Clemens Pietzonka

Philipps-Universität Marburg, Marburg, Hesse, Germany

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Publications (37)105.17 Total impact

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    ABSTRACT: A first systematic study upon the preparation and exploration of a series of iron 10-thiacorroles with simple halogenido (F, Cl, Br, I), pseudo-halogenido (N3 , I3 ) and solvent-derived axial ligands (DMSO, pyridine) is reported. The compounds were prepared from the free-base octaethyl-10-thiacorrole by iron insertion and subsequent ligand-exchange reactions. The small N4 cavity of the ring-contracted porphyrinoid results in an intermediate spin (i.s., S=3/2) state as the ground state for the iron(III) ion. In most of the investigated cases, the i.s. state is found unperturbed and independent of temperature, as determined by a combination of X-ray crystallography and magnetometry with (1) H NMR-, EPR-, and Mössbauer spectroscopy. Two exceptions were found. The fluorido iron(III) complex is inhomogenous in the solid and contains a thermal i.s. (S=3/2)→high spin (h.s., S=5/2) crossover fraction. On the other side, the cationic bis(pyridine) complex resides in the expected low spin (l.s., S=1/2) state. Chemically, the iron 10-thiacorroles differ from the iron porphyrins mainly by weaker axial ligand binding and by a cathodic shift of the redox potentials. These features make the 10-thiacorroles interesting ligands for future research on biomimetic catalysts and model systems for unusual heme protein active sites.
    Chemistry 01/2014; · 5.93 Impact Factor
  • Advanced Materials Interfaces 01/2014;
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    ABSTRACT: Paramagnetic di([5]trovacenyl)arsinous acid was prepared and characterized by X-ray crystallography, cyclic voltammetry, EPR spectroscopy and magnetic susceptometry. A weak intramolecular electronic communication is observed. XRD demonstrates an intermolecular hydrogen bonds directed tetramer. It represents the first structural characterization of organometallic arsinous acid.
    CrystEngComm 04/2013; 15(18):3525-3528. · 3.88 Impact Factor
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    ABSTRACT: Nanocomposite patterns and nanotemplates are generated by a single-step bottom-up concept that introduces laser-induced periodic surface structures (LIPSS) as a tool for site-specific reaction control in multicomponent systems. Periodic intensity fluctuations of this photothermal stimulus inflict spatial-selective reorganizations, dewetting scenarios and phase segregations, thus creating regular patterns of anisotropic physicochemical properties that feature attractive optical, electrical, magnetic, and catalytic properties.
    Advanced Materials 03/2013; · 14.83 Impact Factor
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    ABSTRACT: CaFeGe2O6, the germanium-analogue to the mineral Hedenbergite, has been synthesized at 1273 K in evacuated SiO2-glass - tubes. Powder neutron diffraction data collected between 4 K and 300 K were used to evaluate the magnetic spin as well as the nuclear crystal structure and its T - evolution. CaFeGe2O6 is monoclinic, C2/c, a = 10.1778(5) Å, b = 9.0545(4) Å, c = 5.4319(3) Å,  = 104.263(3)°, Z = 4 at room temperature. No change of symmetry was observed down to 4 K. Below 43 K, additional magnetic Bragg reflections appear, which can be indexed on the basis of a commensurate magnetic propagation vector k [1,0,0]. The successful description of the magnetic spin structure reveals a ferromagnetic spin coupling within the Fe2+O6 M1 chains, while the coupling between the chains is antiferromagnetic. Spins are oriented collinearly within the a-c plane and form an angle of ~60° with the crystallographic a-axis. The magnetic moment at 4 K amounts to about 4.4 µB. The observed magnetic structure is similar to that of other Ca-clinopyroxenes. The present data is put into context with the structural and magnetic properties of other pyroxenes – among them magnetoelectric and multiferroic pyroxene-type compounds.
    Zeitschrift für Kristallographie. 02/2013; 228(3):140-150.
