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.
The most fruitful synthetic route to metalloid tin clusters applies the disproportionation reaction of metastable Sn(I) halide solutions, whereby Si(SiMe₃)₃ is mostly used as the stabilizing ...substituent. Here, we describe the synthesis and application of the slightly modified substituent Ge(SiMe₃)₃, which can be used for the synthesis of metalloid tin clusters to give the neutral cluster Sn
Ge(SiMe₃)₃₆ as well as the charged clusters {Sn
Ge(SiMe₃)₃₅}
and {Sn
Ge(SiMe₃)₃₄}
. The obtained metalloid clusters are structurally similar to their Si(SiMe₃)₃ derivatives. However, differences with respect to the stability in solution are observed. Additionally, a different electronic situation for the tin atoms is realized as shown by
Sn Mössbauer spectroscopy, giving further insight into the different kinds of tin atoms within the metalloid cluster {Sn
Ge(SiMe₃)₃₄}
. The synthesis of diverse derivatives gives the opportunity to check the influence of the substituent for further investigations of metalloid tin cluster compounds.
We have synthesized two new Eu-based compounds, EuSr2Bi2S4F4 and Eu2SrBi2S4F4, which are derivatives of Eu3Bi2S4F4, an intrinsic superconductor with Tc = 1.5 K. They belong to a tetragonal structure ...(SG: I4/mmm, Z = 2), similar to the parent compound Eu3Bi2S4F4. Our structural and 151Eu Mössbauer spectroscopy studies show that, in EuSr2Bi2S4F4, Eu-atoms exclusively occupy the crystallographic 2a-sites. In Eu2SrBi2S4F4, 2a-sites are fully occupied by Eu-atoms and the other half of Eu-atoms and Sr-atoms together fully occupy 4e-sites in a statistical distribution. In both compounds Eu atoms occupying the crystallographic 2a-sites are in a homogeneous mixed valent state ∼2.6-2.7. From our magnetization studies in an applied H ≤ 9 T, we infer that the valence of Eu-atoms in Eu2SrBi2S4F4 at the 2a-sites exhibits a shift toward 2+. Our XPS studies corroborate the occurrence of valence fluctuations of Eu and after Ar-ion sputtering show evidence of enhanced population of Eu2+-states. Resistivity measurements, down to 2 K, suggest a semimetallic nature for both compounds.
The oxohydroxoferrates(III) A2Fe2O3(OH)2 (A=K, Rb, Cs) were synthesized under hydroflux conditions. Approximately equimolar mixtures of the alkali metal hydroxides and water were reacted with ...Fe(NO3)3 ⋅ 9H2O at about 200 °C. The product formation depends on the hydroxide concentration, therefore also other reaction products, such as KFeO2, K2−xFe4O7−x(OH)x or α‐Fe2O3, are obtained. The crystal structures of the oxohydroxoferrates(III) A2Fe2O3(OH)2 follow the same structural principle, yet differ in their layer stacking or/and their hydrogen bonding systems depending on A and temperature. In the resulting four different orthorhombic structure types, FeO3OH4− tetrahedra share their oxide corners to create folded ∞2
Fe2O3(OH)22− layers. The terminal hydroxide ligands form hydrogen bonds between and/or within the layers. The positions of the hydrogen atoms in these networks are correlated. The A+ cations are located between the folded anionic layers as well as in their trenches. Under reaction conditions, the potassium compound crystallizes in the space group Cmce (Pearson symbol oC88), showing a bimodal disorder of the hydrogen atoms in hydrogen bridges. In a virtually hysteresis‐less first‐order transition at 340(2) K, the structure slightly distorts into the room‐temperature modification with the subgroup Pbca (oP88), and the hydrogen atoms order. The rubidium and caesium compounds are isostructural to each other but not to the potassium compound, and are always obtained as mixtures of two modifications with space groups Cmce (oC88′) and Immb (oI88). Upon heating, the oxohydroxoferrates decompose into their anhydrides AFeO2 and water. The type of hydrogen bonding network influences the decomposition temperature, the structure and the morphology of the crystals. Despite the presence of iron(III), which was confirmed by 57Fe‐Mössbauer spectroscopy, K2Fe2O3(OH)2 is diamagnetic in the investigated temperature range between 1.8 and 300 K. Neutron diffraction revealed strong antiferromagnetic coupling of the magnetic moments, which are inverted in neighboring tetrahedra.
