Multistep nucleation of nanocrystals in aqueous solution : Nature Chemistry : Nature Research

October 1, 2017

Multistep nucleation of nanocrystals in…solution Creation of Au-Au pair, expelling water, drives cluster formation

To explain how the gold-rich aqueous phase forms and breaks down in Figures 1A and 2A, we
performed ab-initio calculations of a hydrated gold atom pair (Figure 4). This hydrated atom pair
becomes ionized when brought closer together: the left gold atom plus two nearby water molecules
form a linear cationic coordination complex, [Au(H2O)2]+1, while the right gold atom becomes an
anion surrounded by a simple hydration shell. Other (square planar and linear) complexes involving
chloride and hydroxide ligands may also participate, depending on pH (26, 33) (Section SI2). For
nanoclusters to form inside the gold-rich aqueous phase, pairs of gold atoms within it must be partially
dehydrated. In our calculations (Figure 4), this dehydration is delayed by a 7.6 kcal/mol (12.9 kBT)
energy barrier required to breakdown the linear cationic complex (close to the gold anion).