A pair of bis‐thiosemicarbazonato‐Ni(II) complexes with pendant polyamines, (N,N′‐(dimethylethylenediaminothiosemi‐carbazonato)‐4‐(methylthiosemi‐carbazonato)butane‐2,3‐diimine)‐nickel(II) (1) and (N,N′‐bis(dimethylethyl‐enediaminothiosemi‐carbazonato)butane‐2,3‐diimine)‐nickel(II) (3), have been synthesized. Methylation at the terminal amines yields the cationic derivatives 2 and 4. All complexes are fully characterized by spectroscopic, electrochemical, and single‐crystal X‐ray diffraction methods. Single crystal X‐ray diffraction studies on all four Ni(II) complexes confirm a square planar Ni(II) framework with no significant changes in the coordination environment as a function of the pendant groups. Spectroscopic studies are consistent with a similar electronic structure in all complexes. However, electrochemical investigations reveal significant cathodic shifts in the Ni(II)L/Ni(II)L·– and Ni(II)L·–/Ni(I)L·2– reduction potentials of the methylated vs. non‐methylated species. The HER activity of all four nickel complexes were evaluated in acetonitrile with glacial acetic acid. The 3 complex was shown to have the highest activity with a TOF of 6.3 × 103 s‐1, an overpotential of 0.56 V, and faradaic efficiency of 100 %.
A series of new bis(thiosemicarbazonato) Cu(II) complexes with pendent polyamines, diacetyl-(N,-dimethylethylenediaminothiosemicarbazonato)-(N'-methyl-3-thio-semicarbazonato)butane-2,3-diimine)-copper(II) (Cu-1), diacetyl-bis (N-dimethylethylenediamino-3-thiosemicarbazonato)butane-2,3-diimine)-copper(II) (Cu-3), and their cationic derivatives Cu-2 and Cu-4, have been synthesized and fully characterized by spectroscopic, electrochemical, and X-ray diffraction methods. Complexes Cu-1-Cu-4 are analogues of Cu(ATSM), which contains a similar N 2 S 2 donor core with terminal non-coordinating amines. Substitution of the methyl group(s) of the terminal amines of H 2 ATSM with N,N-dimethylethylenediamine followed by alkylation generates a charged quaternary amine in the ligand framework. The charged site tunes the redox potentials of the complexes with minimal changes in their physical and electronic properties. The HER activity of all four copper complexes were evaluated in acetonitrile with glacial acetic acid. All of the complexes have lower HER overpotentials than Cu(ATSM), which is attributed to charge effects. The pendent amines of Cu-1 and Cu-3 have the lowest HER overpotential as the pendent tertiary amine also serves as a proton relay to enhance proton rearrangement under catalytic conditions. Complex Cu-3 showed the highest activity with a TOF of 12 × 10 3 s À 1 , an overpotential of 0.65 V, and faradaic efficiency of 100 %.
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