Anionic Framework Research Articles

Cation Charge as a Tool to Change Dimensionality in Organic–Inorganic Hybrids Based on Copper Thiocyanate Templated by 1,4-Diazabicyclo[2.2.2]octane

The first three compounds based on a {copper-thiocyanate-dabco} combination, namely, (Hdabco)[Cu2(NCS)3] (1), (H2dabco)[Cu(NCS)3] (2), and [Cu(Hdabco)2(NCS)4]∙2dmso (3), where dabco = 1,4-diazabicyclo[2.2.2]octane were synthesized and characterized by single-crystal XRD, elemental analysis, Raman, and partial IR spectroscopy. In copper(I) derivatives, the influence of the charge of the organic cation on the dimensionality of the crystal structure is observed. Thus, in the case of 1, monoprotonated Hdabco+ cations provide the template for the formation of a polymeric anionic 3D framework {[Cu2(NCS)3]-}n, while in the case of 2, diprotonated H2dabco2+ cations together with discrete [Cu(SCN)3]2- anions generate a simple ionic 0D structure with an island-like crystal lattice. The anionic {[Cu2(SCN)3]-}n framework has infinite square channels of 10 × 10 Å size running along the 001 crystallographic direction. In 3, both the Hdabco+ and thiocyanato units behave as terminal monodentate ligands attached to copper(II) centers via N-donor atoms, forming neutral molecular complexes with an elongated (4+2) octahedral environment. The crystallization molecules of dmso are hydrogen bonded to the protonated parts of the coordinated dabco molecules. A series of by-products Cu(SCN)2(dmso)2 (4), (Hdabco)SCN (5), (H2dabco)(SCN)2 (6), and (H2dabco)(SCN)2∙H2O (7) were identified and characterized.

The Tetrel Bond and Tetrel Halide Perovskite Semiconductors.

The ion pairs [Cs+•TtX3-] (Tt = Pb, Sn, Ge; X = I, Br, Cl) are the building blocks of all-inorganic cesium tetrel halide perovskites in 3D, CsTtX3, that are widely regarded as blockbuster materials for optoelectronic applications such as in solar cells. The 3D structures consist of an anionic inorganic tetrel halide framework stabilized by the cesium cations (Cs+). We use computational methods to show that the geometrical connectivity between the inorganic monoanions, [TtX3-]∞, that leads to the formation of the TtX64- octahedra and the 3D inorganic perovskite architecture is the result of the joint effect of polarization and coulombic forces driven by alkali and tetrel bonds. Depending on the nature and temperature phase of these perovskite systems, the Tt···X tetrel bonds are either indistinguishable or somehow distinguishable from Tt-X coordinate bonds. The calculation of the potential on the electrostatic surface of the Tt atom in molecular [Cs+•TtX3-] provides physical insight into why the negative anions [TtX3-] attract each other when in close proximity, leading to the formation of the CsTtX3 tetrel halide perovskites in the solid state. The inter-molecular (and inter-ionic) geometries, binding energies, and charge density-based topological properties of sixteen [Cs+•TtX3-] ion pairs, as well as some selected oligomers [Cs+•PbI3-]n (n = 2, 3, 4), are discussed.

A sulfonate-functionalized covalent organic framework for record-high adsorption and effective separation of organic dyes

