Synthesis, structure, and physical properties for a series of monomeric iron(III) hydroxo complexes with varying hydrogen-bond networks.
Mononuclear iron(III) complexes with terminal hydroxo ligands are proposed to be important species in several metalloproteins, but they have been difficult to isolate in synthetic systems. Using a series of amidate/ureido tripodal ligands, we have prepared and characterized monomeric Fe (III)OH complexes with similar trigonal-bipyramidal primary coordination spheres. Three anionic nitrogen donors define the trigonal plane, and the hydroxo oxygen atom is trans to an apical amine nitrogen atom. The complexes have varied secondary coordination spheres that are defined by intramolecular hydrogen bonds between the Fe (III)OH unit and the urea NH groups. Structural trends were observed between the number of hydrogen bonds and the Fe-O hydroxo bond distances: the more intramolecular hydrogen bonds there were, the longer the Fe-O bond became. Spectroscopic trends were also found, including an increase in the energy of the O-H vibrations with a decrease in the number of hydrogen bonds. However, the Fe (III/II) reduction potentials were constant throughout the series ( approximately 2.0 V vs [Cp 2Fe] (0/+1)), which is ascribed to a balancing of the primary and secondary coordination-sphere effects.
Mukherjee
Jhumpa
J
Department of Chemistry, University of California, Irvine, 1102 Natural Science II, Irvine, California 92697, USA.
Lucas
Robie L
RL
Zart
Matthew K
MK
Powell
Douglas R
DR
Day
Victor W
VW
Borovik
A S
AS
D005290:Ferric Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D006860:Hydrogen Bonding; D015394:Molecular Structure; D017550:Spectroscopy, Fourier Transform Infrared
D005290:Ferric Compounds