Efficient Direct X-ray Detection and Imaging Based on a Lead-Free Electron Donor-Acceptor MOF.

Metal-organic frameworks (MOFs) have recently gained extensive attention as potential materials for direct radiation detection due to their strong radiation absorption, long-range order, and chemical tunability. However, it remains challenging to develop a practical MOF-based X-ray direct detector that possesses high X-ray detection efficiency, radiation stability, and environmental friendliness. The integration of donor-acceptor (D-A) pairs into crystalline MOFs is a powerful strategy for the precise fabrication of multifunctional materials with unique optoelectronic properties. Herein, a new lead-free MOF, Cu2I2(TPPA) (CuI-TPPA, TPPA = tris[4-(pyridine-4-yl)phenyl]amine), with a 6-fold interpenetrated structure is designed and synthesized based on the electron donor-acceptor strategy. CuI-TPPA has a large mobility-lifetime (µτ) product of 5.8 × 10-4 cm2 V-1 and a high detection sensitivity of 73.1 µC Gyair-1 cm-2, surpassing that of commercial α-Se detectors. Moreover, the detector remains fairly stable with only a 2% reduction in photocurrent under continuous bias irradiation conditions with a total dose of over 42.83 Gyair. The CuI-TPPA/poly(vinylidene fluoride) flexible composite X-ray detector films are successfully manufactured with different thicknesses. Through multifaceted assessments, the optimal thickness is found with a high detection sensitivity of up to 143.6 µC Gyair-1 cm-2. As proof-of-concept, 11 × 9 pixelated X-ray detectors are fabricated on the same composite film to realize X-ray direct imaging. This work opens up potential applications of MOFs in environmentally friendly and wearable devices for direct X-ray detection and imaging.

Thermally Activated Delayed Fluorescence (TADF)-active Coinage-metal Sulfide Clusters for High-resolution X-ray Imaging.

The study of facile-synthesis and low-cost X-ray scintillators with high light yield, low detection limit and high X-ray imaging resolution plays a vital role in medical and industrial imaging fields. However, the optimal balance between X-ray absorption, decay lifetime and excitonic utilization efficiency of scintillators to achieve high-resolution imaging is extremely difficult due to the inherent contradiction. Here two thermally activated delayed fluorescence (TADF)-actived coinage-metal clusters M6 S6 L6 (M=Ag or Cu) were synthesized by simple solvothermal reaction, where the cooperation of heavy atom-rich character and TADF mechanism supports strong X-ray absorption and rapid luminescent collection of excitons. Excitingly, Ag6 S6 L6 (SC-Ag) displays a high photoluminescence quantum yield of 91.6 % and scintillating light yield of 17420 photons MeV-1 , as well as a low detection limit of 208.65 nGy s-1 that is 26 times lower than the medical standard (5.5 µGy s-1 ). More importantly, a high X-ray imaging resolution of 16 lp/mm based on SC-Ag screen is demonstrated. Besides, rigid core skeleton reinforced by metallophilicity endows clusters M6 S6 L6 strong resistance to humidity and radiation. This work provides a new view for the design of efficient scintillators and opens the research door for silver clusters in scintillation application.

Refinement of sensitive azides via in situ generated azole-based metal-organic frameworks towards stable energetic materials.

Energetic materials (EMs) have been widely employed in both military and civilian areas for nearly two centuries. The introduction of high-energy azide anions to assemble energetic metal-organic frameworks (EMOFs) is an efficient strategy to enhance energetic properties. However, azido-based EMOFs always suffer low stabilities to external mechanical stimulation. Herein, we employed an in situ hydrothermal reaction as a technique to refine azide anions with a neutral triazole-cyano-based ligand TrzAt (TrzAt = 2-(1H-1,2,4-triazol-1-yl)acetonitrile) to yield two tetrazole-based EMOFs, namely, [ZnBr(trmetz)]n1 and [Cd(trmetz)2]n2 (Htrmetz = 5-(1,2,4-triazol-1-ylmethyl)-1H-tetrazole). Compound 1 features a closely packed 2D layered network, while compound 2 exhibits a 3D architecture. With azide anions inlaid into a nitrogen-rich and chelating ligand in the EMOFs, compounds 1 and 2 present remarkable decomposition temperatures (Tdec ≥ 300 °C), low impact sensitivities (IS ≥ 32 J) and low friction sensitivities (FS ≥ 324 N). The calculated heat of detonation (ΔHdet) values of 1 and 2 are 3.496 and 4.112 kJ g-1, respectively. In particular, the ΔHdet value of 2 is higher than that of traditional secondary explosives such as 2,4,6-trinitrotoluene (TNT, ΔHdet = 3.720 kJ g-1). These results indicate that EMOFs 1 and 2 may serve as potential replacements for traditional secondary explosives. This work provides a simple and effective strategy to obtain two EMOFs with satisfactory energy densities and reliable stabilities through an in situ hydrothermal technique for desensitization of azide anions.

