Anion Effects on the Structural and Magnetic Properties of a Series of Trinuclear Cu ^II –Ln ^III –Cu ^II Complexes

Two series of heterometallic Cu^II ₂Ln^III complexes, ([Cu₂Ln-(<b>H</b> _<b>4</b> <b>L</b>)₂(MeOH)₂Br]-(MeOH)₄(Et₂O)-(Br₂), where Ln = Y (<b>1</b>), Gd (<b>2</b>), Er (<b>3</b>), Tb (<b>4</b>)), and ([Cu₂Ln-(<b>H</b> _<b>4</b> <b>L</b>)₂(MeOH)₂Cl₂]-(MeOH)₄(Et₂O)-Cl, where Ln = Y (5), Gd (6), Er (7), Tb (8), and H₆L = (<i>N</i>,<i>N</i>'-bis-(2,3,4-trihydroxybenzylidene)-1,2-phenylenediamine), were designed, synthesized, and characterized through X-ray and magnetic analyses. X-ray analysis revealed that the bromide containing complexes <b>1</b>-<b>4</b> possessed identical supramolecular arrangements, crystallizing in layers of 2D sheets, while chloride containing complexes <b>5</b>-<b>8</b> formed a 3D supramolecular lattice possessing an additional π-π stacking interaction per complex. DC magnetic susceptibility measurements showed that complexes <b>3</b> and <b>7</b> exhibited antiferromagnetic coupling between copper and erbium centers while the gadolinium (<b>2</b> and <b>6</b>) and terbium (<b>4</b> and <b>8)</b> containing complexes displayed ferromagnetic CuLn coupling upon cooling. AC magnetic susceptibility measurements revealed that complexes <b>4</b> and <b>8</b> also displayed zero-field SMM behavior with <i>U</i> _eff = 17.8 and 16.0 K, respectively. The larger bromide anion in complex <b>4</b> aids in the isolation of the magnetic centers, resulting in a <i>U</i> _eff value higher than that of the chloride analogue.