Dia Topology Research Articles

Ionic Covalent Organic Frameworks Consisting of Tetraborate Nodes and Flexible Linkers.

Covalent organic frameworks (COFs) have emerged as versatile materials with many applications, such as carbon capture, molecular separation, catalysis, and energy storage. Traditionally, flexible building blocks have been avoided due to their potential to disrupt ordered structures. Recent studies have demonstrated the intriguing properties and enhanced structural diversity achievable with flexible components by judicious selection of building blocks. This study presents a novel series of ionic COFs (ICOFs) consisting of tetraborate nodes and flexible linkers. These ICOFs use borohydrides to irreversibly deprotonate the alcohol monomers to achieve a high degree of polymerization. Structural analysis confirms the dia topologies. Reticulation is explored using various monomers and metal counterions. Also, these frameworks exhibit excellent stability in alcohols and coordinating solvents. The materials have been tested as single-ion conductive solid-state electrolytes. ICOF-203-Li displays one of the lowest activation energies reported for ion conduction. This tetraborate chemistry is anticipated to facilitate further structural diversity and functionality in crystalline polymers.

Influence of Metal Ions on the Structural Complexity of Mixed-Ligand Divalent Coordination Polymers

The reactions of the angular ligand 4,4′-oxybis(N-(pyridin-3-yl)benzamide) (L1) and 1,4-naphthalenedicarboxylic acid (1,4-H2NDC) with divalent metal salts yielded three distinct coordination polymers (CPs): {[Zn2(L1)(1,4-NDC)2]·MeOH}n, 1, {[Cu(L1)(1,4-NDC)(H2O)]·3H2O}n, 2, and {[Cd(L1)(1,4-NDC)]·2H2O}n, 3. Complex 1 features a 2-fold interpenetrated 3D framework with the (412·63)-pcu topology, while complex 2 reveals a 1D triple-strained helical chain and complex 3 displays a 3-fold interpenetrated 3D framework with (66)-dia topology. Additionally, the reactions of the flexible ligand N,N′-bis(3-methylpyridyl) adipoamide (L2) afforded {[Co4(L2)0.5(1,4-NDC)3(H2O)3(µ3-OH)2]·EtOH·2H2O}n, 4, {[Zn2(L2)(1,4-NDC)2]·2CH3OH}n, 5, and [Cd(L2)(adipic)(H2O)]n (H2adipic = adipic acid), 6, exhibiting a self-catenated 3D framework with the (420·68)-8T32 topology, a 2D layer with the (413·62) − (4,4)IIb topology, and a 2D layer with the (44·62)-sql topology, respectively. The structural diversity observed in complexes 1–6 highlights the pivotal influence of the metal center on the degree of entanglement in CPs within mixed-ligand systems. The thermal stability and luminescent properties of complexes 1–3, 4, and 6 are also discussed.

Tailoring body center tetragonal allotropes Cx (x = 8, 12, 16, 20) with C(sp3) and hybrid C(sp3)/C(sp2): Crystal chemistry and ab initio investigations of the physical properties

Based on literature tetragonal ths topology C8 characterized by trigonal C(sp2), selective insertions of carbon induce large structural changes leading to C(sp3) C12 with dia topology after geometry optimizations to ground state structure using calculations within the quantum density functional theory DFT. Further crystal engineering operated on C12 lead to complete the series with novel C16 and C20. Such allotropes respectively characterized by ene (C=C) and propadiene (C=C=C) -like units beside C4 tetrahedra reveal hybrid C(sp3)/C(sp2) with complex stc topology. Alike ths C8, all three allotropes (C12, C16, and C20) identified in high symmetry I41/amd (No. 141) space group are cohesive with larger magnitude for C12 than for ths C8 and close energies for C16 and C20. Mechanical properties show diamond-like Vickers hardness HV for C12 (HV = 95 GPa) and smaller magnitudes for mixed C(sp3)/C(sp2) C16 (HV = 26 GPa) and C20 (HV = 47 GPa), noting that C8 with C(sp2) was found with the largest compressibility with HV = 19 GPa. Dynamically, all allotropes are stable from positive phonon acoustic and optic frequencies with the largest frequency magnitudes for C16 and C20 corresponding to CC and C=C=C vibrations respectively. Thermodynamically, the temperature changes of the specific heat CV show close agreement with diamond experimental values for C12 and larger magnitudes for the three other allotropes. Electronic band structure analyses reveal conductive C8 and C16, insulating C12 with a large band gap close to diamond's and semi-conducting C20 with small band gap.

