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

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 [S 4 Cd 17 (SPh) 28 ] 2 - with thiols (HSR), dithiols (HSRSH), thiol acids (HSRCOOH), thio acids (RCOSH), thiol alcohols (HORSH), diethyldithiocarbamate [Et 2 NCSS] -, isopropylxanthate [(CH 3 ) 2 CHOCSS] - and 3-mercaptopropyltrimethoxysilane [HS(CH 2 ) 3 Si(OCH 3 ) 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 [(C 2 H 5 ) 2 NCSS] - and isopropylxanthate [(CH 3 ) 2 CHOCSS] - remove cadmium atoms from the surface of the cluster due to the formation of terminal S,S-chelating bonds. 3-Mercaptopropyltrimethoxysilane HS(CH 2 ) 3 Si(OCH 3 ) 3 readily exchanged to yield the silane-functionalized clusters [S 4 Cd 17 (SPh) 28 - n {S(CH 2 ) 3 Si(OCH 3 ) 3 } n ] 2 - ( n = 1−11).