Quantum chemical studies on chameleonic ligand and its grid-type copper(I) and zinc(II) complexes

The reactions of the chameleonic ligand L, comprising NNO donor atom units, with appropriate metal ions lead to different structural motifs of resulting compounds depending on the kind of metal ions used in coordination. Quantum mechanical MP2 and B3LYP calculations provided insight into conformational diversity of the chameleonic ligand, its recognition process and the electronic structure of Zn(II) and Cu(I) complexes. The conformation of the chameleonic ligand capable of forming complexes with metals is energetically disfavored by about 5 kcal mol−1 for each half of the molecule due to steric repulsion between aromatic hydrogen atoms. Thus, energy exerted during complexes formation must at least balance the adoption of energetically unfavorable conformation of the ligand itself. We examined the self-organization process occurring between the chameleonic ligand and isoelectronic cation centers Zn(II) leading to tetranuclear grid-type complex with Zn center coordinated octahedrally and Cu(I) center generating [2 × 2] grid with Cu atom coordinated tetrahedrally. Our calculations suggest that the energetical cost of adopting geometry suitable for forming octahedral complexes is by further ca. 5 kcal mol−1 less favorable than for tetrahedral ones. In the case of Cu(I) and Zn(II) complexes it means that for Cu(I) tetrahedral coordination is energetically preferred by 15.2 kcal mol−1 while octahedral coordination is energetically favored by 18.5 kcal mol−1 over tetrahedral coordination for Zn(II). These results are a consequence of preferred metal coordination geometry and their electronic properties.