119Sn MAS NMR Research Articles

Carboxylic Acid-Assisted Synthesis of Tin(II) Iodide: Key for Stable Large-Area Lead-Free Perovskite Solar Cells.

Despite significant progress in tin-based perovskites, the development of stable and high-performance tin-based perovskite solar cells (TPSCs) remains a challenge. In this pursuit, a multitude of strategies have been explored, encompassing the use of reducing agents, antioxidants, bulky cations, and customized solvent systems. We propose an improved approach for synthesizing SnI2 from elemental tin and iodine. Here, we generate tin nanoparticles grafted with a carboxylic acid in situ from tin powder-carboxylic acid-assisted synthesis (CAAS). This methodology not only improves the synthesis process of SnI2 but also enhances precursor stability against oxidation. We use 119Sn MAS NMR to study the atomic-level structure of the resulting FASnI3 thin films and find that the CAAS approach leads to highly pure and unoxidized material. We report remarkable reproducibility in fabricating large-area (1 cm2) flexible TPSCs with significant improvement in open-circuit voltage leading to the champion device showing a power conversion efficiency of 8.35%.

Amphoteric SnO2 nanoparticles via pH-controlled continuous flow solvothermal synthesis

Amphoteric oxides can be challenging to produce in phase pure form due to their sensitivity to the pH of the reaction mixture. The high-pressure, high-temperature reaction conditions of hydrothermal processes make the pH difficult to control. Here we report a simple approach to obtain nanoparticles of amphoteric oxides, where cheap metal nitrate precursors are reacted in alcohol (2-propanol) water mixtures (25 vol%:75 vol%) to maintain a neutral pH under solvothermal conditions. Phase pure SnO2 nanoparticles were synthesized in a continuous flow solvothermal reactor at 250 °C, 300 °C, 350 °C and 400 °C with sizes ranging from 3 nm to 7 nm. The nanoparticles were characterized using powder X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy, 119Sn MAS NMR spectroscopy, Brunauer-Emmett-Teller nitrogen adsorption, UV–VIS, and as anode material in CR2032 Li-ion battery cells. To demonstrate generality, amphoteric oxides ZnO, Bi2O3, Cr2O3 and γ-AlOOH were also synthesized.

Li5 SnP3 - a Member of the Series Li10+4x Sn2-x P6 for x=0 Comprising the Fast Lithium-Ion Conductors Li8 SnP4 (x=0.5) and Li14 SnP6 (x=1).

The targeted search for suitable solid‐state ionic conductors requires a certain understanding of the conduction mechanism and the correlation of the structures and the resulting properties of the material. Thus, the investigation of various ionic conductors with respect to their structural composition is crucial for the design of next‐generation materials as demanded. We report here on Li5SnP3 which completes with x=0 the series Li10+4x Sn2−x P6 of the fast lithium‐ion conductors α‐ and β‐Li8SnP4 (x=0.5) and Li14SnP6 (x=1). Synthesis, crystal structure determination by single‐crystal and powder X‐ray diffraction methods, as well as 6Li, 31P and 119Sn MAS NMR and temperature‐dependent 7Li NMR spectroscopy together with electrochemical impedance studies are reported. The correlation between the ionic conductivity and the occupation of octahedral and tetrahedral sites in a close‐packed array of P atoms in the series of compounds is discussed. We conclude from this series that in order to receive fast ion conductors a partial occupation of the octahedral vacancies seems to be crucial.

Crystallochemical Characterizations, Raman Spectroscopy and Studies Nuclear Magnetic Resonance (NMR) of Cu<sub>2</sub>Zn(Sn, Si)S<sub>4 </sub> Compounds for Photovoltaic Applications

