Sanping Chen

Environmentally friendly high-energy MOFs: crystal structures, thermostability, insensitivity and remarkable detonation performances

An alternative method to prepare new-generation green high-energy-density materials with excellent performances has been developed on the basis of a coordination chemistry strategy. In the present work, hydrothermal reaction of Cu(II)/Cu(I) with a rigid nitrogen-rich ligand, 3-(1H-tetrazol-5-yl)-1H-triazole (H2tztr), led to three high-energy metal–organic frameworks (MOFs): [Cu(Htztr)2(H2O)2]n (1), {[Cu(tztr)]·H2O}n (2) and [Cu(Htztr)]n (3). Referring to the coordination geometry configuration of Cu(II)/Cu(I) and flexible coordination fashion of the ligand, the energies of the complexes 1–3 are gradually improved when they are structurally transformed from 1, a mononuclear structure to 2, a 3D porous MOF incorporated with guest water molecules to 3, a well-isolated layer structure. The title complexes show outstanding thermostability (Tdec = 345 °C for 1, 325 °C for 2 and 355 °C for 3) and low sensitivity, confirmed by experimental and theoretical characterization. Notably, complex 3 features superior detonation properties to that of known energetic MOFs.

Synthesis and characterization of an energetic compound Cu(Mtta)2(NO3)2 and effect on thermal decomposition of ammonium perchlorate.

An energetic coordination compound Cu(Mtta)(2)(NO(3))(2) has been synthesized by using 1-methyltetrazole (Mtta) as ligand and its structure has been characterized by X-ray single crystal diffraction. The central copper (II) cation was coordinated by four O atoms from two Mtta ligands and two N atoms from two NO(3)(-) anions to form a six-coordinated and distorted octahedral structure. 2D superamolecular layer structure was formed by the extensive intermolecular hydrogen bonds between Mtta ligands and NO(3)(-) anions. Thermal decomposition process of the compound was predicted based on DSC and TG-DTG analyses results. The kinetic parameters of the first exothermic process of the compound were studied by the Kissingers and Ozawa-Doyles methods. Sensitivity tests revealed that the compound was insensitive to mechanical stimuli. In addition, compound was explored as additive to promote the thermal decomposition of ammonium perchlorate (AP) by differential scanning calorimetry.

Single-Ion-Magnet Behavior in a Two-Dimensional Coordination Polymer Constructed from CoII Nodes and a Pyridylhydrazone Derivative

A novel two-dimensional (2D) coordination polymer, [Co(ppad)2]n (1), resulted from the assembly of Co(II) ions based on a versatile ligand termed N(3)-(3-pyridoyl)-3-pyridinecarboxamidrazone. Alternating/direct-current magnetic studies of compound 1 indicate that the spatially separated high-spin Co(II) ions act as single-ion magnets (SIMs). The present work represents the first case of a 2D Co(II)-based SIM composed of a monocomponent organic spacer.

A New Strategy for Storage and Transportation of Sensitive High-Energy Materials: Guest-Dependent Energy and Sensitivity of 3D Metal–Organic-Framework-Based Energetic Compounds

Reaction of Co(II) with the nitrogen-rich ligand N,N-bis(1H-tetrazole-5-yl)-amine (H2bta) leads to a mixed-valence, 3D, porous, metal-organic framework (MOF)-based, energetic material with the nitrogen content of 51.78%, [Co9(bta)10(Hbta)2(H2O)10]n⋅(22 H2O)n (1). Compound 1 was thermohydrated to produce a new, stable, energetic material with the nitrogen content of 59.85% and heat of denotation of 4.537 kcal cm(-3), [Co9(bta)10(Hbta)2(H2O)10]n (2). Sensitivity tests show that 2 is more sensitivity to external stimuli than 1, reflecting guest-dependent energy and sensitivity of 3D, MOF-based, energetic materials. Less-sensitive 1 can be regarded as a more safe form for storage and transformation to sensitive 2.

High-energy-density materials with remarkable thermostability and insensitivity: syntheses, structures and physicochemical properties of Pb(II) compounds with 3-(tetrazol-5-yl) triazole

Two energetic compounds, [Pb(Htztr)2(H2O)]n (1) and [Pb(H2tztr)(O)]n (2), were synthesized and then structurally characterized (N% = 39.4% for 1, N% = 27.2% for 2), where Htztr represents 3-(tetrazol-5-yl)triazole. Structural analysis revealed that both compounds have reticular two-dimensional structures. Remarkably, thermogravimetric measurements demonstrated that the compounds possess excellent thermostabilities with high decomposition temperatures up to 340 °C for (1) and 318 °C for (2). The kinetic parameters of exothermic processes were studied by the Kissingers and Ozawa–Doyles methods. The standard molar enthalpies of formation were obtained from the determination of constant-volume combustion energies. The calculated detonation properties showed that compound (1) can be used as a potential explosive. Sensitivity tests revealed that the compounds are extremely insensitive. In addition, two compounds were examined for use as additives to promote the thermal decomposition of ammonium perchlorate and hexahydro-1,3,5-trinitro-1,3,5-triazine.

