Non-covalent interactions in hexanuclear polyoxidometalates [V^IV₆B₂₀O₅₀H₈]⁸⁻. An experimental and theoretical approach

A complete study of the optical and magnetic properties of three new {V₆-type} polyoxidometalates (NH₃CH₂CH₂CH₂NH₃)₄{V₆B₂₀O₅₀H₈}·4H₂O 1, K₂(NH₃CH₂CH₂NH₃)_2.5(NH₃CH₂CH₂NH₂){V₆B₂₀O₅₀H₈}·2H₂O 2, and K₂(NH₃CH₂CH₂CH₂NH₃)₂(H₃O)₂{V₆B₂₀O₅₀H₈}·8H₂O 3 is presented. Using TD-DFT calculations, the assignment of the experimental UV–Visible spectra was established with four absorption bands: a higher in energy assigned to metal-to-metal charge transfer and the remaining associated principally to d-d transitions, demonstrating that the {V₆^IVO₁₈}¹²⁻ ring is the principal chromophore for these systems and that the surrounding packing does not have an influence on it. On the other hand, the differences observed in the magnetic properties are caused by the influence of the non-covalent interactions between the potassium ions with some oxygen atoms of the V^IV coordination spheres, thus modifying the V^IV-V^IV exchange coupling. This effect was demonstrated using a simplified binuclear DFT model that predicts a higher V^IV-V^IV antiferromagnetic coupling when the K cations become closer to the oxygen bridge atoms that link the V^IV centres of the {V₆^IVO₁₈}¹²⁻ ring.