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Fehse, Constanze
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article
The germanides Sc<i>T</i>Ge<sub>2</sub> (<i>T</i> = Fe, Co, Ru, Rh) – crystal chemistry, <sup>45</sup>Sc solid-state NMR and <sup>57</sup>Fe Mössbauer spectroscopy
Abstract
<jats:title>Abstract</jats:title><jats:p>The TiMnSi<jats:sub>2</jats:sub>-type (space group <jats:italic>Pbam</jats:italic>) germanides Sc<jats:italic>T</jats:italic>Ge<jats:sub>2</jats:sub> (<jats:italic>T</jats:italic> = Fe, Co, Ru, Rh) were synthesized from the elements by arc-melting. Single crystals were grown by annealing sequences of the arc-melted buttons in an induction furnace. The structures of ScFeGe<jats:sub>2</jats:sub>, ScRuGe<jats:sub>2</jats:sub> and ScRhGe<jats:sub>2</jats:sub> were refined from single-crystal X-ray diffraction data. In ScRuGe<jats:sub>2</jats:sub>, the ruthenium atoms have distorted octahedral germanium coordination (242–268 pm Ru–Ge). Three <jats:italic>trans</jats:italic>-face-sharing octahedra form a sub-unit which is condensed via common edges in <jats:italic>c</jats:italic> direction and connected <jats:italic>via</jats:italic> common corners with four adjacent blocks, forming a three-dimensional [RuGe<jats:sub>2</jats:sub> type] substructure. The two crystallographically independent scandium sites have coordination numbers 15 (Sc1@Ge<jats:sub>8</jats:sub>Ru<jats:sub>4</jats:sub>Sc<jats:sub>3</jats:sub>) and 17 (Sc2@Ge<jats:sub>7</jats:sub>Ru<jats:sub>6</jats:sub>Sc<jats:sub>4</jats:sub>). Electronic band structure calculations for ScCoGe<jats:sub>2</jats:sub> and ScRuGe<jats:sub>2</jats:sub> show a net charge transfer from the scandium to the transition metal and germanium atoms, leading to a description with polyanionic networks Sc<jats:sup><jats:italic>δ</jats:italic>+</jats:sup>[<jats:italic>T</jats:italic>Ge<jats:sub>2</jats:sub>]<jats:sup>δ−</jats:sup>. The two crystallographically independent Sc sites are easily distinguishable by <jats:sup>45</jats:sup>Sc magic-angle spinning (MAS)-NMR spectroscopy. Isotropic chemical shift values and nuclear electric quadrupolar interaction parameters were deduced from an analysis of the triple-quantum (TQ)-MAS NMR spectra. The electric field gradient parameters deduced from these experiments are in good agreement with quantum-chemical calculations using the <jats:sc>Wien</jats:sc>2<jats:sc>k</jats:sc> code. Likewise, the two crystallographically independent iron sites in ScFeGe<jats:sub>2</jats:sub> could be discriminated in the <jats:sup>57</jats:sup>Fe Mößbauer spectra through their isomer shifts and quadrupole splitting parameters: <jats:italic>δ</jats:italic> = 0.369(1) mm s<jats:sup>−1</jats:sup> and ∆<jats:italic>E</jats:italic><jats:sub>Q</jats:sub> = 0.232(2) mm s<jats:sup>−1</jats:sup> for Fe1 and <jats:italic>δ</jats:italic> = 0.375(2) mm s<jats:sup>−1</jats:sup> and ∆<jats:italic>E</jats:italic><jats:sub>Q</jats:sub> = 0.435(4) mm s<jats:sup>−1</jats:sup> for Fe2 (data at <jats:italic>T</jats:italic> = 78 K).</jats:p>