The emerging global water crisis necessitates the development of solid adsorbents for the removal of organic pollutants from wastewater. Herein, we develop an anionic sulfonate-functionalized covalent organic framework (COF), termed TpStb-SO3Na, by the Schiff-base condensation between 2,4,6-triformylphloroglucinol (Tp) and 4,4′-diaminostilbene-2,2′-disulfonic acid (Stb-SO3H) under solvothermal conditions in the presence of sodium acetate. Thanks to the dense sulfonate groups in the periodic one-dimensional channels, the negatively charged TpStb-SO3Na displayed rapid kinetics (average ∼ 99% uptake in merely 10 min) and ultrahigh adsorption capacities for multiple cationic dyes including methylene blue (MB, 1078 mg g−1), crystal violet (CV, 1861 mg g−1), malachite green (MG, 5857 mg g−1) and janus green B (JGB, 1339 mg g−1) at room temperature. Noteworthy, the adsorption capacities of TpStb-SO3Na toward CV, MG, and JGB were the record-high values among the documented COFs, metal–organic frameworks (MOFs), and other benchmark adsorbents. In addition, the adsorption behaviors of MB, CV, MG, and JGB on TpStb-SO3Na obeyed the pseudo-second-order adsorption kinetic model. On the contrary, TpStb-SO3Na presented low adsorption capacity for anionic dyes like methyl orange (MO) and fluorescein sodium (FS), rendering it a promising sorbent for the separation of cationic and anionic dyes based on charge difference. Furthermore, TpStb-SO3Na was easily regenerated and reused for five cycles with no obvious loss in its adsorption performance. This work uncovers the vast potential of anionic COFs for the effective removal of organic dye pollutants in wastewater.

Realizing Enhanced Thermoelectric Performance in Zintl-Phase SrCuSb by Reducing the Thermal Conductivity

Zintl-phase compounds have been extensively studied in recent years due to their phonon-glass and electron-crystal structure. As a ZrBeSi-type Zintl-phase compound, SrCuSb exhibits both high electrical transport properties and thermal conductivity because of the fully occupied anionic framework. In this work, the thermoelectric properties of SrCuSb were refined by Sr self-doping. The increased Sr content not only suppressed the secondary phase SrCu2Sb2 but also lowered the carrier contribution to the thermal conductivity. A zT value of ∼0.36 was achieved for Sr1.05CuSb at 700 K. To further decrease the thermal conductivity, Ba was introduced to the alloy at the Sr site. Benefiting from the point defect scattering, the lattice thermal conductivity was reduced to ∼0.7 W K–1 m–1 at 760 K for the Sr0.75Ba0.3CuSb sample. Finally, a peak zT of ∼0.5 was obtained for Sr0.75Ba0.3CuSb at 773 K.

Understanding of the structural chemistry in the uranium oxo-tellurium system under HT/HP conditions.

The study of phase formation in the U-Te-O systems with mono and divalent cations under high-temperature high-pressure (HT/HP) conditions has resulted in four new inorganic compounds: K2 [(UO2) (Te2O7)], Mg [(UO2) (TeO3)2], Sr [(UO2) (TeO3)2] and Sr [(UO2) (TeO5)]. Tellurium occurs as TeIV, TeV, and TeVI in these phases which demonstrate the high chemical flexibility of the system. Uranium VI) adopts a variety of coordinations, namely, UO6 in K2 [(UO2) (Te2O7), UO7 in Mg [(UO2) (TeO3)2] and Sr [(UO2) (TeO3)2], and UO8 in Sr [(UO2) (TeO5)]. The structure of K2 [(UO2) (Te2O7)] is featured with one dimensional (1D) [Te2O7]4- chains along the c-axis. The Te2O7 chains are further linked by UO6 polyhedra, forming the 3D [(UO2) (Te2O7)]2- anionic frameworks. In Mg [(UO2) (TeO3)2], TeO4 disphenoids share common corners with each other resulting in infinite 1D chains of [(TeO3)2]4- propagating along the a-axis. These chains link the uranyl bipyramids by edge sharing along two edges of the disphenoids, resulting in the 2D layered structure of [(UO2) (Te2O6)]2-. The structure of Sr [(UO2) (TeO3)2] is based on 1D chains of [(UO2) (TeO3)2]∞ 2- propagating into the c-axis. These chains are formed by edge-sharing uranyl bipyramids which are additionally fused together by two TeO4 disphenoids, which also share two edges. The 3D framework structure of Sr [(UO2) (TeO5)] is composed of 1D [TeO5]4- chains sharing edges with UO7 bipyramids. Three tunnels based on 6-Membered rings (MRs) are propagating along [001] [010] and [100] directions. The HT/HP synthetic conditions for the preparation of single crystalline samples and their structural aspects are discussed in this work.