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    ABSTRACT: The oligosulfur-bridged dinuclear paramagnetic complexes di([5]trovacenyl) sulfide (3··), di([5]trovacenyl) trisulfide (5··), di([5]trovacenylthio)methane (6··), and di([5]trovacenyl) tetrasulfide (7··) have been prepared by the metathesis reactions of [5]trovacenyllithium with SCl2, and [5]lithiotrovacenylthiolate (2·) with SCl2, CH2Cl2, and S2Cl2, respectively, in which 2· was obtained by the reaction of [5]trovacenyllithium with 1 equiv. of elemental sulfur at ambient temperature. Combined with the previously reported di([5]trovacenyl) disulfide (4··), these complexes have been systematically investigated by means of cyclic voltammetry, electron paramagnetic resonance (EPR) spectroscopy, magnetic susceptometry, and/or X-ray diffraction analysis, which reveal weak antiferromagnetic spin–spin exchange interactions. The monosulfur-bridged 3··, in particular, displays the strongest intramolecular spin–spin exchange interaction of |JEPR| = 2.8 cm–1 and Jχ = –1.39 cm–1. This study also indicates that with an increasing number of sulfur atoms in the bridge, the intramolecular communication of biradicals throught the 1D saturated sulfur atom bridge significantly weakens both in solution and in the solid state compared to those of unsaturated carbon-based bridges.
    Berichte der deutschen chemischen Gesellschaft 08/2012; 2012(24). · 2.94 Impact Factor
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    ABSTRACT: The clinopyroxene-type compound FeGeO3 was synthesized using ceramic sintering techniques at 1273 K in evacuated silica tubes and investigated by powder neutron diffraction between 4 and 300 K, X-ray diffraction, SQUID magnetometry, and Fe-57 Mossbauer spectroscopy. The title compound shows space group C2/c symmetry (high pressure, HP-topology) between 4 and 900 K. No structural phase transition is present within this temperature interval, whereas lattice parameters show discontinuities around 50 and 15 K, which are due to magnetic phase transitions and the associated magneto-elastic coupling of the lattice. The magnetic susceptibility data show two maxima in their temperature dependence, one at similar to 47 K, the second around 12 K (depending on the external field), indicative of two magnetic transitions in the title compound. Neutron data shows that for T < 45 K, FeGeO3 orders magnetically, having a simple collinear structure, with space group C2/c, and with the spins aligned parallel to the crystallographic b-axis, both on M1 and M2. The coupling within the M1/M2 band is ferromagnetic, whereas between them it is anti ferromagnetic. As the bulk magnetic measurements in the paramagnetic state revealed a dominating ferromagnetic coupling, the intra-chain interactions dominate the inter-chain interaction. At 12 K, additional magnetic reflections appear, revealing a second magnetic phase transition. Spins are rotated away from the b-axis toward the a-c plane. The coupling within the M1 chain is still ferromagnetic and antiferromagnetic between the M1 chains. However, spins on M1 and M2, are no longer collinear. The moment on the M2 site is rotated further away from the b-axis than on M1.
    American Mineralogist 04/2012; 97(4):694-706. · 2.20 Impact Factor
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    ABSTRACT: Two types of manganese complexes with [Mn4] cores featuring the unusual distorted cube topology are presented, the first of which comprises new modifications of the reported complex [MnIII4(sao)4(saoH)4]·3CHCl3: [Mn4(sao)4(saoH)4]·1.32(C4H10O)·0.43(CH4O) (1a) and [Mn(sao)4(saoH)4]·0.5(CH4O)·0.5(C2H3N) (1b) sao = salicylaldoxime. The second, 0.55[Mn4Cl4(C12H9N2O)4(CH3OH)2(H2O)2]·0.45[Mn4Cl4(C12H9N2O)4(CH3OH)4] (2), is the first reported case of a {MnII4} core of this topology besides known {MnIII4} compounds. Differences between the {MnII4} and {MnIII4} situation are discussed, and so far overlooked differences in magnetic properties between different {MnIII4} compounds are pointed out.
    Zeitschrift für anorganische Chemie 04/2011; 637(5). · 1.16 Impact Factor
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    ABSTRACT: Magnetic iron oxide nanoparticles have found application as contrast agents for magnetic resonance imaging (MRI) and as switchable drug delivery vehicles. Their stabilization as colloidal carriers remains a challenge. The potential of poly(ethylene imine)-g-poly(ethylene glycol) (PEGPEI) as stabilizer for iron oxide (γ-Fe₂O₃) nanoparticles was studied in comparison to branched poly(ethylene imine) (PEI). Carrier systems consisting of γ-Fe₂O₃-PEI and γ-Fe₂O₃-PEGPEI were prepared and characterized regarding their physicochemical properties including magnetic resonance relaxometry. Colloidal stability of the formulations was tested in several media and cytotoxic effects in adenocarcinomic epithelial cells were investigated. Synthesized γ-Fe₂O₃ cores showed superparamagnetism and high degree of crystallinity. Diameters of polymer-coated nanoparticles γ-Fe₂O₃-PEI and γ-Fe₂O₃-PEGPEI were found to be 38.7 ± 1.0 nm and 40.4 ± 1.6 nm, respectively. No aggregation tendency was observable for γ-Fe₂O₃-PEGPEI over 12 h even in high ionic strength media. Furthermore, IC₅₀ values were significantly increased by more than 10-fold when compared to γ-Fe₂O₃-PEI. Formulations exhibited r₂ relaxivities of high numerical value, namely around 160 mM⁻¹ s⁻¹. In summary, novel carrier systems composed of γ-Fe₂O₃-PEGPEI meet key quality requirements rendering them promising for biomedical applications, e.g. as MRI contrast agents.
