Lukáš Palatinus

A transmission electron microscopy (TEM) study of four troilite grains from enstatite chondrites (Y‐691, Y‐791790, Y‐86004, A‐881314) and two grains from aubrites (Y‐793592, Mayo Belwa) addressed their crystal structures and nanoscale mineralogical relationships. The crystal structure of troilite in enstatite‐rich meteorites is predominantly consistent with the space group , except for the FeS phase from Mayo Belwa, which exhibits a complex modulated structure consistent with a trilling of the modulated N C pyrrhotite superstructure. TEM energy‐dispersive X‐ray spectroscopy (TEM‐EDS) analyses confirmed the incorporation of chromium and titanium into the troilite crystal structure, even in samples containing nanometer‐sized daubréelite exsolution lamellae (A‐881314, Y‐793592). Nanometer‐sized inclusions of (Mn,Mg,Fe)S monosulfide solid solution occur in troilite in Y‐791790. Crystallographic orientation relationships between troilite and associated sulfide phases (daubréelite and keilite) indicate semi‐coherent intergrowths at the nanoscale. The absence of nanometer‐sized daubréelite in Y‐86004 and Y‐791790 suggests rapid cooling of the Cr‐Fe sulfide solution and quenching of the chemical composition of the phase stable above 700°C, consistent with the impact melt origin of these meteorites. Additional weak, diffuse diffractions observed in selected area electron diffraction patterns for troilites from Y‐86004, Y‐791790, and Y‐793592 are attributed to the development of vacancy ordering with variable periodicity along the c ‐axis, corresponding to N C ‐type superstructures. The detailed nature of vacancy ordering and the contributions of Cr and Ti substitution to the observed superstructure features remain unresolved and require comprehensive structure analysis.

We unravel the complete structural architecture of the polymorphic Na ₃ [Ag ₂₉ (BDT) ₁₂ (TPP) ₄ ] nanocluster (NC) using three‐dimensional electron diffraction (3D ED) of microscopic crystals. By drop‐casting nanocluster solution directly onto microscopy grids, we achieve in situ crystallization of nanometer‐sized polymorphs and independently resolve co‐existing cubic and trigonal phases crystal‐by‐crystal from a single grid square. Using difference electrostatic potential (DESP) maps derived from empirical 3D ED data, we pinpoint the specific lattice locations of the elusive Na ⁺ counterions and observe distinct coordination environments across the two polymorphs. In the densely packed, solvent‐free cubic phase, Na ⁺ binds exclusively to thermodynamically favored pockets formed by one core‐anchored and two staple sulfur atoms. Conversely, within the open, solvated trigonal lattice, Na ⁺ occupies both these core‐anchored sites and alternative positions coordinated entirely by three sulfur atoms of an outer Ag ₃ S ₃ staple motif. These findings establish 3D ED as a powerful tool for resolving nanoscale polymorphic mixtures and demonstrate how macroscopic crystal packing influences local ionic interactions, providing key structural insights for the design of cluster‐based assemblies.

We unravel the complete structural architecture of the polymorphic Na ₃ [Ag ₂₉ (BDT) ₁₂ (TPP) ₄ ] nanocluster (NC) using three‐dimensional electron diffraction (3D ED) of microscopic crystals. By drop‐casting nanocluster solution directly onto microscopy grids, we achieve in situ crystallization of nanometer‐sized polymorphs and independently resolve co‐existing cubic and trigonal phases crystal‐by‐crystal from a single grid square. Using difference electrostatic potential (DESP) maps derived from empirical 3D ED data, we pinpoint the specific lattice locations of the elusive Na ⁺ counterions and observe distinct coordination environments across the two polymorphs. In the densely packed, solvent‐free cubic phase, Na ⁺ binds exclusively to thermodynamically favored pockets formed by one core‐anchored and two staple sulfur atoms. Conversely, within the open, solvated trigonal lattice, Na ⁺ occupies both these core‐anchored sites and alternative positions coordinated entirely by three sulfur atoms of an outer Ag ₃ S ₃ staple motif. These findings establish 3D ED as a powerful tool for resolving nanoscale polymorphic mixtures and demonstrate how macroscopic crystal packing influences local ionic interactions, providing key structural insights for the design of cluster‐based assemblies.

