Synthesis and characterization of a topologically constrained tetraaza macropolycycle and its copper(II) complex

A new macropolycycle, 2,13-dimethyl-1,5,12,16-tetraazapentacyclo[14.6.2.25.12.06.11.017.22]hexacosane (L3), has been prepared by the reaction of 3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.07.12]docosane (L1) with 1-bromo-2-chloroethane. The macropolycycle readily reacts with anhydrous copper(II) ion to yield [CuL3]2+ in dry methanol but does not with nickel(II) ion, showing a high copper(II) ion selectivity. Crystal structure of [CuL3](ClO4)2 shows that the complex has a distorted square-planar coordination polyhedron with a trans-IV type N-conformation. The Cu–N distances [1.989(3) and 2.015(3) Å] of [CuL3](ClO4)2 are distinctly shorter than those of [CuL1](ClO4)2 and other related macrocyclic copper(II) complexes. The d–d transition band for [CuL3](ClO4)2 is observed at 447 nm, which is ca. 40 nm shorter than that for [CuL1](ClO4)2.