In this study, Si-doped Cu2ZnSnS4 compounds (Cu2ZnSn1-xSixS4, 0 ≤ x ≤ 1) were prepared by solid state reaction method for use of materials for photovoltaic cells. The structural and spectroscopic properties of the as-prepared compounds were studied by X-ray diffraction (XRD), 119Sn, 29Si and 65Cu Magic Angle Spinning nuclear magnetic resonance (MAS NMR) and Raman spectroscopy. The Si-substitution in the Sn-site induces three different types of XRD patterns which depend largely on the Si content in the compound. For 0 ≤ x ≤ 0.5, XRD analysis reveals the presence of a pure tetragonal phase of solid solution with I-42m as a space group. Mixed tetragonal and orthorhombic phases were observed for 0.5 1 at high content of Si (x ≥ 0.8). 119Sn MAS NMR spectra show the presence of Sn/Si disorder as a function of the Si content. The 65Cu MAS NMR spectra of the quadratic solid solution confirm the presence of the two copper sites (Cu-2a and Cu-2c) at 780 ppm while in the case of the orthorhombic solid solution samples, a very broad band is observed. The optical properties were investigated of all compounds by UV-Vis diffuse reflectance and the obtained optical band gap values (1.31 to 2.43 eV) confirm a semiconductor character.

Tuning of Sn-BEA Reactivity by Controlling Tin Location in the BEA Framework

The combined application of 119Sn MAS NMR spectroscopy, adsorption of probe molecules, and catalytic testing in the MPVO conversion of cyclohexanone into cyclohexanol have been used to uncover T-po...

Variation of structural disorder in Zr substituted Y2Sn2O7: Its impact on photocatalysis

Variation in degree of disorder and its impact on photocatalytic dye degradation has been studied in Y2Sn2-xZrxO7 series. The structural variations of the compositions were thoroughly characterized by X-ray diffraction, Raman spectroscopy, 119Sn MAS NMR, EXAFS and XPS. A phase transition from ordered pyrochlore to disordered fluorite could be observed in the series whilst transiting from Y2Sn2O7 to Y2Zr2O7 without any signature of presence of bi-phasicity. Formation of a random solid solution phase has been confirmed by 119Sn MAS NMR results. All the compositions until x ​= ​1.0 remain as pyrochlore whereas the compositions with x ​≥ ​1.5 preferentially adopt defect-fluorite structure. X-ray photoelectron spectroscopy clearly demonstrates that the coordination environment Zr and O varies with increase in Zr content, however, the coordination environment of Sn does not alter with substitution. The phase transformation from pyrochlore to defect fluorite occurs at relatively higher Zr rich composition than expected from classical radius ratio rule due to higher covalency present in Sn–O bond. With increase in Zr content in the series crystallite size, surface charge, nature BO6 octahedra etc. varies and it has been found that these parameters has strong bearing on catalytic property of the materials. A generic understanding for the photocatalytic degradation of cationic methylene blue dye was achieved as a function of structural disordering in the Y2Sn2-xZrxO7 system.

Sol-gel synthesis of SnO2 nanoparticles doped with Zr+4/Cd+2 and Co-doped with F−: Their structural, optical and electrical properties

Abstract Some nanoscale particles of SnO2 doped with Zr+4 (1), Zr+4 and co-doped with F− (2), Cd+2 (3) and with Cd+2 and co-doped with F− (4) have been prepared by sol–gel technology in basic medium using SnCl2·2H2O as precursor in isopropanol as solvent. Structural analysis by XRD patterns have shown formation of particles at nanoscale and retention of tetragonal rutile structure in SnO2 network. This fact was further confirmed by 119Sn MAS NMR spectroscopy. SEM images have shown formation of various geometrical patterns. In the IR spectra, O-Sn-O absorption bands appeared at their expected positions. UV–Vis spectroscopy has shown an increase in optical band gap. Photoluminescence spectra of all these derivatives are found to be almost similar, again indicated retention of tetragonal rutile SnO2 framework. I-V curves are non-linear showing schottky contacts in the material.

New synthesis route to kesterite Cu2ZnSnS4 semiconductor nanocrystalline powders utilizing copper alloys and a high energy ball milling-assisted process

