The role of mono- and dicarboxylic acids in the building of oxomolybdates containing {MoO4}, {Mo2O5}, {Mo2O6}, {Mo3O8}, {Mo5O17}, {Mo5O18}, {Mo8O26}, and {SiMo12O40} units

Seven tetraammineoxalatocobalt(iii) salts with oxomolybdate anions of different nuclearities, such as [Co(C2O4)(NH3)(4)](2)[MoO4]center dot H2O (1), [Co(C2O4)(NH3)(4)](2)[Mo2O4(mu-O)(C2O4)(2)(H2O)(2)]center dot 4H(2)O (3), Na-2[Co(C2O4)(NH3)(4)](2)[Mo2O4(mu-O)(2)(C2O4)(2)]center dot 4H(2)O (4), [Co(C2O4)(NH3)(4)](4)[Mo3O6(mu-O)(2)(C2O4)(3)(H2O)(2)]center dot 5H(2)O (5), [Co(C2O4)(NH3)(4)](4)[Mo8O26]center dot 12H(2)O (8), [Co(C2O4)(NH3)(4)](4)[SiMo12O40]center dot 6H(2)O (9) and [Co(C2O4)(NH3)(4)](4)[Mo8O26]center dot 10H(2)O (10), along with [Mo5Co2O17(HCO3)(H2C3O4H)(NH3)(7)]center dot 5H(2)O (6) and [Mo5Co2O18(NH3)(7)]center dot 5H(2)O (7), were isolated using a one-pot reaction of sodium molybdate with [Co(C2O4)(NH3)(4)]NO3 center dot H2O or [Co(CO3)(NH3)(4)]NO3 center dot H2O and mono- or dicarboxylic acids in an aqueous medium. Polyoxomolybdate anions are built up from {MoO4}, {Mo2O4(mu-O)}, {Mo2O4(mu-O)(2)}, {Mo3O6(mu-O)(2)}, {Mo5O17}, {Mo5O18}, {Mo8O26} and {SiMo12O40} units, respectively, depending on the nature of the carboxylic acid additive used in the synthesis. The isolation of these salts confirmed that the carboxylic acids act not only as ligands, primarly, but also as structure-directing agents in the polyoxoanion self-assembly processes. All products were characterized in the solid state via single-crystal and powder X-ray diffraction, infrared spectroscopy as well as thermogravimetric and elemental analyses.

Automated summary

Seven different nuclearities of tetraammineoxalatocobalt(III) salts with oxomolybdate anions were successfully isolated using a one-pot reaction method, confirming that carboxylic acids act as both ligands and structure-directing agents. The polyoxomolybdate anions were built from various units depending on the carboxylic acid additive used during synthesis, and the products were characterized using a variety of analytical techniques.