Anion- π interactions in hollow crystals of a copper(II)-cyamelurate coordination complex

Abstract

A novel cyamelurate-based copper(II) coordination compound has been designed from a computational approach to show anion−π interactions between the s-heptazine core and perchlorate anions; therefore, a complex of formula {[Cu(pmta)]3cyam}(ClO4)3 (1) [pmta = N,N,N′,N′′,N′′- pentamethyl-diethylenetriamine and cyam = cyamelurate ligand] was synthesized. The cationic molecule stabilizes in the solid state with two perchlorate anions one above and the other below the cyamelurate aromatic rings in a polar conformation, crystallizing in the R3c noncentrosymmetric space group with a close cubic packing of the cations. The binding energies were calculated to be ca. −175 kcal/mol for the two species 1:OClO3 − and 1:O3ClO−, and the anion-π contribution could also be calculated, being ca. −10 kcal/mol. The dielectric and magnetic properties were analyzed showing a semiconductor behavior in the temperature range studied (300−458 K) and a weak antiferromagnetic interaction among the three Cu(II) ions. The crystals of 1 show a hollowed hexagonal prismatic morphology, with hollow diameters up to 300 μm. A mechanism based on oriented growth, dissolution, and recrystallization of the outer shell was proposed to explain these hollowed structures.