Muffin-like lanthanide complexes with an N5O2-donor macrocyclic ligand showing field-induced single-molecule magnet behaviour

Abstract

Three mononuclear lanthanide complexes of a 2-pyridylmethyl pendant-armed 15-membered ligand {(3,12-bis(2-pyridylmethyl)-3,12,18-triaza-6,9-dioxabicyclo-[12.3.1]octadeca-1,14,16-triene); L} with general formula [Ln(L)(H₂O)(NO₃)](NO₃)₂ (Ln = Tb (1), Dy (2), and Er (3)) are reported. Based on X-ray diffraction analysis of 1 and 2, the central lanthanide atoms are nine-coordinated with the N₅O₄ donor set originating from the ligand L and one coordinated water molecule and one monodentate-bonded nitrato ligand. The coordination geometry of the [LnN₅O₄] cores can be described as a muffin-like shape. Magnetic measurements revealed that all three compounds show field-induced single-molecule magnet behaviour, with estimated energy barriers U ≈ 44–82 K. The experimental study was complemented by CASSCF calculations showing a trend of an increasing first excited energy gap (Tb → Dy → Er) within the muffin-like geometry with the lowest magnetization tunnelling probability for the Dy^III complex 2.