Bis(di-tert-butylindenyl)tetrelocenes

The synthesis and characterization of bis(di-tert-butylindenyl) germanium(II), tin(II) and lead(II) complexes are reported, which includes the first structurally authenticated example of a bis(indenyl)germanocene. The species were studied in detail in solution and in the solid, which includes single crystal X-ray diffraction and NMR spectroscopy, as well as Mössbauer spectroscopy of the tin compound

Crystal structure of europium dichromium icosaaluminum, EuCr2Al20

EuCr2Al20, cubic, Fd3‾m $Fd\overline{3}m$ (no. 227), a = 14.5245(7) Å, V = 3064.1(3) Å3, Z = 8, R gt(F) = 0.0351, wR ref(F 2) = 0.0402, T = 293 K

Switching Lead for Tin in the ‘De-Leadification’ of PbHfO3: Noncubic Structure of SnHfO3

The removal of lead from commercialized perovskite-oxide-based piezoceramics has been a recent major topic in materials research owing to legislation in many countries. In this regard, Sn(II)-perovskite oxides have garnered keen interest due to their predicted large spontaneous electric polarizations and isoelectronic nature for substitution of Pb(II) cations. However, they have not been considered synthesizable owing to their high metastability. Herein, the perovskite lead hafnate, i.e., PbHfO3 in space group Pbam, is shown to react with SnClF at a low temperature of 300 °C, and resulting in the first complete Sn(II)-for-Pb(II) substitution, i.e. SnHfO3. During this topotactic transformation, a high purity and crystallinity is conserved with Pbam symmetry, as confirmed by X-ray and electron diffraction, elemental analysis, and 119Sn Mössbauer spectroscopy. In situ diffraction shows SnHfO3 also possesses reversible phase transformations and is potentially polar between ~130-200 °C. This so-called ‘de-leadification’ is thus shown to represent a highly useful strategy to fully remove lead from perovskite-oxide-based piezoceramics, and opening the door to new explorations of polar and antipolar Sn(II)-oxide materials

Bis(tetrelocenes) – fusing tetrelocenes into close proximity

We report the synthesis and structure of two bis(germanocenes) and a bis(stannocene), obtained by the reaction of unsymmetric ansa bis(cyclopentadienyl) ligands with germanium and tin dichloride. DFT calculations show that the formation of these bis(tetrelocenes) is energetically favoured over the formation of the corresponding [1]tetrelocenophanes. In the crystal structure authenticated structural motif, the two tetrel(II) centers are forced into close proximity to each other, resulting in weak donor–acceptor interactions, according to Natural Bond Orbital (NBO) and Atoms in Molecules (AIM) analyses

Synthesis and Kinetic Stabilization of a Theoretically Predicted Sn(II)-Perovskite Oxide as a Nanoshell

Kinetically-stabilized, i.e., metastable, semiconductor dielectrics represent a major new frontier within many key technological fields as compared to thermodynamically-stable solids that have received considerably more attention. Of longstanding interest are Sn(II) perovskites (e.g., Sn(Zr1/2Ti1/2)O3, SZT), which are theoretically predicted Pb-free analogues of (Pb(Zr1/2Ti1/2)O3, PZT), a commercial piezoelectric compound that is dominant in the electronics industry. Herein, we describe the synthesis of this metastable SZT dielectric through a low-temperature flux reaction technique. The SZT has been found, for the first time, to grow and to be stabilized as a nanoshell at the surfaces of Ba(Zr1/2Ti1/2)O3 (BZT) particles, i.e., forming as BZT-SZT core-shell particles, as a result of Sn(II) cation exchange. In situ powder X-ray diffraction (XRD) and transmission electron microscopy data show that the SZT nanoshells result from the controlled cation diffusion of Sn(II) cations into the BZT particles, with tunable thicknesses of ~25 nm to 100 nm. The SZT nanoshell is calculated to possess a metastability of about 0.5 eV atom–1 with respect to decomposition to SnO, ZrO2, and TiO2, and thus cannot currently be prepared as stand-alone particles. Rietveld refinements of XRD data are consistent with a two-phase BZT-SZT model, with each phase possessing a generally cubic perovskite-type structure and nearly identical lattice parameters. Mössbauer spectroscopic data (119Sn) are consistent with Sn(II) cations within the SZT nanoshells and an outer ~5 to 10 nm surface region comprised of oxidized Sn(IV) cations after exposure to air and water. The optical band gap of the SZT shell was found to be ~2.2 eV, which is redshifted by ~1.2 eV as compared to BZT. This closing of the band gap was probed by X-ray photoelectron spectroscopy and found to stem from a shift of the valence band edge to higher energies (~1.07 eV) as a result of the addition of the Sn 5s2 orbitals forming a new higher-energy valence band. In summary, a novel synthetic tactic is demonstrated to be effective in preparing highly metastable SZT and representing a generally useful strategy for the kinetic stabilization of other predicted, metastable dielectrics

Unveiling Stability Factors in Sn(II)-Containing Oxides: Discovery of a Polar Tin Titanate Perovskite and Photocatalytic Activity for Overall Water Splitting

The discovery of multinary Sn(II)-containing oxides 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) solids 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 ten predicted new Sn(II)-containing oxides that are proposed to fall within reasonable synthetic limits. Increasing stability was found for structures possessing smaller amounts of Sn(II) with local asymmetric coordination environments allowing expression of its stereoactive lone pair. As a test of these results, synthetic efforts to prepare one of the proposed compounds starting from BaLa4Ti4O15 yielded the predicted noncentrosymmetric layered perovskite SnLa4Ti4O15 (SLTO). The new SLTO crystallizes with hexagonal plate-shaped morphologies in the polar P3c1 space group (No. 158), as confirmed by Rietveld refinements of powder X-ray diffraction data and second harmonic generation activity. Full Sn(II) substitution was confirmed by 119Sn Mössbauer spectroscopy, SEM-EDS, and X-ray photoelectron spectroscopy. UV-vis diffuse reflectance data confirmed that SLTO has a visible-light bandgap of ~2.4 eV and is thus predicted to be promising photocatalyst for solar energy conversion. After loading its surfaces with a Rh/Cr2O3-CoOx dual-cocatalyst, SLTO is the first Sn(II)-containing oxide to show activity for overall water splitting into H2 and O2 with an apparent quantum yield of ~21.7%. Thus, these results highlight the synergistic combination of chemical intuition, predictive modeling, and synthetic design in the synthesis of new Sn(II)-containing oxides for promising optical properties and photocatalytic activities for water splitting