Chiroptical Activity Enhancement via Structural Control: The Chiral Synthesis and Reversible Interconversion of Two Intrinsically Chiral Gold Nanoclusters

We
report the synthesis and crystal structure determination of
two novel chiral gold nanoclusters. By utilizing BINAP, we isolate
atomically precise intrinsically chiral Au nanoclusters [Au9(R-/S-BINAP)4]­(CF3COO)3 and [Au10(R-/S-BINAP)4(p-CF3C6H4CC)]­(CF3COO)3 in
high yield with one-pot synthesis. Au9 has C2 geometry, while Au10 is C1 symmetric.
Interestingly, reversible interconversion between Au9 and Au10 can be realized by the addition or removal of a RCCAu component.
The transformation from Au9 to Au10 leads to significant enhancement
of CD signals. The maximum anisotropy factor in the visible region
of [Au10(BINAP)4(p-CF3C6H4CC)]3+ is the hitherto
largest (up to 6.6 × 10–3) among gold nanoclusters,
which is approximately twice of that of [Au9(BINAP)4]3+. This work demonstrates that the chiroptical
activity of gold nanoclusters can be modulated by structural control
through the introduction of second ligands.