TY - JOUR
T1 - Geometric and electronic structures of peroxomanganese(III) complexes supported by pentadentate amino-pyridine and -imidazole ligands
AU - Geiger, Robert A.
AU - Leto, Domenick F.
AU - Chattopadhyay, Swarup
AU - Dorlet, Pierre
AU - Anxolabéhère-Mallart, Elodie
AU - Jackson, Timothy A.
PY - 2011/10/17
Y1 - 2011/10/17
N2 - Three peroxomanganese(III) complexes [Mn III(O 2)(mL 5 2)] +, [Mn III(O 2)(imL 5 2)] +, and [Mn III(O 2)(N4py)] + supported by pentadentate ligands (mL 5 2 = N-methyl-N,N′,N′-tris(2- pyridylmethyl)ethane-1,2-diamine, imL 5 2 = N-methyl-N,N′,N′-tris((1-methyl-4-imidazolyl)methyl)ethane-1, 2-diamine, and N4py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) were generated by treating Mn(II) precursors with H 2O 2 or KO 2. Electronic absorption, magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD data demonstrate that these complexes have very similar electronic transition energies and ground-state zero-field splitting parameters, indicative of nearly identical coordination geometries. Because of uncertainty in peroxo (side-on η 2 versus end-on η 1) and ligand (pentadentate versus tetradentate) binding modes, density functional theory (DFT) computations were used to distinguish between three possible structures: pentadentate ligand binding with (i) a side-on peroxo and (ii) an end-on peroxo, and (iii) tetradentate ligand binding with a side-on peroxo. Regardless of the supporting ligand, isomers with a side-on peroxo and the supporting ligand bound in a tetradentate fashion were identified as most stable by >20 kcal/mol. Spectroscopic parameters computed by time-dependent (TD) DFT and multireference SORCI methods provided validation of these isomers on the basis of experimental data. Hexacoordination is thus strongly preferred for peroxomanganese(III) adducts, and dissociation of a pyridine (mL 5 2 and N4py) or imidazole (imL 5 2) arm is thermodynamically favored. In contrast, DFT computations for models of [Fe III(O 2)(mL 5 2)] + demonstrate that pyridine dissociation is not favorable; instead a seven-coordinate ferric center is preferred. These different results are attributed to the electronic configurations of the metal centers (high spin d 5 and d 4 for Fe III and Mn III, respectively), which results in population of a metal-peroxo σ-antibonding molecular orbital and, consequently, longer M-O peroxo bonds for peroxoiron(III) species.
AB - Three peroxomanganese(III) complexes [Mn III(O 2)(mL 5 2)] +, [Mn III(O 2)(imL 5 2)] +, and [Mn III(O 2)(N4py)] + supported by pentadentate ligands (mL 5 2 = N-methyl-N,N′,N′-tris(2- pyridylmethyl)ethane-1,2-diamine, imL 5 2 = N-methyl-N,N′,N′-tris((1-methyl-4-imidazolyl)methyl)ethane-1, 2-diamine, and N4py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) were generated by treating Mn(II) precursors with H 2O 2 or KO 2. Electronic absorption, magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD data demonstrate that these complexes have very similar electronic transition energies and ground-state zero-field splitting parameters, indicative of nearly identical coordination geometries. Because of uncertainty in peroxo (side-on η 2 versus end-on η 1) and ligand (pentadentate versus tetradentate) binding modes, density functional theory (DFT) computations were used to distinguish between three possible structures: pentadentate ligand binding with (i) a side-on peroxo and (ii) an end-on peroxo, and (iii) tetradentate ligand binding with a side-on peroxo. Regardless of the supporting ligand, isomers with a side-on peroxo and the supporting ligand bound in a tetradentate fashion were identified as most stable by >20 kcal/mol. Spectroscopic parameters computed by time-dependent (TD) DFT and multireference SORCI methods provided validation of these isomers on the basis of experimental data. Hexacoordination is thus strongly preferred for peroxomanganese(III) adducts, and dissociation of a pyridine (mL 5 2 and N4py) or imidazole (imL 5 2) arm is thermodynamically favored. In contrast, DFT computations for models of [Fe III(O 2)(mL 5 2)] + demonstrate that pyridine dissociation is not favorable; instead a seven-coordinate ferric center is preferred. These different results are attributed to the electronic configurations of the metal centers (high spin d 5 and d 4 for Fe III and Mn III, respectively), which results in population of a metal-peroxo σ-antibonding molecular orbital and, consequently, longer M-O peroxo bonds for peroxoiron(III) species.
UR - http://www.scopus.com/inward/record.url?scp=80053933448&partnerID=8YFLogxK
U2 - 10.1021/ic201168j
DO - 10.1021/ic201168j
M3 - Article
C2 - 21875042
AN - SCOPUS:80053933448
SN - 0020-1669
VL - 50
SP - 10190
EP - 10203
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 20
ER -