Facile synthesis of Au-23(SC(CH3)(3))(16) clusters

Mono-dispersed Au-23 clusters protected by 16 tert-butyl thiols, a bulky-aliphatic ligand, have been synthesized using a one-pot protocol. The protocol yields two fractions in high yields. While both fractions are soluble in dichloromethane (and tetrahydrofuran, acetone, and toluene), one can be isolated from the other by washing the solid mixture sample with acetonitrile. Electrospray ionization mass spectrometry showed accurate match between the experimental and simulated values, indicating Au-23(SC4H9)(16) for both fractions. MALDI MS experiments provide evidence that the core-shell structural formula consists of Au(SR)(2) and Au-2(SR)(3) units. The UV-visible spectra of each fraction show a peak at 566 nm, with the HOMO-LUMO gaps of the acetonitrile and dichloromethane fractions being 1.88 and 1.94 eV, respectively. Both fractions show photoluminescence peak emission in the near-infrared region at 830 and 838 nm, for acetonitrile and dichloromethane fractions, respectively. The electrochemistry of the two fractions also revealed similar features, with irreversible peaks at 0.74 and -1.58 V vs. SCE resulting in an estimation of the HOMO-LUMO gap after charge correction of ca. 1.86 and 1.95 eV for acetonitrile and dichloromethane fractions, in close agreement with the optical values.