abstract
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 = Ni2+, 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) Angstrom and 2.021(9) to 2.284(8) Angstrom, respectively. In contrast, the M-O distances are markedly different, 2.060(6) and 2.449(8) Angstrom in the Ni-II complex, and 2.027(7) and 2.941(9) Angstrom 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 Cult 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 (sigma*) contribution of the axially bound phenolate residue.
keywords
DENSITY-FUNCTIONAL THEORY; MOLECULAR-ORBITAL METHODS; EFFECTIVE CORE POTENTIALS; GAUSSIAN-TYPE BASIS; MACROCYCLIC LIGANDS; ZINC(II) COMPLEXES; CRYSTAL-STRUCTURE; COORDINATING 2-PYRIDYLMETHYL; NUMERICAL-INTEGRATION; NICKEL(II) COMPLEXES
subject category
Chemistry
authors
Cui, XL; Calhorda, MJ; Costa, PJ; Delgado, R; Drew, MGB; Felix, V
our authors
Paulo Jorge Ferreira de Matos Costa
Post-doc Fellowship