A family of tetrahedral coordination cages with different symmetries by assembly of bis-bidentate bridging ligands with first-row transition metal dications

A series of M4L6 tetrahedral cages, with a metal ion at vertex and a bis-bidentate bridging ligand spanning each edge, have been prepared and structurally characterised using three new ligands L-1-L-3. L-1 contains two chelating pyrazolyl-pyridine termini connected to a 2,6-napthalene-diyl spacer by methylene groups: L-2 and L-3 contain chelating pyrazolyl-pyrazine termini connected to 1,8-naphthalene-diyl or 3,3-biphenyl centre units by methylene groups. The cages with L-2 and L-3 contain anions encapsulated in the central cavity. Although all three types of cage have the same basic tetrahedral structure, the cages display a range of molecular symmetries (S-4, T and C-3 for L-1-L-3, respectively) according to the combination of fac and mer tris-chelate metal sites in the complexes arising from the flexibility of the ligands.