Lone Pair Effect Research Articles

Structural Phase Transition in 0D (3,5-DMP)2Bi1-xSbxCl5 Metal Halides: Expression of the Lone Pair Effect and Polyhedral Distortion.

Low-dimensional Bi/Sb-based organic-inorganic metal halides (OIMHs) have attracted immense attention from the research community because of their structural diversity and efficient luminescence properties. Further understanding of the relationship between the structure and luminescence properties of these materials is of utmost importance for tuning the luminescence properties for various practical applications. Herein, we have synthesized two lead-free Bi/Sb-based novel OIMHs, (3,5-DMP)2BiCl5 and (3,5-DMP)2SbCl5 [(3,5-DMP) = 3,5-dimethylpiperidine], with zero-dimensional (0D) structures and crystallizing in triclinic (P space group) and monoclinic (P21/c space group) crystal systems, respectively. Both the compounds behave as typical semiconductors with indirect optical band gaps of 3.34 and 3.36 eV for pristine Bi and Sb compounds. These compounds exhibit higher environmental and thermal stability at ambient conditions. Gradual substitution of Sb at the Bi site in (3,5-DMP)2Bi1-xSbxCl5 resulted in the introduction of structural strain due to the significant expression of the lone pair effect, thus leading to a structural transition from the triclinic to monoclinic phase. The effect of the structural phase transition on the optical properties is also studied in (3,5-DMP)2Bi1-xSbxCl5. This work may offer new direction and guidance for exploring various 0D hybrid metal halides and tuning the structures for improvement in the luminescence properties.

Band engineering of single-halogen layered Sillén oxyhalide, BaBiO2X (X = Cl, Br, and I): The role of lone-pair effect in photocatalysts

Band structure engineering is an effective way to improve the performance of photocatalysis. Herein, layered oxyhalides, BaBiO2X (X = Cl, Br, and I), with single halogen layers were synthesized by using molten salt synthesis method. Density functional theory (DFT) calculation reveals that the valance band maximum (VBM) of BaBiO2X mainly consists of O 2p orbitals, not halogen p orbitals (Cl-3p, Br-4p, and I-5p), which means that this X1 oxyhalide owns the stability against self-degradation by photogenerated holes during the photocatalytic process. Simultaneously, with the increasing of atomic number from BaBiO2Cl to BaBiO2I, the band gap (Eg) decreases from 3.523 eV to 2.777 eV. Eventually, BaBiO2I exhibits the highest photocatalytic RhB degradation performance among all samples, mostly owning to the enhanced light absorption and improved separation and migration efficiency of photogenerated carriers. This study provides a new idea for designing bismuth-based photocatalysts by band engineering to solve environmental pollution.

Theoretical investigation of structural instabilities of newly predicted superconducting Heusler alloys Rh2NbZ (Z = Al, Ga, Sn): Ab initio approach

We systematically investigate the structural and elastic properties of Rh2NbZ (Z = Al, Ga, Sn) through ab initio calculations. We determine the equilibrium lattice parameters in the cubic austenitic phase of Rh2NbZ and observe martensitic structural transitions in all compositions. These transitions are attributed to the lone pair effect of s electrons on the Z element, leading to a paramagnetic ground state for all alloys. In addition, we discover superconducting behavior of Rh2NbZ, as evident from the total density of states plots. Furthermore, we calculate various elastic parameters in cubic phase to understand the structural stability.

Tuning Structure and Excitonic Properties of 2D Ruddlesden-Popper Germanium, Tin, and Lead Iodide Perovskites via Interplay between Cations.

