Recent advances in crystalline hydrated borates with non-metal or transition-metal complex cations

M6[Cd2(CO3)2(B12O18)(OH)6] (M = K, Rb): Borate-Carbonates with Two CdCO3 Embedded in a Cyclic Oxoboron Anion

Two metal borate-carbonates, M6[Cd2(CO3)2(B12O18)(OH)6] [M = K (1), Rb (2)], were obtained under surfactant-thermal conditions. In 1 and 2, each cyclic [(B12O18)(OH)6]6- anion captures two CdCO3 in two sides of the rings and finally forms the unusual (CdCO3)2@[(B12O18)(OH)6] cluster. Both 1 and 2 show moderate birefringence. Density functional theory calculations indicate that carbonate groups have a major contribution to electron-related optical transition.

Novel application of imidazole-based ligand-templated borates in a zinc-air battery

Two templated borates, [Co(1-EI)2]·[B5O7(OH)3] (1) and [Ga(1-MI)2·B6O9(OH)4]·[H3BO3]·H[1-MI] (2), have been synthesized using a mild method. Notably, they exhibit an excellent ORR performance with an E1/2 value of 0.84 V and are the first to be used as the positive electrode catalyst for a zinc-air battery, which opens a pathway for the application of borate-based oxide catalysts.

Co(II)-doped hybrid Zn(II) tetraborate complexes, [ZnxCo(1-x)(1,3-dap)B4O7] (1,3-dap = 1,3-diaminopropane): BET analysis and N2/H2O/D2O adsorption studies

A series of mono/bimetallic isostructural hybrid tetraborates of the general formula [ZnxCo(1-x)(1,3-dap)B4O7] has been prepared using a solvothermal method. Their adsorption/desorption curves for H2O and D2O demonstrate that these materials have a stronger affinity for H2O than for D2O and enrich the D2O content of D2O/H2O mixtures.

Thermodynamic Properties and DFT Study on Highly Frustrated Cr3BO6: Coexistence of Spin-Singlets with Long-Range Magnetic Order

The triangle-based magnetic subsystem of borates with the mineral norbergite structure M3BO6 (M = Fe, Cr, V) makes these compounds unique to investigate rare quantum ground states influenced by strong magnetic frustration. In this work, we investigated the thermal and magnetic properties of Cr3BO6 to find that despite very large negative Weiss temperature Θ = -160.7 K, it orders only at TN = 4.5 K and experiences a spin-flop transition at µ0H = 5 T. Density functional theory (DFT) calculations of exchange interaction parameters allow for suggesting the model of magnetic subsystem in chromium borate Cr3BO6. The results prove the decisive role of magnetic frustration on the formation of long-range order, providing therefore a basis for future study. Both experimental data and first-principles calculations point to the coexistence of chromium spin-singlets with long-range antiferromagnetic order.

Synthesis and Thermal Studies of Two Phosphonium Tetrahydroxidohexaoxidopentaborate(1-) Salts: Single-Crystal XRD Characterization of [iPrPPh3][B5O6(OH)4]·3.5H2O and [MePPh3][B5O6(OH)4]·B(OH)3·0.5H2O

Two substituted phosphonium tetrahydoxidohexaoxidopentaborate(1-) salts, [iPrPPh3][B5O6(OH)4]·3.5H2O (1) and [MePPh3][B5O6(OH)4]·B(OH)3·0.5H2O (2), were prepared by templated self-assembly processes with good yields by crystallization from basic methanolic aqueous solutions primed with B(OH)3 and the appropriate phosphonium cation. Salts 1 and 2 were characterized by spectroscopic (NMR and IR) and thermal (TGA/DSC) analysis. Salts 1 and 2 were thermally decomposed in air at 800 °C to glassy solids via the anhydrous phosphonium polyborates that are formed at lower temperatures (<300 °C). BET analysis of the anhydrous and pyrolysed materials indicated they were non-porous with surface areas of 0.2-2.75 m2/g. Rhe recrystallization of 1 and 2 from aqueous solution afforded crystals suitable for single-crystal XRD analyses. The structure of 1 comprises alternating cationic/anionic layers with the H2O/pentaborate(1-) planes held together by H-bonds. The cationic planes have offset face-to-face (off) and vertex-to-face (vf) aromatic ring interactions with the iPr groups oriented towards the pentaborate(1-)/H2O layers. The anionic lattice in 2 is expanded by the inclusion of B(OH)3 molecules to accommodate the large cations; this results in the formation of a stacked pentaborate(1-)/B(OH)3 structure with channels occupied by the cations. The cations within the channels have vf, ef (edge-to-face), and off phenyl embraces. Both H-bonding and phenyl embrace interactions are important in stabilizing these two solid-state structures.

