A loose cage for transition metals

The bistern cage L rapidly and reversibly incorporates Ni(super II), Cu(super II) and Zn(super II) ions in aqueous solution to afford a 1:1 stoichiometry. Stable metal complexes of protonated forms of the ligand are present as major species in a slightly acidic solution. The crystal structure of (Ni(super II)(LH+))(ClO4)3 complex reveals that the metal is six-coordinate and displaced toward one end og the cavity, while the proton is bound to one of the secondary N atoms at the other end.