The compositional tunability of 2D metal halide perovskites enables exploration of diverse semiconducting materials with different structural features. However, rationally tuning the 2D perovskite structures to target physical properties for specific applications remains challenging, especially for lead-free perovskites. Here, we study the effect of the interplay of the B-site (Ge, Sn, and Pb), A-site (cesium, methylammonium, and formamidinium), and spacer cations on the structure and optical properties of a new series of 2D Ruddlesden-Popper perovskites using the previously unreported spacer cation 4-bromo-2-fluorobenzylammonium (4Br2FBZ). We report eight new crystal structures and study the consequence of varying the B-site (Pb, Sn, Ge) and dimension (n = 1, 2, vs 3D). Dimension strongly influences local distortion and structural symmetry, and the increased octahedral tilting and lone pair effects in Ge perovskites lead to a polar n = 2 perovskite that exhibits second harmonic generation, (4Br2FBZ)2(Cs)Ge2I7. In contrast, the analogous Sn and Pb perovskites remain centrosymmetric, but the B-site metal influences the photoluminescence properties. The Pb perovskites exhibit broad, defect-mediated emission at low temperature, whereas the Sn perovskites show purely excitonic emission over the entire temperature range, but the carrier recombination dynamics depend on dimensionality and dark excitonic states. Wholistic understanding of these differences that arise based on cations and dimensionality can guide the rational materials design of 2D perovskites for targeting physical properties for optoelectronic applications based on the interplay of cations and the connectivity of the inorganic framework.

Customizing the trade-off between breakdown strength and polarizability in BaTiO3-based ceramics for superior energy storage capability

Electrostatic capacitors as vital electronic components are extensively studied for applications in lightweight electrification systems. However, it is imperative to develop electrostatic capacitors with concurrently high breakdown strength and polarizability to achieve large energy densities. Herein, we design a weakly coupled relaxor ferroelectric ceramic of BaTiO3-K0.5Bi0.5TiO3-Bi(Ni2/3Nb1/3)O3 (BT-BKT-BNN). The introduction of BKT matrix with A-site lone pair effect, greatly increases saturated polarization strength. Additionally, incorporation of BNN with valence mismatched ions Ni2+ and Nb5+ hinders long-range polar coupling and resulted in the creation of polar nanoregions. By combining a high breakdown strength (Eb ~ 700kVcm-1), large polarization (~ 30.7 µC cm−2), and negligible remnant polarization (< 2 µC cm−2), a remarkable energy density (Wrec) of 6.1Jcm−3 and an efficiency (η) of 87.7% are attained. Specifically, the system demonstrates a superb cycling stability, frequency-insensitive and good temperature stability. This article affords an effective strategy for tailoring high-performance relaxor ferroelectrics.

Stibiotantalite from the Nanyangshan LCT Pegmatite, North Qinling Orogen, Central China: Occurrence and New Data on its Crystal Chemistry

ABSTRACT Stibiotantalite, SbTaO4, from the Nanyangshan LCT pegmatite, North Qinling Orogen, Central China is described. The mineral is associated with oxystibiomicrolite, oxycalcioroméite, hydrokenomicrolite, hydroxynatromicrolite, hydromicrolite, stibnite, bismuthinite, tantalite-(Mn), columbite-(Mn), spodumene, polylithionite, trilithionite, luanshiweiite, fluorluanshiweiite, elbaite, albite, and quartz. Results from electron microprobe data analysis (n = 4) yield the average empirical formula (based on O = 4): (Sb0.96Bi0.04)Σ1.00(Ta0.85Nb0.15)Σ1.00O4. The seven strongest X-ray powder diffraction lines are [d in Å (I)(hkl)] 3.126(100)(121), 2.964(81)(040), 5.976(27)(020), 3.515(22)(111), 1.891(22)(240), 1.736(19)(161), and 2.693(16)(131). Single-crystal X-ray diffraction (SXRD) patterns show strong reflections consistent with space group Pna21. The refined unit-cell parameters from the SXRD data are a 5.5419(2) Å, b 4.9200(2) Å, c 11.8003(5) Å, and V 321.75(2) Å3 with Z = 4. The structure has been refined to a final R1 = 0.0173 on the basis of 766 reflections with Fo &amp;gt; 4σ(Fo). In the previous study, the AO6 octahedron of stibiotantalite was close to an ideal octahedron. The new structure refinement of stibiotantalite from the Nanyangshan pegmatite indicates that the AO6 octahedron has a larger distortion due to the lone-pair effect of Sb3+. The high-quality structural data presented in this study gives a more accurate portrayal of the crystal structure of stibiotantalite than provided in the original description of the mineral.

