Crystal and molecular structure of the macrocyclic nickel(II) complex [Ni(C18H14N4)]: dibenzo[b,i][1,4,8,11]tetraaza[14]annulenenickel(II)

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.

Group 5 chemistry supported by β-diketiminate ligands

β-Diketiminate (BDI) ligands are widely used supporting ligands in modern organometallic chemistry and are capable of stabilizing various metal complexes in multiple oxidation states and coordination environments.

A resonance Raman, surface-enhanced resonance Raman, IR, and ab initio vibrational spectroscopic study of nickel(II) tetraazaannulene complexes

The IR and resonance Raman spectra of the nickel(II) complexes of dibenzo[b,i][1,4,8,11]tetraaza[14]annulene (TAA) and 5,7,12,14-tetramethyldibenzo[b,i][1,4,8,11]tetraaza[14]annulene (TMTAA) have been measured and compared with ab initio calculations of the vibrational wavenumbers at the B3-LYP level using the LanL2DZ basis set. An excellent fit is found between the experimental and calculated data, enabling precise vibrational assignments to be made. Surface-enhanced resonance Raman spectra were obtained following adsorption on Ag electrodes, with potentials in the range -0.1 to -1.1 V vs Ag/AgCl. There is evidence for contributions from both the electromagnetic and charge transfer (CT) surface enhancement mechanisms. The data indicate that variations in band intensities with electrode potential can be interpreted in terms of the CT mechanism.