FUNCTIONALIZATION AND CAPPING OF A CDS NANOCLUSTER - A STUDY OF LIGAND-EXCHANGE BY ELECTROSPRAY MASS-SPECTROMETRY

Electrospray mass spectrometry is a powerful technique for investigati ng the capping and the functionalization of the surface of a CdS nanoc luster, via ligand-exchange reactions. The reactions of the thiophenol ate-capped CdS cluster [S4Cdl7(SPh)(28)](2-) with thiols (HSR), dithio ls (HSRSH), thiol acids (HSRCOOH), thio acids (RCOSH), thiol alcohols (HORSH), diethyldithiocarbamate [Et2NCSS](-), isopropylxanthate [(CH3) (2)CHOCSS](-) and 3-mercapto-propyltrimethoxysilane [HS(CH2)(3)Si(OCH3 )(3)] have been investigated. Information about the extent of exchange , bonding modes and cluster transformations is obtained. Almost comple te exchange was observed for p-toluenethiol while the exchange with o- toluenethiol and 1-dodecanethiol was restricted owing to steric hindra nce. 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 ex change with the thio acids [RCOSH] involves terminal [RCOS](-) ions. D iethyldithiocarbamate [(C2H5)(2)NCSS](-) and isopropylxanthate [(CH3)( 2)CHOCSS](-) remove cadmium atoms from the surface of the cluster due to the formation of terminal S,S-chelating bonds. 3-Mercapto-propyltri methoxysilane HS(CH2)(3)Si(OCH3)(3) readily exchanged to yield the sil ane-functionalized clusters [S4Cdl7(SPh)(28-n){S(CH2)(3)Si(OCH3)(3)}(n )](2-)(n = 1-11).