Highly Sensitive Direct X-Ray Detector Based on Copper(II) Coordination Polymer Single Crystal with Anisotropic Charge Transport.

Anisotropic charge transport plays a pivotal role in clarifying the conductivity mechanism in direct X-ray detection to improve the detection sensitivity. However, the anisotropic photoelectric effect of semiconductive single crystal responsive to X-ray is still lacking of theoretical and experimental proof. The semiconductive coordination polymers (CPs) with designable structures, adjustable functions, and high crystallinity provide a suitable platform for exploring the anisotropic conductive mechanism. Here,the study first reveals a 1D conductive transmission path for direct X-ray detection from the perspective of structural chemistry. The semiconductive copper(II)-based CP 1 single crystal detector exhibits unique anisotropic X-ray detection performance. Along the 1D π-π stacking direction, the single crystal device (1-SC-a) shows a superior sensitivity of 2697.15 µCGyair -1  cm-2 and a low detection limit of 1.02 µGyair  s-1 among CPs-based X-ray detectors. This study provides beneficial guidance and deep insight for designing high-performance CP-based X-ray detectors.

Improving X-ray Scintillating Merits of Zero-Dimensional Organic-Manganese(II) Halide Hybrids via Enhancing the Ligand Polarizability for High-Resolution Imaging.

Luminescent metal halides have been exploited as a new class of X-ray scintillators for security checks, nondestructive inspection, and medical imaging. However, the charge traps and hydrolysis vulnerability are always detrimental to the three-dimensional ionic structural scintillators. Here, the two zero-dimensional organic-manganese(II) halide coordination complexes 1-Cl and 2-Br were synthesized for improvements in X-ray scintillation. The introduction of a polarized phosphine oxide can help to increase the stabilities, especially the self-absorption-free merits of these Mn-based hybrids. The X-ray dosage rate detection limits reached up to 3.90 and 0.81 µGyair/s for 1-Cl and 2-Br, respectively, superior to the medical diagnostic standard of 5.50 µGyair/s. The fabricated scintillation films were applied to radioactive imaging with high spatial resolutions of 8.0 and 10.0 lp/mm, respectively, holding promise for use in diagnostic X-ray medical imaging.

Coordination polymerization of nitrogen-rich linkers and dicyanamide anions toward energetic coordination polymers with low sensitivities.

The design and synthesis of energetic materials (EMs) with high energy and reliable stabilities has attracted much attention in the field of EMs. In this work, we employed a strategy of the coordination polymerization of mild dicyanamide ions (DCA-), two isomeric ligands 1-methyl-5-aminotetrazole (1-MAT) and 2-methyl-5-aminotetrazole (2-MAT) to construct energetic coordination polymers (ECPs). Four new ECPs {[Co(DCA)2(1-MAT)2]·H2O}n1, [Cu(DCA)2(1-MAT)]n2, [Cd(DCA)2(1-MAT)2]n3 and [Cd(DCA)2(2-MAT)2]n4 were successfully synthesized through solvent evaporation routes. Compounds 1 and 4 display 1D chains, while 2 and 3 exhibit 2D-layered structures. Compounds 1-3 with the 1-MAT ligand all exhibit reliable thermal stabilities (> 200 °C). The calculated heats of detonation (ΔHdet) of 1-3 are all higher than 1.4 kJ g-1, which are higher than traditional explosive TNT (1.22 kJ g-1) and the reported ECP AgMtta (HMtta = 5-methyl-1H-tetrazole, ΔHdet = 1.32 kJ g-1). Furthermore, sensitivity testing demonstrates that 1-4 features low mechanical sensitivity to external mechanical action in contrast with the extremely sensitive azide-based ECPs [Cu3(2-MAT)2(N3)6]n. In addition, compound 2 shows hypergolic properties via an 'oxidizer-fuel' drop experiment, demonstrating its application prospects in the field of propellants. This work details an approach of synthesizing multipurpose ECPs with reliable stabilities by introducing mild dicyanamide anions into nitrogen-rich skeletons.

