TY - JOUR A1 - Mehner, Hartmut A1 - Feist, M. A1 - Stößer, R. A1 - Scholz, G. A1 - Kemnitz, E. A1 - Dwelk, H. T1 - Halogeno metallates of transition elements with cations of nitrogen-containing heterocyclic bases, IX. Moessbauer and ESR spectroscopic investigation of aquachloro- and bromoferrates(III). On the compatibility of structural information obtained by spectroscopic and diffraction methods N2 - The 57Fe-Moessbauer spectrum of (dmpipzH2)2[FeIII(H2O)2Cl4][FeIII Cl4]Cl2 (1) consists of two doublets caused by a strongly distorted octahedral and a non-distorted tetrahedral component. Both (dmpipzH2)[FeIIIBr4]2 (2) and (trienH2)[FeIIIBr4]Br (3) show only one doublet indicating a more strongly distorted iron(III) species for 2 and a less-distorted one in the case of 3. For all compounds investigated, the ESR spectra reveal the existence of ground states with predominant antiferromagnetic coupling. The Néel temperatures amount to <4.2 K for 1, 4 K for 3 and 48 K for 2. In the case of 2, both the Moessbauer and the ESR spectra reveal the formation of exchange-coupled {FeBr4} units which has been attributed to a significant cation influence. The fine structure of residual paramagnetic [FeBr4]- subunits remaining in the crystalline matrix could be directly determined. Temperature dependent AC and DC susceptibility measurements of 2 and 3 confirmed the results. KW - Iron coordination KW - Antiferromagnetic coupling KW - Exchange-coupled units KW - ESR fine structure KW - Magnetic susceptibility PY - 2002 U6 - https://doi.org/10.1016/S1293-2558(01)01193-1 SN - 1293-2558 SN - 1873-3085 VL - 4 IS - 1 SP - 109 EP - 115 PB - Elsevier CY - Amsterdam AN - OPUS4-1311 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Buzaré, J.Y. A1 - Silly, G. A1 - Klein, J. A1 - Scholz, G. A1 - Stösser, R. A1 - Nofz, Marianne T1 - Electron paramagnetic resonance investigations of alpha-Al2O3 powders doped with Fe3+ ions: experiments and simulations N2 - Electron paramagnetic resonance (EPR) of Fe3+ ions in Al2O3 is studied in powder samples prepared by different routes and/or modified by thermal or mechanical treatments, with different doping levels and grain sizes. The measurements are performed in various frequency bands (S, X, K, Q and W) and with bimodal detection in X-band. Simulations of the spectra are achieved with a code designed for computing EPR powder spectra described by any spin Hamiltonian including second-, fourth-and sixth-order ZFS terms (S ? 7/2). The linewidths, intensities and lineshapes are accounted for. The lineshape is Gaussian at low Fe3+ concentration whereas it is Lorentzian for higher concentration. The linewidths are interpreted as the superimposition of three main contributions: intrinsic linewidth, dipolar broadening and broadening due to lattice imperfections. The latter is tentatively interpreted in terms of quadrupolar spin Hamiltonian parameter distributions treated using first-order perturbation theory. Whatever the sample, only the b22 spin Hamiltonian parameter is found to be distributed around a mean zero value which corresponds to rhombic distortions. Angle and bond length distributions are tentatively extracted from the b22 distributions which gives some insight into the local order around the spin probe in relation to the preparation and treatment of the samples. PY - 2002 U6 - https://doi.org/10.1088/0953-8984/14/43/329 SN - 0953-8984 SN - 1361-648X VL - 14 SP - 10331 EP - 10348 PB - IOP Publ. Ltd. CY - Bristol AN - OPUS4-2261 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Nofz, Marianne A1 - Stößer, R. A1 - Sebastian, S. A1 - Scholz, G. A1 - Willer, M. A1 - Jeschke, G. A1 - Schweiger, A. T1 - Pulse EPR Spectroscopy of Cu2+ - Doped Inorganic Glasses KW - EPR Spectroscopy KW - Inorganic glasses PY - 1999 SN - 0937-9347 SN - 1613-7507 IS - 16 SP - 507 EP - 528 PB - Springer CY - Wien AN - OPUS4-760 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Reinsch, Stefan A1 - Dreßler, Martin A1 - Nofz, Marianne A1 - Pauli, Jutta A1 - Jäger, Christian A1 - Scholz, G. ED - Krämer, V. T1 - Phasentransformationen von anorganisch modifizierten Alumo-Xerogelen T2 - Jahrestagung der Gesellschaft für Thermische Analyse e.V. CY - Augsburg, Deutschland DA - 2003-09-15 PY - 2003 SP - 1 EP - 2 AN - OPUS4-2668 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Nofz, Marianne A1 - Stösser, R. A1 - Scholz, G. A1 - Dörfel, Ilona A1 - Schultze, Dietrich T1 - The thermally induced transformation of pseudoboehmite gels - a comparison of the effects of corundum seeding and iron doping N2 - The transformation of doped or seeded pseudoboehmite to corundum was studied by combining thermal analysis, X-ray diffraction, transmission electron microscopy, and electron paramagnetic resonance spectroscopy. The temperature of phase transformation to corundum was lowered by about 130 °C when Fe3+ or corundum seeds were added to the sols. Action of Fe3+ ions depends on the actual degree of thermally induced transformation of pseudoboehmite via transition aluminas to corundum and the ability of these alumina phases to incorporate Fe3+ ions. These ions tend to aggregate with increasing iron concentration of the alumina phases and can work as nucleation centers. Small (not, vert, similar20 nm) corundum particles act as active nucleation sites whereas larger grains (200–400 nm) also present in the samples are less effective. For the first time trapping and stabilization of NO2 molecules in transition aluminas formed by a sol–gel route was shown. KW - Grain size KW - Sol-gel processes KW - Electron microscopy KW - X-ray methods KW - Al2O3 PY - 2005 U6 - https://doi.org/10.1016/j.jeurceramsoc.2004.04.014 SN - 0955-2219 SN - 1873-619X VL - 25 IS - 7 SP - 1095 EP - 1107 PB - Elsevier CY - Oxford AN - OPUS4-7455 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stösser, R. A1 - Scholz, G. A1 - Buzaré, J.-Y. A1 - Silly, G. A1 - Nofz, Marianne A1 - Schultze, Dietrich T1 - A magnetic resonance investigation of the process of corundum formation starting from sol-gel precursors PY - 2005 SN - 0002-7820 SN - 1551-2916 VL - 88 IS - 10 SP - 2913 EP - 2922 PB - Blackwell Publishing CY - Malden AN - OPUS4-11888 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stößer, R. A1 - Nofz, Marianne A1 - Feist, M. A1 - Scholz, G. T1 - Fe3+-assisted formation of alpha-Al2O3, starting from sol-gel precursors N2 - The role of Fe3+ ions in the transformations from boehmites and pseudoboehmite xerogels via transition aluminas to corundum was studied here. Especially, the active iron species responsible for the decrease of the temperature of transformation to corundum were looked for. To enable the formation of various Fe3+ and Fe2+ species, samples were subjected to thermal treatments in different atmospheres as well as mechanically activated. Thermal analysis and ESR spectroscopy served to follow the processes and to characterise the resulting products. It was found that (i) isolated Fe3+ ions can indicate local structural changes but have (almost) no influence on the temperature of corundum formation, (ii) the temperature of corundum formation decreases in the result of action of small α-Fe2O3 particles and (iii) during thermal treatments Fe3+ ions are distributed between different phases or precursors thereof: transition aluminas, corundum, Fe2O3, and a Fe3+ pool. KW - Redox process KW - ESR spectroscopy KW - Thermal analysis KW - Sol-gel process KW - Boehmite KW - Corundum PY - 2006 U6 - https://doi.org/10.1016/j.jssc.2005.11.026 SN - 0022-4596 SN - 1095-726X VL - 179 IS - 3 SP - 645 EP - 657 PB - Elsevier CY - San Diego, Calif. AN - OPUS4-11889 