Search

Several theories have been proposed to explain the co-existence of high conductivity and high salt concentration for water-in-salt electrolytes. Here, we fill the gap related to the structural, physical, and electrochemical properties of the LiTFSI–H2O binary system at high mol kg−1.

In lithium thiocyanate Li(SCN), the temperature regime below the melting point (274 °C) is characterized by excess conductivities over the usual Arrhenius behavior (premelting regime). Here, the Schottky defect pair concentration is high, and the point defect chemistry can no longer be considered as dilute. Coulomb interactions of Schottky pairs are expected to occur lowering the formation energy of new carriers and hence leading avalanche-like to a transition into a fully defective superionic state. The respective non-linear behavior is investigated using the cube-root law approach characterized by a defect interaction parameter

Anhydrous Li(SCN) is systematically doped with Mg2+, Zn2+, and Co2+ to investigate its ion transport properties. A complete quantitative defect chemical model is derived and connections to relevant other Li+ cation conductors are discussed.

Crystal engineering has, so far, exclusively focused on the development of advanced materials based on small organic molecules. We demonstrate how the cocrystallization of a polymer significantly enhances its thermal stability without compromising its mechanical flexibility, while isomorphous replacement of one of the cocrystal components enables the formation of solid solutions with melting points that can be readily fine-tuned over a practically wide temperature range. The results of this study credibly extend the scope of crystal engineering and cocrystallization from small molecules to polymers.

A series of Li3MI6 compounds with M = Lu–Sm were produced by ball milling and solid state synthesis. Cation disorder within the layers largely influences the ionic transport properties, which can be tuned by isovalent and aliovalent substitution.

Acta crystallographica / B 77(6), 986 - 995 (2021). doi:10.1107/S2052520621010088, A new six-membered cyclic alkanolamine with chemical formula C$_6$H$_{15}$N$_3$O$_3$ was synthesized by the reaction of glycolaldehyde with gaseous ammonia. The molecular structure, characterized by a hexagonal ring of alternating carbon and nitro��gen atoms with three hy��droxy��methyl groups attached to the carbon atoms, could not be unambiguously determined by elemental analysis and $^1$H/$^{13}$C/$^{15}$N NMR. The molecular structure and conformation were further determined using a combination of vibrational spectroscopy (IR and Raman) and real-space pair distribution function (PDF) analysis. The crystal structure was determined ab initio from laboratory X-ray powder diffraction (XRPD) with orthorhombic space group Ama2 (No. 40) and unit-cell parameters a = 12.1054 (2) ��, b = 13.5537 (2) �� and c = 5.20741 (8) ��. Consistent structure models could be obtained by symmetry-independent PDF and PDF-Rietveld co-refinements. Independent local structure refinements indicate that the most likely deviations from the average structure consist of small tilting and translational distortions of hydrogen-bonded molecular stacks. Thermal analysis (TG/DTA) and temperature-dependent XRPD measurements were also performed to determine the thermal behavior., Published by Wiley-Blackwell, Oxford [u.a.]

Peak profile functions in powder diffraction are presented with the support of Mathematica scripts, easily usable by interested readers, to explore the effect of different instrumental and microstructural parameters. Subsequent articles will illustrate the most common aberrations to the measured patterns and then total scattering methods., A collection of scholarly scripts dealing with the mathematics and physics of peak profile functions in X-ray powder diffraction has been written using the Wolfram language in Mathematica. Common distribution functions, the concept of convolution in real and Fourier space, instrumental aberrations, and microstructural effects are visualized in an interactive manner and explained in detail. This paper is the first part of a series dealing with the mathematical description of powder diffraction patterns for teaching and education purposes.

The outstanding diversity of Zr-based frameworks is inherently linked to the variable coordination geometry of Zr-oxo clusters and the conformational flexibility of the linker, both of which allow for different framework topologies based on the same linker–cluster combination. In addition, intrinsic structural disorder provides a largely unexplored handle to further expand the accessibility of novel metal–organic frameworks (MOFs) structures that can be formed. In this work we report the concomitant synthesis of three topologically different MOFs based on the same M6O4(OH)4 clusters (M = Zr or Hf) and methane-tetrakis(p-biphenyl-carboxylate) (MTBC) linkers. Two novel structural models are presented based on single crystal diffraction analysis, namely cubic c (4,12)MTBC-M6 and trigonal tr (4,12)MTBC-M6, which comprise 12-coordinated clusters and 4 coordinated tetrahedral linkers. Notably, the cubic phase features a new architecture based on orientational cluster disorder, which is essential for its formation and has been analyzed by a combination of average structure refinements and diffuse scattering analysis from both powder and single crystal X-ray diffraction data. The trigonal phase also features structure disorder, although involving both linkers and secondary building units. In both phases, remarkable geometrical distortion of the MTBC linkers illustrates how linker flexibility is also essential for their formation and expands the range of achievable topologies in Zr-based MOFs and its analogues.

