Abstract
The monovanadium-substituted polyoxometalate anion [VMo7O26]5-, exhibiting a β-octamolybdate archetype structure, was selectively prepared as pentapotassium [hexaikosaoxido(heptamolybdenumvanadium)]ate hexahydrate, K5[VMo7O26]·6H2O (VMo7), by oxidation of a reduced vanadomolybdate solution with hydrogen peroxide in a fast one-pot approach. X-ray structure analysis revealed that the V atom occupies a single position in the cluster that differs from the other positions by the presence of one doubly-bonded O atom instead of two terminal oxide ligands in all other positions. The composition and structure of VMo7 was also confirmed by elemental analyses and IR spectroscopy. The selectivity of the synthesis was inspected by a 51V NMR investigation which showed that this species bound about 95% of VV in the crystallization solution. Upon dissolution of VMo7 in aqueous solution, the [VMo7O26]5- anion is substantially decomposed, mostly into [VMo5O19]3-, α-[VMo7O26]4- and [V2Mo4O19]4-, depending on the pH.
Highlights
Substitution of one Mo atom in a Linqvist-type hexamolybdate, [Mo6O19]2À, by vanadium leads to enhanced photocatalytic degradation of a model organic dye under both aerobic and anaerobic conditions caused by a low-energy O!V LMCT transition in [VMo5O19]3À (Tucher et al, 2012)
We present a regioselective synthesis of a new isomer of [VMo7O26]5À in which the V atom occupies only MoC positions of the parent -octamolybdate structure
Subsequent addition of hydrogen peroxide resulted in an orange solution formed by immediate oxidation with vanadium peroxido complexes (Schwendt et al, 2016)
Summary
Polyoxometalates (POMs) of W, Mo and V represent an important group of inorganic metal–oxide clusters (Pope, 1983) whose structural variability gives rise to an exceptionally wide range of applications in catalysis (Wang & Yang, 2015), magnetism (Clemente-Juan et al, 2012), redox processes (Gumerova & Rompel, 2018) and materials chemistry (Song & Tsunashima, 2012), as well as in biological chemistry (Bijelic & Rompel, 2015, 2017; Molitor et al, 2017; Fu et al, 2015; Bijelic et al, 2018, 2019). Substitution of one Mo atom in a Linqvist-type hexamolybdate, [Mo6O19]2À, by vanadium leads to enhanced photocatalytic degradation of a model organic dye under both aerobic and anaerobic conditions caused by a low-energy O!V LMCT (ligand-to-metal charge transfer) transition in [VMo5O19]3À (Tucher et al, 2012). A monovanadium-substituted derivative was prepared as H4K2Na2(H2O)4(C12H12N4O2)[VMo7O26]Á10H2O (Zhao et al, 2018). In this case, the V atom was claimed to be statistically distributed in all positions of the parent -octamolybdate anion. We present a regioselective synthesis of a new isomer of [VMo7O26]5À in which the V atom occupies only MoC positions of the parent -octamolybdate structure. The peroxide-mediated synthesis route (Schwendt et al, 2016) has already been successfully utilized for the synthesis of several polyoxometalates, such as [HxV10O28](6–x)– (Jahr et al, 1963; Nakamura & Ozeki, 2001), [HxPV14O42](9–x)–, Keggin structures [H3+xPMo12–xVxO40], and Wells–Dawson structures [H6+xP2Mo18–xVxO62] (Odyakov et al, 2015) and [V12O30F4(H2O)2]4À (Krivosudskyet al., 2014)
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