A trinuclear linear Co(II)-Y(III)-Co(II) complex exhibiting field-induced slow magnetic relaxation and electrocatalytic OER activity.

Integrating multiple functionalities within a single molecular system is a key goal in modern coordination chemistry, particularly for coupling single-molecule magnet (SMM) behavior with electrocatalysis. In this work, a heterometallic trinuclear CoII-YIII-CoII complex (complex 1) is synthesized using a pyridine-based ligand, 2,2'-[{(1E,1'E)-pyridine-2,6-diyl-bis(methaneylylidene)}bis(azaneylylidene)diphenol] (LH2). Single-crystal X-ray diffraction analysis revealed that the complex adopted a linear Co-Y-Co configuration, forming a precise 180° angle with terminal Co(II) centers situated in distorted pentagonal bipyramidal N3O4 environments and a distorted octahedral Y(III) site. Additionally, intermolecular O-H⋯Cl hydrogen bonds further organized the lattice into one-dimensional supramolecular chains. Magnetic studies indicated dominant crystal-field effects with weak ferromagnetic coupling between Co(II) ions (J = 0.1482 cm-1), a significant axial zero-field splitting (D = 17.52 cm-1), and an enhanced g value (g = 2.3), consistent with easy-plane anisotropy and incomplete magnetization saturation. Despite the easy-plane anisotropy, ac susceptibility measurements revealed field-induced slow magnetic relaxation governed by competing field-suppressed QTM and field-enhanced direct processes, together with a field-independent contribution consistent with Raman-like two-phonon relaxation rather than a conventional Orbach pathway. When immobilized on nickel foam, the molecular complex functioned as an efficient OER precatalyst in 1 M KOH, requiring an overpotential of 323 mV to achieve 10 mA cm-2 with a Tafel slope of 126 mV dec-1 and stable operation for 50 h. Post-OER analysis confirmed in situ surface reconstruction to mixed-valent cobalt oxyhydroxide (Co-OOH), which constituted the catalytically active phase during water oxidation. The observed OER performance is comparable to representative cobalt-based molecular and precursor-derived systems under similar alkaline conditions.