Co-synthesis of atomically precise nickel nanoclusters and the pseudo-optical gap of Ni4(SR)8

Abstract

Three sizes of atomically precise tiara-like structural Ni_n(SR)_2n (n = 4, 5 and 6) are co-synthesized by a one-pot method and isolated using thin layer chromatography. The molecular formulas of Ni₅(SR)₁₀ and Ni₆(SR)₁₂ are determined using matrix-assisted laser desorption ionization mass spectrometry, and the tiara-like structures of Ni₄(SR)₈ and Ni₆(SR)₁₂ are proved using single-crystal X-ray crystallography. Nuclear magnetic resonance shows that Ni₅(SR)₁₀ has a similar tiara-like structure too. The electrochemical gap enlarges with the increase of the cluster size, which agrees with the calculated HOMO–LUMO gap and optical gap by TD-DFT, but the experimental optical gap is G_O(Ni₄(SR)₈) > G_O(Ni₆(SR)₁₂) > G_O(Ni₅(SR)₁₀) due to Ni₄(SR)₈ owning a pseudo-optical gap at 2.0 eV.