title: Influence of ligand rigidity and ring substitution on the structural and electronic behavior of trivalent iron and gallium complexes with asymmetric tridentate ligands.
abstract: Species 1-6 are [M(III)(L)2]ClO4 complexes formed with the PhO--CH=N-CH2-Py imines, (L(I))- and (L(tBuI))-, and PhO--CH2-NH-CH2-Py amines, (L(A))- and (L(tBuA))-, 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(L(tBuI))2]ClO4 (2), [FeIII(L(tBuA))2]ClO4 (4), and [Ga(III)(L(tBuI))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 (L(tBuI))- and (L(tBuA))- 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.
authors.affiliation: Department of Chemistry, Wayne State University, 5101 Cass Ave. Detroit, Michigan 48202, USA.
authors.forename: Camille
authors.initials: C
authors.lastname: Imbert
authors.forename: Hrant P
authors.initials: HP
authors.lastname: Hratchian
authors.forename: Mauricio
authors.initials: M
authors.lastname: Lanznaster
authors.forename: Mary Jane
authors.initials: MJ
authors.lastname: Heeg
authors.forename: Lew M
authors.initials: LM
authors.lastname: Hryhorczuk
authors.forename: Bruce R
authors.initials: BR
authors.lastname: McGarvey
authors.forename: H Bernhard
authors.initials: HB
authors.lastname: Schlegel
authors.forename: Claudio N
authors.initials: CN
authors.lastname: Verani