Covalent organic frameworks (COFs) with a pore size beyond 5 nm are still rarely seen in this emerging field. Besides obvious complications such as the elaborated synthesis of large linkers with sufficient solubility, more subtle challenges regarding large-pore COF synthesis, including pore occlusion and collapse, prevail. Here we present two isoreticular series of large-pore imine COFs with pore sizes up to 5.8 nm and correlate the interlayer interactions with the structure and thermal behavior of the COFs. By adjusting interlayer interactions through the incorporation of methoxy groups acting as pore-directing "anchors", different stacking modes can be accessed, resulting in modified stacking polytypes and, hence, effective pore sizes. A strong correlation between stacking energy toward highly ordered, nearly eclipsed structures, higher structural integrity during thermal stress, and a novel, thermally induced phase transition of stacking modes in COFs was found, which sheds light on viable design strategies for increased structural control and stability in large-pore COFs.

The Jahn-Teller (JT) theorem constitutes one of the most fundamental concepts in chemistry. In transition-element chemistry, the 3d4 and 3d9 configurations in octahedral complexes are particularly illustrative, where a distortion in local geometry is associated with a reduction of the electronic energy. However, there has been a lasting debate about the fact that the octahedra are found to exclusively elongate. In contrast, for Na9 Bi5 Os3 O24 , the octahedron around Os6+ (5d2 ) is heavily compressed, lifting the degeneracy of the t2g set of 5d orbitals such that in the sense of a JT compression a diamagnetic ground state results. This effect is not forced by structural constraints, the structure offers sufficient space for osmium to shift the apical oxygen atoms to a standard distance. The relevance of these findings is far reaching, since they provide new insights in the hierarchy of perturbations defining ground states of open shell electronic systems.

Summary Covalent organic frameworks (COFs) have emerged as a new class of molecularly precise, porous functional materials characterized by broad structural and chemical versatility, with a diverse range of applications. Despite their increasing popularity, fundamental aspects of COF formation are poorly understood, lacking profound experimental insights into their assembly. Here, we use a combination of in situ X-ray powder diffraction and Raman spectroscopy to elucidate the reaction mechanism of mechanochemical synthesis of imine COFs, leading to the observation of key reaction intermediates that offer direct experimental evidence of framework templating through liquid additives. Moreover, the solid-state catalyst scandium triflate is instrumental in directing the reaction kinetics and mechanism, yielding COFs with crystallinity and porosity on par with solvothermal products. This work provides the first experimental evidence of solvent-based COF templating and is a significant advancement in mechanistic understanding of mechanochemistry as a green route for COF synthesis.

This study is a contribution to development of material based on transition metal oxides with application in electrochemical devices. A pyrochlore-like solid solution with general chemical formula ...

Metal complexes exhibiting multifunctional properties are very rare. Here, we report a Zn(II) complex, [Zn(benzoate)(25F-spy)2], where 25F-spy = 2′,5′-difluoro-4-styrylpyridine, displays unpredicte...

Nature Communications 12(1), 3099 (1-9) (2021). doi:10.1038/s41467-021-23348-w, Porphyrin-based metal–organic frameworks (MOFs), exemplified by MOF-525, PCN-221, and PCN-224, are promising systems for catalysis, optoelectronics, and solar energy conversion. However, subtle differences between synthetic protocols for these three MOFs give rise to vast discrepancies in purported product outcomes and description of framework topologies. Here, based on a comprehensive synthetic and structural analysis spanning local and long-range length scales, we show that PCN-221 consists of Zr$_6$O$_4$(OH)$_4$ clusters in four distinct orientations within the unit cell, rather than Zr$_8$O$_6$ clusters as originally published, and linker vacancies at levels of around 50%, which may form in a locally correlated manner. We propose disordered PCN-224 (dPCN-224) as a unified model to understand PCN-221, MOF-525, and PCN-224 by varying the degree of orientational cluster disorder, linker conformation and vacancies, and cluster–linker binding. Our work thus introduces a new perspective on network topology and disorder in Zr-MOFs and pinpoints the structural variables that direct their functional properties., Published by Nature Publishing Group UK, [London]

