Structural and Electronic Effects Due to Fluorine Atoms on Dibenzotetraaza-Annulenes Complexes

The preparation and characterization of Ni(II) (1F) and Cu(II) (2F) complexes of the ligand 15,16,17,18,19,20,21,22-octafluoro-dibenzotetraaza[14]annulene (L_F) are here reported. These compounds have been characterized by elemental analysis, mass and UV-vis spectroscopies, single-crystal X-ray diffraction, and computational studies. The effects due to the presence of fluorine atoms have been highlighted by comparison with the analogous complexes of the ligand L_H (Ni: 1H; Cu: 2H), which bears hydrogen atoms at the benzenoid rings instead of fluorine. 1F and 2F are isostructural, with the metal ions bound to the four nitrogen atoms in a square-planar geometry and where the planar molecules are arranged in a herringbone motif in the crystal lattice. Remarkable differences in the intermolecular interactions between 1F and 2F and the corresponding H-complexes are shown by Hirshfeld surface calculations. Moreover, the effects of fluorination on the electronic structures have been investigated by density functional theory (DFT) and time-dependent DFT calculations. The compounds with L_F and L_H ligands present corresponding molecular orbitals (MOs) with similar shapes. Furthermore, while the presence of F-atoms lowers the energy of the MOs in comparison with those of the L_H complexes, it does not remarkably affect the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) and HOMO-LUMO + 1 gaps, in agreement with the UV-vis results.