Sodium Selenotetrelates with Isolated TtSe4-Tetrahedra (Tt = Si, Ge, Sn): Synthesis, Crystal Structures, Thermal Behavior, DFT Modeling, and Na Ion Conductivities

Selenotetrelate compounds Na4TtSe4 (Tt = Si, Ge, Sn) were synthesized by solid-state reactions. A new modification of Na4SiSe4 (Na4SiSe4-cP72), which crystallizes in the cubic space group P4̅3n (no. 218) with a = 12.130(1) Å and V = 1784.453(5) Å3, and a new modification of Na4SnSe4 (Na4SnSe4-tI216), which crystallizes in the tetragonal space group I41/acd (no. 142) with a = 14.4053(4) Å, c = 28.5751(8) Å and V = 5929.7(3) Å3, were discovered. All of the title compounds exhibit moderate to good sodium ion conductivities, as revealed by electrochemical impedance spectroscopy. The formation reaction of Na4SiSe4 was further investigated by high-temperature X-ray powder diffraction of the ball-milled reaction mixture. Density functional-based quantum chemical calculations were performed to compare the different modifications of Na4SiSe4 and Na4SnSe4 energetically. Further modifications of Na4SiSe4 and Na4GeSe4 seem plausible, as revealed by density functional theory modeling. The stability of the hypothetic modifications was examined by phonon dispersion calculations

Strong Lewis and Brønsted Acidic Sites in the Borosulfate Mg3[H2O→B(SO4)3]2

Borosulfates provide fascinating structures and properties that go beyond a pure analogy to silicates. Mg-3[H2O -> B(SO4)(3)](2) is the first borosulfate featuring a boron atom solely coordinated by three tetrahedra. Thus, the free Lewis acidic site forms a Lewis acid-base adduct with a water molecule. This is unprecedented for borosulfate chemistry and even for borates. Quantum chemical calculations on water exchange reactions with BF3 and B(C6F5)(3) revealed a higher Lewis acidity for the borosulfate anion. Moreover, proton exchange reactions showed a higher Bronsted acidity than comparable silicates or phosphates. Additionally, Mg-3[H2O -> B(SO4)(3)](2) was characterised by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and density functional theory (DFT) calculations

The Stacking Faulted Nature of the Narrow Gap Semiconductor Sc2_{2}Si2_{2}Te6_{6}

Crystals of Sc$_{2}$Si$_{2}$Te$_{6}$ have been grown and its crystal, micro- and electronic structures were investigated. The layered character of the title compound exhibits stacking faults that impede a full structural characterization by single crystal X-ray diffraction due to diffuse scattering. Based on high resolution transmission electron micrographs and diffraction patterns, the stacking faulted nature of the real structure of Sc$_{2}$Si$_{2}$Te$_{6}$ has been revealed. Different stacking models were derived from the idealized, faultless structure and the stacking disorder was quantitatively analyzed by Rietveld refinement of powder X-ray diffraction patterns. An energetic comparison of the stacking models by density functional theory is in line with the experimental observations. Further, the bonding situation was investigated by electronic structure calculations. Sc$_{2}$Si$_{2}$Te$_{6}$ is a narrow gap semiconductor with an indirect band gap of 0.65 eV

Surface Accumulation of Cerium, Self-Assembling Peptide, and Fluoride on Sound Bovine Enamel

The accumulation of caries-preventive compounds on sound enamel is crucial in order to improve the inhibition of carious lesion initiation. The aim of this research was to investigate the initial accumulation of cerium, oligopeptide p11-4, and fluoride from NaF or amine fluoride (AmF) on sound enamel in vitro by means of energy dispersive X-ray spectroscopy (EDX). Polished bovine enamel specimens (n = 120 from 60 teeth) were fabricated. Out of these, 12 specimens each were treated with CeCl3 (cerium(III) chloride heptahydrate 25%), oligopeptide p11-4 (Curodont Repair, Credentis), NaF (10,000 ppm F−), AmF (amine fluoride, Elmex Fluid, CP-GABA GmbH, 10,000 ppm F−), or Aqua demin (control). After rinsing with water, the surface elemental composition (Ce, N, F, Ca, P, O, Na, Mg) was measured (EDX; EDAX Octane Elect detector, APEX v2.0), expressed in atomic percent (At%) and analyzed (non-parametric statistics, α = 0.05, error rates method). Another 12 specimens per treatment group were fabricated and used for analyzing accumulation in cross-sections with EDX linescans and two-dimensional EDX-mappings. The surface median atomic percent of cerium (At%Ce) was 0.8 for CeCl3, but no Ce was found for any other group. N, specifically for oligopeptide p11-4, could not be detected. Fluorine could only be detected on fluoridated surfaces. The median atomic percent of fluorine (At%F) was 15.2 for NaF and 17.0 for AmF. The Ca/P ratio increased significantly compared to the control following the application of NaF and AmF (p < 0.001), but decreased significantly for CeCl3 (p < 0.001). In cross-sectioned specimens of the CeCl3-group, 12.5% of the linescans revealed cerium at the enamel surface, whereas 83.3% of the NaF linescans and 95.8% of the AmF linescans revealed fluorine at the enamel surface. Following the application of oligopeptide p11-4, no traces of N were detectable. In the depth of the samples, no signal was detected for any of the corresponding elements exceeding the background noise. Cerium and fluorine (from both NaF and AmF), but not the oligopeptide p11-4, precipitated on sound enamel

