Metal-free energetic materials generally have the advantages of high gas yield and metal-free residue after combustion or explosion, enabling them to be widely used as explosives and propellant ...components. As part of a series of our investigations on ABX3 molecular perovskite high-energetic materials, here we report five new metal-free members, (H2A)NH4(ClO4)3, by using different organic cations H2A2+, i.e., 1-hydroxy-1,4-diazabicyclo2.2.2octane-1,4-diium for DAP-O4, piperazine-1,4-diium for PAP-4, 1-methyl-piperazine-1,4-diium for PAP-M4, homopiperazine-1,4-diium for PAP-H4, and 1-methyl-1,4-diazabicyclo-2.2.2octane-1,4-diium for DAP-M4, respectively. Together with the previously reported member, (H2dabco)NH4(ClO4)3 (DAP-4, H2dabco2+ = 1,4-diazabicyclo2.2.2octane-1,4-diium), these six metal-free molecular perovskite high-energetic materials provide nice instances to fine-tune the oxygen balance, crystal density, thermal stability, and detonation performance, by changing the A-site organic cations solely. The density functional theory (DFT) calculations and the Kamlet–Jacob (K–J) equation suggested that improving the oxygen balance while keeping the spherical shape of the organic cations to match the anionic cage in these metal-free energetic materials facilitates obtaining a better detonation performance, providing an important clue for designing advanced practicable high-energetic materials. It is worth noting that three compounds (PAP-4, PAP-H4, and DAP-O4) are expected to exceed the performances of RDX as both explosive and propellant, in which DAP-O4 has the highest detonation heat (6.21 kJ mol–1), detonation velocity (8.900 km s–1), and detonation pressure (35.7 GPa), as well as a higher specific impulse value (262 s).
The coexistence of multiferroic orders has attracted increasing attention for its potential applications in multiple-state memory, switches, and computing, but it is still challenging to design ...single-phase crystalline materials hosting multiferroic orders at above room temperature. By utilizing versatile ABX
3
-type perovskites as a structural model, we judiciously introduced a polar organic cation with easily changeable conformations into a tetrafluoroborate-based perovskite system, and successfully obtained an unprecedented molecular perovskite, (homopiperazine-1,4-diium)K(BF
4
)
3
, hosting both ferroelectricity and ferroelasticity at above room temperature. By using the combined techniques of variable-temperature single-crystal X-ray structural analyses, differential scanning calorimetry, and dielectric, second harmonic generation, and piezoresponse force microscopy measurements, we demonstrated the domain structures for ferroelectric and ferroelastic orders, and furthermore disclosed how the delicate interplay between stepwise changed dynamics of organic cations and cooperative deformation of the inorganic framework induces ferroelectric and ferroelastic phase transitions at 311 K and 455 K, respectively. This instance, together with the underlying mechanism of ferroic transitions, provides important clues for designing advanced multiferroic materials based on organic-inorganic hybrid crystals.
An unprecedented tetrafluoroborate-based perovskite reveals the coexistence of ferroelastic and ferroelectric transitions arising from delicate interplay between stepwise frozen organic cations and cooperative deformation of the framework.
Using bulky amides as the structure-directing agents (SDAs) is an alternative synthetic strategy for the exploration of crystalline large pore (≥12-membered ring) zeolitic imidazolate frameworks ...(ZIFs). Specifically, by using the bulky amides, dibutylformamide (DBF) and dipropylformamide (DPF) as solvent and imidazole (Im) as a ligand, two ZIFs mimicking the CAN and AlPO-5 (AFI) zeotypes with 12-membered ring (MR) pore openings were synthesized, and denoted as CAN-Zn(Im)2 and AFI-Zn(Im)2, respectively. These two materials are the first known examples of Zn(Im)2 polymorphs with 12-MR pores and AFI-Zn(Im)2 has the largest pore apertures reported to date for ZIF materials. The concept that the bulky amides used were not simply acting as the solvent, but were in fact acting as SDAs or templates during the synthesis of the large pore ZIFs, was suggested by the closeness of the geometrical fit between the guest DBF and the can cages (composite building units) of the CAN-Zn(Im)2.
In recent years, molecular perovskite energetic materials have attracted more attention because of their simple synthesis processes, high thermal stabilities, excellent performances, and great ...significance as a design platform for energetic materials. To explore the possibility of the application of molecular perovskite energetic materials in heat-resistant explosives, four silver(I)-based molecular perovskite energetic compounds, (H2A)Ag(ClO4)3, where H2A = piperazine-1,4-diium (H2pz2+) for PAP-5, 1-methyl-piperazine-1,4-diium (H2mpz2+) for PAP-M5, homopiperazine-1,4-diium (H2hpz2+) for PAP-H5, and 1,4-diazabicyclo2.2.2octane-1,4-diium (H2dabco2+) for DAP-5, were synthesized by a one-pot self-assembly strategy and structurally characterized. The single-crystal structures indicated that PAP-5, PAP-M5, and DAP-5 possess cubic perovskite structures while PAP-H5 possesses a hexagonal perovskite structure. Differential thermal analyses showed that their onset decomposition temperatures are >308.3 °C. For PAP-5 and DAP-5, they have not only exceptional calculated detonation parameters (D values of 8.961 and 8.534 km s–1 and P values of 42.4 and 37.9 GPa, respectively) but also the proper mechanical sensitivity (impact sensitivities of ≤10 J for PAP-5 and 3 J for DAP-5 and friction sensitivities of ≤5N for both PAP-5 and DAP-5) and thus are of interest as potential heat-resistant primary explosive components.
