Structure, Characterization, and Metal‐Complexation Properties of a New Tetraazamacrocycle Containing Two Phenolic Pendant Arms

Abstract

The new tetraazamacrocycle 2 ( 2,2'- 7,11,.1]heptadeca-1(17),13,15-triene-3,11-diyl]bis(methylene)]bis(4-bromophenol)) was synthesized and used as a ligand for different metalion complexes. The X-ray crystal structures of the complexes of the general formula [M(H-2)] NO, in which only one of the two pendant phenolic OH groups of 2 is deprotonated, were determined. In both complexes, the coordination environment is of the [5 1] type, the four N-atoms of the macrocyclic framework defining a square-planar arrangement around the metal center, with similar NiÀN and ZnÀN distances of 1.961(9) to 2.157(9) ä and 2.021(9) to 2.284(8) ä, respectively. In contrast, the MÀO distances are markedly different, 2.060(6) and 2.449(8) ä in the Ni II complex, and 2.027(7) and 2.941(9) ä in the Zn II complex. The UV/VIS spectra of the Ni II and Cu II complexes with ligand 2, and the EPR spectra of the Cu II system, suggest the same type of structure for the complexes in solution as in the solid state. Theoretical studies by means of density functional theory (DFT) confirmed the experimental structures of the Ni II and Zn II complexes, and led to a proposal of a similar structure for the corresponding Cu II complex. The calculated EPR parameters for the latter and comparison with related data support this interpretation. The singly occupied molecular orbital (SOMO) in these systems is mainly made of a d orbital of Cu, with a strong antibonding (s*) contribution of the axially bound phenolate residue.

Two macrocyclic pentaaza compounds containing pyridine evaluated as novel chelating agents in copper(II) and nickel(II) overload

“…The 1.75 and 1.50 ratios between the near IR (ν 1 ) and the visible (ν 2 ) bands and the corresponding magnetic moments of 3.24 BM and of 3.37 BM calculated for the two complexes, respectively, are characteristic of high-spin six coordinate nickel(II) centre in distorted tetragonal symmetry [39], where the five positions are occupied by nitrogen atoms of the backbone and the last position by the solvent (water or metal counter-ion nitrate). Therefore, in solution both complexes exhibit structures that are not quite different, even though the Ni [15] .…”