Cathode Surface Segregating Modification for Boosting Oxygen Reduction Reactions: Coupling Theory and Experiment in Proton Conducting Solid Oxide Fuel Cells (H-SOFCs)

The surface electrochemical catalysis reaction is complex due to the unpredictable surface morphology and severe reaction environment, especially for cathodes in proton conducting solid oxide fuel cells (H-SOFCs) where water vapor is generated and evaporated at a high operating temperature. The first-generation cathode materials (LaxSr1-xMO3-δ, M=Fe, Co, Mn) tend to have A-site cation segregation, and this segregation layer reduces the performance. Surface segregation phenomena tends to be ignored by computer simulations because surface termination is described as a highly crystallized layer, misleading the development of material computing science. Therefore, a combination of theory and surface investigation is essential for future work in this community. In this work, we use density functional theory (DFT) for designing a higher-performing cathode material, La0.35Bi0.15Sr0.5FeO3-δ (LBSF), for improvement of both bulk and surface electrochemical character in an intrinsic manner, predicting a candidate material with good performance that can be used in solid oxide proton conducting fuel cells (H-SOFCs). By combining a sensitive surface analysis technique, low energy ion scattering (LEIS), surface segregation is finely considered and determined that the particles are fully covered with a Sr segregation layer on the outer most surface. Aberration-Corrected transmission electron microscopy (ACTEM) is also applied and shows an amorphous structure at the particle edge. With the determination of this segregation layer, a reality-closed model is given, and related surface reactions are modelled based on this layer instead of a conventional cleaved, well-crystallized surface. Also, as bismuth diffuses towards the surface due to the lone pair effect, the segregation becomes an oxygen reduction reaction preferred layer instead of a blocking layer. After computational prediction and surface analysis, LBSF is successfully applied into H-SOFCs and shows excellent performance with a peak power density of 1630 mW cm−2 at 700 oC. In addition, long term stability tests were conducted to ensure stability in future commercial use, and the experimental results show that LBSF works stable under extremely high temperature operating environments. In addition, a full cell was stabilized for about 300 hours, indicating a potential commercial application in the future.

Temperature-dependent dielectric measurements and structural properties of barium stannate (BaSnO3)

Cubic perovskite BaSnO3, synthesized by solid-state reaction method, was structurally characterized using temperature-dependent X-ray and Raman spectroscopy studies along with room temperature neutron diffraction analysis. Here, we report the effect of temperature on the structural parameters of BaSnO3 in correlation with dielectric properties. Sample homogeneity and elemental composition were studied by scanning electron microscopy and energy dispersive X-ray spectroscopy methods. The compound maintains cubic symmetry even at high temperatures and exhibits gradual increase in unit cell volume owing to thermal expansion. To understand high temperature phase transition, if any, and capacitance behavior, high temperature dielectric measurements were carried out. High value of dielectric constant was obtained at low frequencies as the temperature was increased, which may be due to the presence of oxygen vacancies or the lone-pair effect.

Captodative Effect Facilitates the Excitation in Diboron Molecule (CAAC)2 B2 (SH)2.

Given the extraordinary versatility in chemical reactions and applications, boron compounds have gained increasing attentions in the past two decades. One of the remarkable advances is the unprecedented preparation of unsaturated boron species. Notably, Braunschweig et al. found that the cyclic (alkyl)(amino) carbenes (CAACs) stabilized diboron molecules (CAAC)2 B2 (SR)2 host unpaired electrons and exist in the 90°-twisted diradical form, while other analogues, such as N-heterocyclic carbenes (NHCs), stabilized diboron molecules prefer a conventional B=B double bond. Since previous studies recognized the differences in the steric effect between CAAC and NHC carbenes, here we focused on the role of thiol substituents in (CAAC)2 B2 (SR)2 by gradually localizing involved electrons. The co-planarity of the thiol groups and the consequent captodative effect were found to be the culprit for the 90°-twisted diradical form of (CAAC)2 B2 (SR)2 . Computational analyses identified two forces contributing to the π electron movements. One is the "push" effect of lone pairs on the sulfur atoms which boosts the π electron delocalization between the BB center and CAACs. The other is the π electron delocalization within each (CAAC)B(SR) fragment where the pull effect originates from the π electron withdrawal by CAACs. There are two such independent and orthogonal push-pull channels which function mainly in individual (CAAC)B(SR) fragments. This enhanced π push-pull effect in the triplet state facilitates the electronic excitation in (CAAC)2 B2 (SR)2 by reducing the singlet-triplet gap.

