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

Table 2 The respective conditions for the syntheses of Au ₂₀ , Au _24, and mixed Au _39/40

	Cluster size	Stage I	Stage II	Amount of NaBH₄(concentration, 0.44 M) per mole of gold and speed of addition	Aging time
		Stirring speed at the stage of Au(III) reduction to Au(I) by 3X HSC₂H₄Ph	Stirring speed at the stage of Au(I) reduction to clusters by NaBH₄
1	Au₂₀	Stationary	Approximately 50 rpm	1 mL (1×), dropwise added over a 30-min period	Approximately 6 hrs
2	Au₂₄	50 to 100 rpm	Approximately 100 rpm	1 mL (1×), dropwise added over a 15-min period	Overnight
3	Au_39/40	50 to 100 rpm	Approximately 400 rpm	1 mL (1×), dropwise added over a 15-min period	Overnight
4	Au₂₅	50 to 100 rpm	50 to 400 rpm	5 mL (5×), Dropwise added over a 50-min period	Overnight