Unusually strong dipole–dipole and dipole–quadrupole interactions in a nanoporous solid. Crystal structure and related properties of (vo)₃[m(cn)₆]₂·nh₂o (m = fe, co)

In porous Prussian blue (PB) analogues, the partially naked central metal atoms found at the cavities surface are responsible for many of their physical properties, among them the adsorption potentials. In the as-synthesized PB analogues, such metal sites stabilize water molecules inside the cavity through coordination bond formation. The filling of the cavity volume is completed with water molecules linked to the coordinated ones through hydrogen bonds formation. Vanadyl-based PB analogue shows quite different features. The metal(V) at the cavities surface has saturated its coordination sphere with the O atom of the vanadyl ion (V=O). In this material, the V=O group preserves enough strong dipole moment to stabilize adsorbed species at the cavity through dipole–dipole and dipole–quadrupole in-teractions. This contribution reports the preparation, crystal structure and properties for (VO)₃[M(CN)₆]₂·nH₂O (M = Fe, Co). According to the refined crystal structure, IR spectra and TG data, six water molecules remain stabilized inside the cavities through a strong dipole– dipole coupling with the vanadyl group. The cavity contains additional water molecules interacting through hydrogen bond bridges with the water molecules coupled to the V=O group. The vanadyl ion is free of hydrogen bonding interactions with the water molecules. The recorded adsorption isotherms for N₂, CO₂ and H₂, three molecules with only quadrupole moment, reveal presence of relative strong adsorption forces due to dipole-quadrupole interactions.