Heptanuclear Mixed-Valence Co4IIICo3II Molecular Wheel─A Molecular Analogue of Layered Double Hydroxides with Single-Molecule Magnet Behavior and Electrocatalytic Activity for Hydrogen Evolution Reactions

We present a bifunctional heptanuclear cobalt(II)/cobalt(III) molecular complex formulated as [Co<inf>7</inf>(μ<inf>3</inf>-OH)<inf>4</inf>(H<inf>2</inf>L¹)<inf>2</inf>(HL²)<inf>2</inf>](NO<inf>3</inf>)<inf>6</inf>·6H<inf>2</inf>O (1) (where H<inf>5</inf>L¹ is 2,2′-(((1E,1′E)-((2-hydroxy-5-methyl-1,3-phenylene)bis(methanylylidene))bis(azanylylidene))bis(propane-1,3-diol)) and H<inf>2</inf>L² is 2-amino-1,3-propanediol). Compound 1 has been characterized by single-crystal X-ray diffraction analysis along with other spectral and magnetic measurements. Structural analysis indicates that 1 contains a mixed-valence Co<inf>7</inf> cluster where a central Co(II) ion is connected to six different Co centers (four Co^III and two Co^II ions) by four μ<inf>3</inf>-OH groups, giving rise to a planar heptanuclear cluster that resembles a molecular fragment of a layered double hydroxide (LDH). Two triply deprotonated (H<inf>2</inf>L¹)^3- ligands form the outer side of the cluster while two singly deprotonated (HL²)⁻ ligands are located at the top and bottom of the central heptanuclear core. Variable temperature magnetic measurements indicate the presence of weak ferromagnetic Co^II···Co^II interactions (J = 3.53(6) cm^-1) within the linear trinuclear Co^II cluster. AC susceptibility measurements show that 1 is a field-induced single-molecule magnet (SMM) with τ<inf>0</inf> = 8.2(7) × 10^-7 s and U<inf>eff</inf> = 11.3(4) K. The electrocatalytic hydrogen evolution reaction (HER) activity of 1 in homogeneous phase shows an overpotential of 455 mV, with a Faradaic efficiency of 81% and a TOF of 8.97 × 10⁴ μmol H<inf>2</inf> h^-1 mol^-1