Two d10 2D Cathode-Ray Scintillation Coordination Polymers with High Efficiency and High-Voltage Stability.

Two examples of efficient cathode-ray scintillation coordination polymers with good stability at high voltage were prepared by conjugating luminescent groups with d10 metal ions. The synergistic effect of inorganic metal and organic ligand suppresses the self-quenching of the conjugated luminescent groups and enhances the scintillation performance. This work provides new ideas for the design of new field-emission displays and cathode-ray scintillation materials.

Heat-resistant Pb(ii)-based X-ray scintillating metal-organic frameworks for sensitive dosage detection via an aggregation-induced luminescent chromophore.

The synergy of unusual X-aggregation induced luminescent chromophores and heavy Pb(ii) ions has facilitated excellent X-ray scintillation of two structurally similar Pb-SMOFs, which are heat-resistant due to solvent-free lattices. Owing to their higher Pb(ii) contents, Pb-SMOFs with larger X-ray absorption coefficients are more sensitive for X-ray dosage detection than powdered CsPbBr3.

Calcium-based efficient cathode-ray scintillating metal-organic frameworks constructed from π-conjugated luminescent motifs.

Efficient cathode-ray scintillating metal-organic frameworks are constructed from a π-conjugated luminescent motif and light Ca(ii) ions. The luminescence self-quenching pathway has been effectively hindered through coordination. In situ vacuum ultraviolet fluorescent spectra have shown the excitons recombining in the scintillation process for the first time.

Highly Stable Energetic Coordination Polymer Assembled with Co(II) and Tetrazole Derivatives.

A solvothermal reaction of Co(CH3COO)2·4H2O and 5-mercapto-1-methyl-tetrazole (Hmmtz) in methanol (MeOH) yielded a one-dimensional solvent-free energetic coordination polymer, namely, [Co(mmtz)2] n 1, which was structurally characterized. The enthalpy of formation (Δf H°) of 1 (907 kJ mol-1) is much larger than that of commercial 2,4,6-trinitrotoluene (-59 kJ mol-1). The impact sensitivity and the friction sensitivity are greater than 40 J and 360 N, respectively, indicating that compound 1 exhibits a potential application as a safe explosive. Temperature-dependent molar magnetic susceptibilities show that weak antiferromagnetic behavior exists in 1.

Efficient X-ray scintillating lead(ii)-based MOFs derived from rigid luminescent naphthalene motifs.

Solid-state X-ray scintillators are widely applied in medical imaging and space exploration. However, it is still a great challenge to probe into the intrinsic nature of scintillating behaviour due to the ambiguous structure-function relationship. Herein, four structure-defined X-ray scintillating Pb(ii)-based metal-organic frameworks (SMOFs) were successfully obtained under solvothermal conditions, [Pb(1,4-ndc)(DMF)]n (SMOF-1), [Pb(1,4-ndc)(DMA)]n (SMOF-2), [Pb2(2,6-ndc)2(H2O)]n·nDMF (SMOF-3) and [Pb4(2,6-ndc)3Cl2]n (SMOF-4), where 1,4-H2ndc = 1,4-naphthalene dicarboxylate, 2,6-H2ndc = 2,6-naphthalene dicarboxylate, DMF = N,N-dimethylformamide, and DMA = N,N-dimethylacetamide. SMOFs 1-4 show scintillating signals under X-rays triggered by a highly purified tungsten target. Compared with SMOFs 1-3, SMOF-4 exhibits excellent scintillating performance owing to its solvent-free and denser structure, which favours more efficient conversion ability of X-rays to visible light. X-ray stimulated luminescence (XSL) spectra present multiple emission peaks, which is further confirmed by wavelength-dependent luminescence spectra under UV-Vis light, and density of state and DFT calculations. The synergistic effects of heavy metal Pb(ii) centres as effective X-ray absorbers and organic ligands as luminescent motifs endow these Pb(ii)-based MOFs with application prospects in X-ray detection.

