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Synthesis and characterization of [Co(en)3]2[Mo7O24]·8H2O

The main driving forces responsible for the formation of polyoxomolybdates (POMos) are various interactions and self-assembly processes between [MoO4] 2- anions. The chemistry of POMos has been investigated since 19th century when a yellow precipitate of ammonium phosphomolybdate, (NH4)6PMo12O40 was obtained from ammonium molybdate and phosphoric acid. [1] The main goal of modern POMo studies is the synthesis of materials with specific properties and applications. In our previous research we have postulated that hydrogen bonding capacity of counterions and reaction conditions greatly influences the condensation processes in POMo chemistry [2] which led us to use [Co(en)3] 3+ as a counterion in POMo synthesis in the presence of succinic acid. Although succinic acid was not found to be present in any of the isolated products, its presence appeared to be essential for POMo formation. Different synthetic methods were used, such as solution-based synthesis and liquid-assisted ball milling followed by vapour- assisted aging. Solution-based reactions were performed in an aqueous medium at room temperature or at 110°C, all reaction mixtures were at pH 4. All synthetic methods while using the molar ratio 1:1:1 of Na2MoO4, succinic acid and [Co(en)3]Cl3 resulted in the formation of yellow rod-like crystals of [Co(en)3]2[Mo7O24]∙8H2O, and a molar ratio 6:1:1 in favor of molybdate resulted in the formation of orange needle-like crystals of Na[Co(en)3]5[Mo22O74]∙nH2O.

hydrothermal synthesis ; self-assemby ; polyoxomolybdates ; cobalt(III) complexes

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