Presented is a new mechanochemically assisted synthesis route to kesterite Cu2ZnSnS4 semiconductor for perspective photovoltaic applications. Initially, the combined copper Cu, zinc Zn, and tin Sn powders in atomic ratio 2:1:1 were subjected to high energy ball milling in a planetary ball mill under the highest reported to date rotation speeds of 900 and 1000 rpm to yield a definite nanopowder mixture of the copper intermetallic phases, i.e., γ Cu5Zn8-type and η’ Cu6Sn5-type of non-stoichiometric compositions. Upon addition of a suitable amount of sulfur S, the reactive milling was continued affording a pure sphalerite-type cubic phase tentatively called a pre-kesterite. As expected from our earlier research, this by-product did not exhibit any 65Cu and 119Sn MAS NMR spectra or clearly-defined absorption in the UV–vis range. The disordered and very much random Cu-Zn-Sn metal site occupation of all metal layers in the structure is proposed to account for the observed properties of pre-kesterite. The subsequent annealing under argon at temperatures around 500−550 °C resulted in the cubic phase conversion to the tetragonal phase of kesterite, prevailingly, by metal center reconfiguration into distinct Cu-Sn and Cu-Zn layers accompanied by crystal growth/particle recrystallization. The micro-Raman spectra were consistent with similar bonding and lattice phonon characteristics in both related materials. The XPS data confirmed the same oxidation states and comparable energy level characteristics of the constituent elements. The annealed nanocrystalline powders showed the anticipated 65Cu and 119Sn MAS NMR features, while supporting remnant paramagnetism, and UV–vis semiconducting characteristics of the target kesterite.

Magnetism of Kesterite Cu2ZnSnS4 Semiconductor Nanopowders Prepared by Mechanochemically Assisted Synthesis Method.

High energy ball milling is used to make first the quaternary sulfide Cu2ZnSnS4 raw nanopowders from two different precursor systems. The mechanochemical reactions in this step afford cubic pre-kesterite with defunct semiconducting properties and showing no solid-state 65Cu and 119Sn MAS NMR spectra. In the second step, each of the milled raw materials is annealed at 500 and 550 °C under argon to result in tetragonal kesterite nanopowders with the anticipated UV-Vis-determined energy band gap and qualitatively correct NMR characteristics. The magnetic properties of all materials are measured with SQUID magnetometer and confirm the pre-kesterite samples to show typical paramagnetism with a weak ferromagnetic component whereas all the kesterite samples to exhibit only paramagnetism of relatively decreased magnitude. Upon conditioning in ambient air for 3 months, a pronounced increase of paramagnetism is observed in all materials. Correlations between the magnetic and spectroscopic properties of the nanopowders including impact of oxidation are discussed. The magnetic measurements coupled with NMR spectroscopy appear to be indispensable for comprehensive kesterite evaluation.

Neutral Hexacoordinate Tin(IV) Halide Complexes with 4,4'‐Dimethy‐2,2'‐bipyridine

A series of three neutral, hexacoordinate tin(IV) complexes were synthesized by the reaction of 4,4'‐dimethyl‐2,2'‐bipyridine (DMB) with SnX4, X = Cl, Br, and I, as starting materials. The complexes (DMB)SnX4 were characterized in solution by 1H, 13C, and 119Sn NMR spectroscopy, and in the solid‐state by 119Sn MAS NMR spectroscopy. In addition, single‐crystal X‐ray diffraction and elemental analysis were used to confirm the molecular structures. In these complexes, the tin atom adopts a distorted octahedral arrangement and the DMB acts as a bidentate N,N'‐chelate ligand. Computational DFT methods were also employed to gain more insight into the nature of the bonding in these complexes, including the hypothetical complexes (DMB)SnX4 (X = F, At). Additionally, the validity and reliability of the 119Sn NMR chemical shifts were examined. The calculated values were compared with the experimental signals and the effects of structure and solvent are discussed. Finally, all of the complexes (DMB)SnX4 were successfully tested for the ring‐opening polymerization (ROP) of bulk ε‐caprolactone under non‐dried and aerobic conditions as precatalyst.

From magnetic cubic pre-kesterite to semiconducting tetragonal kesterite Cu2ZnSnS4 nanopowders via the mechanochemically assisted route

Presented is a study on the mechanochemically assisted synthesis of kesterite Cu2ZnSnS4 from the elements for photovoltaic applications. Initial application of high energy ball milling under selected conditions, including the highest achievable rotation speeds up to 1000 rpm, affords a pure cubic nanophase with the nominal kesterite composition. The phase is tentatively called a pre-kesterite and it is shown by EPR to be magnetic. Accordingly, it does not produce either 65Cu or 119Sn MAS NMR spectra. Also, the material shows no well-defined absorption in the UV–vis range and, based on this, does not exhibit definite semiconducting properties. The highly disordered and defected structure with random metal site occupation originated in the mechanochemical synthesis step is proposed to account for the observed properties of pre-kesterite. Upon subsequent pyrolysis under argon at temperatures above 300 °C, preferably at around 500 °C, the cubic phase is converted to the tetragonal phase of kesterite, apparently, by metal site reconfiguration. The annealed nanopowders show the expected 65Cu and 119Sn MAS NMR characteristics. The Raman spectra support similar bonding environment and lattice phonon characteristics for both related phases as well as the eventual formation of kesterite nanopowders whereas their UV–vis spectra provide the direct band gap in the range of 1.35–1.48 eV, typical for semiconducting kesterite.