Nitrogen-Rich Tetranuclear Metal Complex as a New Structural Motif for Energetic Materials.

For designing energetic materials (EMs), the most challenging issue is to achieve a balance between energetic performance and reliable stability. In this work, we employed an efficient and convenient method to synthesize a new class of EMs: nitrogen-rich tetranuclear metal complexes [M(Hdtim)(H2O)2]4 (M = Zn 1, Mn 2; H3dtim = 1H-imidazol-4,5-tetrazole) with the N content of >46%. The structural analyses illustrate that isomorphous compounds 1 and 2 feature isolated hollow ellipsoid tetranuclear units, which are linked by both π-π interactions and hydrogen-bonding interactions to give a 3D supramolecular architecture. Compounds 1 and 2 exhibit prominent energetic characteristics: excellent detonation performances and reliable thermal, impact, and friction stabilities. Being nitrogen-rich tetrazolate compounds, the enthalpies of combustion of 1 (-11.570 kJ g-1) and 2 (-12.186 kJ g-1) are higher than those of classical EMs, RDX and HMX, and they possess high positive heats of formation. Sensitivity tests demonstrate that 1 and 2 are insensitive to external mechanical action. Excellent energetic performances and low sensitivities promote 1 and 2 to serve as a new class of promising EMs with a desirable level of safety.

Grinding size-dependent mechanoresponsive luminescent Cd(ii) coordination polymer.

In this work, we report a new mechanoresponsive luminescent Cd(ii) coordination polymer that exhibits a sensitivity to mechanical stimulation. The luminescence colour changed gradually from weak yellowish-green to bright cyan in response to different grinding sizes, thereby showing interesting mechanochromic properties, namely a grinding-enhanced luminescence and good crystalline maintenance ability.

Tetrazole-Viologen-based Flexible Microporous Metal-Organic Framework with High CO2 Selective Uptake.

A flexible metal-organic framework (FMOF) with functionalized pores was hydrothermally synthesized to improve CO2 affinity and selectivity. The obtained FMOF exhibits a reversible shrinking and swelling framework transformation, which is triggered by the adsorption of CO2 rather than by the adsorption of N2 and CH4. At ambient temperature and an atmospheric pressure, this FMOF shows not only a high CO2 uptake (98 cm(3) g(-1), 19.3 wt %) but also a good calculated adsorption selectivity for CO2 over both CH4 and N2 (CO2/CH4 50:50 v/v: 28.6:1, CO2/N2 15:85 v/v: 210.4:1 calculated by ideal adsorbed solution theory), indicating potential applications in the purification of natural gas and industrial flue gas.

Color tunable and near white-light emission of two solvent-induced 2D lead(II) coordination networks based on a rigid ligand 1-tetrazole-4-imidazole-benzene.

Two new lead(II) coordination polymers, [Pb(NO3)(tzib)]n (1) and [Pb(tzib)2]n (2), were successfully synthesized from the reaction of a rigid ligand 1-tetrazole-4-imidazole-benzene (Htzib) and lead(II) nitrate in different solvents. The obtained polymers have been characterized by single-crystal X-ray diffraction analyses, which show that both polymers feature 2D layer structures. The inorganic anion nitrate in 1 shows a µ2-κO3:κO3 bridging mode to connect adjacent lead ions into a zigzag chain, and then the organic ligands tzib(-) join the neighboring chains into a 2D layer by a µ3-κN1:κN2:κN6 connection mode. In 2, there are two different bridging modes of the tzib(-) ligand: µ3-κN1:κN2:κN6 and µ3-κN1:κN6 to coordinate the lead ions into a 2D layer structure. Interestingly, both polymers displayed broadband emissions covering the entire visible spectra, which could be tunable to near white-light emission by varying excitation wavelengths.

Intense photo- and tribo-luminescence of three tetrahedral manganese(II) dihalides with chelating bidentate phosphine oxide ligand.

