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ChemInform Abstract

The structures of the compounds (III) (space group P2₁/n, Z = 2) and (VI) (C2/c, 4) are determined by single crystal XRD and that of (IV) (Imma, 4) by powder XRD. The structure of (III) consists of an extended Prussian Blue type framework containing face-capped octahedral [Re₆S₈]²⁺ clusters and [Co₂(μ-OH₂)₂]⁴⁺ cluster cores enclosing water-filled cavities ≈258 Å in volume. The structure of (VI) consists of a network of Co²⁺ and [Co₂(μ-OH₂)₂]⁴⁺ ions connected through [Re₆Se₈(CN)₆]^4- clusters, defining channels with minimum internal diameters of 4.8 Å. Upon exposure to Et₂O vapor the color of (III) and (VI) immediately changes from orange to an intense blue-violet or blue; other polar solvents induce different colors. It is proposed that the vapochromic response is due to solvent molecules entering the pores of the solid and disrupting the hydrogen-bonded water network. Release of bound water from the [Co₂(μ-OH₂)₂]⁴⁺ clusters results in a change of the Co coordination sphere from octahedral to tetrahedral. Spectroscopic and magnetic measurements confirm the change in coordination geometry and the trends in solvent response (MeOH < EtOH < PrOH < iPrOH) are consistent with a reduced ability to support the bridging water ligands of the clusters. Size-selective sensing is demonstrated with tert.-butyl ether, which causes a color change in (VI), but not in (III). Compound (IV) displays no vapochromic effect.