Recent Progress in Crystalline Borates with Edge-Sharing BO4 Tetrahedra

Crystalline borates have received great attention due to their various structures and wide applications. For a long time, the corner-sharing B-O unit is considered a basic rule in borate structural chemistry. The Dy₄B₆O₁₅ synthesized under high-pressure is the first oxoborate with edge-sharing [BO₄] tetrahedra, while the KZnB₃O₆ is the first ambient pressure borate with the edge-sharing [BO₄] tetrahedra. The edge-sharing connection modes greatly enrich the structural chemistry of borates and are expected to expand new applications in the future. In this review, we summarize the recent progress in crystalline borates with edge-sharing [BO₄] tetrahedra. We discuss the synthesis, fundamental building blocks, structural features, and possible applications of these edge-sharing borates. Finally, we also discuss the future perspectives in this field.

Structural Regulation and Oxygen Reduction Reaction Activity of [Co(bpy)2BO2(OH)] and [Cu(bpy)(OH)]2- Complex Templated Borates

Two templated borates, [Co(bpy)₂BO₂(OH)]·[B₅O₆(OH)₄]·H₃BO₃·H₃O·H₂O (1) and [Cu(bpy)(OH)]₂·[B₅O₆(OH)₄]₂·H₂O (2), have been synthesized successfully and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, and Fourier transform infrared. The [Co(bpy)₂BO₂(OH)] complex in 1 shows a very rare coordination mode between Co²⁺ and BO₂(OH)^2-. The structures of 1 and 2 can be adjusted by changing the reagent. The oxygen reduction reaction activity of these Co- and Cu-based catalysts was studied. The E_1/2 values of Co-C-750 and Cu-C-750 are 0.864 and 0.837 V, respectively.

Structural (XRD) Characterization and an Analysis of H-Bonding Motifs in Some Tetrahydroxidohexaoxidopentaborate(1-) Salts of N-Substituted Guanidinium Cations

The synthesis and characterization of six new substituted guanidium tetrahydroxidohexaoxidopentaborate(1-) salts are reported: [C(NH₂)₂(NHMe)][B₅O₆(OH)₄]·H₂O (1), [C(NH₂)₂(NH{NH₂})][B₅O₆(OH)₄] (2), [C(NH₂)₂(NMe₂)][B₅O₆(OH)₄] (3), [C(NH₂)(NMe₂)₂][B₅O₆(OH)₄] (4), [C(NHMe)(NMe₂)₂][B₅O₆(OH)₄]·B(OH)₃ (5), and [TBDH][B₅O₆(OH)₄] (6) (TBD = 1,5,7-triazabicyclo [4.4.0]dec-5-ene). Compounds 1-6 were prepared as crystalline salts from basic aqueous solution via self-assembly processes from B(OH)₃ and the appropriate substituted cation. Compounds 1-6 were characterized by spectroscopic (NMR and IR) and by single-crystal XRD studies. A thermal (TGA) analysis on compounds 1-3 and 6 demonstrated that they thermally decomposed via a multistage process to B₂O₃ at >650 °C. The low temperature stage (<250 °C) was endothermic and corresponded to a loss of H₂O. Reactant stoichiometry, solid-state packing, and H-bonding interactions are all important in assembling these structures. An analysis of H-bonding motifs in known unsubstituted guanidinium salts [C(NH₂)₃]₂[B₄O₅(OH)₄]·2H₂O, [C(NH₂)₃][B₅O₆(OH)₄]·H₂O, and [C(NH₂)₃]₃[B₉O₁₂(OH)₆] and in compounds 1-6 revealed that two important H-bonding R₂²(8) motifs competed to stabilize the observed structures. The guanidinium cation formed charge-assisted pincer cation-anion H-bonded rings as a major motif in [C(NH₂)₃]₂[B₄O₅(OH)₄]·2H₂O and [C(NH₂)₃]₃[B₉O₁₂(OH)₆], whereas the anion-anion ring motif was dominant in [C(NH₂)₃][B₅O₆(OH)₄]·H₂O and in compounds 1-6. This behaviour was consistent with the stoichiometry of the salt and packing effects also strongly influencing their solid-state structures.