While silicate nanotubules are unknown in synthetic materials so far, naturally occurring minerals provide several examples of nanoscopic tubular structural building units based upon silicate oxyanions. The crystal structure of eveslogite, a chemically and structurally complex natural silicate mineral from Eveslogchorr mountain, Khibiny massif, Kola Peninsula, Russia, with an idealized sum formula of K _17.5 (Ba,Sr) ₄ (Na,Ca) ₄₀ [(Ti,Nb,Fe,Mn) ₁₁ Si ₆₂ O ₁₇₉ (OH,F) ₁₂ (O,OH) ₁₃ ](H ₂ O) has been solved using modern electron crystallography techniques. This study reveals the first example of a binary structure formed by two different types of transition-metal-modified silicate nanotubular units in a fibrous crystal. One of these is closely related to the nanorod occurring in the unitary nanotubule-based structure of yuksporite, whereas the other is unprecedented and can be considered as an (Nb, Ti)-modified derivative of the [Si ₁₂ O ₃₀ ] ¹²⁻ nanotubular units occurring in the binary all-silicate nanotubule-based structures of charoite polytypes. The eveslogite tubular units are packed in a tight arrangement and linked with each other through secondary interactions involving Ca ²⁺ - and Na ⁺ -centered polyhedra. The interiors and walls of the tubules are occupied by K ⁺ and Ba ²⁺ cations as well as H ₂ O molecules. Topological analysis of the interpolyhedral connectivity shows that the walls of the nanotubules possess topologies related to those of lamprophyllite and delhayelite-group minerals. This topological relationship may indicate possible structural pathways linking these framework types and highlights interesting similarities of exfoliation processes that are well known in modern soft chemistry nanotechnologies. Information-based structural complexity calculations place eveslogite among the most complex minerals known so far. Our study further demonstrates the enormous potential of mineralogy to discover structures unprecedented among the currently known synthetic materials and may serve as an inspiration for the preparation of novel types of artificial nanostructures and their possible technical applications in various fields.

Charge density wave (CDW) phases are unconventional quantum states that often arise in low-dimensional metallic systems and are themselves found alongside other exotic phenomena. Finding such states in porous materials is exceedingly rare. In fact, [Ln­(NO₃)_1–x ]₃(HOTP)₂ (Ln = La, Nd; H₆HOTP = 2,3,6,7,10,11-hexahydroxytriphenylene; LnHOTP) is the only example of a porous material wherein a CDW state has been proposed on the basis of a structural modulation. However, whether the modulation is trivial, and thus purely structural in nature, or it stems from a CDW, and thus has electronic origin, remains unknown. Here, low-temperature and high-pressure crystallography provide evidence for an electronic origin of the CDW phase in a series of LnHOTP (Ln = La, Ce, Pr, Nd, and Sm) MOFs, including the original La and Nd materials. We show that the modulation affects the relative rotation of neighboring HOTP ligands, and that the magnitude of the wavevector that defines the modulation, q, is sensitive to pressure. Importantly, the wavevector exhibits commensurability lock-in at one-third of the c unit cell parameter, q = ¹/₃ c, providing key evidence for energetic stabilization of the CDW phase.

Understanding structure at the atomic scale is fundamental for understanding the functioning and the development of materials with improved properties. Compared with other probes providing atomic resolution, electrons offer the strongest interaction in combination with minimal radiation damage, which makes them an ideal tool for investigating very small and radiation-sensitive samples [Henderson (1995), Q. Rev. Biophys. 28 , 171–193]. However, these benefits are often offset by the laborious preparation of nanometre-sized samples that are not visible using a light microscope, and the fact that experiments are largely restricted to ultra-high vacuum [Duyvesteyn et al. (2018), Proc. Natl Acad. Sci. USA 115 , 9569–9573; Gruene et al. (2021), Nat. Rev. Chem. 5 , 660–668]. Here, we report the successful implementation of MeV electron diffraction for ab initio 3D structure determination of the quasi-2D material muscovite and the quantum material 1 T -TaS ₂ at atomic resolution. By employing ultrashort electron pulses from the REGAE (Relativistic electron gun for atomic exploration) accelerator, we obtained high-quality diffraction datasets suitable for structural refinements based on dynamical scattering theory, enabling precise localization of even hydrogen atoms. The increased penetration depth of MeV electrons significantly expands the applicable thickness range of samples, overcoming previous restrictions associated with traditional electron diffraction. These findings establish MeV electron diffraction as a viable approach for investigating a broad range of materials, including nanostructures and radiation-sensitive compounds, and open up new opportunities for in situ and time-resolved experiments [Chao et al. (2023), Chem. Rev. 123 , 8347–8394; Filippetto et al. (2022), Rev. Mod. Phys. 94 , 045004].

