A new macrocyclic cryptand with squaramide moieties:: An overstructured CuII complex that selectively binds halides:: Synthesis, acid/base- and ligational behavior, and crystal structures

The synthesis and characterization of the novel 24,29-dimethyl-6,7,15,16-tetraoxotetracyclo- [19.5.5.0(5,8).0(14,17)]-1,4,9,13,18,21,24,29-octaazaenatriaconta-Delta(5,8), Delta(14,17)-diene (L) are reported. Molecule L incorporates two squaramide functions in a overstructured chain connecting two opposite nitrogen atoms of the Me-2[12]aneN(4) polyaza macrocyclic base to obtain a cage topology. The basicity and binding properties of L towards Cu-II were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, 1=0.15 mol dm(-3)). Molecule L behaves as a diprotic base under the experimental conditions employed and forms only mononuclear Cull complexes in which the squaramide moieties are not involved in the stabilization of the metal ion that is stabilized by the amine functions of the polyaza base inside the three-dimensional cavity. The [CuL](2+) species was tested as a host for the series of halide anions. UV-visible spectrophotometric experiments permitted the determination of the addition constants of halides to the Cu-II-complexed species. The [CuL](2+) species binds the anions F-, Cl-, and Br- by forming the [CuLX](+) species, but does not bind the biggest I- anion. A trend of selectivity