Mg(SCN)2·4H2O can be converted into previously unknown compounds Mg(SCN)2·(4 − x) H2O·xTHF with x = 0, 2 and 4 by multiple recrystallization in tetrahydrofuran (THF). The phases were characterized by infrared spectroscopy (IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and their crystal structures were solved from X-ray powder diffraction (XRPD) data. In the crystal structures isolated Mg(NCS)2(H2O)4−x(THF)x units form layered motifs. The thermal behavior of Mg(SCN)2·4H2O and Mg(SCN)2·4THF was investigated by temperature dependent in situ XRPD, where Mg(SCN)2·4THF was found to acquire a room temperature (α-form) and high temperature modification (β-form). The phase transformation is associated with an order–disorder transition of the THF molecules and with a reversion of the stacking order of the layered motifs. Further heating eventually leads to the formation of Mg(SCN)2·2THF. There thiocyanate related sulfur atoms fill the voids in the coordination sphere of magnesium, which leads to the formation of one dimensional electroneutral ∞[Mg(NCS)2/2(SCN)2/2(THF)2] chains. All investigated Mg(SCN)2·(4 − x) H2O·xTHF phases exhibit a remarkable anisotropic thermal expansion, and Mg(SCN)2·4H2O and Mg(SCN)2·2THF were found to show both positive and negative thermal expansion coefficients.

Li[SCN]·THF and Li[SCN]·2THF can be obtained from solutions of anhydrous Li[SCN] in tetrahydrofuran (C4H8O, THF). Both compounds are very hygroscopic and slowly decompose even at room temperature. At ambient conditions Li[SCN]·THF crystallizes in the monoclinic space group P21/c with the lattice parameters a = 574.41(2), b = 1643.11(6), c = 830.15(3) pm and β = 99.009(1)° for Z = 4 as determined by laboratory X-ray powder diffraction. Its crystal structure contains Li+ cations surrounded by one THF molecule and three thiocyanate anions [SCN]− forming {Li[NCS]2[SCN](OC4H8)}2− tetrahedra, which join together as pairs via shared N⋯N edges. CHNS combustion analysis and vibrational spectroscopy confirmed its composition, whereas differential scanning calorimetry and thermogravimetric analysis coupled with a mass spectrometer were applied to record its thermal behaviour. Li[SCN]·2THF crystallises in a primitive monoclinic lattice as well, but in the space group P21/n with the lattice parameters a = 1132.73(3), b = 1637.98(3), c = 1264.88(2) pm and β = 94.393(2)° for Z = 8 as determined from single-crystal X-ray diffraction data at 100 K. Its structure contains two crystallographically independent Li+-centred tetrahedra {Li[NCS]2(OC4H8)2}−, which form dimers {(C4H8O)2Li[μ2-NCS]2Li(OC4H8)2} via shared N⋯N edges. They are merely stabilised by weak agostic H⋯S interactions between some CH2-groups of the C4H8O molecules and the [NCS]− ligands.

Tb-diluted and Tb-rich apatite-type silicates with compositions Y7.75Tb0.25Ca2(SiO4)6O2 and Tb8Ca2(SiO4)6O2, respectively, exhibit field induced multiple slow relaxation of magnetization. The former reveals two slow relaxation paths, the latter only one with a longer relaxation time of several seconds. The relaxation features of the Tb-diluted one are comparable with those of analogue compounds, where Tb is replaced by Dy, as well as with those of a Tb-doped calcium phosphate apatite. The relaxation parameters of the Tb-rich compound virtually match those of the Dy-based analogue Dy8Ca2(SiO4)6O2. The latter represents the first instance of independence of magnetization relaxation on the nature of a paramagnetic rare-earth metal ion in single ion magnet like materials.

Dehydration of calcium acetate monohydrate (Ca(CH3COO)2·H2O) by heating to 300 °C leads to the formation of anhydrous α-Ca(CH3COO)2. During heating and cooling cycles a high- and a low temperature ...