Solvent-Induced Syntheses, Crystal Structures, Magnetic Properties, and Single-Crystal-to-Single-Crystal Transformation of Azido-Cu(II) Coordination Polymers with 2-Naphthoic Acid as Co-ligand

Based on the solvent-induced effect, three new azido-copper coordination polymers--[Cu(2-na)(N3)] (1), [Cu(2-na)(N3)] (2), and [Cu(2-na)(N3)(C2H5OH)] (3) (where 2-na = 2-naphthoic acid)--have been successfully prepared. Structure analysis shows that the Cu(II) cations in compounds 1-3 present tetra-, penta-, and hexa-coordination geometries, respectively. Compound 1 is a well-isolated one-dimensional (1D) chain with the EO-azido group, while 2 is an isomer of 1 and exhibits a two-dimensional (2D) layer involving the EE-azido group. Thermodynamically, density functional theory (DFT) calculation reveals that 2 occupies the stable state and 1 locates in the metastable state. Compound 3 consists of a 1D chain with triple bridging mode, which is derived from 1, and undergoes a single-crystal-to-single-crystal transformation by soaking in ethanol solvent; the powdery product of 1, namely 1b, could be yielded after the dealcoholization of compound 3. Magnetic measurements indicate that compounds 1-3 perform strong intrachain ferromagnetic interactions, experiencing long-range magnetic ordering and slow magnetic relaxation. Compound 1 features the metamagnetic behavior with a transition temperature of 15 K, while 2 and 3 display spin glass behavior with the phase transition temperatures of 15 and 12 K, respectively. Magneto-structure relationships are investigated as well.

3D high-energy-density and low sensitivity materials: synthesis, structure and physicochemical properties of an azide–Cu(II) complex with 3,5-dinitrobenzoic acid

A novel 3D energetic coordination polymer of azide–Cu(II), Cu(3,5-DNBA)(N3), was synthesized and structurally characterized by single crystal X-ray diffraction, where 3,5-DNBA represents 3,5-dinitrobenzoic acid. Structural analysis reveals that the central Cu(II) ion coordinates with two azide anions and three 3,5-dinitrobenzoic acid anions to form a five-coordinated tetragonal pyramid structure. Remarkably, one oxygen atom in the nitro group displays rare coordination to the Cu(II) ions in the complex. The as-prepared compound showed abrupt thermal decomposition at 268 °C, representing explosive performance and superior thermostability based on DSC and TG-DTG analyses. Sensitivity tests revealed that the title complex was insensitive to external stimuli. The kinetic parameters of an exothermic process for the complex were studied by Kissingers and Ozawa–Doyles methods. In addition, the constant-volume combustion energy of the complex was determined using a precise rotating-bomb calorimeter, and the standard molar enthalpy of combustion and the standard molar enthalpy of formation were calculated.

Lanthanide coordination compounds with 1H-benzimidazole-2-carboxylic acid: syntheses, structures and spectroscopic properties

A flexible multidentate ligand, 1H-benzimidazole-2-carboxylic acid, was synthesized to construct a series of lanthanide coordination polymers [Ln(HBIC)3]n (Ln = Eu (1), Tb (2), Gd (3), Pr (4), Nd (5); H2BIC = 1H-benzimidazole-2-carboxylic acid) under hydrothermal conditions. All the compounds were fully characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, thermal analysis and various spectroscopic techniques. Structural analyses reveal that they are isostructural and feature a 2D wave-like layer structure with distorted grids, in which the adjacent Ln3+ centers are bridged by the HBIC− ligands with two kinds of new coordination modes and the adjacent HBIC− ligands are tightly bound by two types of distinct intra-layer hydrogen bonds. The adjacent 2D layers are further interconnected by strong inter-layer hydrogen bond ring motifs R22(10) to generate a 3D supramolecular architecture. Optical studies indicate that the compounds 1, 2, 4 and 5 exhibit characteristic luminescence emission bands of the corresponding lanthanide ions in the visible or near-infrared regions at room temperature. In particular, compound 2 displays bright green luminescence in the solid state with a satisfactory 5D4 lifetime of 1.2 ms and a high overall quantum yield of 31%, due to an ideal energy gap between the lowest triplet state energy level of H2BIC ligand and the 5D4 state energy level of Tb3+. The energy transfer mechanisms in compounds 1 and 2 were also described and discussed.

High-Performance Energetic Characteristics and Magnetic Properties of a Three-Dimensional Cobalt(II) Metal–Organic Framework Assembled with Azido and Triazole

A three-dimensional metal-organic framework based, high-energy-density compound, [Co5(3-atrz)7(N3)3] (3-atrz = 3-amine-1H-1,2,4-triazole), features superior detonation properties, insensitivity, and thermostability. Magnetic studies show that the compound characterizes the coexistence of remarkable coercivity, metamagnetism, long-range ordering, and relaxation dynamics. The heat-capacity measurement confirms the typical long-range antiferromagnetic ordering below 16 K. This difunctional system exemplifies an effective attempt at developing advanced magnetoenergetic materials.

Magnetization Dynamics Changes of Dysprosium(III) Single-Ion Magnets Associated with Guest Molecules

Two Dy(III) single-ion magnets with a trigonal dodecahedron (D2d) for 1 and an approximately square-antiprismatic (SAP, D4d) N2O6 coordination environment for 2, formulated as [Dy(Phen)(tfmb)3] (1) and [Dy(Phen)(tfmb)3]·0.5(1,4-dioxane) (2) (tfmb = 4,4,4-trifluoro-1-(4-methylphenyl)-1,3-butanedione, Phen = 1,10-phenanthroline), were obtained. Therein, complex 1 was transformed to 2 in 1,4-dioxane solution. Structural analysis shows that complexes 1 and 2 have differing local symmetry of Dy(III) ions. Magnetic studies indicate that the barrier heights (ΔE/kB) of 1 and 2 are 63.56 and 102.82 K under zero dc field as well as 118.50 and 164.55 K under 1200 Oe dc field, respectively. Based on the frequency dependencies of the ac susceptibilities, the effective barriers (ΔE/kB) and the pre-exponential factors (τ0) are 67.05 K and 4.57 × 10(-6) s for 1 and 95.88 K and 2.39 × 10(-7) s for 2 under zero dc field. The present work illustrates that guest-determined notable structure change results in different barrier heights.