Chemical bonding induces one-dimensional physics in bulk crystal BiIr4Se8

One-dimensional (1D) systems persist as some of the most interesting because of the rich physics that emerges from constrained degrees of freedom. A desirable route to harness the properties therein is to grow bulk single crystals of a physically three-dimensional (3D) but electronically 1D compound. Most bulk compounds which approach the electronic 1D limit still field interactions across the other two crystallographic directions and, consequently, deviate from the 1D models. In this paper, we lay out chemical concepts to realize the physics of 1D models in 3D crystals. These are based on both structural and electronic arguments. We present BiIr4Se8, a bulk crystal consisting of linear Bi2+ chains within a scaffolding of IrSe6 octahedra, as a prime example. Through crystal structure analysis, density functional theory calculations, X-ray diffraction, and physical property measurements, we demonstrate the unique 1D electronic configuration in BiIr4Se8. This configuration at ambient temperature is a gapped Su-Schriefer-Heeger system, generated by way of a canonical Peierls distortion involving Bi dimerization that relieves instabilities in a 1D metallic state. At 190 K, an additional 1D charge density wave distortion emerges, which affects the Peierls distortion. The experimental evidence validates our design principles and distinguishes BiIr4Se8 among other quasi-1D bulk compounds. We thus show that it is possible to realize unique electronically 1D materials applying chemical concepts.This research was primarily supported by the Princeton Center for Complex Materials, a National Science Foundation (NSF)-MRSEC program (DMR-2011750), the Gordon and Betty Moore Foundation’s EPIQS initiative (grant numbers GBMF9064 and GBMF9466), and the David and Lucille Packard foundation. C.J.P. is supported by the NSF Graduate Research Fellowship Program under grant number DGE-2039656. G.S. is supported by the Arnold and Mabel Beckman foundation through an AOB postdoctoral fellowship. NSF’s ChemMatCARS, Sector 15 at the Advanced Photon Source, Argonne National Laboratory, is supported by the Divisions of Chemistry (CHE) and Materials Research (DMR), National Science Foundation, under grant number NSF/CHE-1834750. This research used resources of the Advanced Photon Source, a U.S. Department of Energy Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under Contract no. DE-AC02-06CH11357.M.G.V., I.E., and M.G.A acknowledge the Spanish Ministerio de Ciencia e Innovacion (grants PID2019-109905GB-C21, PID2022-142008NB-I00, and PID2022-142861NA-I00). I.E. acknowledges the Department of Education, Universities and Research of the Eusko Jaurlaritza and the University of the Basque Country UPV/EHU (Grant no. IT1527-22). M.G.V. thanks support to the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) GA 3314/1-1─FOR 5249 (QUAST) and partial support from European Research Council grant agreement no. 101020833. M.G.A. thanks the Department of Education of the Basque Government for a predoctoral fellowship (grant no. PRE_2019_1_0304). This work has been financially supported by the Ministry for Digital Transformation and of Civil Service of the Spanish Government through the QUANTUM ENIA project call - Quantum Spain project, and by the European Union through the Recovery, Transformation and Resilience Plan - NextGenerationEU within the framework of the Digital Spain 2026 Agenda.Peer reviewe

Synthesis‐controlled polymorphism and optical properties of phyllosilicate‐analogous borosulfates M[B2(SO4)4] (M = Mg, Co)

Increased synthetic control in borosulfate chemistry leads to the access of various new compounds. Herein, the polymorphism of phyllosilicate-analogous borosulfates is unraveled by adjusting the oleum (65 % SO3) content. The new polymorphs beta-Mg[B-2(SO4)(4)] and alpha-Co[B-2(SO4)(4)] both consist of similar layers of alternating borate and sulfate tetrahedra, but differ in the position of octahedrally coordinated cations. The alpha-modification comprises cations between the layers, whereas in the beta-modification cations are embedded within the layers. With this new synthetic approach, phase-pure compounds of the respective polymorphs alpha-Mg[B-2(SO4)(4)] and beta-Co[B-2(SO4)(4)] were also achieved. Tanabe-Sugano analysis of the Co(2+)polymorphs reveal weak ligand field splitting and give insights into the coordination behavior of the two-dimensional borosulfate anions for the first time. DFT calculations confirmed previous in silico experiments and enabled an assignment of the polymorphs by comparing the total electronic energies. The compounds are characterized by single-crystal XRD, PXRD, FTIR, and UV/Vis/NIR spectroscopy, thermogravimetric analysis (TGA), and density functional theory (DFT) calculations

Li₃As and Li₃P revisited: DFT modelling on phase stability and ion conductivity

Phase pure Li₃As and Li₃P were synthesized from the elements by a high temperature route. Crystal structures were refined from powder X-ray diffraction data. The title compounds were further characterized by difference thermal analysis, temperature dependent X-ray powder diffraction and impedance spectroscopy, proving unexpected Li ion conductivity for Li₃As. High pressure behaviour of the title compounds was modeled via density functional theory, confirming the experimentally reported cubic modifications of Li₃P and Li₃As

Li₃Tr As₂ ( Tr =Al, Ga, In) – Derivatives of the antifluorite type structure, conductivities and electronic structures

Li3AlAs2, Li3GaAs2 and Li3InAs2 were obtained from the elements via high temperature synthesis. Li3AlAs2 and Li3GaAs2 crystallize in a distorted 2 ⋅ 2 ⋅ 1 superstructure of the antifluorite structure type. The orthorhombic crystal structure is isotypic to Li3AlP2 and Li3GaP2, space group Cmce (No. 64) showing layers of condensed TrAs4-tetrahedra (Tr=Al, Ga). Li3InAs2 crystallizes isotypic to Li3InP2 in a distorted 2 ⋅ 2 ⋅ 4 antifluorite type superstructure. The crystal structure is tetragonal, space group I41/acd (No. 142), showing a 3D-network of In4As10-supertetrahedra. Structural characterization by powder X-ray diffraction, thermal analysis, conductivity measurements and band structure calculations show ion conductivity for Li3InAs2 and electronic charge transport for Li3AlAs2 and Li3GaAs2