Crystal Structures and Physicochemical Properties of Be2N and Mg2N as Electride Materials

Electrides are a special family of materials with exotic physical properties and various crystal structures in different dimensions. Among them, alkaline-earth metal nitrides (${\mathrm{AE}}_{2}\mathrm{N}$) have attracted enormous attention, since the synthesis of ${\mathrm{Ca}}_{2}\mathrm{N}$ as a two-dimensional (2D) electride. However, apart from ${\mathrm{Ca}}_{2}\mathrm{N}$, the physicochemical properties of other ${\mathrm{AE}}_{2}\mathrm{N}$ are not well understood, and in some cases, their crystal structures remain unknown. To overcome these issues, here, we conduct systematic investigations into the crystal structures, electronic structures, and optical properties of two typical ${\mathrm{AE}}_{2}\mathrm{N}$, i.e., ${\mathrm{Mg}}_{2}\mathrm{N}$ and ${\mathrm{Be}}_{2}\mathrm{N}$, based on first-principles calculations. By symmetry analysis, we derive a crystal structure with $R\overline{3}m$ symmetry for ${\mathrm{Be}}_{2}\mathrm{N}$, which is energetically more stable than all the other structures proposed previously. Our calculations show that $R\overline{3}m$ ${\mathrm{Be}}_{2}\mathrm{N}$ is a 2D electride with the anionic electrons located in the interstitial space, forming a 2D Kagome lattice. Moreover, distinct from traditional 2D electrides, it exhibits anomalous physicochemical properties, such as having a small interstitial space, a high work function, and a large cleavage energy, mainly due to the relatively strong bonding effect between anionic electrons and cationic framework. For ${\mathrm{Mg}}_{2}\mathrm{N}$, on the other hand, we find that the most stable structure has R3m symmetry, which shows a total energy of 0.005 eV per formula unit lower than the previously predicted Cmcm structure. Moreover, different from $R\overline{3}m$ ${\mathrm{Be}}_{2}\mathrm{N}$, R3m ${\mathrm{Mg}}_{2}\mathrm{N}$ is identified as a zero-dimensional (0D) electride with a semiconducting band structure, since its anionic electrons are confined in separated 0D cavities and cannot interact with each other. These studies thus provide a deeper understanding of the crystal structures and physicochemical properties of ${\mathrm{Be}}_{2}\mathrm{N}$ and ${\mathrm{Mg}}_{2}\mathrm{N}$ as potential electride materials.

A light-sensitive metal-organic framework composite encapsulated by ion exchange for photocatalytic organic reaction

In this work, ZJU-28, a typical anionic metal-organic framework, was selected as the functional carrier to encapsulate [Ir(ppy)2bpy]+ (ppy ​= ​2-phenylpyridine, bpy ​= ​2,2′-bipyridine) cation through ion exchange, and a new composite photocatalyst [Ir(ppy)2bpy]+@ZJU-28 was obtained therefore. The composite material was detailly characterized by powder X-ray diffraction (PXRD), fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), UV–Vis (UV) absorption spectra and ICP-OES. [Ir(ppy)2bpy]+@ZJU-28 showed favorable photocatalytic activity for visible light promoted organic transformations. More importantly, it exhibited super stability and excellent recovery & reuse performance.

A squaramide-based anionic hydrogen-bonded organic framework: enhancing sensing performance for pesticides by post-metallization with in situ imaging

A lanthanide modified squaramide-based anionic hydrogen-bonded organic framework could be used as a sensitive sensor for rapid detection of DCN pesticide residues in fresh produce nondestructively.

CaZn(HPO3)2 and Ba2Zn(HPO3)3: novel alkaline-earth zincophosphites with diversified anionic frameworks.

