Group‐subgroup relations are a compact and concise tool for structure systemization. The present review summarizes the use of Bärnighausen trees for classification of intermetallic structures into ...structural families. The overview starts with group‐subgroup relationships between the structures of the metallic elements (W, In, α‐Po, β‐Po, Pa, α‐Sn, β‐Sn) followed by examples for ordered close‐packed arrangements that derive from fcc, hcp, and bcc subcells (e.g. CuAu, Cu3Au, MoNi4, ZrAl3, FeAl, MoSi2). The main focus lies on more complex structures that derive from aristotypes with comparatively high space group symmetry: AlB2, Fe2P, U3Si2, BaAl4, La3Al11, NaZn13, CaCu5, and Re3B. The symmetry reductions arise from coloring of sites with different atoms or from distortions / puckering due to size restrictions (different radii of atoms). The resulting superstructures are discussed along with the consequences for diffraction experiments, chemical bonding, and physical properties.
Tetrylidynes (Me3P)2(Ph3P)Rh≡SnAr* (10) and (Me3P)2(Ph3P)Rh≡PbAr* (11) are accessed for the first time via dehydrogenation of dihydrides (Ph3P)2RhH2SnAr* (3) and (Ph3P)2RhH2PbAr* (7) ...(Ar*=2,6‐Trip2C6H3, Trip=2,4,6‐triisopropylphenyl), respectively. Tin dihydride 3 was either synthesized in reaction of the dihydridostannate Ar*SnH2− with (Ph3P)3RhCl or via reaction between hydrides (Ph3P)3RhH and 1/2
(Ar*SnH)2. Homologous lead hydride (Ph3P)2RhH2PbAr* (7) was synthesized analogously from (Ph3P)3RhH and 1/2
(Ar*PbH)2. ion of hydrogen from 3 and 7 supported by styrene and trimethylphosphine addition yields tetrylidynes 10 and 11. Stannylidyne 10 was also characterized by 119Sn Mössbauer spectroscopy. Hydrogenation of the triple bonds at room temperature with excess H2 gives the cis‐dihydride (Me3P)2(Ph3P)RhH2PbAr* (12) and the tetrahydride (Me3P)2(Ph3P)RhH2SnH2Ar* (14). Complex 14 eliminates spontaneously one equivalent of hydrogen at room temperature to give the dihydride (Me3P)2(Ph3P)RhH2SnAr* (13). Hydrogen addition and elimination at stannylene tin between complexes 13 and 14 is a reversible reaction at room temperature.
Heavy rhodium carbynes featuring a Rh≡Sn or Rh≡Pb triple bond were synthesized via dehydrogenation of the respective rhodium dihydride complexes (Ph3P)2RhH2SnAr* and (Ph3P)2RhH2PbAr*. The syntheses were accomplished by reacting the nucleophilic organodihydridostannate with (Ph3P)3RhCl or in a hydride transfer reaction between (Ph3P)3RhH and organoelement hydrides of tin or lead.
Directed design of new photocatalysts remains a challenging task in materials chemistry. One approach in metal oxides is to engineer the bulk electronic structure to achieve enhanced visible-light ...absorption and favorable hole transport through the incorporation of heavy main group cations with lone pair electron configurations (Sn2+, Pb2+, Bi3+). Here, we exemplify this strategy with layered SnTiO3, which displays an extremely wide valence band resulting in a favorable band gap (E g = 1.90 eV), a hole effective mass which is among the lowest known for oxides (m h */m 0 = 0.37 in-plane, 0.60 out-of-plane) and visible-light H2 evolution activity. While bulk probes suggest powders of SnTiO3 are stable in air, microscopy, photoemission and 2D nuclear magnetic resonance spectroscopies, and comparison of Mott–Schottky analysis with ab initio band positions indicate the formation of a thin, oxidized passivation layer at the surface which prevents efficient extraction of photoexcited holes and acts as a sink for photoexcited electrons. Extending these ab initio calculations to several Sn(II) oxide semiconductors leads to a remarkably wide range of valence band maxima (spanning ∼4 eV) and suggests an inherent competition between a favorably dispersive valence band and stability against oxidation. In addition to the covalency-driven influence of the valence band width, electrostatics are shown to play a decisive role, with open, low-dimensional structures and cations of lower formal charge leading to smaller ionization potentials. These ab initio band alignments reconcile the experimental observations of (in)stability across several Sn(II) oxides and underscore the utility of this technique as an early, inexpensive screening tool for assessing the suitability of new materials for (opto)electronic and catalytic applications.