    International Journal of Pharmaceutics 02/2011; 408(1-2):130-7. · 3.99 Impact Factor
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    ABSTRACT: The title compound is prepared from the elements (1173 K, 4 d) and characterized by single crystal XRD, Moessbauer spectroscopy, electrical resistivity, and magnetic susceptibility measurements, and by LMTO calculations.
    ChemInform 01/2011; 42(4).
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    ABSTRACT: The title compound Ru(9)Zn(7)Sb(8) was synthesized via a high-temperature reaction from the elements in a stoichiometric ratio, and its structure was solved by a single-crystal X-ray diffraction method. The structure [cubic, space group Fm3m, Pearson symbol cF96, a = 11.9062(14) Å (293 K), and Z = 4] adopts a unique 2a(hh) × 2a(hh) × 2a(hh) supercell of a normal half-Heusler phase and shows abnormal features of atomic coordination against the Pauling rule. The formation of this superstructure was discussed in light of the valence electron concentration per unit cell. It is a metallic conductor [ρ(300 K) = 16 μΩ·m], and differential scanning calorimetry revealed that Ru(9)Zn(7)Sb(8) undergoes a transformation at 1356(1) K and melts, by all indications, congruently at 1386 K. At room temperature, its thermal conductivity is about 3 W/m·K, which is only one-quarter of that of most normal half-Heusler phases. Ru(9)Zn(7)Sb(8) as well as its analogues of iron-, cobalt-, rhodium-, and iridium-containing compounds are expected to serve as a new structure type for exploring new thermoelectric materials.
    Inorganic Chemistry 10/2010; 49(22):10536-42. · 4.59 Impact Factor
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    ABSTRACT: The thermionic emission of potassium and cesium ions from Leucite type materials has been investigated as a function of temperature and electric field across the surface. The temperature dependence reveals classical Richardson–Dushman behavior. For small electric fields typically smaller than 1000 V/cm applied orthogonal to the emitter surface, the emitted ion density follows the Langmuir–Child law. The ion density follows Schottky behavior at higher electric fields typically larger than 2000 V/cm. The cross over is interpreted in terms of a transition from space-charge limited ion emission to one limited by the effective work function for ion emission. © 2010 American Institute of Physics.
    Journal of Applied Physics 01/2010; 107. · 2.21 Impact Factor
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 12/2009; 40(48).
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    ABSTRACT: The clinopyroxene compounds LiFeSi{sub 2}O{sub 6} and LiFeGe{sub 2}O{sub 6} have been investigated by constant wavelength neutron diffraction at low temperatures and by bulk magnetic measurements. Both compounds are monoclinic, space group P2{sub 1}/c and do not exhibit a change in nuclear symmetry down to 1.4 and 5 K respective. However, they transform to a magnetically ordered state below 20 K. LiFeSi{sub 2}O{sub 6} shows a simple magnetic structure with no indication of an incommensurate modulation. The magnetic space group is P2{sub 1}/c' and the structure is described by a ferromagnetic coupling of spins within the infinite M1 chains of edge-sharing octahedra, while the coupling between these M1 chains is antiferromagnetic. The magnetic phase transition is accompanied by magnetostriction of the lattice when passing through the magnetic phase transition. The magnetic structure of LiFeGe{sub 2}O{sub 6} is different to the silicate: the space group is P2{sub 1}{sup '}/c and the magnetic unit cell doubled along the a-direction. Within the M1 chains spins are coupled antiferromagnetically, while the chain to chain coupling is antiferromagnetic when coupling goes via the GeB tetrahedron and ferromagnetic when it goes via the GeA tetrahedron. - Graphical abstract: Section of the nuclear and magnetic structure of the synthetic clinopyroxene-type compound LiFeGe{sub 2}O{sub 6} displaying the antiferromagnetic coupling of spins within the chains of Fe{sup 3+}O{sub 6} octahedra and the antiferromagnetic (via GeB sites) and ferromagnetic (via GeA sites) coupling between these chains.
