Researcher:
Afyon, Semih

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Master Student

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Semih

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Afyon

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Afyon, Semih

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2006 - 200912010 - 20132

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    Synthesis, crystal structures, and vibrational spectra of novel azidopalladates of the alkali metals cs-2[pd(n-3)(4)] and rb-2[pd(n-3)(4)]center dot 2/3h(2)o
    (Wiley-V C H Verlag Gmbh, 2010) Hoehn, Peter; N/A; Department of Chemistry; Afyon, Semih; Somer, Mehmet Suat; Master Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178882
    The transparent dark orange compounds Cs-2[Pd(N-3)(4)] and Rb-2[Pd(N-3)(4)]center dot 2/3H(2)O are synthesized by reaction of the respective binary alkali metal azides with K2PdCl4 in aqueous solutions. According to single-crystal X-ray diffraction investigations, the novel ternary azidopalladates(II) crystallize in the monoclinic space group P2(1)/c (no. 14) with a = 705.7(2) pm, b = 717.3(2) pm, c = 1125.2(5) pm, beta = 104.58(2)degrees, mP30 for Cs2[Pd(N-3)(4)] and a = 1041.4(1) pm, b 1292.9(2) pm, c = 1198.7(1) pm, beta = 91.93(1)degrees, MP102 for Rb-2[Pd(N-3)(4)]center dot 2/3H(2)O, respectively. Predominant structural features of both compounds are discrete [Pd-II(N-3)(4)](2-) anions with palladium in a planar coordination by nitrogen, but differing in point group symmetries. The vibrational spectra of the compounds are analyzed based on the idealized point group C-4h of the spectroscopically relevant unit, [Pd(N-3)(4)](2-) taking into account the site symmetry splitting due to the symmetry reduction in the solid phase.
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    Thermal and hydrothermal stability of flame hydrolytically synthesized SiO2/TiO2 mixed oxides
    (Elsevier, 2013) Hagemann, Michael; Isfort, Christian Schulze; N/A; Department of Chemistry; Afyon, Semih; Somer, Mehmet Suat; Master Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178882
    The phase stability of the two TiO2 modifications (anatase and rutile) in fumed SiO2/TiO2 nano-composites (0-24.8 wt-% silica) under thermal and hydrothermal conditions was investigated by Xray powder diffraction, transmission electron microscopy (TEM) and gas adsorption methods (BET). The results show that the phase transformation from anatase to rutile type of structure and the growth of anatase crystallites are significantly retarded by mixing small amounts of SiO2 into TiO2, while the specific surface area is maintained. The SiO2/TiO2-composites reveal a remarkable shift in the anatase to rutile transformation temperature from approx. 500 degrees C (pure TiO2) to approx. 1000 degrees C (samples with SiO2 contents of more than 10%). The rate of phase transformation from anatase to rutile is enhanced under hydrothermal conditions compared to conventional thermal treatment, e.g. pure titania (AEROXIDE((R)) TiO2 P25) annealed under hydrothermal conditions (100 g/m(3) absolute humidity, 4 h at 600 degrees C) had a rutile content of 85%, while the same specimens annealed in absence of humidity contained only 46% rutile. However, the difference in rate of phase transformation became less pronounced when the silica content in SiO2/TiO2-composites was further increased. TEM results showed that the surface of the anatase crystallites was covered with silica. This averts coalescence of anatase crystallites and keeps them under a critical size during the annealing process. When the crystal domains grew larger, a rapid conversion to rutile took place. The critical size of anatase crystallites for the phase transformation was estimated to be 15-20 nm. (C) 2013 Elsevier Masson SAS. All rights reserved.
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    Azidoaurates of the alkali metals
    (Wiley, 2006) Hoehn, Peter; Armbruester, Marc; Baranov, Alexey; Wagner, Frank R.; Kniep, Ruediger; N/A; Department of Chemistry; Afyon, Semih; Somer, Mehmet Suat; Undergraduate Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178882
    Synthesis, crystal structure as well as IR- and Raman-spectroscopic properties of the new ternary azidoaurates(III) A[Au(N-3)(4)] (A = K Rb, Cs) are reported. The translucent orangered compounds were prepared by reaction of the respective binary azides with HAuCl4 in aqueous solutions at room temperature. The crystal structures determined by single crystal X-ray diffraction methods are monoclinic (C2/c (No. 15), K/Rb/Cs[Au(N-3)(4)]: a = 1049.30(9) pm / 1033.93(10) pm / 1011.9(8) pm, b = 1047.52(8) pm / 1064.20(11) pm / 1093.8(8) pm, c = 776.97(7) pm / 809.79(8) pm / 858.4(6) pm, beta = 91.220(5)degrees / 90.322(5)degrees / 92.72(5)degrees) and provide the first examples for azidoaurates with mono-atomic cations. The unusual reduction of the lattice parameter a with increasing cation size in the isotypic series is discussed in detail. IR and Raman-spectroscopic measurements show strongly covalent gold-nitrogen contacts, a bonding situation which is further supported by quantum chemical calculations and ELF-analyses.