Supramolecular Entanglement in a Hydrogen‐Bonded Organic Framework Enables Flexible‐Robust Porosity for Highly Efficient Purification of Natural Gas

AbstractThe development of porous materials with flexible‐robust characteristics shows some unique advantages to target high performance for gas separation, but remains a daunting challenge to achieve so far. Herein, we report a carboxyl‐based hydrogen‐bonded organic framework (ZJU‐HOF‐8a) with flexible‐robust porosity for efficient purification of natural gas. ZJU‐HOF‐8a features a four‐fold interpenetrated structure with dia topology, wherein abundant supramolecular entanglements are formed between the adjacent subnetworks through weak intermolecular hydrogen bonds. This structural configuration could not only stabilize the whole framework to establish the permanent porosity, but also enable the framework to show some flexibility due to its weak intermolecular interactions (so‐called flexible‐robust framework). The flexible‐robust porosity of ZJU‐HOF‐8a was exclusively confirmed by gas sorption isotherms and single‐crystal X‐ray diffraction studies, showing that the flexible pore pockets can be opened by C3H8 and n‐C4H10 molecules rather by C2H6 and CH4. This leads to notably higher C3H8 and n‐C4H10 uptakes with enhanced selectivities than C2H6 over CH4 under ambient conditions, affording one of the highest n‐C4H10/CH4 selectivities. The gas‐loaded single‐crystal structures coupled with theoretical simulations reveal that the loading of n‐C4H10 can induce an obvious framework expansion along with pore pocket opening to improve n‐C4H10 uptake and selectivity, while not for C2H6 adsorption. This work suggests an effective strategy of designing flexible‐robust HOFs for improving gas separation properties.

Luminescence sensing for nitroaromatics of a two-fold interpenetrating znic based metal-organic framework

A zinc based metal-organic framework (MOF), namely, {Zn(L)·2H2O}n (1) {H2L = 4-(3,5-dicarboxyphenyl)-4,2′:6′,4′'-terpyridine}, has been successfully assembled in a hydrothermal environment. The single-crystal X-ray diffraction demonstrate that the structure of complex 1 features a two-fold interpenetrating diamond-like 3D network with four-connected dia topology. Luminescent sensing research shows that 1 can selectively detect nitro-aromatic compounds (NACs), especially for 4-nitroaniline (4-NA) that with high quenching constant (KSV = 1.66 × 104 M−1) and low limit of detection (LOD: 36.97 μM). The sensing mechanism of NACs by 1 may come from the resonance energy transfer (RET) between substrate and sensor; however, for 4-NA, 2-NP, and 4-NP, photo-induced electron transfer (PET) also exists. Importantly, after five cycles detection test the sensing capability of 1 does not exhibit significant decrease confirms that 1 possesses high stability and good recyclability.

High-Pressure Phases of Boron Pnictides BX (X = As, Sb, Bi) with Quartz Topology from First Principles

The superdense hexagonal boron pnictides BX (X = As, Sb, Bi), whose structures are formed by distorted tetrahedra and characterized by a quartz-derived (qtz) topology, have been predicted from first principles as potential high-pressure phases. From full geometry structure relaxation and ground state energy calculations based on quantum density functional theory (DFT), qtz BX was found to be mechanically (elastic constants) and dynamically (phonons) stable. From the energy–volume equations of state, at high but experimentally accessible pressures, qtz boron pnictides were found to be more energetically favorable than corresponding cubic zinc–blende phases with diamond-like (dia) topology. According to the electronic band structures, the zinc–blende BX have larger band gaps than the qtz phases, which can be attributed to the higher covalence of the latter. A metallic behavior is only observed for qtz BBi, which is related to the dynamic instability as it follows from the phonon band structure.