A new member to the A2 IBIICIVX4 compound family, Cu2ZnSbS4, was synthesized successfully using ball milling and postannealing in H2S-atmosphere. For comparative purposes, Cu3SbS4 was additionally ...prepared using the same synthetic approach. As is common for A2 IBIICIVX4 compounds, Cu2ZnSbS4 crystallizes isostructural to Cu3SbS4 in the stannite-type structure in space group I 42m. Both antimony sulfides contain monovalent diamagnetic copper and are characterized by substantial covalent bonding. This is consistent with the 121Sb isomer shifts occurring for the Mössbauer spectra of Cu2ZnSbS4 (−7.71 mm s–1) and Cu3SbS4 (−7.68 mm s–1) which fall in the region of covalently bonded Sb(V) compounds. These spectroscopic results are supported by electronic structure calculations.
Room-temperature ionic liquids (RTIL) are important alternatives to aqueous electrolytes in electrocatalytic reactions, batteries, and fuel cells. They are known to reduce existing high ...overpotentials and increase CO2 solubility as well as product selectivity in CO2 reduction reactions (CO2RR). In our work, we have studied the activity for CO2RR of Au(111), Cu(111), and Cu-modified Au(111) electrodes with 1/3, 2/3, and 3/3 Cu monolayers, as well as of AuCu and AuCu3 intermetallics in contact with 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide BMIMNTf2 electrolytes with 1.5 M H2O. Using offline gas chromatography (GC), we demonstrate the formation of H2 and mainly CO as the only reduction products at Au(111), while exclusively H2 is formed at Cu(111). Synergistic electronic and geometric effects lead to higher levels of CO formation at Cu-modified Au(111) electrodes in comparison to neat Au(111). Operando IR absorption spectroscopy (IRAS) of the bulk electrolyte shows the formation of a 2-imidazolium carboxylic acid intermediate that can lower the overpotential for CO2 reduction and does not require stabilization of a CO2 – radical anion as an alternative intermediate at the interface. Systematic variation of the copper content at the catalysts’ surfaces enables us to adjust the H2/CO syngas ratio to a maximum of 1.8 for Cu-modified Au(111) electrodes and ∼3.2 for AuCu3 catalysts at electrolysis times of 20 min, demonstrating a large tunability of the syngas ratio with electrode potential. The observed range of H2/CO ratios includes the ideal ratio of 2 for the Fischer–Tropsch process to produce hydrocarbons and the ratio of 3 needed for methanation.
Herein, we present results of the 121Sb Mössbauer spectroscopy in perovskite antimonates Ba1–x K x SbO3, sibling compounds of the well-known high-T c superconductors Ba1–x K x BiO3. Two Sb valence ...states SbIII and SbV, forming a charge-density-wave (CDW) order, are unambiguously revealed in un- and under-doped phases at x = 0–0.5. As the CDW order is suppressed at x = 0.65, the compound becomes superconducting and all of the Sb sites become equivalent with the intermediate valence of +4.65, consistent with that anticipated from the potassium content. These results provide the direct evidence of metal s electrons participating in the formation of the CDW order and superconductivity in the material, and thus they have important implications for clarifying the underlying mechanism related to mixed valence and potential valence fluctuations of metal ions. The use of Mössbauer active nuclei offers a deeper insight into the structural properties and superconductivity in mixed-valence main-group oxides.