Zinc Borate Hydrolysis

The crystalline zinc borate phase ZnB3O4(OH)3, known in commerce as 2ZnO·3B2O3·3.5H2O, is an important industrial material used as a fire-retardant synergist in polymers, a source of micronutrients in agriculture, and a preservative in building materials. It lends durability to wood composite building materials by inhibiting attack by wood destroying organisms. The hydrolysis chemistry of this zinc borate is relevant to its industrial use. ZnB3O4(OH)3 exhibits incongruent solubility, reversibly hydrolyzing at neutral pH to insoluble Zn(OH)2 and soluble B(OH)3. It is sparingly soluble with a room temperature solubility of 0.270 wt% in terms of its equivalent oxide components in solution, comprising 0.0267 wt% B2O3 and 0.003 wt% ZnO. Aspects of the hydrolysis chemistry of zinc borate under neutral pH conditions are discussed.

Two New Nonaborates with {B9} Cluster Open-Frameworks and Short Cutoff Edges

Two new nonaborates, Na₂Ba_0.5[B₉O₁₅]·H₂O (1) and Na₄Ca_1.5[B₉O₁₆(OH)₂] (2), have been solvothermally made with mixed alkali and alkaline-earth metal cationic templates. 1 and 2 are constructed by two different types of nonaborate clusters. In 1, the [B₉O₁₉]¹¹⁻ cluster is composed of three corner-sharing [B₃O₇]⁵⁻ clusters, of which two of them interconnect to the 1D B₃O₇-based chains and are further bridged to the 3D framework with 7 types of 10-MR channels by another [B₃O₇]⁵⁻ bridging cluster. The [B₉O₁₈(OH)₂]¹¹⁻ cluster in 2 is made of four BO₄-sharing [B₃O₈]⁷⁻ clusters. As a 4-connected node, the interconnections of [B₉O₁₈(OH)₂]¹¹⁻ construct the unpreceded 2D layer with large 14-MR windows, which are further joined by H-bonds to the 3D supramolecular framework. UV–Vis absorption spectra reveal that both 1 and 2 have short cutoff edges below 190 nm, exhibiting bandgaps of 6.31 and 6.39 eV, respectively, indicating their potential applications in deep UV (DUV) regions.

Two layered galloborates from centric to acentric structures: syntheses and NLO properties

Two layered galloborates (GBOs), Na₃GaB₄O₉ (1) and Na₅Ga[B₇O₁₂(OH)]₂·2B(OH)₃ (2), have been solvothermally made. 1 exhibits an unprecedented layer built by GaO₄ tetrahedra and B₄O₉ clusters. 2 was made by raising the ratio of B/Ga and the reaction temperature of 1, featuring a 2D acentric layer built by GaO₄ groups and B₇O₁₃(OH) clusters. 2 shows the highest second-harmonic generation (SHG) response of 4.6 times that of KDP (KH₂PO₄) among main group metal borates (MBOs).

Ba2B10O16(OH)2·(H3BO3)(H2O): A Possible Deep-Ultraviolet Nonlinear-Optical Barium Borate

A new acentric barium borate, Ba₂B₁₀O₁₆(OH)₂·(H₃BO₃)(H₂O) (1), was synthesized via a hydrothermal process. Compound 1 contains two different boron oxide units of [B₅O₁₀(OH)]^6- anions and H₃BO₃ molecules and features 9-ring channels along the c axis in a layered structure. This barium borate is a possible deep-ultraviolet nonlinear-optical crystal for its moderate second-harmonic-generation signal and wide transparency window below 190 nm.

