Functionalization and Capping of a CdS Nanocluster: A Study of Ligand Exchange by Electrospray Mass Spectrometry

Abstract

Electrospray mass spectrometry is a powerful technique for investigating the capping and the functionalization of the surface of a CdS nanocluster, via ligand-exchange reactions. The reactions of the thiophenolate-capped CdS cluster [S4Cd17(SPh)28]2- with thiols (HSR), dithiols (HSRSH), thiol acids (HSRCOOH), thio acids (RCOSH), thiol alcohols (HORSH), diethyldithiocarbamate [Et2NCSS]-, isopropylxanthate [(CH3)2CHOCSS]- and 3-mercaptopropyltrimethoxysilane [HS(CH2)3Si(OCH3)3] have been investigated. Information about the extent of exchange, bonding modes and cluster transformations is obtained. Almost complete exchange was observed for p-toluenethiol while the exchange with o-toluenethiol and 1-dodecanethiol was restricted owing to steric hindrance. The thiol acids HSRCOOH bind as the doubly charged [R(S)COO]2- ligand, chelating to neighboring cadmium atoms through both the thiol group and one of the oxygen atoms of the carboxylic acid group. The exchange with the thio acids [RCOSH] involves terminal [RCOS]- ions. Diethyldithiocarbamate [(C2H5)2NCSS]- and isopropylxanthate [(CH3)2CHOCSS]- remove cadmium atoms from the surface of the cluster due to the formation of terminal S,S-chelating bonds. 3-Mercaptopropyltrimethoxysilane HS(CH2)3Si(OCH3)3 readily exchanged to yield the silane-functionalized clusters [S4Cd17(SPh)28-n{S(CH2)3Si(OCH3)3}n]2- (n = 1−11).