Slow magnetic relaxation and selective luminescent probe in a 2p–3d–4f heterotrispin chain

Abstract

Three types of radical–3d/3d–4f heterotrispin complexes [(Cu(hfac)₂)₄(NIT-4-OMe-4PyPh)₂] (1), {[(Cu(hfac)₂)₃(NIT-4-OMe-4PyPh)₂]}_n (2) and {[Cu(hfac)₂][(NIT-4-OMe-4PyPh)]₂[Ln(hfac)₃]}_n (Ln = Gd 3; Tb 4; Dy 5; Ho 6) (NIT-4-OMe-4PyPh = 2-[4-methoxy-3-(4-pyridinylmethoxy)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate) have been successfully synthesized by adjusting various experimental conditions. Compound 1 is a six-spin cyclic structure including a cyclic molecular structure with two Cu(hfac)₂ units linked by free NO groups, while complex 2 possesses a one-dimensional topological structure consisting of cyclic [Cu–radical]₂ dimers bridged by Cu^II ions. Compounds 3–6 display a series of 2p–3d–4f heterotrispin chains in which NIT-4-OMe-4PyPh radical ligands linked Ln^III and Cu^II ions in “head-to-head” mode through pyridine-N atoms and NO moieties. The magnetic behavior for complex 1 revealed a dominant antiferromagnetic exchange interaction between the radical and five coordinated Cu^II ions while for 2, just a ferromagnetic Cu–ON interaction was obviously observed. Furthermore, Tb and Dy heterotrispin chains showed field-induced slow magnetic relaxation behaviors. In particular, Tb derivative shows the characteristic emission peaks of Tb^III ion and can be developed as a prospective recyclable luminescent probe for detecting Fe³⁺ ion.