Inserting -(CH2)n- (n = 2, 3, 4) Spacers into the Reactant Mercapto-methyltetrazole Ligand for Tuning the Multinuclear AgI Clusters in Keggin-Based Compounds

Four SiMo12O404– (SiMo12)-based compounds, namely, [Ag6Cl2(mmt)4(H4SiMo12O40)(H2O)2] (1), [Ag4(bmte)2(H2O)2(SiMo12O40)] (2), [Ag4(bmtr)2(H2O)2(SiMo12O40)] (3), and [Ag4(bmtb)3(SiMo12O40)] (4) (mmt = 1-methyl-5-mercapto-1,2,3,4-tetrazole, bmte = 1,2-bis(1-methyl-5-mercapto-1,2,3,4-tetrazole)ethane, bmtr = 1,3-bis(1-methyl-5-mercapto-1,2,3,4-tetrazole)propane, bmtb = 1,4-bis(1-methyl-5-mercapto-1,2,3,4-tetrazole)butane), have been synthesized under hydrothermal conditions. Single crystal X-ray diffraction analyses reveal that insertion of -(CH2)n- spacers into the reactant mmt ligand plays important roles in constructing multinuclear AgI clusters in the title compounds and tuning the formation of different multinuclear AgI clusters. In compound 1, the mmt ligands link AgI ions forming a three-dimensional non-multinuclear self-penetrating framework with large dimension channels occupied by SiMo12 polyanions. In 2, a tetranuclear [Ag4(bmte)2(H2O)2]4+ and SiMo12 anions arrange alternately forming a one-dimensional (1D) chain. The structure of compound 3 is similar to that of 2, except for different coordination modes of AgI ions in tetranuclear clusters and SiMo12 polyanions owing to the longer -(CH2)3- alkyl skeleton of bmtr ligand. Compound 4 exhibits a two-dimensional grid layer formed by a 1D AgI "ribbon" based on binuclear AgI clusters and bridging bmtb ligands with the longest -(CH2)4- alkyl skeleton. The SiMo12 polyanions as tetradentate inorganic linkages reside in the grids. The influences of -(CH2)n- spacers on forming and tuning different multinuclear AgI clusters have been discussed. Furthermore, the photochemical catalysis and electrochemical properties of the title compounds have been studied.