    Journal of Solid State Chemistry 09/2009; 182(9). · 2.04 Impact Factor
  • Berichte der deutschen chemischen Gesellschaft 07/2009; 2009(24):3628 - 3635. · 2.94 Impact Factor
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    ABSTRACT: The compounds CaFeSi2O6 (hedenbergite), CaNiGe2O6, CaCoGe2O6 and CaMnGe2O6 have been synthesized by hydrothermal or ceramic sintering techniques and were Subsequently characterized by SQUID magnetometry and powder neutron diffraction in order to determine the magnetic properties and the spin structure at low temperature. All four compounds reveal the well-known clinopyroxene structure-type with monoclinic symmetry, space group C2/c, Z = 4 at all temperatures investigated. Below 35 K hedenbergite shows a ferromagnetic (FM) coupling of spins within the infinite MI chains of edge-sharing octahedra. This FM coupling dominates an antiferromagnetic (AFM) coupling between neighbouring chains. The magnetic moments lie within the a-c plane and form an angle of 43 degrees with the crystallographic a-axis. Magnetic ordering in CaFeSi2O6 causes significant discontinuities in lattice parameters, Fe-O bond lengths and interatomic Fe-Fe distances through the magnetic phase transition, which could be detected from the Rietveld refinements of powder neutron diffraction data. CaCoGe2O6 and CaNiGe2O6 show magnetic ordering below 18 K, the spin structures are similar to the one in hedenbergite with an FM Coupling within and an AFM coupling of spins between the MI chains. The moments lie within the a-c plane. The paramagnetic Curie temperature, however, decreases from CaFeSi2O6, (+40.2 K) to CaCoGe2O6 (+20.1 K) and CaNiGe2O6 (-13.4 K), suggesting an altered interplay between the concurring AFM and FM interaction in and between the MI chains. CaMnGe2O6 finally shows an AFM ordering below 11 K. Here the magnetic moments are mainly oriented along the a-axis with a small tilt out from the a-c plane. (C) 2008 Elsevier Inc. All rights reserved.
    Journal of Solid State Chemistry 11/2008; 181(11):3163-3176. · 2.04 Impact Factor
  • Zeitschrift für anorganische Chemie 09/2008; 634(11). · 1.16 Impact Factor
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 02/2008; 39(9).
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    ABSTRACT: A unique series of halogenidoiron(III) complexes of the open-chain tetrapyrrolic ligand 2,2'-bidipyrrin (bpd) ([FeX(bdp)] X=F, Cl, Br, I) was prepared from simple pyrrolic and bipyrrolic precursors and iron chloride by a one-pot condensation/metalation strategy, followed by salt metathesis with CsF, LiBr, or NaI. Crystallographic analysis revealed that in all cases the 2,2'-bidipyrrin ligand is forced to reside in a helical conformation when bound to the iron atom. Whereas the extremely sensitive fluorido derivative was isolated as a CsF adduct and forms 1D polymeric chains in the solid state, the more stable chlorido, bromido, and iodido derivatives crystallize as discrete monomeric molecules with a distorted pentacoordinate iron(III) ion in an intermediate spin ground state. Magnetic susceptibility measurements and Mössbauer data of the compounds are in agreement with this interpretation. In solution, however, all the compounds are pentacoordinate with the iron atom in the high-spin (S=5/2) state and dynamic with respect to helix inversion. In the presence of air, the iron chelates react stepwise with the nucleophiles methanol and imidazolate at the tetrapyrrole terminal alpha,omega-positions, presumably through the hexacoordinate species [Fe(bdp)(MeOH)2]+ and [Fe(im)2-(bdp)](-), respectively. The successive increase of strain at these positions results in increasingly labile intermediates that spontaneously release the iron ion from the mono- or disubstituted tetrapyrrole ligands.
    Chemistry 02/2008; 14(13):4006-16. · 5.83 Impact Factor
  • Advanced Materials 11/2007; 19(23):4244 - 4247. · 14.83 Impact Factor

Publication Stats

110 Citations
105.17 Total Impact Points

Institutions

  • 1998–2014
    • Philipps-Universität Marburg
      • Faculty of Chemistry
      Marburg, Hesse, Germany
  • 2009
    • University of Salzburg
      • Division of Mineralogy
      Salzburg, Salzburg, Austria
  • 2005
    • St. Joseph's College of Bangalore
      • Department of Chemistry
      Bengalore, State of Karnataka, India