Helical motifs are common in nature, for example, the DNA double or the collagen triple helix. In the latter proteins, the helical motif originates from glycine, the smallest amino acid, whose molecular confirmation is closely related to acetic acid. The combination of acetic acid with calcium and water, which are also omnipresent in nature, materializing as calcium acetate hemihydrate, was now revealed to exhibit a collagen‐like triple helix structure. This calcium salt is observed as efflorescence phase on calcareous heritage objects, like historic Mollusca shells, pottery or marble reliefs. In a model experiment pure calcium acetate hemihydrate was crystallized on the surface of a terracotta vessel. Calcium acetate hemihydrate crystallizes in a surprisingly large unit cell with a volume of 11,794.5(3) Å3 at ambient conditions. Acetate ions bridge neighboring calcium cations forming spiral chains, which are arranged in a triple helix motif., Effloresced: Calcium acetate hemihydrate, Ca(AcO)2⋅1/4 H2O, a seemingly simple efflorescence salt grown on calcareous heritage objects was found to crystallize in a surprisingly large unit cell with 11 794.5(3) Å3 and exhibits a collagen‐like triple helix motif.

Chemical science 11(9), 2350 - 2355 (2020). doi:10.1039/C9SC06224F, Using the mechanosynthesis of the calcium urea phosphate fertilizer cocrystal as a model, we provide a quantitative investigation of chemical autocatalysis in a mechanochemical reaction. The application of in situ Raman spectroscopy and synchrotron X-ray powder diffraction to monitor the reaction of urea phosphate and either calcium hydroxide or carbonate enabled the first quantitative and in situ study of a mechanochemical system in which one of the products of a chemical reaction (water) mediates the rate of transformation and underpins positive feedback kinetics. The herein observed autocatalysis by water generated in the reaction enables reaction acceleration at amounts that are up to 3 orders of magnitude smaller than in a typical liquid-assisted mechanochemical reaction., Published by RSC, Cambridge

Apatite-type silicates Y7.75Dy0.25Ca2(SiO4)6O2 and Dy8Ca2(SiO4)6O2 were prepared by high-temperature solid state synthesis. In the crystal lattice, Dy3+ partially substitutes Ca2+, preferably at the 6h Ca2-site, and forms a short bond of 2.2 A with the intra-channel O2-. The imposed strong ligand field anisotropy provides large magnetic anisotropy, which manifests itself as slow relaxation of magnetization at low temperatures. The magnetic dynamics is characterized by three or two characteristic values of relaxation time, respectively, which may be attributed to a single Dy3+ center. A phenomenological model is proposed which explains this response in terms of single paramagnetic center multiple relaxation.

The solid state assembly of two cyclic hexapeptoids decorated respectively with five and six carbon N-alkyl side chains is analyzed by single crystal X-ray diffraction, intermolecular energies and lattice energy calculations. Thermal analysis and variable temperature X-ray powder diffraction were also carried out to analyze their thermal behaviour. The crystal structures of the two compounds feature architectural similarities, but also small relevant differences due to side chains-to-side chains interactions, which can explain the observed differences in the thermal properties. The compound with N-pentyl side chains exhibits a phase transition upon cooling down from room temperature to 100 K, while that with N-hexyl side chains features no phase transformation on cooling, instead a phase transformation occurs at 335 K upon heating.

Time-resolved mechanochemical cocrystallisation studies have so-far focused solely on neat and liquid-assisted grinding. Here, we report the monitoring of polymer-assisted grinding reactions using in situ X-ray powder diffraction, revealing that reaction rate is almost double compared to neat grinding and independent of the molecular weight and amount of used polymer additives.

The reaction of Fe(NCS)2 with 4-picoline in solution leads to two new discrete complexes, Fe(NCS)2(4-picoline)4·solvate (1-Fe) and Fe(NCS)2(4-picoline)2(H2O)2 (2-Fe–H2O). Upon heating, both compounds transform into two isomers with the composition [Fe(NCS)2(4-picoline)2]n (2-Fe/I and 2-Fe/II) that consist of chains and that are related by monotropy, with 2-Fe/I as the thermodynamically stable form. Upon further heating, a transformation into a more condensed chain compound of unusual structure with the composition [Fe(NCS)2(4-picoline)]n (3-Fe) is observed. The crystal structures of 2-Fe/I and 2-Fe/II were determined by Rietveld refinements, as it was found that 2-Fe/I is isotypic to the corresponding Cd compound 2-Cd/I, whereas 2-Fe/II is isotypic to [Cu(NCS)2(4-cyanopyridine)2]n which was reported recently. To retrieve structural information on 3-Fe the corresponding Cd compound (3-Cd) was synthesized and was shown to be isotypic to 3-Fe. Finally, upon heating the already known compounds [Cd(NCS)2(4-picoline)4]·0.67·4-picoline·0.33·H2O solvate (1-Cd) and [Cd(NCS)2(4-picoline)2]n (2-Cd/I) a new thermodynamically metastable modification was found (2-Cd/III) that is isotypic to [Cd(NCS)2(4-cyanopyridine)2]n and behaves monotropically to 2-Cd/I with the latter as the thermodynamically stable phase.