The synergistic effect of electron lone pairs and aromaticity on the binding affinity towards metal surfaces

Non-covalent binding interactions of organic molecules through their electron lone pairs and aromatic functional groups towards metal surface are understood. Four isoxazole derivatives containing different sequential aromatic groups and lone pair of electrons are designed and synthesized along with cobalt nanoparticles as a representative of metal surface and titrated against each other. Multiple characterization techniques including UV-Vis absorption spectroscopy, fluorescence emission spectroscopy, hydrodynamic size, and zeta potential are used to study binding and results are compared to each other. We are able to differentiate and understand binding interactions of these functionalities towards metal surface, where the binding mechanism is different based on variations in these molecules. The binding ability of lone pair of electrons (1.48 × 108) is slightly stronger than the π-bond electronic cloud of aromatic benzene group (1.46 × 108), however presence of both functionalities tends to enhance the binding more than twice (3.24 × 108), a synergistic effect that is very strongly observed. These results are also verified by DFT calculations. This work will certainly be helpful to design molecules for their specific interaction required for various applications.

Imidazole-based fluorescent probes: concomitant effects of N1 substitution and lone pair on selective recognition of picric acid

A series of imidazole-based luminophores with N1-functionalization have been synthesized for selective recognition of nitroaromatic compounds.

Centrosymmetric Tetragonal Tungsten Bronzes A4Bi2Nb10O30 (A = Na, K, Rb) with a Bi 6s Lone Pair

A first-principles study of the tetragonal tungsten bronze (TTB) K4Bi2Nb10O30 has suggested that the Bi 6s lone pair causes in-plane polarization (within the a–b plane), corresponding to the one found in Pb5Nb10O30 (PN), in contrast to the out-of-plane polarization (along c) found in most TTBs. Replacing PN with KBN potentially opens for a lead-free analogue to morphotropic phase boundaries known in TTBs based on PN. Here, we report on the synthesis and properties of A4Bi2Nb10O30 (ABN, A = Na, K, Rb) with the objective to determine the structure and electrical properties, paying particular attention to the role of the Bi 6s lone pair. The ABN materials were synthesized via conventional solid-state synthesis in a two-step process. Convergent-beam electron diffraction demonstrated a centrosymmetric tetragonal space group for the two compounds KBN and RBN, and ferroelectric polarization–electric field measurements confirmed the lack of hysteretic behavior in line with the observed centrosymmetric symmetry. Non-ambient powder X-ray diffraction demonstrated the signature of a phase transition for KBN and RBN, as several weak satellite reflections vanished during heating and reappeared upon cooling. Dielectric spectroscopy supported the observation of an anomaly due to the presence of a weak maximum in the electrical permittivity at temperatures corresponding to the disappearance of the satellite reflections. Possible explanations for the absence of polarization in ABN TTBs are discussed with particular attention to the suppression of the 6s2 lone pair effect of Bi and the size of A-site cations in the TTB crystal structure.

Composition‐independent Curie point (Tc) in ferroelectric (1 − x)PbTiO3–xBi(Li1/2Nb1/2)O3 solid solution

AbstractA new ferroelectric solid solution (1 − x)PbTiO3–xBi(Li1/2Nb1/2)O3 has been explored to develop high‐temperature piezoelectric material. An interesting observation has been found regarding its Curie point (TC) and tetragonal lattice strain (c/a − 1). With increasing composition (x), the Curie point (TC) decreases up to x = 0.10 and thereafter remains constant. In concurrence with the TC, the tetragonal lattice strain (c/a − 1) follows a similar trend. Neutron powder diffraction analysis suggests this anomalous behavior is due to the robust off‐centering characteristic of the Bi+3 ion 6S2 lone pair effect at the A‐site compared to ions at B‐site.

Lead(II) complexes with Kemp’s tricarboxylate: Can lone pair activity be discerned?

