Unusual reactivity of dithiol protected clusters in comparison to monothiol protected clusters: studies using Ag51(BDT)19(TPP)3 and Ag29(BDT)12(TPP)4

We report the synthesis and unique reactivity of a new green dithiol protected cluster (DTPC), Ag-51(BDT)(19)(TPP)(3) (BDT and TPP are 1,3-benzenedithiol and triphenylphosphine, respectively). The cluster composition was confirmed by electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) mass spectrometric studies as well as by other supporting data. Surprisingly, the chemical reactivity between this DTPC and Au-25(SR)(18) involves only metal ion exchange in Au-25(SR)(18) without any ligand exchange, while reactions between monothiol protected clusters (MTPCs) show both metal and ligand exchange, an example being the reaction between Ag25DMBT18 and Au25PET18 (where DMBT and PET are 2,4-dimethylbenzenethiol and phenylethanethiol, respectively). The conclusions have been confirmed by the reaction of another DTPC, Ag-29(BDT)(12)(TPP)(4) with Au25BT18 (where BT corresponds to butanethiol) in which only metal exchange happens in Au25BT18. We also show the conversion of Ag-51(BDT)(19)(TPP)(3) to Ag29(BDT)(12)(TPP)(4) in the presence of a second monothiol, DMBT which does not get integrated into the product cluster. This is completely different from the previous understanding wherein the reaction between MTPCs and a second thiol leads to either mixed thiol protected clusters with the same core composition or a completely new cluster core protected with the second thiol. The present study exposes a new avenue of research for monolayer protected clusters, which in turn will give additional impetus to explore the chemistry of DTPCs.