Reciprocating thermal behavior and thermometry studies of Tb3+- and Gd3+-oxamato single-ion magnets

Abstract

Single-ion magnets (SIMs) are prominent candidates for promoting new technologies in quantum information processing (QIP). Herein, we present two new isostructural oxamato derivatives, namely, {n-Bu₄N[Ln(H₂edpba)₂]}_n, Ln = Tb³⁺ (1) and Gd³⁺ (2) [H₂edpba²⁻ = N,N′-2,2′-ethylenediphenylenebis(oxamate)], that are thermostable up to ∼290 °C. Single-crystal X-ray diffraction reveals that 1 and 2 are one-dimensional coordination polymers with a ribbon-like structure, and their metal centers are eight-coordinated with a D_4d symmetry. Cryomagnetic studies disclose the presence of slow magnetic relaxation (SMR) behavior for 1 and 2. For 1, the Raman effect dominates the SMR at a zero magnetic field, while Raman, Orbach, and reciprocating thermal behavior (RTB) mechanisms arise at higher fields. Conversely, RTB and the bottleneck effect were observed at 2. Solid-state photoluminescent data display a remarkable green luminescence emission, with intense and sharp bands ranging from 480 to 700 nm in the spectra, which are attributed to the ⁵D₄ → ⁷F_J (J = 6–0) transitions of terbium(III) ions. By monitoring the temperature-dependent lifetime of the ⁵D₄ state after the intensity decay of the emission band attributed to the ⁵D₄ → ⁷F₅ (546 nm) transition, the complex shows a reasonable thermometric performance with a relative sensitivity of 2.77% K⁻¹ at 448 K. 1 behaves as a zero-field SIM and as a photoluminescent thermometer.