Two 3D Zn(II)/Co(II)-CPs as fluorescent sensors for turn-on and red-shift sensing of tryptophan and norfloxacin

Two three-dimensional (3D) coordination polymers (CPs), namely {[M(seb)(bbimb)]·3H2O}n (M = Zn for 1; Co for 2), were obtained via hydrothermal method using sebacic acid (H2seb) mixed with 1,4-bis(benzoimidazol-1-yl)butane (bbimb). The structures of 1 and 2 both display as 3D frameworks with a 5-fold interpenetrating dia topology. CPs 1 and 2 both exhibit excellent luminescent properties and good water stability. Fluorescence sensing experiments demonstrate that 1 and 2 both can selectively detect tryptophan (Trp) and norfloxacin (Nor) in aqueous solution through turn-on and red-shift effect with remarkable anti-interference ability and low detection limits. The limits of detection (LOD) toward Trp-and Nor are 0.07 μM, 0.08 μM for 1 and 0.41 μM, 0.11 μM for 2. In addition, theoretical calculations and different detection methods were utilized to thoroughly investigate the potential sensing mechanisms for Trp-and Nor. Importantly, 1 and 2 represent two rare examples for sensing both Trp-and Nor via turn-on and red-shift effects. The fluoresence test films of 1 and 2 were prepared which can detect Trp-and Nor quickly with naked eye.

Self-correcting mismatches in metastable hydrogen-bonded organic frameworks with an 11-fold interpenetrated array.

The polymorphic self-correction from a metastable phase to a stable one often occurs and plays crucial roles in synthesizing robust hydrogen-bonded organic frameworks (HOFs). However, identifying metastable phases and understanding the self-correcting mechanisms is a challenging venture due to their intrinsic instability. Here, we for the first time introduce 1,8-naphtholactam (Np) as a hydrogen-bonding synthon positioned on the periphery of a bicarbazole to create a versatile molecular unit for 3D HOFs. The as-synthesized NCU-HOF1, analyzed by single-crystal X-ray diffraction (SCXRD), is found to be metastable. It exhibits an 11-fold interpenetrated dia topology with a quarter of the Np units exhibiting monomeric N-H⋯O interactions between adjacent Np link sites, which readily self-correct upon desolvation to form fully dimeric ones. Consequently, the resultant NCU-HOF1a becomes highly robust in polar solvents, strong acid or alkaline aqueous solutions, and has permanent porosity with contracted cavities for selective adsorption and efficient "turn-up" fluorescent sensing of C2H4 gas. This work not only debuts a new hydrogen-bonding synthon but offers more insights into investigating solid-state dynamics in metastable HOFs.

Nonlinear and Emissive {[MIII(CN)6]3-···Polyresorcinol} (M = Fe, Co, Cr) Cocrystals Exhibiting an Ultralow Frequency Raman Response.

Optically active functional noncentrosymmetric architectures might be achieved through the combination of molecules with inscribed optical responses and species of dedicated tectonic character. Herein, we present the new series of noncentrosymmetric cocrystal salt solvates (PPh4)3[M(CN)6](L)n·msolv (M = Cr(III), Fe(III), Co(III); L = polyresorcinol coformers, multiple hydrogen bond donors: 3,3',5,5'-tetrahydroxy-1,19-biphenyl, DiR, n = 2, or 5'-(3,5-dihydroxyphenyl)-3,3″,5,5″-tetrahydroxy-1,19:3',1″-terphenyl, TriRB, n = 1) denoted as MDiR and MTriRB, respectively. The hydrogen-bonded subnetworks {[M(CN)6]3-;Ln}∞ of dmp, neb, or dia topology are formed through structural matching between building blocks within supramolecular cis-bis(chelate)-like {[M(CN)6]3-;(H2L)2(HL)2} or tris(chelate)-like {[M(CN)6]3-;(H2L)3} fragments. The quantum-chemical analysis demonstrates the mixed electrostatic and covalent character of these interactions, with their strength clearly enhanced due to the negative charge of the hydrogen bond acceptor metal complex. The corresponding interaction energy is also dependent on the geometry of the contact and size matching of its components, rotational degree of freedom and extent of the π-electron system of the coformer, and overall fit to the molecular surroundings. Symmetry of the crystal lattices is correlated with the local symmetry of coformers and {complex;(coformer)n} hydrogen-bonded motifs characterized by the absence of the inversion center and mirror plane. All compounds reveal second-harmonic generation activity and photoluminescence diversified by individual UV-vis spectral characteristics of the components, and interesting low-frequency Raman scattering spectra within the subterahertz spectroscopic domain. Vibrational (infrared/Raman), UV-vis electronic absorption (experimental and calculated), and 57Fe Mössbauer spectra together with electrospray ionization mass spectrometry (ESI-MS) data are provided for the complete description of our systems.

