A conformationally adaptable host capable of encapsulating single cations or homo and hetero dinuclear assemblies

3,6-Diformylpyridazine has been incorporated into a crypt ligand (L) for the first time by condensation with tris(2-aminoethyl)amine (tren). This crypt is shown to be an accommodating host, being able to encapsulate none, one or two metal ion guests. The free crypt, disilver(I) complex and monocobalt(II) complex have been structurally characterised. Electrochemical studies establish that the π-acceptor ligand L effectively stabilises the cobalt ion in the +2 oxidation state.