Hybrid organic-inorganic polyoxovanadates with [M(en) n ] (M=Co, Ni, Cu, Zn) displaying (V 4 O 13 ), (V 15 O 36 ) or (V 18 O 42 ) morphologies

Abstract

Hybrid organic-inorganic crystals are attractive due to their large structural diversity and easy fabrication. The polyoxometalates including the polyoxovanadates (POVs) have gained interest e.g. for biomedical or battery applications and they can be prepared with a plethora of cation matrixes to balance the anionic charge of the metal-oxo cluster. Here we employ a simple solvothermal synthesis for producing hybrid organic-inorganic crystals between the anionic "inorganic" vanadate and the cationic "organic" metal-ethylenediamine (en) complexes [M(en)n]. A series of different 3d metals were tested with Co (reported in a previous publication), Ni, Cu and Zn producing crystals of high enough quality for single crystal X-ray diffraction structure investigation. Co, preferring the +3 oxidation state, forms crystals in the supernatant between [Co(en)3] and (V4O13) 1D-POVs with chains of corner sharing (V5+ O4)-tetrahedra. The other 3d metals Ni, Cu and Zn, prefer the +2 oxidation state, and form crystals in the precipitate with mixed oxidation state (V4+/V5+) spherical (V15O36) or (V18O42) molecular-POVs. The (V15O36) or (V18O42) POV morphology is selectively tuneable by pH when using the amphoteric Zn precursor. We report crystal structures of 4[Ni(en)3]·(V18O42Cl)·13.26(H2O), 4[Cu(en)2]·(V18O42Cl)·4(H2O), and a high quality structure of 2[Zn(en)2(enH)](V15O36Cl)(enH2)⋅5.63 H2O crystallizing in the orthorhombic space group Pbca.