Structural characterization of spherical octadecavanadates encapsulating Cl– and H2O

Abstract

Spherical octadecavanadate complexes K_9.5[H_3.5V₁₈O₄₂Cl]·11.5H₂O 1 and K₁₀[H₂V₁₈O₄₂(H₂O)]·16H₂O 2 have been photochemically prepared by self-assembly of the components in solution under ambient conditions, and characterized by elemental analyses, IR spectra, crystal structure determinations and magnetic susceptibility measurements. They consist of (VO)₁₈O₂₄ shells encapsulating Cl^– and H₂O at the centre, respectively. Each shell is composed of eighteen edge-sharing V^IVO₅ square pyramids and has approximate D_4d symmetry. The inner diameter of the shell is 0.1–0.2 Å smaller for 1 than for 2. This can be explained by the electrostatic attraction between V^IV and Cl^– which results in shorter V^IV⋯ V^IV distances due to weakening of the electrostatic repulsion between V^IV atoms, and is reflected in both the IR spectra and magnetic properties. The V–O–V vibrational stretching modes for 1 are shifted to slightly higher wavenumbers. The magnetic susceptibility, which shows a strong coupling within the V^IV⋯ V^IV pairs in the two anions which leaves six to four V^IV atoms uncoupled at 50 ⩽T⩽ 300, is also slightly higher for 1.