Ligand exchange in TREN-based Cobalt (II) funnel complexes in the solid state

The coordination of CoII with two calixarene-based TREN [tris(2-aminoethyl)amine] ligands is reported. The two ligands differ for the presence of three anisole groups (in Calix-TRENMe) or three phenol groups (in Calix-TRENH) in the macrocyclic structure surrounding the CoIITREN core. Dicationic complexes were synthesized and fully characterized both in solution and in the solid state. Surprisingly, a crystal-to-crystal transformation led to the substitution of the acetonitrile guest ligand by a pair of H-bonded water molecules. This gave rise to the first example of an X-ray characterized aqua-complex with a CoII center confined in a neutral, 5-coordinate N4(OH2) environment.