Controlled reduction for size selective synthesis of thiolate-protected gold nanoclusters Au(n)(n = 20, 24, 39, 40)

This work presents a controlled reduction method for the selective synthesis of different sized gold nanoclusters protected by thiolate (SR = SC(2)H(4)Ph). Starting with Au(III) salt, all the syntheses of Au(n)(SR)(m) nanoclusters with (n, m) = (20, 16), (24, 20), (39, 29), and (40, 30) necessitate experimental conditions of slow stirring and slow reduction of Au(I) intermediate species. By controlling the reaction kinetics for the reduction of Au(I) into clusters by NaBH(4), different sized gold nanoclusters are selectively obtained. Two factors are identified to be important for the selective growth of Au(20), Au(24), and Au(39/40) nanoclusters, including the stirring speed of the Au(I) solution and the NaBH(4) addition speed during the step of Au(I) reduction to clusters. When comparing with the synthesis of Au(25)(SC(2)H(4)Ph)(18) nanoclusters, we further identified that the reduction degree of Au(I) by NaBH(4) also plays an important role in controlling cluster size. Overall, our results demonstrate the feasibility of attaining new sizes of gold nanoclusters via a controlled reduction route.