Bifunctional heterobimetallic 3d–4f [Co(<scp>ii</scp>)-RE, RE = Dy, Eu, and Y] ionic complexes: modulation of the magnetic-luminescence behaviour

This work reports the engineering and functional properties of an emerging class of heterobimetallic 3d-4f ionic complexes designed with cobalt and rare-earth (RE) metals. We present a comprehensive examination of the structural, magnetic, optical, and thermal properties of the heterobimetallic ionic complexes with the general formula [Co(hfa)₃]^-[RE(hfa)₂tetraglyme]⁺ (RE = Dy, Eu, and Y), where the metal centres are coordinated by hexafluoroacetylacetonate (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione), β-diketone and tetraglyme (2,5,8,11,14-pentaoxapentadecane) polyether. Structural analysis reveals an octahedral coordination geometry enveloping the cobalt(II) centre, characterized by inherent symmetry properties consistent across the derivatives, while a capped square-antiprism coordination polyhedron is observed for the RE ions. Electron paramagnetic resonance (EPR) spectroscopy confirms the constancy of the electronic structure of the cobalt(II) moiety and the significant contribution of the lanthanide ions to the magnetic properties of the compounds. The non-trivial single-ion magnetic properties of cobalt(II), dysprosium(III), and europium(III) centres, and the effect of their interactions are investigated by a detailed static and dynamic magnetic susceptibility study. Moreover, optical analyses have been carried out showing the π-π* intraligand (IL) transition of the β-diketonate ligand and the d-d cobalt(II) transitions. Luminescence characterization of dysprosium(III) and europium(III) derivatives exhibits their characteristic emission bands, indicative of the unique photophysical properties conferred by the lanthanide ions. Thermal studies using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) reveal good thermal stability and volatility properties, underscoring the interesting nature of these ionic complexes for potential deposition on suitable substrates. In summary, these heterobimetallic complexes show intriguing optical and magnetic properties with potential implications across diverse scientific disciplines, including molecular magnetism, optoelectronics, and materials science.