Two novel alkaline-earth zincophosphites, namely CaZn(HPO3)2 and Ba2Zn(HPO3)3, were successfully synthesized under hydrothermal conditions. CaZn(HPO3)2 exhibits a three-dimensional (3D) anionic framework with a 6-connected uni-nodal pcu α-Po primitive cubic topology, constructed by unique Zn2O8 dimers and HPO3 pseudo-tetrahedra, while Ba2Zn(HPO3)3 displays one-dimensional (1D) [Zn(HPO3)3]4- anionic chains. It is worth mentioning that CaZn(HPO3)2 represents the first example of an alkaline-earth zincophosphite compound with a 3D framework structure. Our research also revealed the importance of both alkaline earth cation sizes and Zn/P ratios in anionic open-framework formation. The crystal structures of both compounds were further verified by energy dispersive spectroscopy, IR spectroscopy and Raman spectroscopy. Optical diffuse reflectance spectra, coupled with Tauc's fitting, revealed direct bandgaps with energy values of 4.33 and 4.48 eV for CaZn(HPO3)2 and Ba2Zn(HPO3)3, respectively, which differ from the prediction of theoretical calculations. Density of states calculations were conducted to reveal the origin of the bandgaps and bond interactions. Both compounds exhibited moderate birefringence values. This work may have implications for the design and synthesis of novel metal phosphites with desired properties.

New insights into aliovalent substituted halide solid electrolytes for cobalt-free all-solid state batteries

Achieving a balance between lithium ion and vacant site contents plays a crucial role in obtaining optimal ionic conductivity in halide electrolytes, especially with a hexagonal close packing (hcp) anion framework.

An anionic porphyrinylphosphonate-based hydrogen-bonded organic framework: optimization of proton conductivity through the exchange of counterions.

Hydrogen-bonded organic frameworks (HOFs) possessing high crystallinity, simple synthetic procedure and easy regeneration provide high efficiency as multifunctional systems, including applications as proton conductors. Porphyrinylphosphonates having acidic moieties, which can form multiple hydrogen bonds, together with tunable physical-chemical properties of a macrocycle may significantly improve the proton conductivity of such materials. Herein, the synthesis, characterization and proton-conducting properties of a novel anionic HOF based on a new complex of palladium(II) with meso-tetrakis(4-(phosphonatophenyl))porphyrin, HOF-IPCE-1Pd, are reported. Directed structural transformation of the framework by the exchange of dimethylammonium counterions for ammonium cations along with the absorption of ammonia and water molecules led to the formation of a more hydrolytically stable structure of HOF-IPCE-1Pd-NH3, demonstrating the proton conductivity of 1.27 × 10-3 S cm-1 at 85 °C and 85% RH, which is one of the highest among all known HOFs based on porphyrins. It is noteworthy that the reversible absorbance of water/ammonia molecules preserves the crystal structure of HOF-IPCE-1Pd-NH3.

Highly efficient removal of Cs+from water by an ionic lamellar carbon nitride framework

137Cs+is strongly radioactive, and is thus a highly hazardous pollutant. An anionic lamellar carbon nitride framework (CN–Na) exhibits remarkable performance in selective removal of Cs+in waterviaan ion-exchange mechanism.

Co-substitution design: a new glaserite-type rare-earth phosphate K2RbSc(PO4)2 with high structural tolerance.

An alkali rare-earth phosphate K2RbSc(PO4)2 was successfully obtained as a derivative of glaserite-type K3Na(SO4)2 by co-substitution of K(1)O12 → RbO12, K(2)O10 → KO7, NaO6 → ScO6 and SO4 → PO4, while maintaining the original anionic framework. K2RbSc(PO4)2 exhibits a layered [Sc(PO4)2]∞ framework built from ScO6 octahedra and PO4 tetrahedra, with K and Rb residing in the interlayers. Its isostructural lanthanide analogues K2RbEr(PO4)2 and K2RbLu(PO4)2, inspired by an elemental substitution strategy, were also prepared by a high-temperature solid state reaction. The successful substitution indicates that the skeleton of K2RbSc(PO4)2 is stable with high structural tolerance, which can provide a possibility for substitution of resident ions to obtain diverse structural types and applications.