Metallo-stannosilicate heterogeneous catalyst for biodiesel production using edible, non-edible and waste oils as feedstock

This study reports the synthesis, physicochemical characterization by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and solid-state MAS NMR (1H, 23Na, 29Si and 119Sn MAS NMR) of a metallo-stannosilicate and its application as a heterogeneous catalyst for biodiesel production via ethanolysis and methanolysis routes using edible, non-edible an waste oils as feedstocks. XRD characterization of the metallo-stannosilicate has revealed a typical structure of mixed octahedral-pentahedral-tetrahedral material with an orthorhombic unit cell (a = 14.522 Ǻ, b = 12.469 Ǻ, and c = 10.654 Ǻ). 119Sn single-pulse MAS NMR results presented two resonance lines, at δ1 = -683.8 ppm and δ2 = -690.9 ppm, which were assigned to the tin octahedrally coordinated in the metallo-stannosilicate structure. Heterogenous catalytic studies in the transesterification of refined edible, non-edible, and waste oils have resulted in high yields of FAMEs and FAEEs (fatty acid methyl and ethyl esters), nevertheless the highest FAMES (98.2%) and FAEEs (96.6%) yields were obtained for non-edible microalgae oil extracted from the genetically modified heterotrophic algal strain Prototheca moriformis. Catalytic studies also using non-edible macaw palm oil (Acrocomia aculeata) with a high content of free fatty acids (FFAs) demonstrated that the catalyst could simultaneously perform esterification and transesterification reactions. These findings indicate the potential application of this novel metallo-stannosilicate in the production of renewable and environmentally clean biofuels, like biodiesel, using different sources of lipids feedstocks, notably those that do not compete with food production.

Mesoporous tin oxide: An efficient catalyst with versatile applications in acid and oxidation catalysis

Mesoporous tin oxide was prepared by template assisted and template-free methods. As-prepared materials were calcined at various temperatures to generate different nature (Brønsted and Lewis), amount and strength of acidic sites. The physico-chemical properties of the catalysts were studied by XRD, N2 sorption, pyridine-FTIR, NH3-TPD, DRS UV-vis, TGA, SEM, TEM, 1H MAS and 119Sn MAS NMR analyses. The catalytic behavior of mesoporous tin oxide catalysts was evaluated for acetalization and ketalization of glycerol with benzaldehyde and acetone respectively under solvent free conditions. The catalytic performance of mesoporous tin oxide was compared with that of other conventional solid acid catalysts namely H-ZSM-5, H-mordenite, H-beta, Al-MCM-41, Al-SBA-15 and Al-TUD-1. The efficiency of mesoporous tin oxide was also tested for cyclohexene epoxidation reaction. The catalyst prepared by template assisted method showed excellent catalytic performance compared to other catalysts due the difference in nature and amount of acidic sites in the catalyst. Meso-SnO2-T-350 was stable and reusable catalyst for four cycles without any appreciable loss in activity, and therefore it offers a good catalyst for potentially wide applications.

The structure-directing amine changes everything: structures and optical properties of two-dimensional thiostannates.

