| 1. |
- Mitoudi Vagourdi, Eleni, 1988-
(författare)
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Design of new materials with crystal structure-related properties : The role of lone pair cations
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Non-centrosymmetry and low-dimensional arrangements, e.g. chains or layers, are very attractive structural characteristics of crystalline compounds since they are linked to some physical properties including nonlinear optical activity, ferroelectricity and magnetic frustration. The insertion of a lone-pair cation, equipped with a stereochemically active electron pair into a compound may increase its structural variety and induce the aforementioned characteristics.In this thesis some novel oxide and oxohalide compounds are described. They contain a transition metal and also a p-element lone-pair cation. Relevant synthesis details, crystal structure and physical properties of the compounds will be presented.Chemical systems containing iodate ions and either Cu2+ or Sc3+ have been explored in an effort to find new non-centrosymmetric compounds. The compounds contain also K+ due to its tendency to form highly coordinated asymmetric units. The new iodates are KCu(IO3)3 and the non-centrosymmetric compounds K3Sc(IO3)6 and KSc(IO3)3Cl.Only a few oxofluoride compounds that contain lone-pair cations have been reported in the literature, mainly due to synthetic difficulties. In this work new oxofluoride compounds containing the transition metals Cu2+, Co2+, or Sc3+ and the lone pair cations Bi3+ or Se4+ have been synthesized, where the transition metal octahedra form low-dimensional arrangements in form of chains or layers. The electronegative F ̶ anions behave like O2 ̶ and bridge in between different building blocks. The new oxofluorides are Cu2SeO3F2, CoBi2O2F4 and ScBi2O3F3. The first is a framework-like compound and the latter two are layered and belong to the Aurivillius family with one perovskite like layer. The inclusion of F made it possible to broaden this Aurivillius family to contain low-oxidation state transition metals. The magnetic properties of the new compounds containing Cu2+ and Co2+ were characterised and the Sc3+ containing non-centrosymmetric iodates were found to show non-linear optical properties.
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| 2. |
- Bedin, Michele, PhD, 1984-
(författare)
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Iron, Manganese and Iridium Complexes From Models of RNR and Catalase to Water Oxidation
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this thesis has been synthesise and study metal complexes that mimic the structure and function of the active site in two particular metalloenzymes, ribonucleotide reductase (RNR) and manganese catalase (MnCAT). These two metalloenzymes both have two transition metals ions in the cofactor: two manganese ions in MnCAT and either two iron, iron-manganese or two manganese ions in RNR.Three different ligands were synthetized to make model complexes for these cofactors. The first ligand, BPMP, can bind two metal ions and provides two symmetric pockets with two pyridine groups and one amine each, plus a phenolate group that can bridge the two metals. The second ligand DPCPMP had one carboxylate group instead of a pyridine group in one pocket, creating an asymmetric ligand, and the third ligand BPCPMP, had two carboxylate groups, one in each pocket. From the first and the second ligands it was possible to obtain six complexes: low-valent homometallic Mn/Mn and Fe/Fe complexes and a heterometallic complex for each ligand. For the third ligand, only the Fe/Fe complex was synthetized.All seven complexes were characterized by a number of spectroscopic methods. The presence of carboxylate groups in the ligand shifted the redox potential for the metal complexes towards more negative values, particularly in the case of the homometallic Fe/Fe complexes. Surprisingly, for the asymmetric ligand the placement of the metal ions in the two pockets was not dictated by the asymmetry. Additionally, the relative stability of the homometallic complexes versus the heterometallic complexes and the possibility to transform a homometallic complex into a heterometallic complex were investigated. By titrating one metal into a solution containing the other homometallic dimer it was possible to observe that Fe2+ added to a solution of a Mn/Mn complex led to the replacement of one Mn ion in the complex with a Fe ion.The manganese complex of DPCPMP was investigated as a functional model for MnCAT, catalysing the disproportionation of H2O2 to oxygen and water. In the presence of H2O2 this complex also forms a high-valent species with a di-µ-oxo bridge similar to the MnCAT and RNR.Finally, the methodology used for the study of these complexes was also applied to a set of Ir complexes that act as water oxidation catalysts, and we could show that the presence of a pendant group stabilizes the metal at higher oxidation states leading to higher activity for the catalyst.
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| 3. |
- Svensson, Fredric G., et al.
(författare)
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Rare-Earth-Modified Titania Nanoparticles : Molecular Insight into Synthesis and Photochemical Properties
- 2021
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:19, s. 14820-14830
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Tidskriftsartikel (refereegranskat)abstract
- A molecular precursor approach to titania (anatase) nanopowders modified with different amounts of rare-earth elements (REEs: Eu, Sm, and Y) was developed using the interaction of REE nitrates with titanium alkoxides by a two-step solvothermal-combustion method. The nature of an emerging intermetallic intermediate was revealed unexpectedly for the applied conditions via a single-crystal study of the isolated bimetallic isopropoxide nitrate complex [Ti2Y((PrO)-Pr-i)(9)(NO3)(2)], a nonoxo-substituted compound. Powders of the final reaction products were characterized by powder X-ray diffraction, scanning electron microscopy-energy-dispersive spectroscopy, Fourier transform infrared, X- ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence (PL). The addition of REEs stabilized the anatase phase up to ca. 700 degrees C before phase transformation into rutile became evident. The photocatalytic activity of titania modified with Eu3+ and Sm3+ was compared with that of Degussa P25 titania as the control. PL studies indicated the incorporation of Eu and Sm cations into titania (anatase) at lower annealing temperatures (500 degrees C), but an exclusion to the surface occurred when the annealing temperature was increased to 700 degrees C. The efficiency of the modified titania was inferior to the control titania while illuminated within narrow wavelength intervals (445-465 and 510-530 nm), but when subjected to a wide range of visible radiation, the Eu3+- and Sm3+-modified titania outperformed the control, which was attributed both to doping of the band structure of TiO2 with additional energy levels and to the surface chemistry of the REE-modified titania.
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