817161-25-4Relevant academic research and scientific papers
Structure, characterization, and metal-complexation properties of a new tetraazamacrocycle containing two phenolic pendant arms
Cui, Xiuling,Calhorda, Maria Jose,Costa, Paulo J.,Delgado, Rita,Drew, Michael G. B.,Felix, Vitor
, p. 2613 - 2628 (2004)
The new tetraazamacrocycle 2 (=2,2′-[[7-Methyl-3,7,11,17- tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene-3,11-diyl]bis(methylene)] bis(4-bromophenol)) was synthesized and used as a ligand for different metal-ion complexes. The X-ray crystal structures of the complexes of the general formula [M(H-2)]+NO3-·MeOH (M = Ni 2+, Zn2+), 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 Ni-N and Zn-N distances of 1.961(9) to 2.157(9) A and 2.021(9) to 2.284(8) A, respectively. In contrast, the M-O distances are markedly different, 2.060(6) and 2.449(8) A in the NiII complex, and 2.027(7) and 2.941(9) A in the ZnII complex. The UV/VIS spectra of the NiII and CuII complexes with ligand 2, and the EPR spectra of the CuII 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 NiII and ZnII complexes, and led to a proposal of a similar structure for the corresponding CuII 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 (σ*) contribution of the axially bound phenolate residue.