Li2AB5O8F2 (A = Na and K): two new deep-ultraviolet transparent fluorooxoborates with moderate birefringence designed by targeted dimensional modulation

Two mixed alkali-metal fluorooxoborates, Li2KB5O8F2 and Li2NaB5O8F2, were designed and synthesized by using the strategy of targeted dimensional modulation through adjusting component ratio in the sealed system. Li2KB5O8F2 exhibits a short ultraviolet cutoff edge (<196 nm), possessing moderate birefringence (about 0.05@1064 nm) which was mainly contributed by the [B5O8F2]∞2 wave layer. Further, the investigation on the relationship among (AI + F)/B (AI: alkali-metal cations) ratio and dimensionality of the anionic framework as well as birefringence has been conducted in available anhydrous alkali-metal fluorooxoborates for providing an idea in the synthesis of fluorooxoborates with desirable performances.

Open honeycomb frameworks of sulphides AHg4Ga5S12 (A = Rb, Cs) exhibiting infrared nonlinear optical properties.

A crystal structure with a diamond-like anionic framework belongs to a non-centrosymmetric macrostructure due to the aligned arrangement of tetrahedral units, meeting the premise of second-order nonlinear optical (NLO) materials. Herein, two new Hg-based sulphides, namely RbHg4Ga5S12 (1) and CsHg4Ga5S12 (2), which are isostructural and crystallise in the trigonal space group R3, are successfully isolated in sealed silica tubes by a solid-state reaction. The features of their three-dimensional open honeycomb frameworks are attributed to the parallel alignment of tetrahedral MS4 (M is disordered by 0.444 Hg and 0.555 Ga) building motifs, accompanied by Rb+ (or Cs+) reseating in the cavities. Notably, although the band gap values of 1 and 2 are 2.30 and 2.36 eV, separately, their thermal expansion anisotropies (0.15 and 0.41, respectively) are favourable for achieving laser-induced damage thresholds (5.6 and 5.8 times that of AgGaS2 for 1 and 2, respectively). In addition, the strong polarisability of tetrahedral MS4 building motifs in the diamond-like anionic structures is responsible for the promising second-harmonic generation (SHG) intensities (1.1 and 1.8 times that of AgGaS2 for 1 and 2, respectively) in the particle size range of 50-75 μm with non-phase-matchable behaviour at 1910 nm. Furthermore, theoretical investigation elaborates that electron transitions in compounds 1 and 2 mainly occur from valence band S-3p to conduction band Hg-6s and Ga-4s states, demonstrating that the linear and nonlinear optical properties originate primarily from the synergy of tetrahedral MS4 units.

Mg assists in modulating the dimensionalities of the anionic frameworks of borates.

Three Mg-containing borates were obtained by high-temperature spontaneous crystallization. In the (A2O)- or (A2O-MO)-MgO-B2O3system (A is alkali metal and M is alkaline-earth metal) reported in the ICSD, Li4Mg3SrB12O24 is the first compound that contains one-dimensional infinite anionic chains, and the two examples of the isostructural A2Mg3B16O28 (A = Rb, Cs) exhibit a two-dimensional infinite bilayer structure for the first time, which contributes to the enrichment of the structural chemistry of Mg-containing borates. Besides, the results of comparison and analysis in this system clearly show that Mg not only affects the anionic frameworks of borates to produce low-dimensional structures but, together with the ratio of Ncation/NB, is responsible for the dimensionalities of the anionic frameworks in borates. The optical properties of the three compounds also show that they all have short cutoff edges, and Cs2Mg3B16O28, in particular, could reach the deep-ultraviolet region (<200 nm).