Charge density wave (CDW) phases are unconventional quantum states that often arise in low-dimensional metallic systems and are themselves found alongside other exotic phenomena. Finding such states in porous materials is exceedingly rare. In fact, [Ln(NO ₃ ) _1-x ] ₃ (HOTP) ₂ (Ln = La, Nd; H ₆ HOTP = 2,3,6,7,10,11- hexahydroxytriphenylene; LnHOTP ) is the only example of a porous material wherein a CDW state has been proposed on the basis of a structural modulation. However, whether the modulation is trivial, and thus purely structural in nature, or it stems from a CDW, and thus has electronic origin, remains unknown. Here, low-temperature and high-pressure crystallography provide evidence for an electronic origin of the CDW phase in a series of LnHOTP (Ln = La, Ce, Pr, Nd, and Sm) MOFs, including the original La and Nd materials. We show that the modulation affects the relative rotation of neighboring HOTP ligands, and that the magnitude of the wavevector that defines the modulation, q , is sensitive to pressure. Importantly, the wavevector exhibits commensurability lock-in at one third of the c unit cell parameter, q = 1/3 c , providing key evidence for energetic stabilization of the CDW phase.

3D electron diffraction (3D ED) has undergone impressive development in the last decade. However, its accuracy and reproducibility have never been tested, up to now, in different laboratories on the same batch of samples. This paper reports a round robin on three test structures, two inorganic and one organic, solved and refined with 3D ED in seven different laboratories employing different transmission electron microscopes, with different acceleration voltages, different methodologies and different detectors. The results of the round robin show a remarkable accuracy of the technique that, in the case of kinematical refinement, is around 0.05 Å error on atomic positions for the inorganic samples and 0.15 Å for the beam-sensitive organic crystal. Dynamical refinement further improves the accuracy. The analysis of diverse samples and numerous data sets again confirms that dynamical refinement is a well established procedure, significantly reducing the refinement R factors, improving the accuracy of the structure models in most cases, and providing fine structural details, such as hydrogen-atom positions and the absolute structure, for both inorganic and organic samples.

The structures of 2-amino-4′-chlorobenzophenone and 2-amino-4′-bromobenzophenone, previously determined at room temperature in the space group Pna2₁, have been redetermined at low-temperature revealing two different reversible phase transitions. Additionally, high-pressure X-ray diffraction studies were conducted to allow for a comparison of the behavior of these structures in response to different external stimuli. Variable temperature analyses reveal that 2-amino-4′-bromobenzophenone transitions to the monoclinic space group Pa accompanied by a nonmerohedral twinning. The monoclinic phase exhibits approximate symmetry mimicking that of the supergroup Pna2₁ but with a metric symmetry that precludes true Pna2₁ symmetry. The structure of 2-amino-4′-chlorobenzophenone transitions to an incommensurately modulated phase upon cooling. The changes in the structure are attributed to slight conformational variations and a rearrangement of the hydrogen bonding networks in the structure in response to stimuli. The phase transition for 2-amino-4′-bromobenzophenone is classified as second order and a mechanism involving multiple coincident nucleation events is inferred from the conformational change and the incidence of twinning. The transformation of 2-amino-4′-chlorobenzophenone to an incommensurate phase is proposed to arise due to thermal contraction of the structure, which allows distinct competing hydrogen bonding networks between neighboring molecules to evolve.