A new method was developed for the preparation of highly monodisperse isotopically enriched Si-29 silica nanoparticles ( 29 Si-silica NPs) with the purpose of using them as spikes for isotope dilution mass spectrometry (IDMS) quantification of silica NPs with natural isotopic distribution. Si-29 tetraethyl orthosilicate ( 29 Si-TEOS), the silica precursor was prepared in two steps starting from elementary silicon-29 pellets. In the first step Si-29 silicon tetrachloride ( 29 SiCl 4 ) was prepared by heating elementary silicon-29 in chlorine gas stream. By using a multistep cooling system and the dilution of the volatile and moisturesensitive 29 SiCl 4 in carbon tetrachloride as inert medium we managed to reduce product loss caused by evaporation. 29 Si-TEOS was obtained by treating 29 SiCl 4 with absolute ethanol.Structural characterisation of 29 Si-TEOS was performed by using 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy and Fourier-transform infrared (FTIR) spectroscopy. For the NP preparation, a basic amino acid catalysis route was used and the resulting NPs were analysed using transmission electron microscopy (TEM), small angle Xray scattering (SAXS), dynamic light scattering (DLS) and zeta potential measurements.

The compound Fe[C(SiMe 3 ) 3 ] 2 has been prepared and investigated by the means of powder X-ray diffractometry and 57 Fe Mössbauer spectroscopy. The compound's unique geometry, in which iron is linearly coordinated by the two C(SiMe 3 ) 3 ligands, results in a unusual electronic structure of iron, which is visualized as an extreme high hyperfine magnetic field of 157.5(8) T as sensed by the 57 Fe nucleus at T = 20 K. In order to obtain information on the electronic structure of iron and on the bonds to the ligands, DFT (density functional theory) calculations were carried out on Fe[C(SiMe 3 ) 3 ] 2 . The high-spin state of iron was found to be energetically favored: an Fe(II) electron configuration of 3d 5.83 4s 0.72 is predicted, where the 4s electron density is only slightly polarized, and most of the unpaired electrons have 3d character. By assuming a linear crystal field, and associated 3d level scheme as a starting point, it is suggested that the extreme high hyperfine magnetic field, observed along with an apparently negative quadrupole splitting, is perpendicular to the C-Fe

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A series of novel [Fe(MeiPrGlyoxH) 2 (amine) 2 ] complexes have been synthesized [(MeiPrGlyoxH 2 = methylisopropylglyoxime, amine = 3,5-dimethylpyridine, 4-(dimethylamino)pyridine, 4-(phenylamino)phenol, 2-imidazolidone)] and characterized by 57 Fe Mössbauer, FTIR, UV-Vis spectroscopy, mass spectrometry, AFM and thermoanalytical methods. Quantum chemical (DFT) computations of [Fe(MeiPrGlyoxH) 2 (3,5-dimethyl-Py) 2 ] (Py = pyridine) complex were also performed. The square-planar structure of [Fe(MeiPrGlyoxH) 2 ] moiety is similar to that of [Fe(MeEtGlyoxH) 2 ]. The incorporation of branching alkyl chains (isopropyl) in the complexes alters the Fe-N bond length and results in high-spin iron(II) state.