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-l-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 [Ln(2)(1-tza)(4)(NO3)(2)(2,2'-bipy)(2)] (Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5)), [Dy-2(1-tza)(4)Cl-2(2,2'-bipy)(2)] (6), and [Yb-2(1-tza)(4)(NO3)(2)(2,2'-bipy)(2)] (7) (1-tza = tetrazole-l-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 1-6 were measured. Both Dy-III complexes (5 and 6) display field-induced single-molecule magnet behaviors. Ab initio calculations revealed that the Dy-III complex 6 possesses a more anisotropic Dy-III ion in comparison to that in 5. The room-temperature photoluminescence spectra of Sm-III (1), Eu-III (2), Tb-III (4), and Dy-III (5 and 6) complexes exhibit strong characteristic emissions in the visible region, whereas the Yb-III (7) complex shows near-infrared (NIR) luminescence.