We report near-infrared to ultraviolet (UV) upconversion emissions in triply-doped Gd3+–Tm3+–Yb3+ fluoride–phosphate glasses. Emission at 310 nm, originated from the Gd3+:6P7/2 → 8S7/2 transition, ...was observed for the first time in glasses. The high-purity glasses prepared exhibit extended transparency in the UV down to 200–250 nm. The mixed fluoride–phosphate environment of the rare-earth ions was characterized by means of NMR techniques using scandium as a diamagnetic mimic for the luminescent species, for which the ligand distribution was quantified by 45Sc{31P} rotational echo double-resonance NMR. Both the intensity of the Gd3+ emission as well as those of the UV emissions at 290, 347, and 363 nm increase with increasing ratio of fluoride to phosphate ligands coordinating to the rare-earth ion.
By combining experimental and computational studies, the orthorhombic stannide CeMgSn with a TiNiSi-type structure has been characterized as a potential hydrogen storage material. Experimental ...studies of the formed monohydride CeMgSnH including hydrogen absorption–desorption, thermal desorption spectroscopy, synchrotron and neutron powder diffraction (298 and 2 K), magnetization, and 119Sn Mössbauer spectroscopic measurements are discussed in parallel with ab initio electronic structure calculations. A small, 1.27 vol %, expansion of the unit cell of CeMgSn during its transformation into a thermally stable CeMgSnH monohydride is caused by an ordered insertion of H atoms into half of the available Ce3Mg tetrahedral interstices leaving the CeMg3 tetrahedra unoccupied. The bonding in CeMgSnH is dominated by strong Ce–Sn and Mg–Sn interactions which are almost not altered by hydrogenation, whereas the H atoms carry a small negative charge and show bonding interactions with Ce and Mg. Hydrogenation causes a conversion of the antiferromagnetic CeMgSn into ferromagnetic CeMgSnH with the Ce moments aligned along 001 with a magnetic moment of 1.4(3) μB. The 119Sn isomer shifts and the values of quadrupole splitting in the Mössbauer spectra suggest a similar s-electron density distribution for the Ce- and La-containing REMgSnH monohydrides.
The discovery of Sn(II)-containing oxide semiconductors has been severely limited by a lack of understanding of the factors leading to their thermodynamic stability, e.g., chemical compositions and ...structure types, as well as by the absence of productive synthetic routes. The relatively few reported Sn(II)–O–M (M = early transition-metal cation) semiconductors frequently decompose at moderate to low temperatures. Herein, a large-scale predictive modeling approach was used to assess the structural factors yielding their enhanced thermodynamic stability. This has resulted in 10 new predicted Sn(II)-containing oxides that are proposed to fall within reasonable synthetic limits. Increasing stability was found for structures possessing lower Sn(II)/M ratios and local asymmetric coordination environments allowing the expression of the Sn(II) stereoactive lone pair. As a test of these results, synthetic efforts to prepare one of the proposed compounds starting from BaLa4Ti4O15 yielded the predicted layered-perovskite SnLa4Ti4O15 (SLTO). The new SLTO crystallizes in the noncentrosymmetric and polar P3c1 space group (no. 158) as confirmed by Rietveld refinements of powder X-ray diffraction (XRD) data and second harmonic generation activity. Full Sn(II) substitution was confirmed by a combination of XRD structural refinements, 119Sn Mössbauer spectroscopy, SEM-EDS, and X-ray photoelectron spectroscopy. UV–vis diffuse reflectance data confirmed that SLTO has a visible-light absorbing band gap of ∼2.4 eV and is a promising photocatalyst for solar energy conversion. After loading its surfaces with a Rh/Cr2O3–CoO x dual-cocatalyst, SLTO with hexagonal plate-shaped morphologies showed activity for overall water splitting at a rate of ∼317 μmol g–1 h–1 H2 and an apparent quantum yield of ∼22%. Thus, these results highlight the synergistic combination of chemical intuition, predictive modeling, and synthetic design in the synthesis of new Sn(II)-containing semiconductors for promising applications of their optical properties and photocatalytic activities for water splitting.
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