Kristel HEERWEGH - Academia.edu (original) (raw)

Uploads

Papers by Kristel HEERWEGH

Research paper thumbnail of Synthetic and spectroscopic explorations of iron porphyrin complexes and spectroscopic characterization of two iron and manganese trimers

Research paper thumbnail of Synthesis, Structure and Magnetic Properties of a Linear Trimanganese(III,II,III) Complex Bridged with a (.mu.-Hydroxo)bis(.mu.-acetato) Unit

Proteins containing a polymanganese site bridged with carboxylate groups have recently emerged. F... more Proteins containing a polymanganese site bridged with carboxylate groups have recently emerged. For most of these proteins, catalytic chemistry is accompanied by redox chemistry with 11, 111, and IV oxidation states of manganese. In several of these proteins, mixed valence states of MnnMnm and Mn"'-MnN have been reported.z In order to uncover the unique electronic structures of these metal sites, the magnetic properties of mixed valence manganese complexes with carboxylate bridges have been the subject of numerous s t u d i e~.~ As part of our synthetic explorations of manganese complexes with HB-(3,5-iPr2~z)3,~-~ we now report a novel MnmMnnMnm complex bridged with a (y-hydroxo)bis(y-acetato) unit. Reaction of a dimanganese(I1) complex [Mn(HB(3,5-iPr~pz)3)]2(OH)z with 1 equiv of acetic acid under argon gave a (p-hydroxo)(y-acetato) complex [Mn(HB(3,5-iPr~pz)3)]~(OH)-(OAc) (l).9 When this complex was treated with 20 equiv of H202 in toluene at room temperature for 1 h, the slightly yellow color of the solution turned deep brown. Removal of the solvent followed by fractional recrystallization from MeCN gave 44% yield (based on acetate) of a novel binuclear complex formulated [Mn(HB(3,5-iPr~pz)~)](OH)(OAc)~Mn(OH)(OAc)~[~(HB(3,5-iPrzpz)3)]*3,5-iPr2pzH3(MeCN) (2-3,5-iPrzpzH3(MeCN)) as crystals suitable for X-ray diffraction (Scheme l).Io The

Research paper thumbnail of Monomeric Carboxylate Ferrous Complexes as Models for the Dioxygen Binding Sites in Non-Heme Iron Proteins. The Reversible Formation and Characterization of .mu.-Peroxo Diferric Complexes

Journal of the American Chemical Society, 1994

A series of monomeric carboxylate ferrous complexes with a tripodal N3 ligand HB(3,5-iPrzpz)3 has... more A series of monomeric carboxylate ferrous complexes with a tripodal N3 ligand HB(3,5-iPrzpz)3 has been synthesized and characterized to model the iron site in non-heme iron proteins which bind or activate dioxygen. The structures of Fe(OAc)(HB(3,54Przpz)3) (2), Fe(OBz)(MeCN)(HB(3,5-iPrzpz)3) (3), and Fe(OOCtBu)(HB(3,5-iPrzpz)s) (13) were determined by X-ray crystallography. The five-coordinate complex Fe(OBz)(HB(3,54Pr~pz)~) (4) was found to bind a variety of a-donating ligands such as dimethyl sulfoxide and pyridine at the open coordination site. The reaction between the ferrous complexes and dioxygen has been explored. Fe(OBz)(HB(3,5-iPr~pz)p) (4) was found to bind dioxygen to form an adduct which is reasonably stable below-20 OC. The dioxygen adduct wascharacterized by dioxygen uptake measurement, and UV-vis, resonance Raman, 'H-NMR, and X-ray absorption spectroscopy. On the basis of these results, the Fe:02 stoichiometry of 2:1, an intense absorption band at 682 nm, u (0-0) at 876 cm-1, and F w F e separation of 4.3 A estimated from EXAFS, the dioxygen adduct was identifed as a p-peroxo dinuclear ferric complex. The variable temperature magnetic susceptibility measurement of the isolated p-peroxo complex indicates that the complex is antiferromagnetically coupled with J =-33 cm-l, which is weaker than those known for other p-peroxo dinuclear ferric complexes. This characteristic feature may be associated with the structurally unique Fe-O-GFe frame, which is discussed on the basis of the extended Hiickel calculations. Above-20 OC, the reaction of 4 with dioxygen causes irreversible oxidation, resulting in formation of a trimeric ferric complex (HB(3,5-iPr2pz)~)Fe(OBz)~(0)Fe(OH)(OBz)~Fe(HB(3,5-iPr~pz)~) (16). This assignment is consistent with the magnetic property, Massbauer spectrum, and X-ray analysis.