Superdense Hexagonal BP and AlP with Quartz Topology: Crystal Chemistry and DFT Study

The superdense hexagonal phosphides BP and AlP, whose structures are formed by distorted tetrahedra and characterized by quartz-derived (qtz) topology, were predicted from crystal chemistry and first principles as potential high-pressure phases. From full geometry structure relaxations and ground state energy calculations based on quantum density functional theory (DFT), qtz BP and AlP were found to be less cohesive than the corresponding cubic zinc-blende (zb) phases with diamond-like (dia) topology, but were confirmed to be mechanically (elastic constants) and dynamically (phonons) stable. From the energy–volume equations of state, qtz phases were found to be energetically favorable at small volumes (high pressures), with zb-to-qtz transition pressures of 144 GPa for BP and 28 GPa for AlP. According to the electronic band structures and the site projected density of states, both phosphides exhibit larger band gaps of the zinc-blende phases compared to the qtz phases; the smaller values for the latter result from the smaller volumes per formula unit, leading to increased covalence.

Experimental Investigation of Thermodynamic Stabilization in Boron Imidazolate Frameworks (BIFs) Synthesized by Mechanochemistry.

This study experimentally explores the energetics for the formation of boron-imidazolate frameworks (BIFs), which are synthesized by mechanochemistry. The topologically similar frameworks employ the same tetratopic linker based on tetrakis(imidazolyl)boric acid but differ in the monovalent cation metal nodes. This permits assessment of the stabilizing effect of metal nodes in frameworks with sodalite (SOD) and diamondoid (dia) topologies. The enthalpy of formation from endmembers (metal oxide and linker), which define thermodynamic stability of the structures, has been determined by use of acid solution calorimetry. The results show that heavier metal atoms in the node promote greater energetic stabilization of denser structures. Overall, in BIFs the relation between cation descriptors (ionic radius and electronegativity) and thermodynamic stability depends on framework topology. Thermodynamic stability increases with the metallic character of the cation employed as the metal node, independent of the framework topology. The results suggest unifying aspects for thermodynamic stabilization across MOF systems.

A luminescent anionic Cadmium(II)-MOF for the detection of nitrophenol compounds and metal ions in an aqueous solution

An anionic MOF, namely, {(CH3)2NH2)2[Cd(µ4-PPTA)]·DMF·7H2O}n (1) was synthesized with 4,4′,4″,4‴-(1,4-phenylenbis(pyridine-4,2,6-triyl))tetrabenzoic acid (H4PPTA) and characterized. X-ray results showed that 1 had a four-fold interpenetrating 3D framework with dia topology and the charged balance was provided by dimethylamine cations in the framework. Due to the high emission property and stability of 1 in water, the luminescence detections of nitroaromatic compounds and metal ions were performed with 1. 1 could detect the nitrophenol compounds and metal ions in water via luminescence quenching. The detection limits were 6.84 µM for 4-nitrophenol (NP), 1.85 µM for 2,4-dinitrophenol (DNP) and 2.76 µM for 2,4,6-trinitrophenol (TNP) and 94.4 µM for Al3+, 66 µM for Cr3+, 18.3 µM for Fe3+ and 27.6 µM for Cu2+. The detections of the nitrophenol compounds by 1 were due to hydrogen bonding interaction and resonance energy transfer. Moreover, the detections of metal ions by 1 were assigned to competitive absorption and electrostatic interactions with the anionic framework.

