Interaction between aromatic rings as organizing tools and semi-coordination in Cu(II) compounds

In this paper, we present the use of the interaction between aromatic rings—usually called π–π interaction—as the main tool in the organization of coordination complexes in a crystal. To do so, we selected coordination compounds with aromatic rings pointing outside the molecules to favor their self-assembly through these interactions. Here, we report the molecular and crystal structures of three Cu(II) complexes: [Cu2(terpy)2(bz)2](ClO4)2 (1), [Cu2(terpy)2(tfipth)2] (2) and [Cu4(terpy)4(tfipth)2(ClO4)2](ClO4)2 (3), where terpy = 2,2′:6′,2′′ terpyridine, bz = benzoate and tfipth = tetrafluoro-isophthalate. In the three crystals, the interaction between aromatic rings organizes molecules in chains that closely pack with disordered anions or water molecules located in the space between the chains. A study of the Crystal Structure Database (CSD) indicates that the main interaction in terpy molecules is between a lateral ring and the central ring of different molecules and when terpy molecules point in opposite directions, they tend to form chains, suggesting that these interactions can be used as a design tool. The metal complexes were designed to obtain a square pyramidal structure around the metal ion, but we observed a contact between the non-coordinated O (carboxylate) and the Cu(II) ion. We studied the presence of this interaction and its nature with computational chemistry.