Single-crystal to single-crystal transformation from a hydrophilic–hydrophobic metal–organic framework to a layered coordination polymer

[2+1] Cycloadditions Modulate the Hydrophobicity of Ni-N4 Single-Atom Catalysts for Efficient CO2 Electroreduction

Microenvironment regulation of M-N4 single-atom catalysts (SACs) is a promising way to tune their catalytic properties toward the electrochemical CO2 reduction reaction. However, strategies that can effectively introduce functional groups around the M-N4 sites through strong covalent bonding and under mild reaction conditions are highly desired. Taking the hydrophilic Ni-N4 SAC as a representative, we report herein a [2+1] cycloaddition reaction between Ni-N4 and in situ generated difluorocarbene (F2C:), and enable the surface fluorocarbonation of Ni-N4, resulting in the formation of a super-hydrophobic Ni-N4-CF2 catalyst. Meanwhile, the mild reaction conditions allow Ni-N4-CF2 to inherit both the electronic and structural configuration of the Ni-N4 sites from Ni-N4. Enhanced electrochemical CO2-to-CO Faradaic efficiency above 98 % is achieved in a wide operating potential window from -0.7 V to -1.3 V over Ni-N4-CF2. In situ spectroelectrochemical studies reveal that a highly hydrophobic microenvironment formed by the -CF2- group repels asymmetric H-bonded water at the electrified interface, inhibiting the hydrogen evolution reaction and promoting CO production. This work highlights the advantages of [2+1] cycloaddition reactions on the covalent modification of N-doped carbon-supported catalysts.

Capped Nanojars: Synthesis, Solution and Solid-State Characterization, and Atmospheric CO2 Sequestration by Selective Binding of Carbonate

Nanojars are a class of supramolecular anion-incarcerating coordination complexes that self-assemble from Cu²⁺ ions, pyrazole, and a strong base in the presence of highly hydrophilic anions. In this work, we show that if the strong base (e.g., NaOH or Bu₄NOH) is replaced by a weak base such as a trialkylamine, capped nanojars of the formula [{Cu₃(μ₃-OH)(μ-pz)₃L₃}CO₃⊂{Cu(μ-OH)(μ-pz)}_n] (pz = pyrazolate anion; L = neutral donor molecule; n = 27-31) are obtained instead of the conventional nanojars. Yet, to obtain capped nanojars, the conjugate acid side product originating from the weak base must be separated by transferring it to water either by precipitation of the water-insoluble capped nanojars or by liquid-liquid extraction. Full characterization using electrospray ionization mass spectrometry, UV-vis and variable-temperature ¹H NMR spectroscopy in solution, and single-crystal X-ray diffraction, elemental analysis, and solubility studies in the solid state reveals similarities as well as drastic differences between capped nanojars and nanojars lacking the [Cu₃(μ₃-OH)(μ-pz)₃L₃]²⁺ cap. Acid-base reactivity studies demonstrate that capped nanojars are intermediates in the pH-controlled assembly-disassembly of nanojars. During the self-assembly of capped nanojars, CO₂ is selectively sequestered from air in the presence of other atmospheric gases and converted to carbonate, the binding of which is selective in the presence of NO₃^-, ClO₄^-, BF₄^-, Cl^-, and Br^- ions.

Spontaneous single-crystal to single-crystal transition with self-healing cracks involving solvent exchange

A single crystal of darunavir dihydrate was obtained by SCSCT, accompanied by crystal breaking to self-healing.

Polymorphism, phase transformation and energetic properties of 3-nitro-1,2,4-triazole

We report the preparation, analysis, and phase transformation behavior of polymorphs of 3-nitro-1,2,4-triazole. The compound crystallizes in two different polymorphic forms, Form I (tetragonal, P4₁2₁2) and Form II (monoclinic, P2₁/c). Analysis of the polymorphs has been investigated using microscopy, differential scanning calorimetry, in situ variable-temperature powder X-ray diffraction, and single-crystal X-ray diffraction. On heating, Form II converts into Form I irreversibly, and on further heating, decomposition is observed. In situ powder X-ray diffraction studies revealed that Form II transforms to Form I above 98 °C, indicating that Form I is more stable than Form II at high temperature. Form II of 3-nitro-1,2,4-triazole has good detonation properties (V_det = 8213 m s⁻¹, P_C–J = 27.45 GPa), and low sensitivity (IS > 40 J, FS = 360 N, ESD = 29 J), which make it a competitive candidate for use as a new insensitive explosive.

On heating, Form II converts into Form I irreversibly, which indicates Form I is more stable at higher temperatures.

Transition metal complexes with oligopeptides: single crystals and crystal structures

The coordination chemistry of short chain peptides with transition metals is described in terms of the available crystal structures. Despite their high interest as synthetic models for metalloproteins and as building blocks for molecular materials based on the tuneable properties of oligopeptides, single crystal X-ray diffraction studies are scarce. A perusal of the most relevant results in this field allows us to define the main characteristics of oligopeptide-metal interactions, the fundamental problems for the crystallization of these complexes, and some hints to identify future promising approaches to advance the development of metallopeptide chemistry.