The reaction of 1,3-bis[(4-chloro)benzene]triazene (HL) and CuCl2 center dot 2H(2)O affords a dinuclear triazenido-copper(II) complex [Cu2L4(NCCH3)] (1), a new molecular electrocatalyst, which has been determined by X-ray crystallography. Electrochemical studies show that complex 1 can catalyze hydrogen evolution from acetic acid or water. Turnover frequency (TOF) reaches a maximum of 43 (in DMF) and 174 (in phosphate buffer, pH 6) moles of hydrogen per mole of catalyst per hour, respectively. Sustained proton reduction catalysis occurs at glassy carbon (GC) electrode to give H-2 over a 72 h electrolysis period and no observable decomposition of the catalyst. (C) 2014 Elsevier B.V. All rights reserved.