Hydrothermal synthesis and characterization of the tri-capped and mono-supported pseudo-Keggin-type tungstovanadophosphate: {PW4W5V3O40(VO)3[Cu(en)2]}

A novel polyoxometalate Cu(phen)₂]₃{PW₄^VIW₅^VV₃^IVO₄₀(V^IVO)₃Cu(en)₂]}4H₂O 1 (en=ethylenediamine, phen=1,10-phenanthroline) has been synthesized hydrothermally and characterized by elemental analysis, IR, XPS, TG, EPR and single-crystal X-ray diffraction analysis. The crystal structure analysis shows that compound 1 contains a novel highly reduced tri-capped and mono-supported pseudo-Keggin-type heteropolyanion, {PW₄^VIW₅^VV₃^IVO₄₀(V^IVO)₃Cu(en)₂]}⁶⁻, three Cu(phen)₂]²⁺ cations and four lattice water molecules. They are further linked to form three-dimensional supramolecular networks through extensive hydrogen bonding and π–π stacking interactions. Interestingly, the water dimer and terminal oxygen of the cluster polyanion constitute a beautiful supramolecular helix chain. The heteropolyanion is the first example of tri-capped and mono-supported pseudo-Keggin-type tungstovanadophosphate and the pH value is crucial for obtaining compound 1 in synthetic procedure.