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

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posted on 29.08.2018, 09:48 authored by Luca Pilia, Yoshiaki Shuku, Simon Dalgleish, Kunio Awaga, Neil Robertson
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.