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hemmann, F. A1 - Scholz, G. A1 - Scheurell, K. A1 - Kemnitz, E. A1 - Jäger, Christian T1 - Time-optimized 15N qNMR determination of Lewis and Brønsted site concentrations and chemical bonding of pyridine at Brønsted sites in amorphous aluminium hydroxide fluoride N2 - Time-optimized 15N quantitative NMR (qNMR) is described for the precise determination of Lewis and Brønsted site concentrations per gram catalyst, enabling a measurement time reduction of more than a factor of 10. The proof-of-principle is demonstrated for amorphous aluminum hydroxide fluorides with their tunable Lewis to Brønsted functionalities and relevance to highly active and selective heterogeneous catalysis using pyridine as a widely accepted probe molecule for Lewis and Brønsted sites. Two different Lewis centers were found, and reliable site concentrations down to the micromole per gram region can be determined. Furthermore, 1H{15N} REDOR NMR for the acid proton at the Brønsted site yields a distance of the 15N atom of bonded pyridine to this acid proton of (0.112 ± 0.002) nm, such that fast motion/diffusion of the Brønsted site-bonded pyridine at the surface can be excluded. KW - Catalysis KW - Lewis/Brønsted acid sites KW - Acid site concentration KW - Pyridine KW - Quantitative NMR KW - 15N KW - REDOR PY - 2012 U6 - https://doi.org/10.1021/jp212045w SN - 1932-7447 SN - 1089-5639 VL - 116 IS - 19 SP - 10580 EP - 10585 PB - Soc. CY - Washington, DC AN - OPUS4-27724 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - König, R. A1 - Scholz, G. A1 - Veiczi, M. A1 - Jäger, Christian A1 - Troyanov, S.I. A1 - Kemnitz, E. T1 - New crystalline aluminium alkoxide oxide fluorides: evidence of the mechanism of the fluorolytic sol-gel reaction N2 - This study reports three new crystalline aluminum isopropoxide oxide fluorides with molar ratios of Al:F equal to 1:1 and 1:1.25. These are the first three representatives isolated without the incorporation of external donor molecules. Compound 1 Al4F4(µ4-O)(µ-O'Pr)5[H(O'Pr)2] contains a tetranuclear unit consisting of two different five fold coordinated AlFO4-units, with F exclusively in the terminal position. Compound 2, Al4F4(µ4-O)(µ-O'Pr)5[H(O'Pr)2]·Al5F5(µ5-O)(µ-O'Pr)8, contains both a tetranuclear unit (as in 1) and a pentanuclear Al-unit. Al-atoms in the latter are five- and six fold coordinated. Compound 3, Al16F20(µ4-O)4(µ-O'Pr)20·2('PrOH), exhibits a slightly higher fluorination degree and contains an oligomeric chain of four F-linked tetranuclear Al-units. In addition to X-ray structure analysis, compound 1 was characterized by different solid state MAS NMR techniques, including 27Al triple quantum MAS NMR and 1H, 1H→13C CP, 19F and 27Al MAS NMR. On the basis of the collected data, a reliable decomposition of 27Al single pulse MAS NMR spectra and an unambiguous assignment of the resonances to the respective structural AlFO4-units are given. The new crystalline aluminum isopropoxide oxide fluorides are direct evidence of the fluorolytic sol–gel mechanism previously discussed. KW - Aluminium fluorine KW - MAS NMR KW - Qudrupolar nuclei KW - Crystalline aluminium isopropoxide fluoride PY - 2011 U6 - https://doi.org/10.1039/c1dt10514k SN - 1477-9226 SN - 1477-9234 SN - 1364-5447 VL - 40 IS - 34 SP - 8701 EP - 8710 PB - RSC CY - Cambridge AN - OPUS4-26245 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - König, R. A1 - Scholz, G. A1 - Kemnitz, E. A1 - Jäger, Christian A1 - Pawlik, Alf A1 - van Rossumm, B. A1 - Oschkinat, H. T1 - Crystalline aluminium hydroxy fluorides: Structural insights obtained by high field solid state NMR and 27Al chemical shift trend analysis T2 - Gesellschaft Deutscher Chemiker CY - Regensburg, Germany DA - 2008-09-22 PY - 2008 AN - OPUS4-17956 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -