Luminescent Ir(iii)–Ln(iii) coordination polymers showing slow magnetization relaxation

Abstract

A series of iridium(III)–lanthanide(III) bimetallic coordination polymers were successfully obtained by hydrothermal reactions based on the Ir unit [Ir(ppy)₂(Hdcbpy)], namely, [Ln{Ir(ppy)₂(dcbpy)}₂(NO₃)(H₂O)_n]·solvent (Ir₂Ln, n = 5, Ln = Gd and Dy; and n = 4, Ln = Er and Yb) and [Ln₂(OH){Ir(ppy)₂(dcbpy)}₄(NO₃)(H₂O)₄]·solvent (Ir₄Ln₂, Ln = Gd, Dy, Er, and Yb). Compounds Ir₂Ln show chain structures in which the lanthanide ions are bridged by the Ir(ppy)₂(dcbpy)⁻ ligands through the carboxylate groups. Compounds Ir₄Ln₂ have double-chain structures, in which the dimers of Yb₂(OH) are connected by the Ir(ppy)₂(dcbpy)⁻ ligands. Magnetic studies reveal that Ir₂Dy and Ir₄Dy₂ exhibit slow magnetic relaxation behaviour in zero dc field, which is characteristic of single molecule magnets, but Ir₂Er, Ir₄Yb₂, Ir₄Er₂ and Ir₄Yb₂ require a field to induce such characteristics. Moreover, since the iridium(III) moiety can serve as an “antenna” to effectively sensitize the f–f transitions of the lanthanide ions, near-infrared luminescence has been observed for the Yb^III and Er^III complexes. As far as we know, this is the first observation of SMM behaviour and NIR luminescence in iridium(III)–lanthanide(III) bimetallic coordination polymers.