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

摘要

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.