Heptanuclear Mixed-Valence Co 4 III Co 3 II 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 7 (μ 3 -OH) 4 (H 2 L 1 ) 2 (HL 2 ) 2 ](NO 3 ) 6 ·6H 2 O ( 1 ) (where H 5 L 1 is 2,2'-(((1E,1'E)-((2-hydroxy-5-methyl-1,3-phenylene)bis(methanylylidene))bis(azanylylidene))bis(propane-1,3-diol)) and H 2 L 2 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 7 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 3 -OH groups, giving rise to a planar heptanuclear cluster that resembles a molecular fragment of a layered double hydroxide (LDH). Two triply deprotonated (H 2 L 1 ) 3- ligands form the outer side of the cluster while two singly deprotonated (HL 2 ) - 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 0 = 8.2(7) × 10 -7 s and U eff = 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 × 10 4 μmol H 2 h -1 mol -1 .