Anion binding by a copper(II) complex of a reinforced open-chain tetramine

The copper(II) complex of the reinforced tetramine (1,3-propane-bis-[1-methyl-4-piperazine]) [CuII(2)](ClO4)2, exhibits a square-pyramidal geometry, with a perchlorate anion in the apical position. The [CuII(2)]2+ species, in an MeCN solution, binds inorganic anions, to give five-coordinated complexes. Binding selectivity reflects the intensity of the metal–anion interaction, as shown by a satisfactory correlation with d–d spectral properties. Comparison with the anion binding tendencies of the square planar copper(II) complex of the plain tetramine 1 (N,N′-bis(-2-aminoethyl)-propane-1,3-diamine) discloses the inference of steric repulsive effects in the formation of the square-pyramidal adducts