Theoretical Predictions of a New ∼14 kDa Core-Mass Thiolate-Protected Gold Nanoparticle: Au₆₈(SR)₃₆

As an important intermediate link between the smaller and larger size thiolate-protected gold nanoparticles (RS-AuNPs), the molecular formula and atomic structure of the ∼14 kDa core-mass RS-AuNP species (containing around 70 core gold atoms) have not been determined unambiguously. In this work, we theoretically predict an unprecedented ∼14 kDa core-mass AuNP species, denoted as Au₆₈(SR)₃₆, which is composed a symmetric, face-centered-cubic (fcc) 68-gold atom framework. The fcc gold kernel in the Au₆₈(SR)₃₆ is made of eight 13-atom Au-cubotahedrons sharing 12 square faces, showing a standard 2 × 2 × 2 magic cube formula. The Au₆₈(SR)₃₆ is thought to be a key intermediate NP bridging the evolution of Au₄₄(SR)₂₈ and Au₉₂(SR)₄₄. The DFT calculations indicate the Au₆₈(SR)₃₆ has a sizable HOMO-LUMO gap of 0.98 eV and relative high thermodynamic stability. The fcc 68-atom gold framework in the Au₆₈(SR)₃₆ also presents a new candidate to address the atomic structure of recently reported water-soluble mercaptobenzoic acid protected Au₆₈NPs.