Diverse structures and adsorption properties of quasi-Werner-type copper(ii) complexes with flexible and polar axial bonds

Abstract

The quasi-Werner-type copper(II) complex, [Cu(PF₆)₂(4-mepy)₄] (1), in which 4-mepy is the 4-methylpyridine ligand, has flexible and polar axial bonds of Cu–PF₆. Flexibility of the Cu–PF₆ bonds induces diverse and unprecedented guest-inclusion structures, such as {[Cu(PF₆)₂(4-mepy)₄][Cu(PF₆)(4-mepy)₄(acetone)]·PF₆·4acetone} (γ-1⊃2.5acetone), {[Cu(PF₆)₂(4-mepy)₄][Cu(PF₆)(4-mepy)₄(2-butanone)]·PF₆·3.5(2-butanone)} (γ-1⊃2.25(2-butanone)), {[Cu(PF₆)₂(4-mepy)₄][Cu(PF₆)(4-mepy)₄(H₂O)]·PF₆·4benzene} (γ-1⊃0.5H₂O·2benzene), and {[Cu(PF₆)₂(4-mepy)₄]·2benzene} (γ-1⊃2benzene). Exposure of the dense form, α-1, to benzene vapor affords the benzene-inclusion complex {[Cu(PF₆)₂(4-mepy)₄]·2benzene} (γ-1⊃2benzene), all benzene guests of which are easily removed by vacuum drying, reforming guest-free, dense α-1′ with smaller sized crystals than α-1. In contrast to α-1, which shows almost no CO₂ adsorption, α-1′ adsorbs CO₂ gas with structural transformations, this being the first example that exhibits adsorption of gas in a dense Werner-type complex and a drastic change in adsorption properties depending on the size of the crystals.