Na3B6O10(HCOO): an ultraviolet nonlinear optical sodium borate-formate

A new sodium borate-formate, which displays a pcu-type open framework and ultraviolet nonlinear optical properties, has been synthesized under surfactant-thermal conditions.

Identical in Formula but Not Isotypic in Configuration: Discovery of a New Highly Polymerized [B12O24] Cluster in Cs3AlB6O12

The discovery of new borates with unique structures has always been a growing part of solid-state chemistry, especially for polyborates. Herein, a new aluminoborate, Cs₃AlB₆O₁₂, has been discovered by a high-temperature solution in a vacuum system. The highly polymerized [B₁₂O₂₄] cluster, unlike the annular configuration in previously reported polyborates, is found in Cs₃AlB₆O₁₂ for the first time. The different linkage reflected by the local symmetry in cluster makes these borates not isotypic, although the formula of [B₁₂O₂₄] is identical. Experimental measurement performed on Cs₃AlB₆O₁₂ powder reveals the deep-ultraviolet transparent spectral feature.

Oxidoborates Templated by Cationic Nickel(II) Complexes and Self-Assembled from B(OH)3

Several oxidoborates, self-assembled from B(OH)3 and templated by cationic Ni(II) coordination compounds, were synthesized by crystallization from aqueous solution. These include the ionic compounds trans-[Ni(NH3)4(H2O)2][B4O5(OH)4].H2O (1), s-[Ni(dien)2][B5O6(OH)4]2 (dien = N-(2-aminoethyl)-1,2-ethanediamine (2), trans-[Ni(dmen)2(H2O)2] [B5O6(OH)4]2.2H2O (dmen = N,N-dimethyl-1,2-diaminoethane) (3), [Ni(HEen)2][B5O6(OH)4]2 (HEen = N-(2-hydroxyethyl)-1,2-diaminoethane) (4), [Ni(AEN)][B5O6(OH)4].H2O (AEN = 1-(3-azapropyl) -2,4-dimethyl-1,5,8-triazaocta-2,4-dienato(1-)) (5), trans-[Ni(dach)2(H2O)2][Ni(dach)2] [B7O9(OH)5]2.4H2O (dach = 1,2-diaminocyclohexane) (6), and the neutral species trans-[Ni(en)(H2O)2{B6O7(OH)6}].H2O (7) (en = 1,2-diaminoethane), and [Ni(dmen)(H2O){B6O7(OH)6}].5H2O (8). Compounds 1–8 were characterized by single-crystal XRD studies and by IR spectroscopy and 2, 4–7 were also characterized by thermal (TGA/DSC) methods and powder XDR studies. The solid-state structures of all compounds show extensive stabilizing H-bond interactions, important for their formation, and also display a range of gross structural features: 1 has an insular tetraborate(2-) anion, 2–5 have insular pentaborate(1-) anions, 6 has an insular heptaborate(2-) anion (‘O+’ isomer), whilst 7 and 8 have hexaborate(2-) anions directly coordinated to their Ni(II) centers, as bidentate or tridentate ligands, respectively. The Ni(II) centers are either octahedral (1–4, 7, 8) or square-planar (5), and compound 6 has both octahedral and square-planar metal geometries present within the structure as a double salt. Magnetic susceptibility measurements were undertaken on all compounds.

Recent Advances in Crystalline Oxidopolyborate Complexes of d-Block or p-Block Metals: Structural Aspects, Syntheses, and Physical Properties

Crystalline materials containing hybrid inorganic–organic metal borates (complexes with oxidoborate ligands) display a variety of novel framework building blocks. The structural aspects of these hybrid metallaoxidoborates containing Cd^(II), Co^(II), Cu^(II), Ga^(III), In^(III), Mn^(II), Ni^(II) or Zn^(II) metal centers are discussed in this review. The review describes synthetic approaches to these hybrid materials, their physical properties, their spectroscopic properties and their potential applications.

