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Effect of Stacking Interactions on the Translation of Structurally Related Bis(thiosemicarbazonato)nickel(II) HER Catalysts to Modified Electrode Surfaces

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journal contribution
posted on 03.09.2019, 18:04 by Alexander J. Gupta, Nicholas S. Vishnosky, Oleksandr Hietsoi, Yaroslav Losovyj, Jacob Strain, Joshua Spurgeon, Mark S. Mashuta, Rahul Jain, Robert M. Buchanan, Gautam Gupta, Craig A. Grapperhaus
A series of crystalline nickel­(II) complexes (13) based on inexpensive bis­(thiosemicarbazone) ligands diacetylbis­(4-methyl-3-thiosemicarbazone) (H2ATSM), diacetylbis­(4,4-dimethyl-3-thiosemicarbazone) (H2ATSDM), and diacetylbis­[4-(2,2,2-trifluoroethyl)-3-thiosemicarbazone] (H2ATSM-F6) were synthesized and characterized by single-crystal X-ray diffraction and NMR, UV–visible, and Fourier transform infrared spectroscopies. Modified electrodes GC-1GC-3 were prepared with films of 13 deposited on glassy carbon and evaluated as potential hydrogen evolution reaction (HER) catalysts. HER studies in 0.5 M aqueous H2SO4 (10 mA cm–2) revealed dramatic shifts in the overpotential from 0.740 to 0.450 V after extended cycling for 1 and 2. The charge-transfer resistances for GC-1GC-3 were determined to be 270, 160, and 630 Ω, respectively. Characterization of the modified surfaces for GC-1 and GC-2 by scanning electron microscopy and Raman spectroscopy revealed similar crystalline coatings before HER that changed to surface-modified crystallites after conditioning. The surface of GC-3 had an initial glasslike appearance before HER that delaminated after HER. The differences in the surface morphology and the effect of conditioning are correlated with crystal-packing effects. Complexes 1 and 2 pack as columns of interacting complexes in the crystallographic a direction with short interplanar spacings between 3.37 and 3.54 Å. Complex 3 packs as columns of isolated molecules in the crystallographic b direction with long-range interplanar spacings of 9.40 Å.

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