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
(LF) 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 LH (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
LF and LH 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 LH 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.