End-to-End Azido-Bridged Lanthanide Chain Complexes (Dy, Er, Gd, and Y) with a Pentadentate Schiff-Base [N₃O₂] Ligand: Synthesis, Structure, and Magnetism

Abstract

The syntheses, structure and magnetic properties are reported for five novel 1D polymeric azido-bridged lanthanide complexes with the general formula {[Ln(DAPMBH)(N₃)C₂H₅OH]C₂H₅OH}_<i>n</i> where H₂DAPMBH = 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone)-a new pentadentate pyridine-base [N₃O₂] ligand and Ln = Dy (<b>1</b>), Y_0.930Dy_0.070 (<b>2</b>), Er (<b>3</b>), Y_0.923Er_0.077 (<b>4</b>), and Gd (<b>5</b>). X-ray diffraction analysis of <b>1</b>-<b>5</b> show that the central lanthanide atoms are eight-coordinated with the N₅O₃ donor set originating from the ligand DAPMBH, one coordinated ethanol molecule and two end-to-end type N₃^- bridges connecting the metal centers into infinite chain. The [LnN₅O₃] coordination polyhedron can be regarded as a distorted dodecahedron (<i>D</i>_2<i>d</i>). AC magnetic measurements revealed that compounds <b>1</b>-<b>4</b> show field-induced single-molecule magnet behavior, with estimated energy barriers <i>U</i>_eff ≈ 47-17 K. The experimental study of magnetic properties was complemented by theoretical analysis based on crystal-field calculations. Direct current magnetic susceptibility studies revealed marginally weak intrachain exchange interaction between Ln³⁺ ions mediated by the end-to-end azide bridging groups (<i>J</i> ≈ -0.015 cm^-1 for <b>5</b>). Comparative analysis of static and dynamic magnetic properties of magnetically concentrated (<b>1</b>, <b>3</b>) and diluted (<b>2</b>, <b>4</b>) Dy and Er compounds showed that, despite fascinating 1D azido-bridged chain structure, compounds <b>1</b> and <b>3</b> are not single-chain magnets; their magnetic behavior is largely due to single-ion magnetic anisotropy of individual Ln³⁺ ions.