CrystEngComm 24(12), 2305 - 2313 (2022). doi:10.1039/D2CE00162D, We demonstrate the ability to controllably desolvate a crystal-solvate system in a step-wise fashion through polymer-assisted grinding by varying the type and proportion of polymer agent used. A plausible mechanistic explanation is proposed based on a combination of experimental evidence and computational analysis. Specifically, Raman spectroscopy, total scattering pair distribution function analysis and computed reaction energies suggest that the desolvation process is associated with preferred interactions between the solvent molecules and specific polymers. This approach could potentially be extended to any type of material, including heat-sensitive materials, where classical desolvation by thermal processes is not possible, and provides an additional route for formulation processing., Published by RSC, London

Sodium thiophosphates are promising materials for large-scale energy storage applications benefiting from high ionic conductivities and the geopolitical abundance of the elements. A representative of this class is Na

Sodium thiophophates are promising materials for large-scale energy storage applications benefiting from high ionic conductivities and the-political abundance of the elements. A representative of this class is Na4P2S6, which currently shows two known polymorphs–α and β. This work describes a third polymorph of Na4P2S6, γ, that forms above 580◦C, exhibits fast ion conduction with low activation energy, and is mechanically soft. Based on high-temperature diffraction, pair distribution function analysis, thermal analysis, impedance spectroscopy, and ab initio molecular dynamic calculations, γ-Na4P2S6 is identified to be a plastic crystal, characterized by dynamic orientational disorder of the P2S64– anions on a translationally fixed body centered cubic lattice. The prospect of stabilizing plastic crystals at operating temperatures of solid-state batteries and benefiting from their high ionic conductivities as well as mechanical properties could have a strong impact in the field of solid-state battery chemistry.

Carbon nitrides are among the most studied materials for photocatalysis, however, limitations arise from inefficient charge separation and transport within the material. Here, this aspect is addressed in the 2D carbon nitride poly(heptazine imide) (PHI) by investigating the influence of various counterions, such as M = Li+, Na+, K+, Cs+, Ba2+, NH4+ and tetramethyl ammonium, on the material’s conductivity and photocatalytic activity. These ions in the PHI pores affect the stacking of the 2D layers, which further influences the predominantly ionic conductivity in M-PHI. Na-containing PHI outperforms the other M-PHI in various relative humidity (RH) environments (0-42 %RH) in terms of conductivity, likely due to pore channel geometry and size of the (hydrated) ion. With increasing RH, the ionic conductivity increases by 4-5 orders of magnitude (for Na-PHI up to 10-5 S cm-1 at 42 %RH). At the same time, the highest photocatalytic hydrogen evolution rate is observed for Na-PHI, which is mirrored by increased photo-generated charge carrier lifetimes, pointing to efficient charge carrier stabilization by mobile ions. These results indicate that ionic conductivity is an important parameter that can influence the photocatalytic activity. Besides, RH-dependent ionic conductivity is of high interest for separators, membranes, or sensors.

We provide a proof-of-principle demonstration of the first dual-spectroscopic method for direct and real-time observation of mechanochemical reactions by ball milling, supported by high-level molecular and periodic density-functional theory (DFT) calculations, including periodic time-dependent (TD-DFT) calculations to model solid-state fluorescence spectra. By combining standard Raman and fluorescence benchtop spectrometers in a single readily accessible tandem monitoring technique, we simultaneously observe changes to the supramolecular structure during mechanochemical polymorph transformation and cocrystallization of the model pharmaceutical system indometacin. The observed time-resolved in situ spectroscopic data is supported by ex situ X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy measurements. First principles calculations facilitate the interpretation of both real-time spectroscopic and ex situ data by demonstrating how changes in crystalline environment affect vibrational and electronic excited states.