Three air-stable tetrahedral manganese(ii) dihalide complexes [MnX2(DPEPO)] (DPEPO = bis[2-(diphenylphosphino)phenyl]ether oxide; X = Cl, Br and I) were prepared. All of the obtained compounds were structurally characterized by single-crystal X-ray diffraction analyses, which reveal that they crystallize in centrosymmetric space groups and feature an isolated mononuclear structure with Mn(2+) in a tetrahedral environment. Interestingly, these complexes show excellent photoluminescent performance in neat solid form, with the highest total quantum yield (Φtotal) of up to 70% recorded for the dibromide complex. Intense green flashes of light could be observed by the naked eye when rubbing the manganese(ii) complexes.

Homochiral zinc(II) coordination compounds based on in-situ-generated chiral amino acid-tetrazole ligands: circular dichroism, excitation light-induced tunable photoluminescence, and energetic performance.

We employed two pairs of new in-situ-generated chiral amino acid-tetrazole ligands in constructing homochiral Zn(II) coordination compounds: [Zn(tzet)]n (1a for (S)-tzet and 1b for (R)-tzet, H2tzet = N-[2-(1H-tetrazol-5-yl)ethyl]tryptophan) and [Zn(tzep)(H2O)2]·H2O (2a for (S)-tzep and 2b for (R)-tzep, H2tzep = N-[2-(1H-tetrazol-5-yl)ethyl]proline), which were hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Structural analysis reveals that 1 features a 2D homochiral framework generated by both tetrazolate and carboxylate bridges in tzet(2-) ligands. The isolated structure of 2 is stabilized by extensive hydrogen bonds, which leads to formation of a supramolecular 2D architecture. The absolute configuration induced at the nitrogen atoms of 1 and 2 is strictly related to the neighboring chiral carbon atoms by hydrogen-bond interactions. To further investigate their chirality, the combined experimental and theoretical analyses of circular dichroism spectra reveal the absolute configurations and nature of the Cotton effects. Solid-state excitation and emission spectra for 1 and 2 at room temperature were investigated with relevant density of states calculation, and tunable photoluminescence emission of 1 under different excitation wavelengths was discussed. As nitrogen-rich tetrazolate compounds, 1 and 2 possess higher enthalpies of combustion and may serve as a new family of promising energetic materials.

catena-Poly[di-µ(1,1)-azido-(1,10-phenanthroline)cadmium(II)].

The asymmetric unit of the title Cd(II) compound, [Cd(N(3))(2)(C(12)H(8)N(2))](n), contains a Cd(II) atom, located on a twofold axis passing through the middle of the phenanthroline mol-ecule, one azide ion and half of a 1,10-phenanthroline mol-ecule. The Cd(II) atom exhibits a distorted octa-hedral coordin-ation including one chelating 1,10-phenanthroline ligand and four azide ligands. The crystal structure features chains along the c direction in which azide groups doubly bridge two adjacent Cd(II) atoms in an end-on (EO) mode. Inter-chain π-π stacking inter-actions, with centroid-centroid separations of 3.408 (2) Šbetween the central aromatic rings of 1,10-phenanthroline mol-ecules, lead to a supra-molecular sheet parallel to the bc plane.

A direct white-light-emitting metal-organic framework with tunable yellow-to-white photoluminescence by variation of excitation light.

A direct white-light metal-organic framework (MOF), [AgL](n) x nH(2)O (1, L = 4-cyanobenzoate), obtained by the reaction of deprotonated 4-cyanobenzoic acid and AgNO(3) in water, was found to exhibit tunable yellow-to-white photoluminescence by variation of excitation light. Interestingly, the close pure white emission of 1 has CIE-1931 chromaticity coordinates of (0.33, 0.34) when excited by 349-nm UV light, which is compatible to the light output of the deep UV LED.

A novel metal-organic network with high thermal stability: nonlinear optical and photoluminescent properties.

A novel zinc(II) 4-(5H-tetrazol)benzoic coordination polymer with an in situ generated tetrazole ligand exhibits the gsi (gamma-silicon) topology and high thermal stability; this compound possesses second-order nonlinear optical and interesting heat-induced photoluminescent properties.