Heterobinuclear cryptates; cooperative binding generates two different coordination sites within a symmetrical cryptand

On binding a stereochemically demanding cation a symmetrical cryptand host generates a second non-identical site thereby offering a reliable route to certain types of heterobinuclear cryptates. Specifically, mononuclear complexes [CoIIL](BF4)2 (1) and [CuIIL](BF4)2 (2), of the symmetrical cryptand L [formed by the 3+2 condensation of 3,6-diformylpyridazine with tris(2-aminoethyl)amine (tren)], were reacted with 1 equiv. of Cu(MeCN)4BF4 to yield [CoIICuIL](BF4)3 (3) and [CuIICuIL](BF4)34, respectively.