Two different two-dimensional thiostannates (SnS) were synthesized using tris(2-aminoethyl)amine (tren) or 1-(2-aminoethyl)piperidine (1AEP) as structure-directing agents. Both structures consist of negatively charged thiostannate layers with charge stabilizing cations sandwiched in-between. The fundamental building units are Sn3S4 broken-cube clusters connected by double sulfur bridges to form polymeric (Sn3S72-)n honeycomb hexagonal layers. The compounds are members of the R-SnS-1 family of structures, where R indicates the type of cation. Despite consisting of identical structural units, the band gaps of the two semiconducting compounds were found to differ substantially at 2.96 eV (violet-blue light) and 3.21 eV (UV light) for tren-SnS-1 and 1AEP-SnS-1, respectively. Aiming to explain the observed differences in optical properties, the structures of the two thiostannates were investigated in detail based on combined X-ray diffraction, solid-state 13C and 119Sn MAS NMR spectroscopy and scanning electron microscopy studies. The compound tren-SnS-1 has a hexagonal structure consisting of planar SnS layers with regular hexagonal pores and disordered cations, whereas 1AEP-SnS-1 has an orthorhombic unit cell with ordered cations, distorted hexagonal pores and non-planar SnS layers. In the formation of 1AEP-SnS-1, an intramolecular reaction of the structure-directing piperidine takes place to form an N-heterobicyclic cation through in situ C-H activation. Hirshfeld surface analysis was used to investigate the interaction between the SnS layers and cations in 1AEP-SnS-1 and revealed that the most nucleophilic part of the SnS sheets is one of the two crystallographically distinct double sulfur bridges.

Multinuclear NMR and crystallographic study of diorganotin valproates – Part II

The reactions of SnR2Cl2 {R=Me, Bu and Ph} and sodium valproate, NaO2CCH(CH2CH2CH3)2, NaOVp yielded three diorganotin valproates [{(Me2SnOVp)2O}2] (1), [{(Bu2SnOVp)2O}2] (2) and [{PhSn(O)OVp}6] (3). These stannoxanes have been authenticated in terms of infrared, 1H and 13C NMR, and solution- and solid-state 119Sn NMR and 119Sn Mössbauer spectroscopy. In addition the crystallographic structures of complexes (1)–(3) have been determined by X-ray diffraction. Complexes (1) and (2) displayed two major signals in the 119Sn NMR spectra in solution corresponding to the exo and endocyclic SnR2 moiety of the stannoxanes. Other minor resonances have been also observed due to dynamic processes in solution. However in the 119Sn MAS-NMR experiments only two down field signals were detected for complex (1), according to the presence of the exo and endocyclic organotin fragments, but with different resonance in comparison with the chemical shift obtained in solution. On the other hand little difference was observed in the 119Sn chemical shift of complex (3) since only one resonance was detected in solution- or in the solid-state experiments, and the signals are very close to each other.

(NH4)4Sn2S6·3H2O: Crystal Structure, Thermal Decomposition, and Precursor for Textured Thin Film

Understanding the condensation of the dimeric thiostannate(IV) [Sn2S6]4– to SnS2 is of key importance for the development of solution processing of advanced tin(IV) sulfide based electronic devices such as photovoltaics (e.g., Cu2ZnSnS4, CZTSSe) and thin-film transistors. Here, we report the crystal structure of tetraammonium thiostannate(IV) trihydrate ((NH4)4Sn2S6·3H2O), which can be used as a more environmentally friendly alternative to the hydrazinium analogue in solution processed advanced tin(IV) sulfide based electronic devices, e.g., CZTSSe. Hirshfeld surface analysis shows that crystal bound water molecules play a significant role in the structure and interact strongly with the sulfur atoms in the dimeric thiostannate(IV) complex [Sn2S6]4–. The thermal decomposition and corresponding condensation of ((NH4)4Sn2S6·3H2O) to SnS2 have been studied by TG/DSC-MS and solid-state 119Sn MAS NMR. It involves the formation of the relatively more condensed thiostannate(IV) complex [Sn4S10]4– at 90 °C via eva...

Nature of SnO6 octahedron in bulk and nanoparticles of Y2Sn2O7 probed by experimental and theoretical methods

Based on XRD, 119Sn MAS NMR and Luminescence studies it is confirmed that in very fine nanoparticles of Y2Sn2O7, tin environment is significantly distorted with respect to bulk Y2Sn2O7. NMR studies revealed that electron density around Sn4+ is significantly high in nanoparticles in comparison to bulk. Theoretical studies under DFT formalism has further confirmed that electron density around Sn4+ ions is enriched, as well as distorted in Y2Sn2O7 nanoparticles compared to bulk. The higher electron density around Sn4+ ions has been attributed to elongation in Sn–O bond distance which results in relatively poor charge transfer from tin site to oxygen.

