Anion Effects on Lanthanide(III) Tetrazole-1-acetate Dinuclear Complexes Showing Slow Magnetic Relaxation and Photofluorescent Emission

Three types of lanthanide complexes based on the tetrazole-1-acetic acid ligand and the 2,2′-bipyridine coligand were prepared and characterized by single-crystal X-ray diffraction, IR spectroscopy, and elemental analyses; the formulas of these complexes are [Ln₂(1-tza)₄(NO₃)₂(2,2′-bipy)₂] (Ln = Sm (<b>1</b>), Eu (<b>2</b>), Gd (<b>3</b>), Tb (<b>4</b>), Dy (<b>5</b>)), [Dy₂(1-tza)₄Cl₂(2,2′-bipy)₂] (<b>6</b>), and [Yb₂(1-tza)₄(NO₃)₂(2,2′-bipy)₂] (<b>7</b>) (1-tza = tetrazole-1-acetate and 2,2′-bipy = 2,2′-bipyridine). They are dinuclear complexes possessing similar structures but different lanthanide­(III) ion coordination geometries because of the distinction of peripheral anions (such as NO₃^– and Cl^–) and the effect of lanthanide contraction. The variable-temperature magnetic susceptibilities of <b>1</b>–<b>6</b> were measured. Both Dy^III complexes (<b>5</b> and <b>6</b>) display field-induced single-molecule magnet behaviors. Ab initio calculations revealed that the Dy^III complex <b>6</b> possesses a more anisotropic Dy^III ion in comparison to that in <b>5</b>. The room-temperature photoluminescence spectra of Sm^III (<b>1</b>), Eu^III (<b>2</b>), Tb^III (<b>4</b>), and Dy^III (<b>5</b> and <b>6</b>) complexes exhibit strong characteristic emissions in the visible region, whereas the Yb^III (<b>7</b>) complex shows near-infrared (NIR) luminescence