Inorganic–organic hybrid compounds based on the co-existence of different isomers or forms of polymolybdate

Abstract

Three novel compounds co-existing isomers or forms of polymolybdate, namely, {[Ni(γ-Mo₈O₂₆)(H₂L¹)₂(H₂O)₂](γ-Mo₈O₂₆)(H₂L¹)}·2H₂O (1), {[Co(γ-Mo₈O₂₆)(H₂L¹)₂(H₂O)₂](β-Mo₈O₂₆)[Co(H₂O)₆]}·6H₂O (2) and [Cu^I₆L²₄(β-Mo₈O₂₆)(Mo₆O₁₉)] (3), where L¹ = 1,1′-bis(pyridin-3-ylmethyl)-2,2′-biimidazole, L² = 3-((1H-1,2,4-triazol-1-yl)methyl)pyridine, have been successfully synthesized. Crystal structure analysis reveals that 1 is a 1D + 1D supramolecular structure containing both γ-[Mo₈O₂₆N₂] and γ-[Mo₈O₂₈] units; 2 has γ-[Mo₈O₂₆]⁴⁻ as well as β-[Mo₈O₂₆]⁴⁻ anions and 3 is a (3,4,6)-connected 2D network containing both β-[Mo₈O₂₆]⁴⁻ and [Mo₆O₁₉]²⁻ anions. According to quantum chemical calculations, the transformation from β-[Mo₈O₂₆]⁴⁻ to [Mo₆O₁₉]²⁻ is spontaneous in aqueous solution. Furthermore, we have investigated the optical band gap of compounds 1 and 3, with 3 showing a lower band gap (1.69 eV). Additionally, the photoluminescent property of 3 is also studied, which can be assigned to metal-to-ligand charge transfer (MLCT).