Breaking boundaries: novel tridecavanadate polyoxometalates with a unique six-fold tetradentate coordination capacity for lanthanum(iii) and a two-fold bidentate decavanadate ligand in a single compound

Abstract

For the first time, a tridecavanadate isopolyvanadate species, [V^IVV^V₁₂O₃₈]¹²⁻ (V₁₃), has been identified and synthesized via a pH-controlled slow-evaporation method yielding water-insoluble, black rod-shaped crystals of {[La(H₂O)₃]₂[La(H₂O)₅]₄[μ-V₁₀O₂₈][μ₆-V^IVV^V₁₂O₃₈]}·24H₂O, exhibiting a polymeric structure and characterized through single-crystal X-ray diffraction (XRD) analysis, infrared spectroscopy, atomic absorption spectroscopy (AAS), inductively coupled plasma optical emission spectroscopy (ICP-OES), CHN analysis, photoelectron X-ray spectroscopy and thermal analysis (TGA/DTA). A distinctive feature of V₁₃ is its six-fold tetradentate coordination μ₆-η⁴:η⁴:η⁴:η⁴:η⁴:η⁴ with La(III), showcasing notable bonding characteristics. It was feasible to synthesize two coordination isomers of V₁₃, denoted as 1a and 1b, sequentially. These coordination isomers primarily differ in their La : V molar ratios of the corresponding starting materials, being 3 : 4 for 1a and 2 : 4 for 1b, which in turn influences the crystallization time, purity, structural type, and crystal parameters of the resultant products, but the final products of both 1a and 1b have the same La : V molar ratio as 6 : 23. 1a adopts a linear one-dimensional coordination polymer structure, whereas 1b forms a zig-zag one-dimensional coordination polymer. Additionally, 1b coexists in the solid state with crystals of an unprecedented decavanadate with the proposed formula {[La(H₂O)₇]₂[μ-V₁₀O₂₈]}·8H₂O (2) exhibiting a rare coordination mode μ-η²:η² of the decavanadato ligand. Therefore, the novel V₁₃ expands the horizons of the polyoxovanadates’ structural library by adding a new isopolyvanadate species, opening up avenues for the future to explore and investigate other metal cations with comparable ionic radii to that of La(III) in addition to probing their intrinsic material aptitude and application potential.