Hydroflux conditions provide access to oxohydroxoferrates A2Fe2O3(OH)2 with A=K, Rb, Cs. Hydrogen bonds inside and between layers of corner‐sharing FeO3OH tetrahedra strongly influence decomposition temperatures, crystal structures and morphologies. The magnetic moments of the iron(III) cations are aligned antiparallel in neighboring tetrahedra.
Eu
Mg
Si
≡ (2Eu
)(4Mg
)(3Si
) is an electron-precise Zintl phase. Its Hf
Co
-type structure contains three crystallographically independent europium sites. The divalent state of europium was ...manifested through
Eu Mössbauer spectroscopy. In the paramagnetic regime (
= 78 K) the isomer shifts range from −9.16 to −11.29 mm s
. Eu
Mg
Si
shows complex magnetic hyperfine field splitting at
= 5.7 K with a superposition of three subspectra with magnetic hyperfine fields of 5.4 (Eu2), 20.4 (Eu1) and 22.4 (Eu3) T.
Fourteen X-ray-pure intermetallic compounds
Cd
(
= Ho, Er, Tm, Lu;
= Fe, Co, Ni, Ru) and Y
FeCd
were obtained through high-frequency melting of the elements in sealed niobium tubes and subsequent ...annealing in a muffle furnace. They adopt the Er
FeCd
structure, a ternary ordered version of the Co
Al
type. Temperature-dependent magnetic susceptibility measurements show Pauli paramagnetism for the lutetium compounds Lu
FeCd
, Lu
CoCd
, and Lu
RuCd
. The
Cd
phases with holmium, erbium, and thulium show Curie–Weiss paramagnetism and the experimental magnetic moments match with the free ion values of
. All these compounds order antiferromagnetically. The highest Néel temperature was observed for the holmium compounds, e.g. 46.5 K for Ho
RuCd
. Some of the
Cd
phases show field-induced spin reorientations. A
Fe Mössbauer spectrum of Y
FeCd
confirms the single crystallographic iron site.
The rare earth-rich intermetallic compounds RE
4
OsCd (Gd
4
RhIn type, RE = La–Nd, Sm, Gd) and RE
10
OsCd
3
(Er
10
FeCd
3
type, RE = Y, Sm, Gd–Tm, Lu) were synthesized by induction melting of the ...pure elements in sealed niobium ampoules and characterized through their X-ray powder patterns. The structures of Ce
4
OsCd, Nd
4
Os
0.83
Cd
1.17
, Sm
9.87
OsCd
3.13
, and Tm
9.89
OsCd
3.11
were refined from X-ray single crystal diffractometer data. These intermetallics are the first ternary osmium–cadmium compounds. The striking structural feature is an adamantane-like network of osmium-centered trigonal prisms in the RE
4
OsCd phases with Cd
4
tetrahedra (308 pm Cd–Cd in Ce
4
OsCd) in the cavities. The RE
10
OsCd
3
phases exhibit triangular Cd
3
clusters (328 pm Cd–Cd in Sm
9.87
OsCd
3.13
) which, together with rare earth atoms, form chains of corner- and face-sharing Cd
3
RE tetrahedra. Further motifs are Os@RE
6
trigonal prisms (TP) that are condensed to empty RE
6
octahedra (O), building infinite…TP–O–O… rows in
c
direction. The two types of rows show the motif of a hexagonal rod packing.
Graphical abstract
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