Linear π-conjugated units of the D∞h point group as superior ultraviolet birefringent units.

At present, birefringent materials face a limited selection of large structural anisotropic functional modules (FMs). In this paper, we present a series of linear units which belong to the D∞h point group represented by (BO2)- proposed as novel birefringent active FMs. By analyzing the molecular orbital of the (BO2)- unit, it is found that there are relatively fewer non-bonding orbitals in (BO2)- than in (BO3)3- and the delocalized π bonds in (BO2)- appear in shallow energy levels, which are easily excited. Through first-principles modeling and simulation, it is found that the delocalized π bonds in (BO2)- can still show obvious transition processes, which produce a significant gain to the birefringence. Besides, a series of compounds containing linear anionic frameworks which also belong to the D∞h point group show excellent optical anisotropy in the same way. Therefore, the linear anionic basic units which belong to the D∞h point group have the great potential to become new birefringent FMs.

LiCs3AlB7O14: achieving enhanced optical anisotropy via [AlO4] tetrahedron introduction to rearrange the anionic framework.

Borate has become a hot topic because of its rich structural chemistry and excellent properties for functional materials fields. The rearrangement of π-conjugated B-O units is key to enhancing the optical anisotropy, but it remains a challenge. Herein, by introducing [AlO4] tetrahedra, a new congruent melting aluminoborate LiCs3AlB7O14 with [B7O14] clusters was discovered. This work confirms that the introduction of [AlO4] tetrahedra can lead to the rearrangement of anionic framework of the borate system and thereby enhance the birefringence of LiCs3AlB7O14. The birefringence is about 4.1 times higher than that of its congener Li4Cs3B7O14 with the same [B7O14] clusters. Similarly, the effects of [AlO4] tetrahedra on the rearrangement of the B-O anionic framework are also demonstrated in other known borates.

Noncentrosymmetric versus Centrosymmetric: Halogen Induced Variable Coordination Modes of Sn2+ and Structural Transition in Sn3B3O7X (X = Cl and Br)

Two new borate halides, Sn3B3O7X (X = Cl and Br), were successfully synthesized via introducing Sn2+ with lone-pair and halogen into borate. Interestingly, halogen-induced variable coordination modes of Sn2+ and anion frameworks make them crystallize in different space groups, from noncentrosymmetric (Pna21) to centrosymmetric (Pbca). Sn3B3O7Cl possesses an SHG response of about 0.5 times that of KDP, while Sn3B3O7Br exhibits a large birefringence (0.123@1064 nm). The theoretical calculations were performed to elucidate the structure-property relationships.

Dual-activation interfacial polymerization based anionic covalent organic framework nanofiltration membrane for high-flux dye separation

Covalent organic frameworks (COFs) hold great promise in constructing a new-generation of molecular separation membranes. Significantly, ionic COF membranes endow novel functions distinct from those of neutral membranes. However, ionic COF membranes generally suffer from extremely slow reaction rates and low yields, limiting their widespread application. In this work, a self-standing anionic COF membrane was prepared by a dual-activation interfacial polymerization strategy. And the obtained anionic COF membrane possessed a unique ordered pore structure, superhydrophilicity, as well as good chemical stability. Meanwhile, the as-prepared membrane provided the high-efficiency water transport pathways with effective rejection for dye molecules. As expected, the anionic COF membrane exhibited an excellent water permeability of about 270 L m−2 h−1 bar−1, which was much higher than those of commercial nanofiltration membranes, and also approximately 2–15 times significantly higher than those reported for polymer- or neutral COF-based nanofiltration membranes with similar rejection. Owing to the electrostatic attraction between positively charged dyes and anionic COF channels, the rejection rates of cationic dyes were above 96 %. In addition, the size-exclusion effect dominated rejection efficiency of dyes with molecular sizes larger than COF channels. These findings provided a new candidate membrane for efficient dye wastewater treatment.