Abstract Integrating strain and ligand effects with surface defects can precisely modulate the d-band center of Pt-based core−shell catalysts for boosting their performance in fuel cell applications. However, it remains a challenge to synthesize defect-rich Pt-based core−shell nanocrystals in a water-based protocol and to establish a clear structure−property relationship. Herein, we present a controllable synthesis of defect-rich 20 nm Pd@Pt core−shell nanobranches (NBs) via a stepwise reduction route that simultaneously exploits surface crystal defects, strain, and ligand effects to enhance both activity and stability toward electrocatalytic methanol oxidation. Multitwinned Pd NBs were first prepared through oriented attachment of primary nanocrystals in a one-pot aqueous wet-chemical method. Defect-rich Pd@Pt core−shell NBs were then obtained by introducing Pt precursors into the same protocol. By carefully tuning the precursor concentrations, we achieved precise control over shell thickness and composition, thereby strategically tuning the d-band center of the Pd@Pt NBs. Electrocatalytic evaluation revealed a distinct volcano-type relationship between the d-band center position and activity for the Pd@Pt NBs. Notably, defect-rich Pd5@Pt1 NBs achieved mass activities of 0.7 mA mECSA−2 and 1.47 A mgPGM−1, representing 11.67-fold and 4.45-fold enhancement compared to commercial Pt/C, respectively.
Abstract Iodine pentoxide (I2O5) features a high elemental iodine content, and the composite materials formed with nano-aluminum (n-Al) exhibit both high reactivity and abundant gas generation. However, the n-Al/I2O5 system suffers from a long ignition delay and strong hygroscopicity of I2O5. In this work, a novel iodine-rich energetic oxidizer, [C2H10N2](H2I3O9)2 (EAI-2), was designed and synthesized via weak interaction-driven self-assembly, achieving an ultralow hygroscopicity of ≤0.06% and a high iodine content of 68.26%. Single-crystal X-ray diffraction revealed that the supramolecular architecture was stabilized by cooperative halogen bonds (I···O) and hydrogen bonds (N−H···O). These cooperative interactions effectively shielded the samples from moisture adsorption. Three n-Al/EAI-2 composites were prepared via physical mixing (PM), cooling crystallization (CC), and spray antisolvent (SA) methods. Systematic characterizations demonstrated that the preparation method profoundly affected the crystal morphology, interfacial contact, and mixing uniformity of the composites. SA-n-Al/EAI-2 exhibited the most intimate interfacial contact, attributed to the rapid nucleation and constrained crystal growth during the antisolvent-induced precipitation. Consequently, SA-n-Al/EAI-2 displayed superior sensitivity performances, with an impact sensitivity of >30 J, a friction sensitivity of 108 N, and a flame sensitivity of 7.9 cm, outperforming CC-n-Al/EAI-2. The ignition delay of SA-n-Al/EAI-2 (337.6 ms) was significantly shorter than that of n-Al/I2O5 (1039.6 ms) and PM-n-Al/EAI-2 (946.7 ms), demonstrating the critical role of interfacial engineering in energy release behavior. This study elucidates the relationship between crystallization methodology, supramolecular structure, and energetic performance, providing a crystal-engineering strategy for the design of advanced nano-thermites.
Abstract The crystal packing of five atropisomers with two C(aryl)-N(heterocyle) chiral axes, namely, four 1,3-bis[thioxo-thiazolinyl]- and one 1,3-[oxo/thioxo-thiazolinyl] aromatic compounds, was investigated by single-crystal X-ray diffraction. The aim is to establish the relevance of S···S/S···O chalcogen interactions and S···H weak hydrogen bonds in the crystalline network. The high number of alkyl substituents, together with hindered rotation about the C−N bonds, suggests that dispersion is the primary contributor to crystal cohesion. However, even weak, highly directional contacts such as C−H···S and S···S could be emphasized as significant forces in the crystalline supramolecular network. Chalcogen S···S/OC synthon was identified as a pattern along the series of compounds, and replacing S···SC with S···OC confirmed the propensity of these chalcogen interactions, CO being a stronger nucleophile. DFT, NBO, and QTAIM methods were used to define the type and features of the S···S/S···O interactions even at distances 10% beyond the sum of the Bondi van der Waals radii (ΣvdW). SAPT analysis revealed dispersion-driven interactions even when σ-hole interactions were geometrically within the chalcogen bond definition.
Abstract Diamond-like (DL) chalcogenides have emerged as a highly promising structural framework for infrared nonlinear optical (NLO) materials due to their inherently non-centrosymmetric structures and highly oriented tetrahedral units. Herein, a family of defect DL selenides AIIBIII2Se4 (AII = Zn, Cd; BIII = Al, Ga, In) was systematically investigated by integrating theoretical calculations and experimental characterization. These compounds crystallize in the tetragonal I4̅ space group, adopting a defect DL structure derived from infrared benchmark AgGaS2 (AGS), incorporating cation vacancies and highly distorted [BIIISe4] tetrahedral units, which significantly enhance microscopic second-order polarizability. Experimental results demonstrate that these defect DL selenides exhibit strong second-harmonic generation (SHG) intensities and tunable band gaps. Remarkably, ZnIn2Se4 demonstrates a considerable SHG response, approximately 5.5 times that of the commercial benchmark AGS with phase-matching behavior. First-principles calculations further elucidate that their effective NLO coefficients d14 range from 16.44∼34.04 pm/V (calculated by sum over-states method) and 18.49∼35.11 pm/V (DFPT method), respectively, which are attributed to the pronounced bond-angle distortions within the [BIIISe4] tetrahedra, as well as the Se 4p lone-pair-like electrons. This work confirms that vacancy-driven tetrahedral distortion engineering is a potential design strategy for high-performance infrared NLO crystals.
Abstract This study analyzes the trans−cis isomerization-induced photo-coloration in elastically bendable chalcone single crystals. Crystal’s bendability, fluorescence, photo-coloration, and thermal stability have exhibited substantial changes by para-substitution with chloro, iodo, or methyl groups. It is interesting to notice that when the molecular property, trans−cis isomerization, is invoked, the crystals turn into a polycrystalline conformational mixture, brittle, photo-colored, and highly fluorescing in solution.
