Direct Visualization of Orientation Competition in Protein Epitaxial Crystallization.

Controlled Axial Growth and Morphological Evolution of Three-Dimensional Covalent Organic Frameworks Unveiled by Single-Crystal X-ray Diffraction.

Precisely tailoring the macroscopic morphology of covalent organic frameworks (COFs) fundamentally drives their physicochemical properties. However, the robust and highly directional nature of covalent bonds makes such control at the single-crystal level a formidable challenge. Resolving this bottleneck, we establish a synergistic Brønsted and Lewis dual-acid catalytic strategy to dictate the controlled axial growth and morphological evolution of large (≥50 μm) three-dimensional(3D) COFs single crystals (the XNU-375-X; X = 1-6, a, p, EtOH) featuring a dia topology. Modulating the concentration of dysprosium trifluoromethanesulfonate (Dy(OTf)3), acting as the Lewis acid, drastically suppresses the twinning rate. Consequently, this targeted regulation drives a continuous morphological transition from octahedral to tetragonal bipyramidal geometries. Single-crystal X-ray diffraction (SCXRD) explicitly confirms the microscopic structural consistency throughout this macroscopic evolution. Crucially, during guest solvent removal and exchange, these crystallographic analyses directly capture a rare structural flexibility and dynamic "breathing" effect, evidenced by a massive 46% volume variation. Density functional theory (DFT) calculations elucidate the underlying growth kinetics. Conditional on the specific exposed facets ({100} versus {001}), Dy3+ exhibits differential adsorption behaviors that effectively passivate lateral free amine sites. To the extent that these sites govern horizontal proliferation, this selective binding simultaneously promotes ordered c-axis stacking and intrinsic self-correction. Ultimately, this work bridges the gap in the precision morphological tailoring of 3D COFs single crystals, providing a robust platform for the anisotropic growth and targeted synthesis of complex porous architectures.

CryoTEM as an advanced analytical tool for materials chemists

Crystal clear. Engineering complexity.

The field of structural chemistry has been significantly reshaped by the development of crystal engineering, a subject focused on the strategic design of molecular solids with specific properties. Central to this advancement is the concept of the supramolecular synthon, the core structural module, which can be identified as a synthetic target. Such thinking enables a retrosynthetic approach to crystal design, allowing for the predictable assembly of organic solids using intermolecular interactions as tactical elements that accompany the design strategy. A major shift in our understanding of molecular architecture occurred through the validation of weak hydrogen bonds - specifically C-H...O interactions - as structurally and functionally relevant. Once overlooked, these interactions are now recognized for their essential roles in both small-molecule crystals and complex biological systems. The crystal engineer's palette of interactions has been further expanded to include halogen bonding and other molecular associations involving electrophilic chalcogen, pnictogen and tetrel atoms, leading to standardized international definitions for these bonds. The culmination of these studies treats the molecular crystal not merely as an assembly of parts, but as a complex, holistic system. By framing the crystal as a supramolecular entity, the field has moved toward a predictive science that balances various intermolecular forces to engineer functional materials.

Understanding the Solvent-Regulated Assembly of Conjugated Polymers via Nanoscale Visualization

The multilevel assembly of conjugated polymers critically determines their electronic performance. However, establishing a direct correlation from molecular-level interactions to macroscopic morphology and charge transport properties remains challenging. In this work, advanced characterization techniques were employed to identify and visualize two distinct assembly processes of a representative n-type conjugated polymer, F4BDOPV-2T, in both solution and thin film states, allowing for a structural correlation between solvent affinities and assembly structures. In 1-chloronaphthalene, strong solvation of the conjugated backbones promoted sidechain-dominated growth of nanoscale assemblies and ordered lamellar packing, resulting in compact 3D cluster aggregates in solution and well-oriented, large-scale ordered crystalline grains in the solid state. Conversely, toluene favored sidechain solvation, leading to backbone-dominated assembly growth that formed fiber networks and interconnected crystalline grains. The superior grain connectivity during backbone-dominated growth outweighed the effect of smaller grain size, yielding a three-fold enhancement in electron mobility (μe = 2.05 cm2 V–1 s–1). Through real-space electron microscopy visualization, this work bridges intermolecular interactions with multilevel assembly structures of conjugated polymers, providing fundamental insights into rational solvent regulation and morphological control for high-performance organic electronics.

In Situ Atomic-Scale Visualization of Interface Relaxation Pathways and Stacking-Registry Evolution in 2D MoS2.

Understanding transient kinetic pathways governing the bottom-up synthesis of 2D MoS2 is critical for deterministic growth. Here, utilizing an atomically resolved graphene-based microreactor for in situ heating transmission electron microscopy, we directly visualize the interface relaxation pathways and stacking-registry evolution during the growth of MoS2, advancing beyond the mere observation of its continuous growth dynamics. We reveal that lateral expansion is driven by dynamic edge reconstructions, as kinetically metastable states spontaneously relax into thermodynamically favored zigzag configurations. During subsequent domain coalescence, the dynamic interface relaxation is achieved across three distinct modes: defect-forming gap healing, strain-regulated seamless stitching, and rigid-body oriented attachment, which robustly accommodate lattice misorientations. Furthermore, intrinsic in-plane mirror twin boundaries induce localized structural distortions that mediate out-of-plane interlayer sliding, transiently stabilizing nonequilibrium bilayer stacking registries. By resolving these dynamic atomic fluctuations, our work establishes a fundamental mechanistic framework linking growth kinetics to the synthesis of 2D materials.

Nucleation and Growth Pathway of Magma Crystallisation: A Non-Classical Two-Stage, Four-Step Mechanism

Although non-classical crystallization pathways have been extensively studied in low-temperature systems (e.g. biomineralization), directly observing the dynamics of nucleation and growth under high-temperature and high-pressure magmatic conditions remains a major challenge. Using naturally step-quenched rock samples and high-resolution transmission electron microscopy, we obtained a series of nanoscale ‘snapshots’ of final state inversion crystallization process. Our results reveal that structural units in the melt first assemble into amorphous pre-nucleation clusters. Upon reaching a critical size (~3.5 nm in diameter), these clusters undergo a phase transition into crystal nuclei with a well-defined lattice. Subsequently, structural units migrate toward the crystal nuclei, forming a growth boundary layer at the crystal-melt interface. Within this layer, structural units assemble into growth units, which are integrated into the crystal lattice through a cooperative mechanism, driving crystal growth. These findings uncover a non-classical two-stage, four-step nucleation-growth pathway. Under this mechanism, densely distributed and nearly synchronously formed pre-nucleation clusters and crystal nuclei compete for limited nutrients and growth space, ultimately generating polycrystalline aggregates composed of numerous tiny crystals. Direct observation of crystal nucleation during magma crystallization demonstrates that the uniformly distributed phenocrysts in volcanic rocks and the randomly oriented crystals in near-equigranular intrusive rocks (e.g. granites) result from homogeneous nucleation. Notably, despite the vast environmental differences between high-temperature magmatic systems and low-temperature aqueous solutions, both follow the same energy-optimized crystallization pathway at the atomic scale, which remains unchanged regardless of external conditions (e.g. temperature, pressure, composition, viscosity) that influence crystal growth rates and morphologies. This appears to be a naturally designed, energy-minimizing pathway: pre-nucleation cluster → crystal nucleus → growth boundary layer → polycrystal (or single crystal).