Kemp’s triacid (H3kta; cis,cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid) has been used to synthesize three lead(II) complexes under solvo-hydrothermal conditions. [Pb3(kta)Cl3] (1) and [Pb3(H3kta)(kta)2] (2) are both diperiodic coordination polymers displaying hydrophobic surfaces with protruding methyl groups, complex 2 being isomorphous with an SrII complex previously reported. In contrast, [Pb(Hkta)(phen)] (3), where phen is 1,10-phenanthroline, is a monoperiodic, helical coordination polymer. In all cases, PbII cations are in seven- or eight-coordinate environments of predominantly hemidirected nature. The possible effects of the PbII valence shell lone pair are discussed in terms of coordination geometry and Pb⋅⋅⋅H weak interactions as revealed on Hirshfeld surfaces. Only in complex 1 is a short Pb⋅⋅⋅H contact at 2.84 Å possibly indicative of appreciable basicity of the metal ion. All three complexes show similar weak luminescence, apparently independent of the nature of the ligands.

The Role of the Bi3+ Lone Pair Effect in Bi(H3O)(SO4)2, Bi(HSO4)3, and Bi2(SO4)3.

Three new members in the Bi2O3-SO3-H2O system are identified by single crystal X-ray diffraction and Rietveld refinement after a fundamental examination of this phase space. Bi(H3O)(SO4)2 crystallizes in space group P21/c (no. 14, a = 1203.5(4), b = 682.9(2), c = 821.2(2) pm, β = 102.99(1)°, 861 independent reflections, 88 refined parameters, wR2 = 0.14) homeotypic with Nd(H3O)(SO4)2 featuring edge-sharing BiO9 polyhedra. Bi(HSO4)3 crystallizes in a new structure type in space group P1 (no. 2, a = 492.04(7), b = 910.8(1), c = 1040.8(2) pm, α = 85.443(5)°, β = 86.897(5)°, γ = 74.542(4)°, 3227 independent reflections, 154 refined parameters, wR2 = 0.05) comprising dimers of edge-sharing BiO8 polyhedra. For Bi2(SO4)3, a new modification crystallizing in space group P21/n (no. 14, a = 1308.03(7), b = 473.25(3), c = 1452.61(8) pm, β = 100.886(2)°, 3189 independent reflections, 155 refined parameters, wR2 = 0.03) isotypic to Sb2(SO4)3 with noncondensed BiO7 polyhedra is presented. The role of the Bi3+ lone pair effect as elucidated by density functional theory (DFT) calculations is discussed for all three compounds with respect to their structural and optical properties. Additionally, the Bi3+ lone pair activity is compared to the recently reported borosulfates Bi(H3O)[B(SO4)2]4 and Bi2[B2(SO4)6]. Geometrical calculations based on structural data are correlated with electron localization function (ELF) calculations to establish the origin of the direction and strength of the lone pair stereoactivity of Bi3+ in oxidic compounds. Finally, the thermal properties of the three compounds are reported.

Structure of binary antimony phosphate glasses by diffraction methods

Antimony phosphate glasses (Sb2O3)x(P2O5)1-x with x = 0.05 and 0.80 were measured by neutron and X-ray diffraction with high real-space resolution. The P−O and O−O distance peaks of the PO4 tetrahedra were found with the expected parameters. For the glass of x = 0.80 the Sb−O and O−O coordination numbers and distances suggest highly distorted SbO3 and SbO4 environments according to strong lone-pair effects of the Sb3+. The fraction of SbO4 has the right portion that all oxygens can form Sb−O−Sb or Sb−O−P bridges. Significant numbers of secondary Sb−O bonds (> 0.25 nm) are extracted. The first diffraction peak at 13 nm−1 is related to distances between stacked layers of corner-connected oxygen triangles as in the orthorhombic Sb2O3. For the glass of x = 0.05 the medium-range order reminds that of vitreous P2O5. Its SbO4 units are formed with mean Sb−O bonds of 0.210 nm.

A2P2S6 (A = Ba and Pb): a good platform to study the polymorph effect and lone pair effect to form an acentric structure.

