ic050658j_si_002.pdf (38.62 kB)

Influence of Ligand Rigidity and Ring Substitution on the Structural and Electronic Behavior of Trivalent Iron and Gallium Complexes with Asymmetric Tridentate Ligands

Download (38.62 kB)
journal contribution
posted on 17.10.2005, 00:00 by Camille Imbert, Hrant P. Hratchian, Mauricio Lanznaster, Mary Jane Heeg, Lew M. Hryhorczuk, Bruce R. McGarvey, H. Bernhard Schlegel, Claudio N. Verani
Species 16 are [MIII(L)2]ClO4 complexes formed with the PhO-−CHN−CH2−Py imines, (LI)- and (LtBuI)-, and PhO-−CH2−NH−CH2−Py amines, (LA)- and (LtBuA)-, in which PhO- is a phenolate ring and Py is a pyridine ring and the prefix tBu indicates the presence of tertiary butyl groups occupying the positions 4 and 6 of the phenol ring. Monometallic species with d5 high-spin iron (1, 2, 3, 4) and d10 gallium (5, 6) were synthesized and characterized to assess the influence of the ligand rigidity and the presence of tertiary butyl-substituted phenol rings on their steric, electronic, and redox behavior. Characterization by elemental analysis, mass spectrometry, IR, UV−visible, and EPR spectroscopies, and electrochemistry has been performed, and complexes [FeIII(LtBuI)2]ClO4 (2), [FeIII(LtBuA)2]ClO4 (4), and [GaIII(LtBuI)2]ClO4 (5) have been characterized by X-ray crystallography. The crystal structures show the imine ligands meridionally coordinated to the metal centers, whereas the amine ligands are coordinate in a facial mode. Cyclic voltammetry shows that the complexes with the ligands (LtBuI)- and (LtBuA)- were able to generate ligand-based phenoxyl radicals, whereas unsubstituted ligands displayed ill-defined redox processes. EPR spectroscopy supports high-spin configurations for the iron complexes. UV−visible spectra are dominated by charge-transfer phenomena, and imine compounds exhibit dramatic hyperchromism when compared to equivalent amines. The tertiary butyl groups on the phenolate ring enhance this trend. Detailed B3LYP/6-31G(d)-level calculations have been used to account for the results observed.