We presented two new ABX3 postperovskite coordination polymers, (C5H13NCl)M(dca)3 (dca = N(CN)2 –, M = Mn2+ for 1 and Cd2+ for 2), as well as their phase transition behaviors disclosed by using ...differential scanning calorimetry measurements, variable-temperature single-crystal X-ray analyses, dielectric measurements, and Hirshfeld surface analyses. Both 1 and 2 have same structure (Cmcm) at room temperature, in which their A-site organic cations are fourfold disordered about two mirror planes and undergo order–disorder phase transition mainly caused by the freezing of A-site cations upon cooling. The different metal ions endow them distinct structural flexibility, resulting in different phase transition behaviors and dielectric responses; that is, the smaller and coordinatively rigid Mn2+ ion results in two-step Cmcm (Z = 4) ↔ Pbcm (Z = 4) ↔ Pbca (Z = 8) transitions accompanied with obvious dielectric relaxation, whereas the larger and coordinatively flexible Cd2+ ion results in one-step Cmcm (Z = 4) ↔ Pbca (Z = 16) transition accompanied with a sharp dielectric switching. This study well demonstrates the tunability of postperovskite, as a new kind of host–guest model, for modulating the phase transition and relevant switching physical properties.
Solvothermal reactions of 3-methyl-5-trifluoromethyl-1,2,4-triazole (Hfmtz) with Cu(CH3COO)2 at 120 °C in the presence of Cl– generate two partially fluorinated coordination polymers: i.e., ...Cu4Cl(fmtz)3 (1 or MAF-51) and Cu7Cl(fmtz)6 (2 or MAF-52). Single-crystal X-ray diffraction revealed 1 to have a three-dimensional (3D) nonporous structure with pcu topology consisting of 6-connected Cu4(μ4-Cl) clusters and 2 to possess a highly porous (void ratio 48%) 3D bnn network consisting of 5-connected Cu5(μ5-Cl) clusters. Benefiting from the hydrophobic pendant groups, complete coordination of the ligand N atoms, and strong M–N coordination bonds, 1 and 2 possess high water stability (exposed to water for at least 1 year) and hydrophobicity (water contact angles of 141° and 148°, respectively). The N2 sorption isotherm of activated 2 gave Langmuir/BET surface areas of 1023/848 m2 g–1 and a pore volume of 0.365 cm3 g–1. Moreover, 2 can adsorb large amounts of benzene and methanol but barely adsorb water. Both 1 and 2 show phosphorescence of Cu(I) complexes, but only that of porous 2 is sensitive to O2, showing a linear Stern–Volmer response below 1 mbar with an ultrahigh K sv value of 5234 bar–1 and ultralow limit of detection of 1.9 ppm.
Two new double perovskite-like azido coordination polymers with trimethylammonium as the guest cation, namely, (Me3NH)2CrNa(N3)6 and (Me3NH)2CrK(N3)6, have been prepared. The molecular dynamics for ...both compounds are investigated and are clearly uncovered by the first-principles molecular dynamics simulation and the significant dielectric relaxation. Structural analyses of these compounds in combination with their analogue (Me3NH)Mn(N3)3 reveal that the guest trimethylammonium has flexible structural adaptability, especially with a variety of disordered distributions, to match the different symmetries of varied metal-azido frameworks. Interestingly, the replacement of the divalent metal ion by mixed monovalent/trivalent metal ions can change the symmetry, shape, and charge distribution of the host cage unit; thus it may influence and regulate the arrangement of the guest inclusion and its molecular dynamics as well as the structural phase transition.
The dynamic behaviors of a new type of three-dimensional (3D) water framework symbiotic with 1D stacking organic guests, including an order–disorder transition of hydrogen atoms, a supercooling ...phenomenon during phase transition, and a dipole-glass-like relaxation behavior due to locally trapped water molecules, are presented. This extremely scarce 3D water framework, together with the rich dynamic behaviors it exhibits, provides new clues to design new ice-like models for promoting the fundamental understanding of the dynamic behavior of water in diverse solid-states.
Ein protonenleitendes , wasserstoffverbrücktes organisches Gerüst (HOF) wurde aus einem C3‐symmetrischen hexatopen Carbonsäurederivat mit einer 18‐Krone‐6‐Ether‐Komponente aufgebaut. Trotz der ...Flexibilität des Makrozyklus ermöglichen die H‐Brückenmodule dem Derivat, ein hexagonal vernetztes Gerüst mit permanenter Porosität zu bilden. Wie Takayoshi Nakamura, Ichiro Hisaki et al. in ihrer Zuschrift (e202211686) berichten, besitzt das HOF 1D‐Kanäle mit einem Engpass bestehend aus den Makrozyklen und zeigt Protonenleitfähigkeit (1.12×10−7 S cm−1) mittels Grotthuss‐Mechanismus (Ea=0.27 eV) unter 98 %RH.
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