Non‐Interpenetrated 3D Covalent Organic Framework with Dia Topology for Au Ions Capture

AbstractThe 3D covalent organic frameworks (COFs) have attracted considerable attention owing to their unique structural characteristics. However, most of 3D COFs have interpenetration phenomena, which will result in decreased surface area and porosities, and thus limited their applications in molecular/gas capture. Developing 3D COFs with non‐fold interpenetration is challenging but significant because of the existence of non‐covalent interactions between the adjacent nets. Herein, a new 3D COF (BMTA‐TFPM‐COF) with dia topology and non‐fold interpenetration for Au ion capture is first demonstrated. The constructed COF exhibits a high Brunauer–Emmett–Teller surface area of 1924 m2 g−1, with the pore volume of 1.85 cm3 g−1. The high surface area and abundant cavities as well as the abundant exposed CN linkages due to the non‐interpenetration enable to absorb Au3+ with high capacity (570.18 mg g−1), selectivity (99.5%), and efficiency (68.3% adsorption of maximum capacity in 5 min). This work provides a new strategy to design 3D COFs for ion capture.

Two Cd(II)-MOFs containing pyridylbenzimidazole ligands as fluorescence sensors for sensing enrofloxacin, nitrofurazone and Fe3+

Two Cd(II) metal-organic frameworks (MOFs), namely, [Cd(L1)(1,4-NDA)]n (1) and [Cd2(L2)(TDCA)2(H2O)2·0.5CH3CN]n (2) (L1 = 1,4-bis(1-(piperidin-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)butane, L2 = 1,4-bis(5,6-dimethyl-1-(pyridin-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)butane, 1,4-H2NDA = 1,4-naphthalenedicarboxylic acid, H2TDCA = 2,5 thiophenedicarboxylic acid) were synthesized and characterized. 1 exhibits a 3D dia topology and 2 shows an unprecedented 3D new topology, respectively. Both 1 and 2 behave remarkable chemical stabilities and can be used as good fluorescence sensors for the sensing of Fe3+ with high sensitivity and selectivity. 1 and 2 have shown fluorescent detection capabilities for enrofloxacin and nitrofurazone, which are rarely reported in previous literature. Furthermore, the mechanism of fluorescence quenching was explained.

Exploring the phase stability in interpenetrated diamondoid covalent organic frameworks

Soft porous crystals, which are responsive to external stimuli such as temperature, pressure, or gas adsorption, are being extensively investigated for various technological applications. However, while substantial research has been devoted to stimuli-responsive metal-organic frameworks, structural flexibility in 3D covalent organic frameworks (COFs) remains ill-understood, and is almost exclusively found in COFs exhibiting the diamondoid (dia) topology. Herein, we systemically investigate how the structural decoration of these 3D dia COFs—their specific building blocks and degree of interpenetration—as well as external triggers such as temperature and guest adsorption may promote or suppress their phase transformations, as captured by a collection of 2D free energy landscapes. Together, these provide a comprehensive understanding of the necessary conditions to design flexible diamondoid COFs. This study reveals how their flexibility originates from the balance between steric hindrance and dispersive interactions of the structural decoration, thereby providing insight into how new flexible 3D COFs can be designed.

Solvent-free synthesis of magnesium phosphite-oxalates that show second-harmonic generation responses.

Two new magnesium phosphite-oxalates were prepared under solvent-free conditions using different amines as structure-directing agents. They feature noncentrosymmetric structures with sql and dia topologies, respectively. The two compounds show moderate second-harmonic generation (SHG) responses under 1064 nm laser irradiation. Theoretical calculations were performed to reveal the origin of their SHG responses.

Supramolecular isomerism and structural flexibility in coordination networks sustained by cadmium rod building blocks.

