Hybrid organic–inorganic polyoxovanadates with [M(en)n] (M = Co, Ni, Cu, Zn) displaying (V4O13), (V15O36) or (V18O42) morphologies

Abstract

Hybrid organic–inorganic crystals are attractive due to their large structural diversity and easy fabrication. Polyoxometalates, including polyoxovanadates (POVs), have gained interest e.g. for biomedical or battery applications and they can be prepared with a plethora of cationic matrices to balance the anionic charge of the metal–oxo cluster. Here, we employ a simple solvothermal synthesis to produce 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 1D (V₄O₁₃) 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 the 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.