The Infrequent Cyclic [As ₂ S ₂ (μ ₂ -S)(μ ₂ -S ₂ )] ^2– Moiety in Mn(II) and Cd(II) Polythioarsenate Complexes for the Modification of Ni-Foam Electrodes in Electrocatalytic Oxygen Evo

The pursuit of functional chalcoarsenates is of great significance for potential electrocatalytic oxygen evolution applications. Herein, two transition-metal polythioarsenate complexes {<i>TM</i>(tptz)[As₂S₂(μ₂-S)(μ₂-S₂)]} [<i>TM</i> = Mn²⁺ (<b>1a</b>) and Cd²⁺ (<b>1b</b>), tptz = 2,4,6-tris-2-pyridyl-1,3,5-triazine] have been afforded by the solvothermal method. <b>1a</b> and <b>1b</b> contain a hitherto-unknown acentric cyclic [As₂S₂(μ₂-S)(μ₂-S₂)]^2- moiety that is built from two AsS subunits bridged by S^2- and S₂^2-. This [As₂S₂(μ₂-S)(μ₂-S₂)]^2- moiety serves as a bidentate chelating ligand to unsaturated complexes [<i>TM</i>(tptz)]²⁺, resulting in the rare <i>TM</i> polythioarsenate complexes. The energy gaps achieved from the UV-visible absorption spectrum are 1.33 eV for <b>1a</b> and 1.31 eV for <b>1b</b>, and <b>1a</b> and <b>1b</b> exhibit a remarkable photocurrent response under visible-light irradiation. <b>1a</b> and <b>1b</b> are utilized for the fabrication of the electrodes Ni/<b>1a</b>/NF and Ni/<b>1b</b>/NF (NF = porous Ni foam) as the electrocatalysts, which exhibit excellent oxygen evolution reaction (OER) activity with low overpotentials of 214 mV for Ni/<b>1a</b>/NF and 208 mV for Ni/<b>1b</b>/NF to achieve a current density of 10 mA·cm^-2. This study not only enriches the structural type of chalcoarsenate complexes but also offers the only case of polythioarsenate complexes as OER electrocatalysts.