Abstract
Various covalent decorations and structural transformations of a series of R-C(CH2OH)3 triol ligands on CoII/CoIII-centered Anderson-Evans polyoxomolybdates were studied in aqueous and/or organic solution. Single-crystal X-ray structural analysis demonstrated that four manners, including (1) double-sided χ/χ-isomer and (2) double-sided δ/χ-isomer with CoII central heteroatom, and (3) single-sided δ-isomer and (4) double-sided δ/δ-isomer with CoIII central heteroatom, appeared on the decoration of the mother polyanion [CoII/III(OH)6Mo6O18]4-/3-. Through careful manipulation of the reaction conditions, a gradual oxidation process from CoII to CoIII was disclosed to happen in air, and accompanying that process, the CoII-centered double-sided δ/χ-isomer that formed in the initial stage transformed into a CoIII-centered double-sided δ/δ-isomer. When the electron-withdrawing group -NO2 substituted triol ligand was used to replace CH3C(CH2OH)3, the oxidation process accelerated spontaneously. A further investigation showed that this oxidation process can be blocked by acid. While the triol ligands' decoration on Anderson-Evans polyoxometalates (POMs) took place along with the oxidation of the central heteroatom, that codecoration of other components was also accomplished. In the presence of excess acetic acid, an unprecedented single-sided δ-isomer with an acetate ligand covalently attaching on the other side by replacing one μ3-O atom was obtained in aqueous solution. The reaction of the mother cluster [(n-C4H9)4N]3[Co(OH)6Mo6O18] and triol ligands in methanol resulted in a codecoration of methanol with the double-sided δ/δ-isomer, which has never been reported in B-type Anderson-Evans POMs. The obtained results revealed that the oxidation state of the heteroatom has a significant impact on the triol ligand decoration styles, such as the χ/χ- or δ/χ-isomer for the divalent heteroatom and the δ- or δ/δ-isomer for the trivalent heteroatom.
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