SMM behaviour of butterfly {MIII2DyIII2} complexes; M= Co vs Cr

This abstract describes a comparative study of tetranuclear {M₂^III​Dy₂^III​} butterfly-shaped complexes, focusing on how the transition metal (M=Co,Cr) influences single-molecule magnet (SMM) properties. While {Co₂^III​Dy₂^III​} systems exhibit magnetic relaxation through Orbach and Raman mechanisms, they are frequently limited by fast Quantum Tunneling of Magnetization (QTM). In contrast, substituting diamagnetic Co(III) with paramagnetic Cr(III) yields isostructural complexes with vastly superior performance. The {Cr₂^III​Dy₂^III​} family effectively suppresses QTM, enabling pure Orbach relaxation and the opening of magnetic hysteresis loops at 2 K, with coercive fields reaching up to ca. 3T