Investigation of thiourea-silanes as viable precursors for the sol-gel synthesis of composites containing Zn-S complexes

Sulphur-functionalised trialkoxysilanes are suitable compounds for the sol-gel synthesis of silica glass embedding metal sulphide nanoclusters. In this study, three different thiourea-functionalised silanes, (EtO)3Si(CH2)3NHC(=S)NHPh (SilTu), 1,4-[(EtO)3Si(CH2)3NHC(=S)NH]2Ph (diSilTu) and (MeO)3Si(CH2)3N[C(S)NH(C6 H5 )](CH2)2NH[C(S)NH(C6H5)] (SildiTu), were used together with Zn2+ ions to investigate their potential use in the preparation of ZnS-SiO2 materials. Such precursors provide, in principle, a ''molecule-to-nanocomposite'' path by a direct anchoring of the metal cations to the forming silica network, via metal-sulphur (M-S) interactions. The sol-gel precursors were characterized by IR and NMR spectroscopies, and by electrospray mass spectrometry (ESI-MS). DiSilTu was also characterized by single crystal X-ray analysis. IR and 1H,13C and 29Si NMR measurements confirmed the formation of stable complexes with Zn2+ ions, especially in the case of SilTu, also under sol-gel conditions