Syntheses and structures of a new 2D layered borate and a novel 3D porous-layered aluminoborate

Two new layered and porous-layered borates ([H₂dap][B₇O₁₁(OH)] (1, dap = 1,2-propanediamine) and [H₃O]K_3.52Na_3.48{Al₂[B₇O₁₃(OH)][B₅O₁₀][B₃O₅]}[CO₃] (2)) have been solvothermally made. 1 features a 2D layer made of the [B₇O₁₃(OH)]^6- cluster, in which H₂dap is located in the windows of the layers. The fundamental building block (FBB) [B₇O₁₃(OH)]^6- cluster in 1 represents a new type of FBB of the hepta-borate family. 2 is a novel aluminoborate with a 3D porous-layered structure formed by three types of oxoboron clusters, [B₇O₁₃(OH)]^6-, [B₅O₁₀]^5- and [B₃O₇]^5-, respectively. The strict alternation of the different oxoboron clusters and AlO₄ tetrahedra leads to the abundant channel systems of the structure. 2 is the first aluminoborate (ABO) containing three types of oxoboron clusters and the first 3D porous-layered ABO with seven types of channels. UV-vis diffuse reflectance spectra reveal that both of them are wide band-gap semiconductors and have potential applications in UV regions.

Two novel 3D borates: porous-layer and layer-pillar frameworks

Two new borates, NaK_1.5[B{B₅O₉(OH)}{B₅O₈(OH)₂}_1/2] (1) and Na_3.5[Al{B₃O₆(OH)}{B₅O₁₀}_1/2{BO(OH)}] (2), have been made by a solvothermal method. Structure 1 is made of two types of oxoboron clusters ([B₅O₉(OH)]^4- and [B₅O₈(OH)₂]^3-) and BO₄ tetrahedra to form a 3D porous layer, in which the [B₅O₉(OH)]^4- clusters are bridged by BO₄ groups to produce a 2D B-O layer with 11-membered ring (MR) windows, while the [B₅O₈(OH)₂]^3- clusters as 2-connected pillars join the adjacent B-O layers to make a 3-D porous layer. Structure 2 is built from two types of oxoboron clusters ([B₃O₆(OH)]^4- and [B₅O₁₂]^9-), AlO₄ units and BO₂(OH) triangles to produce 3D pillar-layered aluminoborate (ABO), in which the [B₅O₁₂]^9- clusters are linked together to form a 2-D B-O layer; the [B₃O₆(OH)]^4- clusters and AlO₄ groups join each other to form 1D tubular ABO; and the BO₂(OH) triangles act as linkers to connect the adjacent B-O layer and the ABO tubes, resulting in 3D pillar-layered ABO. Interestingly, the ABO tubes decorated with the BO₂(OH) triangles act as pillars to make a 3D layer-pillared structure. UV-vis diffuse spectra indicate that both have cut-off edges below 190 nm, and the calculated band gaps are 5.75 and 5.78 eV, respectively.

Trinuclear Cd3O14 hexaborate and two nickel borates based on molten salt synthesis and precursor synthesis: structure, characterization, and properties

In this work, different synthetic methods were used to prepare metal borates. One cadmium borate Cd3[B6O9(OH)2]2·2NO3·4H2O (1) and two nickel borate Ni0.8Mn0.2{B6O7(OH)3[O(CH2)2NH2]3} (2), [Ni(1-MI)6]·[B5O6(OH)4]2·2DMF (3, 1-MI = 1-methylimidazole, DMF = N,N-dimethylformamide) species were successfully prepared. The structures of these three compounds were confirmed via single crystal powder X-ray diffraction (SCPXRD), elemental analysis, FTIR, PXRD, and ICP studies. Compound 1 was prepared via molten salt synthesis, and compounds 2 and 3 were prepared via precursor synthesis, which is a synthetic method that uses a certain polyanionic cluster as a reagent. Compound 1 shows a novel three-dimensional (3D) structure, in which the [B6O11(OH)2] units acting as the basic polyanionic cluster form a two-dimensional (2D) anionic structure. In addition, the unexpected Cd3O14 clusters are connected with the 2D structures, leading to the 3D structure. The crystal structure of 2 is packed with very large neutral Ni0.8Mn0.2{B6O7(OH)3[O(CH2)2NH2]3} oxo-metal-boron clusters. The crystal structure of 3 consists of a [B5O6(OH)4]- cluster, a DMF molecule, and a [Ni(1-MI)6]2+ complex. In particular, 2 was successfully constructed using the same hexaborate cluster as its precursor. However, 3 only contains Ni2+ cations when a neutral NixMn1-x[B6O7(OH)6] cluster was used as an initial reagent, and it shows an ability to select a certain metal cation during the self-assembly process. Moreover, compounds 1, 2, and 3 exhibit different wide band gaps of 3.06 eV (1), 3.95 eV (2), and 4.24 eV (3).

