Iron(III) and copper(II) complexes derived from the flavonoids morin and quercetin: Chelation, crystal structure and DFT studies

Abstract

The [Fe(morin)3] structure represents the first example of a single-crystal x-ray structure of any metal ion coordinated to a flavonoid. In this case it is iron(III) coordinated to three equivalents of morin via chelation producing a distorted octahedral coordination geometry around the iron centre. The crystals were successfully grown from a mixture of toluene and ethyl acetate. The complex crystallizes in a monoclinic space group P21/c, with coordination via the carbonyl and hydroxy oxygen atoms of morin’s ring C. There was disorder with the solvent molecules and these were squeezed out using the program SQEEZE. The experimental studies were supported by relative energy and electron density distributions of the associated complexes predicted by Density Functional Theory calculations performed at the M06-2X/def2-SVP level of theory. Furthermore, the Job’s plots (method of continuous variance) method was used to establish the stoichiometry of both quercetin and morin with the metal ions copper(II) and iron(III). Copper(II) shows a stoichiometry of 1:2 for both flavonoids and iron(III) shows a stoichiometry of 1:3 for both which is in agreement with the crystal structure which has been obtained. The synthesized chelating complexes were characterized by FT-IR, mass spectrometry and microanalyses.