism in the solid state. Our concept is based on combining Dy^III complexes bearing O-donor ligands, i.e., 4-pyridone (4-pyone), responsible for the SMM property, with dicyanido-bis(1,10-phenanthroline)iron(II) metalloligands inducing a chemochromic response. We report tetranuclear molecules, {[Dy^III(4-pyone)₅]₂[Fe^II(CN)₂(phen)₂]₂}(CF₃SO₃)₆ (1) containing (4-pyone)-bridged {Dy^III₂}⁶⁺ units which exhibit pronounced SMM characteristics due to the axial alignment of 4-pyone ligands within a pentagonal bipyramidal geometry and the weakening of quantum tunneling of magnetization (QTM) achieved by ligand-mediated exchange coupling. The {Dy^III₂} SMMs are cyanido-bridged to Fe^II complexes and the resulting {Dy^III₂Fe^II₂}⁶⁺ cations could be dissolved in various solvents providing distinct solvatochromism achieved by tunable charge-transfer absorption of dicyanidometallates. The optical sensitivity of 1 to solvent molecules was also found in the solid state unveiling efficient vapochromism related to the incorporation of solvent vapors into the crystals of 1. The variously solvated phases of 1 were isolated from alcohol solutions giving a series of compounds, namely 1·MeOH, 1·EtOH, 1·PrOH, and 1·BuOH, differing not only in light absorption but also in SMM features, including the level of quenching of the QTM.