Three ternary thiophosphates α-Ba2P2S6, β-Ba2P2S6, and Pb2P2S6 were synthesized via a high temperature salt flux method or an I2 transport reaction. β-Ba2P2S6 and Pb2P2S6 were previously structurally characterized without investigating their optical properties. α-Ba2P2S6 was discovered for the first time, and it is isostructural to Pb2P2S6 and crystallizes in the acentric space group Pn (no. 7). β-Ba2P2S6 crystallizes in the centrosymmetric space group P21/n (no. 14). There is a high structural similarity between α-Ba2P2S6, β-Ba2P2S6, and Pb2P2S6 including close unit cell parameters and identical [P2S6] motifs. The structural relationships between α-Ba2P2S6 and β-Ba2P2S6, and β-Ba2P2S6 and Pb2P2S6 were elucidated by single crystal X-ray diffraction, differential scanning calorimetry (DSC), electronic structure calculations, and nonlinear optical property measurements. There are no phase transitions detected between α-Ba2P2S6 and β-Ba2P2S6. From centrosymmetric β-Ba2P2S6 to acentric Pb2P2S6, the chemical characteristics of Pb, such as stereoactive lone pairs, play a key role in the structural difference. Pb2P2S6 is uncovered as a type-I phase-matching material with a moderate second harmonic generation (SHG) response of 1.4 × AgGaS2 and a high laser damage threshold (LDT) of 2.5 × AgGaS2. α-Ba2P2S6 is not a type-I phase-matching material with a moderate second harmonic generation response (1.7 × AgGaS2, a sample of 225 μm particle size) and a high laser damage threshold (5.5 × AgGaS2).

BiSbWO6: Properties of a mixed 5s/6s lone-pair-electron system

• Stereochemical activity of lone-pair electrons as an alloy-design principle. • BiSbWO 6 alloys share narrow thermodynamic stability range. • Sb/Bi lone-pair effects on electronic structure identified and decoupled. • WO 3 used as a control model to isolate role of mixed lone-pair electrons. • Local distortions due to Sb 5s lone-pair electrons upshift conduction band edges. We investigate the behavior of lone-pair electrons in a mixed Sb(5s)/Bi(6s) crystal-environment. Density functional theory is used to calculate the electronic properties of Sb-alloyed-Bi 2 WO 6 and to study the effects of introducing Sb 5s orbitals to the band structure. The band edge positions, partial charge analyses, and band decomposed charge densities of BiSbWO 6 are used to explain the observed trends in relative stabilities and band edge shifts. To isolate the role of the mixed lone-pair, we considered WO 3 as a control model. We find that local distortions caused by Sb 5s lone-pair electrons lead to upshifts in both valence and conduction band edges.

Synthesis, characterization and crystal structure of bis-(methylsulfonylmethyl) sulfone, a symmetric acyclic trisulfone

Bis - (methylsulfonylmethyl) sulfone, BMSMS, was synthesized and characterized through vibrational (IR, Raman) spectroscopy. The crystal structure of BMSMS, determined by X-ray diffraction methods, together with Hirshfeld surfaces analysis were used to evaluate intermolecular interactions. BMSMS can be considered as one-turn helix of about 7.13 Å, further stabilized by weak intra-molecular CH•••O bonds. The experimental results were supplemented by quantum chemical calculations. It was also analyzed the hyperconjugative effects of oxygen atoms lone pairs (LP) on the vibrational behavior of the SO2 group. Besides, biofilm formation and QS activity were evaluated on this new bis- (methylsulfonylmethyl) sulfone.

Understanding the Structural and Electronic Properties of Bismuth Trihalides and Related Compounds.

Bismuth trihalides, BiX3 (X = F, Cl, Br, and I), have been thrust into prominence recently because of their close chemical relationship to the halide perovskites of lead, which exhibit remarkable performance as active layers in photovoltaic cells and other optoelectronic devices. In the present work, we have used calculations based on density functional theory to explore the energetics and electronic properties of BiX3 in a variety of known and hypothetical structure types. The results for BiX3 are compared with those obtained for the halides of the later rare earths, represented by YX3 and LuX3. The relative thermodynamic stabilities of the known and hypothetical structures are calculated, along with their band gaps. For the BiX3 systems, we have explored the role of lone-pair effects associated with bismuth(III), and for BiI3, we have compared the predicted structural behavior as a function of pressure with the available experimental data. We have also attempted to synthesize LuF3 in the perovskite-related ReO3-type structure, which is predicted to be only ∼7.7 kJ mol-1 above the convex hull. This attempt was unsuccessful but led to the discovery of a new hydrated phase, (H3O)Lu3F10H2O, which is isomorphous with the known ytterbium analogue.