End-to-End Azido-Bridged Lanthanide Chain Complexes (Dy, Er, Gd, and Y) with a Pentadentate Schiff-Base [N 3 O 2 ] Ligand: Synthesis, Structure, and Magnetism.

The syntheses, structure and magnetic properties are reported for five novel 1D polymeric azido-bridged lanthanide complexes with the general formula {[Ln(DAPMBH)(N ₃ )C ₂ H ₅ OH]C ₂ H ₅ OH} _n where H ₂ DAPMBH = 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone)-a new pentadentate pyridine-base [N ₃ O ₂ ] ligand and Ln = Dy ( 1 ), Y _0.930 Dy _0.070 ( 2 ), Er ( 3 ), Y _0.923 Er _0.077 ( 4 ), and Gd ( 5 ). X-ray diffraction analysis of 1 - 5 show that the central lanthanide atoms are eight-coordinated with the N ₅ O ₃ donor set originating from the ligand DAPMBH, one coordinated ethanol molecule and two end-to-end type N ₃ ^- bridges connecting the metal centers into infinite chain. The [LnN ₅ O ₃ ] coordination polyhedron can be regarded as a distorted dodecahedron ( D _{2 d} ). AC magnetic measurements revealed that compounds 1 - 4 show field-induced single-molecule magnet behavior, with estimated energy barriers U _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 Ln ³⁺ ions mediated by the end-to-end azide bridging groups ( J ≈ -0.015 cm ^-1 for 5 ). Comparative analysis of static and dynamic magnetic properties of magnetically concentrated ( 1 , 3 ) and diluted ( 2 , 4 ) Dy and Er compounds showed that, despite fascinating 1D azido-bridged chain structure, compounds 1 and 3 are not single-chain magnets; their magnetic behavior is largely due to single-ion magnetic anisotropy of individual Ln ³⁺ ions.