Pentaborate(1-) Salts and a Tetraborate(2-) Salt Derived from C2- or C3-Linked Bis(alkylammonium) Dications: Synthesis, Characterization, and Structural (XRD) Studies

The synthesis of a number of pentaborate(1-) salts from cations arising from N-substituted α,α-, α,β-, and α,γ-diaminoalkanes has been attempted in aqueous solution from B(OH)₃ and the appropriate diammine in a 10:1 ratio. Despite relatively mild work-up conditions the pentaborate(1-) salts prepared were not always as anticipated and the following compounds were isolated in good yield: [Me₂NH(CH₂)₂NHMe₂][B₅O₆(OH)₄]₂ (1), [Et₂NH(CH₂)₂NHEt₂][B₅O₆(OH)₄]₂ (2), [Et₂NH₂][B₅O₆(OH)₄] (3), [Me₂NH₂][B₅O₆(OH)₄] (4), [Me₂NH(CH₂)₃NHMe₂][B₅O₆(OH)₄]₂ (5), [Et₂NH(CH₂)₃NHEt₂][B₅O₆(OH)₄]₂ (6), [Me₃NCH₂CH=CH₂][B₅O₆(OH)₄] (7), and [Me₃N(CH₂)₃NMe₃] [B₅O₆(OH)₄]₂^.0.5H₂O (8). The tetraborate(2-) salt, [Me₃N(CH₂)₂NMe₃][B₄O₅(OH)₄]^.2B(OH)₃^.2H₂O (9) was obtained in moderate yield (41%) from a 3:1 reaction of B(OH)₃ with [Me₃N(CH₂)₂NMe₃](OH)₂. All compounds were characterized by spectroscopy (¹H, ¹¹B, ¹³C NMR and IR) and thermal gravimetric analysis (TGA). BET analysis on materials derived thermally from selected samples (1, 2, 6, 7) all had porosities of < 1 m²/g, demonstrating that they were non-porous. Single-crystal XRD structures were obtained for 2, 3, 7, 8 and 9 and all contain extensive H-bonded polyborate lattices.

Influence of organic matter and CO2 supply on bioremediation of heavy metals by Chlorella vulgaris and Scenedesmus almeriensis in a multimetallic matrix

This research evaluated the influence of organic matter (OM) and CO₂ addition on the bioremediation potential of two microalgae typically used for wastewater treatment: Chlorella vulgaris (CV) and Scenedesmus almeriensis (SA). The heavy metal (HM) removal efficiencies and biosorption capacities of both microalgae were determined in multimetallic solutions (As, B, Cu, Mn, and Zn) mimicking the highest pollutant conditions found in the Loa river (Northern Chile). The presence of OM decreased the total biosorption capacity, specially in As (from 2.2 to 0.0 mg/g for CV and from 2.3 to 1.7 mg/g for SA) and Cu (from 3.2 to 2.3 mg/g for CV and from 2.1 to 1.6 mg/g for SA), but its influence declined over time. CO₂ addition decreased the total HM biosorption capacity for both microalgae species and inhibited CV growth. Finally, metal recovery using different eluents (HCl, NaOH, and CaCl₂) was evaluated at two different concentrations. HCl 0.1 M provided the highest recovery efficiencies, which supported values over 85% of As, 92% of Cu, and ≈100% of Mn and Zn from SA. The presence of OM during the loaded stage resulted in a complete recovery of As, Cu, