Conversion Reactions of Solids: From a Surprising Three-Step Mechanism towards Directed Product Formation.

Directed conversion reactions from binary to multinary compounds are discovered from the reaction of Bi2 S3 and Bi2 Se3 with NiCl2 ⋅6 H2 O in polyol media under basic conditions. Control of the synthesis conditions allows the preparation of NiBiSe and superconducting Ni3 Bi2 S2 and Ni3 Bi2 Se2 . The formation of Ni3 Bi2 S2 from Bi2 S3 is found from an unexpected three-step reaction path with Bi and NiBi as intermediates. In the more complex Ni/Bi/Se system, the mechanism found can be used to selectively direct the reaction between the competing ternaries and to suppress side-product formation. Contrary to solid-state reactions (500-900 °C) control of product formation is reached at reaction temperatures and times between 166-300 °C and 0.5-10 h, respectively. The formation of different phases is discussed from results of DFT calculations.

Tuneable anisotropy and magnetism in Sn2Co3S2-xSex - probed by (119)Sn Mößbauer spectroscopy and DFT studies.

The half metal (HFM) Sn2Co3S2 shows a fascinating S = 1/2 magnetism. Anisotropic coupling of spins in and between Co Kagomé layers by Sn sites is now studied from the substitution effects of S by Se by systematic and local experimental and first principles data. Trends in crystal structure changes (c/a ratio) as retrieved from XRD data on the solid solution Sn2Co3S2-xSex are complemented by DFT modelling on Sn2Co3SeS and hitherto unknown Sn2Co3Se2. The relationship of crystal structure effects with changes in Curie temperatures and magnetic hysteresis is shown from susceptibility measurements. An insight into the role of the Sn sites in magnetism and bonding is gained from (119)Sn Mössbauer spectroscopic measurements. Isomer shifts, quadrupole splitting, and magnetic hyperfine fields are interpreted by DFT calculations on chemical bonding, electric field gradients (EFG), Fermi contact, and spin polarization.

Reaction of Ni(2+) and SnS as a Way to Form Ni@SnS and Sn2Ni3S2 Nanocrystals: Control of Product Formation and Shape.

Reductive diffusion of Ni(2+) into SnS particles was shown to selectively form Sn2Ni3S2, hybrid, or even core-shell Ni@SnS, Ni1.523Sn, and Ni3S2, by tuning the reaction conditions at low temperatures. The mechanism of Ni(2+) reduction and diffusion into SnS was observed in ethylene glycol, which served both as solvent and reducing agent. Tuning of reaction temperature and duration, morphology of the template SnS, and the application of ethylenediamine as supporting chelating agent, influence the formation of the final products. Their formation was controlled by carefully adjusting redox and equilibrium reactions. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy analysis (EDX).