The pyrochlore to defect fluorite phase transition in Y2Sn2−xZrxO7

The system Y2Sn2−xZrxO7 (0.0 ≤ x ≤ 2.0) undergoes a phase transformation from ordered pyrochlore (Fdm) to defect fluorite (Fmm) actuated by the substitution of Zr for Sn. X-ray diffraction patterns map the retention of the pyrochlore structure up to x = 1.2. For samples with x = 1.4–2.0 the structure can be described as defect fluorite in broad terms. Electron diffraction patterns are consistent with this interpretation; however, they also demonstrate that the defect fluorite phase exhibits a strain driven compositional/displacive modulation that changes gradually with increasing Zr content. Raman spectra are consistent with gradual anion disorder up to x = 1.0 and highly disordered anion distributions inferred for x > 1.4, but the spectra also suggest the presence of residual order due to the modulated structure. The phase transformation in this system occurs at a higher Zr content than predicted by classical radius ratio models, consistent with the covalent character of Sn–O bonding. An unusual finding of this work comes from 119Sn MAS NMR and Sn L3-edge XANES analyses, indicating that Sn4+ prefers to occupy lattice sites with a 6-fold local coordination environment throughout the series. These results suggest that the incorporation of Sn or other metal cations having significant covalent bonding or a strong preference for octahedral coordination in pyrochlore-based materials may have a detrimental effect on ionic conductivity.

Framework and Extraframework Tin Sites in Zeolite Beta React Glucose Differently

Here, we show that framework tin sites in pure silica zeolite Beta (Sn-Beta) can isomerize glucose to fructose by a Lewis acid-mediated intramolecular hydride shift in aqueous solvent, but not in methanol solvent. Mechanistic studies using isotopically labeled (2H, 13C) glucose reactants show that in methanol, Sn-Beta instead epimerizes glucose to mannose by a Lewis acid-mediated intramolecular carbon shift mechanism known as the Bilik reaction. We also provide evidence that extraframework tin sites located within the hydrophobic channels of zeolite Beta can isomerize glucose to fructose in both water and methanol solvent, but through a base-catalyzed proton-transfer mechanism. SnO2 particles located at external zeolite crystal surfaces or supported on amorphous silica catalyze isomerization in methanol but not in water, suggesting that contact with bulk water inhibits isomerization at SnO2 surfaces. 119Sn MAS NMR spectroscopy was used to unambiguously identify framework Sn sites, which give resonances for octahedral Sn (−685 to −700 ppm) in hydrated Sn-Beta that disappear upon dehydration, with the concomitant appearance of resonances for tetrahedral Sn (−425 to −445 ppm). In sharp contrast, spectra of hydrated samples containing extraframework SnO2 show resonances for octahedral Sn centered at −604 ppm that do not change upon dehydration. These findings demonstrate that aldose–ketose isomerization reactivity on Sn-zeolite samples cannot be ascribed to the presence of framework Sn sites in the absence of isotopic labeling studies. They also indicate that any Sn-zeolite samples that initially convert glucose to fructose, instead of mannose, in methanol solvent contain Sn species that are structurally different from framework Sn centers.

Hydrothermal synthesis of MWW-type stannosilicate and its post-structural transformation to MCM-56 analogue

A series of novel stannosilicates with the MWW topology, Sn-MWW, was hydrothermally synthesized in alkali medium using boric acid as a crystallization-supporting agent. The Sn-MWW lamellar precursors with a high crystallinity were obtained from the synthetic gels even at Si/Sn ratio of 60. UV–visible and 119Sn MAS NMR characterizations verified that the Sn species were incorporated in the framework, occupying mainly the tetrahedral sites. A mild acid treatment was conducted on the precursors to induce a structural transformation to tin-containing materials structurally analogous to MCM-56. Sn-MCM-56 thus post-synthesized comprised partially delaminated MWW sheets, and possessed larger external surface as well as more open reaction space. Sn-MCM-56 analogue alleviated effectively the steric restriction and diffusion limitation to bulky molecules that the microporous zeolite catalysts usually encountered. It appeared to be more efficient than Sn-MWW in the Baeyer–Villiger oxidation of 2-adamantanone with H2O2. Moreover, Sn-MCM-56 turned to be more active than Sn-Beta when tert-butyl hydroperoxide was employed as an oxidant.