Research paper thumbnail of Spin coupling in metallo-porphyrins and μ-peroxo species

Journal of Inorganic Biochemistry, 1993

Research paper thumbnail of Novel formation of a linear trinuclear ferric complex containing a .mu.-oxo bis(.mu.-acetato) and a .mu.-hydroxo bis(.mu.-acetato) bridge

Inorganic Chemistry, 1993

The reaction of monomeric five-coordinate iron(I1) complexes such as Fe(OBz)(HB(3,5-iPr~pz)~) (1)... more The reaction of monomeric five-coordinate iron(I1) complexes such as Fe(OBz)(HB(3,5-iPr~pz)~) (1) withdioxygen was recently shown to give p-peroxo iron(II1) dimers that are reasonably stable and characterizable.' However, irreversible thermal decomposition proceeds above-20 "C, and it is of interest to learn about the nature of the ultimate product(s). Efforts to identify the irreversible oxidation product from the reaction of dioxygen with 1 have not been successful owing to poor crystallinity. This prompted us to explorea related complex,

Research paper thumbnail of Protonierung einer linearen, Oxo-verbrückten Dieisen-Einheit ohne Rehybridisierung des verbrückenden Sauerstoffatoms: Struktur des (μ-Hydroxy)bis(tetraphenyl-porphyrinato)eisen(III)-Kations

Angewandte Chemie, 1997

Protonierung einer linearen, 0x0-verbruckten Dieisen-Einheit ohne Rehybridisierung des verbrucken... more Protonierung einer linearen, 0x0-verbruckten Dieisen-Einheit ohne Rehybridisierung des verbruckenden Sauerstoffatoms: Struktur des (p-Hydroxy)bis(tetraphenylporphyrinato)eisen(m)-Kations **

Research paper thumbnail of Protonation of a Linear Oxo-Bridged Diiron Unit without Rehybridization of the Bridging Oxygen: Structure of the(μ-Hydroxo)bis-(tetraphenylporphyrinato)iron(III) Cation

Angewandte Chemie International Edition in English, 1997

duction indicating destruction of the indacene structure. At an even higher negative potential re... more duction indicating destruction of the indacene structure. At an even higher negative potential reversible reduction of the phenylanthracene substructure can be observed. Apparently the substructures are electrochemically independent, too. Cyclic voltammetry of 4 a indicated that the oxidation of the dimethylamino group appears between the oxidation and the reduction of the indacene framework. This suggests that the lone electron pair at the amino group is energetically located between the HOMO and the LUMO of the indacene chromophore. The oxidation potential of the protonated dimethylamino group is considerably higher than that of the free base and beyond the accessible potentials in acetonitrile, which is reflected in the CV upon protonation by the disappearance of this peak. This increase of the oxidation potential makes a nonradiative deactivation process like the one described above impossible. The oxidation of the indacene chromophore in the protonated form occurs at the same potential as in the neutral form, where it appears as the second oxidation step. Apparently the indacene chromophore is influenced inductively by a positive charge on the dimethylamino group in the same way no matter how the charge is created, by protonation or oxidation. We have showed that by specific functionalization the electron donor and acceptor properties of the difluoroboradiaza-sindacene chromophore can be directed in a way that leads to electrogenerated luminescence or proton-dependent fluorescence. Presently we aim to incorporate the described dye compounds as active components in OLEDs and to test analytical applications in sensor chemistry. Experimental Section Cyclic voltammetry: Solvent acetonitrile: potentials reported [mV] vs ferrocene (FOC) as internal standard. Experimental conditions: reversible half-wave potentials El,,, room temperature, scan rate 250 mVs-', platinum disc working electrode. Ag, AgCl pseudo-reference electrode, platinum counterelectrode, supporting electrolyte 0 1 M tetrabutylammonium hexafluorophosphate. Spectroelectrochemistry : Solvent acetonitrile, transmission cell with a gold minigrid working electrode or reflection cell with a platinum disc working electrode. Optlcdl spectra: Concentrations IO-'M to 1 0-6~ in chloroform filtered over basic alumina before use Emission spectra are corrected. ECL-measurements: The ECL spectrum was recorded by applying an alternating square wave with redox potentials determined by cyclic voltammetry (switching time 20 ms. solvent dichloromethane). Concentration: IO-'M, supporting electrolyte' 0.1 M tetrabutykammoniurn hexafluorophosphate. The emission is red-shifted because of reabsorption in more highly concentrated solutions.