Bifunctional N-donor carboxylate linkers generally afford dia and sql topology coordination networks of general formula ML2 that are based upon the MN2(CO2)2 molecular building block (MBB). Herein, we report on a new N-donor carboxylate linker, β-(3,4-pyridinedicarboximido)propionate (PyImPr), which afforded Cd(PyImPr)2via reaction of PyImPrH with Cd(acetate)2·2H2O. We observed that, depending upon whether Cd(PyImPr)2 was prepared by layering or solvothermal methods, 2D or 3D supramolecular isomers, respectively, of Cd(PyImPr)2 were isolated. Single crystal X-ray diffraction studies revealed that both supramolecular isomers are comprised of the same carboxylate bridged rod building block, RBB. We were interested to determine if the ethylene moiety of PyImPr could enable structural flexibility. Indeed, open-to-closed structural transformations occurred upon solvent removal for both phases, but they were found to be irreversible. A survey of the Cambridge Structural Database (CSD) was conducted to analyse the relative frequency of RBB topologies in related ML2 coordination networks in order to provide insight from a crystal engineering perspective.

A 3D rare cubane-like tetramer Cu(II)-based MOF with 4-fold dia topology as an efficient photocatalyst for dye degradation

A three dimensional (3D) rare cubane-like tetrameric Cu(II)-based MOF 1 having formula [Cu4(O)(OH)3(bb)4(NO3)30.3 H2O·3CH3CN]n (bb = 4,4'-bis (imidazolyl) biphenyl) has been synthesized and characterized. The MOF 1 possess 4-fold dia topology and effectively catalyzes the photodegradation of basic green (BG), rhodamine B (RhB), methyl blue (MB) and methyl orange (MO) dyes under UV light irradiation. The effects of initial solution pH, concentration of dyes, and photocatalyst dose have been monitored on the photocatalytic performance of 1. The photocatalytic results suggest that MOF 1 exhibits best photocatalytic activity for BG amongst all the four dyes investigated. Under the optimal reaction condition, ∼96.8 % photodegradation of BG has been observed at pH 5, at 40 ppm concentration of BG and 30 mg photocatalyst concentration in 120 min time span. The radical trapping experiments suggest that O2·− and·OH are the main active species that catalyzes the photodecomposition of dyes. The possible mechanism for the BG degradation of 1 is proposed using density of states (DOS) calculations and Hirshfeld surface analysis.

Two new Zn(II) and Cd(II)-based metal-organic frameworks constructed from pamoic acid and N-donor co-ligands

Two new Zn(II) and Cd(II)-based metal-organic compounds, namely [Zn(pam)(bpe)]n (1) and [Cd(pam)(bib)(H2O)2]n·n(DMF) (2) (H2pam = pamoic acid, bpe = 1,2-bis(4-pyridyl)ethylene, bib = 1,4-bis(imidazole-1-yl)butane), have been synthesized by the self-assembly of metal ions, pamoic acid, as well as N-donor co-ligands under hydrothermal or solvothermal conditions. X-ray diffraction analyses revealed that compound 1 is a 4-fold interpenetrated 3D framework, representing a 4-connected dia topology, and compound 2 shows a 2D layer structure with 4-connected sql topology. The luminescent properties of these two compounds were also investigated.

Syntheses of tetrahedral imidazolate frameworks with auxiliary ligand in DMSO

In our former work, we developed one kind of new tetrahedral imidazolate frameworks (TIF-Ax) by adding auxiliary uninegative linker into the zinc-imidazolate assembly in amide. Herein, a series of new compounds (TIF-A4 to TIF-A8) were obtained from imidazolate derivatives and Zinc acetate (acetate as auxiliary ligands) in dimethyl sulfoxide (DMSO). Among them, Zn centers were coordinated by imidazolate derivatives to form 1D chain, differently, TIF-A4 exhibited 3D framework with dia topology and TIF-A5 to TIF-A8 were 4-connected layer with sql topology. These results suggested that DMSO was a good solvent for the syntheses of new TIF-Ax. These compounds were characterized by single crystal XRD, powder XRD, FTIR and TG. In addition, the fluorescence of them were also tested.