Oxidative Dehydrogenation Properties of Novel Nanostructured Polyoxovanadate Based Materials

High Nuclearity Antimonato-Polyoxovanadate Cluster {V15 Sb6 O42 } as a Synthon for the Solvothermal in situ Generation of α- and β-{V14 Sb8 O42 } Isomers

New heteroatom polyoxovanadates (POVs) were synthesized by applying a water-soluble high-nuclearity cluster as new synthon. The [V15 Sb6 O42 ](6-) cluster shell exhibiting D3 symmetry was in situ transformed into completely different cluster shells, namely, the α-[V14 Sb8 O42 ](4-) isomer with D2d and the β-[V14 Sb8 O42 ](4-) isomer with D2h symmetry. The solvothermal reaction of {Ni(en)3 }3 [V15 Sb6 O42 (H2 O)x ]⋅15 H2 O (x=0 or 1; en=ethylenediamine) in water led to the crystallization of [{Ni(en)2 }2 V14 Sb8 O42 ]⋅5.5 H2 O containing the β-isomer. The addition of [Ni(phen)3 ](ClO4 )2 ⋅0.5 H2 O (phen=1,10-phenanthroline) to the reaction slurry gave the new compound {Ni(phen)3 }2 [V14 Sb8 O42 ]⋅phen⋅12 H2 O with the α-isomer. Both transformation reactions are complex due the change of symmetry, the chemical composition, and rearrangement of the VO5 square pyramids and Sb2 O5 handle-like moieties.

Semimetal-functionalised polyoxovanadates

Polyoxovanadates (POVs), known for their wide applicability and relevance in chemical, physical and biological sciences, are a subclass of polyoxometalates and usually self-assemble in aqueous-phase, pH-controlled condensation reactions. Archetypical POVs such as the robust [VO42](12-) polyoxoanion can be structurally, electronically and magnetically altered by heavier group 14 and 15 elements to afford Si-, Ge-, As- or Sb-decorated POV structures (heteroPOVs). These main-group semimetals introduce specific chemically engineered functionalities which cause the generally hydrophilic heteroPOV compounds to exhibit interesting reactivity towards organic molecules, late transition metal and lanthanoid ions. The fully-oxidised (V(V)), mixed-valent (V(V)/V(IV) and V(IV)/V(III)), "fully-reduced" (V(IV)) and "highly-reduced" (V(III)) heteroPOVs possess a number of intriguing properties, ranging from catalytic to molecular magnet characteristics. Herein, we review key developments in the synthetic and structural chemistry as well as the reactivity of POVs functionalised with Si-, Ge-, As- or Sb-based heterogroups.