Research paper thumbnail of Synthetic and spectroscopic explorations of iron porphyrin complexes and spectroscopic characterization of two iron and manganese trimers

Research paper thumbnail of Synthesis, Structure and Magnetic Properties of a Linear Trimanganese(III,II,III) Complex Bridged with a (.mu.-Hydroxo)bis(.mu.-acetato) Unit

Proteins containing a polymanganese site bridged with carboxylate groups have recently emerged. F... more Proteins containing a polymanganese site bridged with carboxylate groups have recently emerged. For most of these proteins, catalytic chemistry is accompanied by redox chemistry with 11, 111, and IV oxidation states of manganese. In several of these proteins, mixed valence states of MnnMnm and Mn"'-MnN have been reported.z In order to uncover the unique electronic structures of these metal sites, the magnetic properties of mixed valence manganese complexes with carboxylate bridges have been the subject of numerous s t u d i e~.~ As part of our synthetic explorations of manganese complexes with HB-(3,5-iPr2~z)3,~-~ we now report a novel MnmMnnMnm complex bridged with a (y-hydroxo)bis(y-acetato) unit. Reaction of a dimanganese(I1) complex [Mn(HB(3,5-iPr~pz)3)]2(OH)z with 1 equiv of acetic acid under argon gave a (p-hydroxo)(y-acetato) complex [Mn(HB(3,5-iPr~pz)3)]~(OH)-(OAc) (l).9 When this complex was treated with 20 equiv of H202 in toluene at room temperature for 1 h, the slightly yellow color of the solution turned deep brown. Removal of the solvent followed by fractional recrystallization from MeCN gave 44% yield (based on acetate) of a novel binuclear complex formulated [Mn(HB(3,5-iPr~pz)~)](OH)(OAc)~Mn(OH)(OAc)~[~(HB(3,5-iPrzpz)3)]*3,5-iPr2pzH3(MeCN) (2-3,5-iPrzpzH3(MeCN)) as crystals suitable for X-ray diffraction (Scheme l).Io The

Research paper thumbnail of Monomeric Carboxylate Ferrous Complexes as Models for the Dioxygen Binding Sites in Non-Heme Iron Proteins. The Reversible Formation and Characterization of .mu.-Peroxo Diferric Complexes

Journal of the American Chemical Society, 1994

A series of monomeric carboxylate ferrous complexes with a tripodal N3 ligand HB(3,5-iPrzpz)3 has... more A series of monomeric carboxylate ferrous complexes with a tripodal N3 ligand HB(3,5-iPrzpz)3 has been synthesized and characterized to model the iron site in non-heme iron proteins which bind or activate dioxygen. The structures of Fe(OAc)(HB(3,54Przpz)3) (2), Fe(OBz)(MeCN)(HB(3,5-iPrzpz)3) (3), and Fe(OOCtBu)(HB(3,5-iPrzpz)s) (13) were determined by X-ray crystallography. The five-coordinate complex Fe(OBz)(HB(3,54Pr~pz)~) (4) was found to bind a variety of a-donating ligands such as dimethyl sulfoxide and pyridine at the open coordination site. The reaction between the ferrous complexes and dioxygen has been explored. Fe(OBz)(HB(3,5-iPr~pz)p) (4) was found to bind dioxygen to form an adduct which is reasonably stable below-20 OC. The dioxygen adduct wascharacterized by dioxygen uptake measurement, and UV-vis, resonance Raman, 'H-NMR, and X-ray absorption spectroscopy. On the basis of these results, the Fe:02 stoichiometry of 2:1, an intense absorption band at 682 nm, u (0-0) at 876 cm-1, and F w F e separation of 4.3 A estimated from EXAFS, the dioxygen adduct was identifed as a p-peroxo dinuclear ferric complex. The variable temperature magnetic susceptibility measurement of the isolated p-peroxo complex indicates that the complex is antiferromagnetically coupled with J =-33 cm-l, which is weaker than those known for other p-peroxo dinuclear ferric complexes. This characteristic feature may be associated with the structurally unique Fe-O-GFe frame, which is discussed on the basis of the extended Hiickel calculations. Above-20 OC, the reaction of 4 with dioxygen causes irreversible oxidation, resulting in formation of a trimeric ferric complex (HB(3,5-iPr2pz)~)Fe(OBz)~(0)Fe(OH)(OBz)~Fe(HB(3,5-iPr~pz)~) (16). This assignment is consistent with the magnetic property, Massbauer spectrum, and X-ray analysis.

