Synthese, Charakterisierung und Bildungsprinzipien von sauren und neutralen Oxoselenaten(IV) und Oxoselenat(IV)-hydraten

Preparation and characterization, the structural chemistry as well as the thermal decomposition/dehydratation of oxoselenates(IV) of monovalent and bivalent metals are presented. For preparation, a modified gradient technique (∆T method) in aqueous media was used. The characterization of the compounds has been performed by means of scanning electron microscopy (imaging, EDX, WDX), vibrational (IR, Raman), impedance and VIS-remission spectroscopy, x-ray diffraction (XPD, XSD), thermal analysis (TG/DTA, DSC), and magnetic measurements. Eight of the presented oxoselenates(IV) crystallize in new structure types, five are isotypic to known compounds and another five are representatives of the hitherto unknown KM II (HSeO 3 ) 3 (M II = Mg, Mn, Co, Ni, Zn) type. An unusual frequentness of acentric structure types was found for oxoselenate(IV)-chlorides. In the case of the acid compound Li 2 Co II Co III (HSeO 3 ) 4 Cl 3 ·10H 2 O, [Cl(H 2 O) 6 )] - octahedra have been observed for the first time. 1D displacement anomalies of trigonal-planar configurated water molecules of crystallization have been observed also in the coordination of differently sized, low valent cations. Therefore, the "polarization power" of small, high-valent cations may be disfavoured as main account for this phenomenon, known as structural instability of crystal water molecules. Especially the observation of a 2D displacement anomaly observed in case of the quasi -linear configurated crystal water molecules Ow2 of Na 2 Zn 2 (SeO 3 ) 3 ·3H 2 O points to a fundamental impact of geometrical effects. The oxygen linked cation topologies as well as the hydrogen bonded anionic partial structures of all known oxochalcogenates(IV) (ICSD data base) were analyzed for (i) the dimensionality of the linking and (ii) the presence of recurrent structural motifs. A general principle of formation as well as a model of pre-organized species was derived, which may serve as the general basis of further experimental and theoretical works in the field of the complex processes of nucleation and crystal growth in aqueous solutions.