Research paper thumbnail of Spin coupling in metallo-porphyrins and μ-peroxo species

Journal of Inorganic Biochemistry, 1993

Research paper thumbnail of Novel formation of a linear trinuclear ferric complex containing a .mu.-oxo bis(.mu.-acetato) and a .mu.-hydroxo bis(.mu.-acetato) bridge

Inorganic Chemistry, 1993

The reaction of monomeric five-coordinate iron(I1) complexes such as Fe(OBz)(HB(3,5-iPr~pz)~) (1)... more The reaction of monomeric five-coordinate iron(I1) complexes such as Fe(OBz)(HB(3,5-iPr~pz)~) (1) withdioxygen was recently shown to give p-peroxo iron(II1) dimers that are reasonably stable and characterizable.' However, irreversible thermal decomposition proceeds above-20 "C, and it is of interest to learn about the nature of the ultimate product(s). Efforts to identify the irreversible oxidation product from the reaction of dioxygen with 1 have not been successful owing to poor crystallinity. This prompted us to explorea related complex,

Research paper thumbnail of Protonierung einer linearen, Oxo-verbrückten Dieisen-Einheit ohne Rehybridisierung des verbrückenden Sauerstoffatoms: Struktur des (μ-Hydroxy)bis(tetraphenyl-porphyrinato)eisen(III)-Kations

Angewandte Chemie, 1997

Protonierung einer linearen, 0x0-verbruckten Dieisen-Einheit ohne Rehybridisierung des verbrucken... more Protonierung einer linearen, 0x0-verbruckten Dieisen-Einheit ohne Rehybridisierung des verbruckenden Sauerstoffatoms: Struktur des (p-Hydroxy)bis(tetraphenylporphyrinato)eisen(m)-Kations **

Research paper thumbnail of Protonation of a Linear Oxo-Bridged Diiron Unit without Rehybridization of the Bridging Oxygen: Structure of the(μ-Hydroxo)bis-(tetraphenylporphyrinato)iron(III) Cation

Angewandte Chemie International Edition in English, 1997

duction indicating destruction of the indacene structure. At an even higher negative potential re... more duction indicating destruction of the indacene structure. At an even higher negative potential reversible reduction of the phenylanthracene substructure can be observed. Apparently the substructures are electrochemically independent, too. Cyclic voltammetry of 4 a indicated that the oxidation of the dimethylamino group appears between the oxidation and the reduction of the indacene framework. This suggests that the lone electron pair at the amino group is energetically located between the HOMO and the LUMO of the indacene chromophore. The oxidation potential of the protonated dimethylamino group is considerably higher than that of the free base and beyond the accessible potentials in acetonitrile, which is reflected in the CV upon protonation by the disappearance of this peak. This increase of the oxidation potential makes a nonradiative deactivation process like the one described above impossible. The oxidation of the indacene chromophore in the protonated form occurs at the same potential as in the neutral form, where it appears as the second oxidation step. Apparently the indacene chromophore is influenced inductively by a positive charge on the dimethylamino group in the same way no matter how the charge is created, by protonation or oxidation. We have showed that by specific functionalization the electron donor and acceptor properties of the difluoroboradiaza-sindacene chromophore can be directed in a way that leads to electrogenerated luminescence or proton-dependent fluorescence. Presently we aim to incorporate the described dye compounds as active components in OLEDs and to test analytical applications in sensor chemistry. Experimental Section Cyclic voltammetry: Solvent acetonitrile: potentials reported [mV] vs ferrocene (FOC) as internal standard. Experimental conditions: reversible half-wave potentials El,,, room temperature, scan rate 250 mVs-', platinum disc working electrode. Ag, AgCl pseudo-reference electrode, platinum counterelectrode, supporting electrolyte 0 1 M tetrabutylammonium hexafluorophosphate. Spectroelectrochemistry : Solvent acetonitrile, transmission cell with a gold minigrid working electrode or reflection cell with a platinum disc working electrode. Optlcdl spectra: Concentrations IO-'M to 1 0-6~ in chloroform filtered over basic alumina before use Emission spectra are corrected. ECL-measurements: The ECL spectrum was recorded by applying an alternating square wave with redox potentials determined by cyclic voltammetry (switching time 20 ms. solvent dichloromethane). Concentration: IO-'M, supporting electrolyte' 0.1 M tetrabutykammoniurn hexafluorophosphate. The emission is red-shifted because of reabsorption in more highly concentrated solutions.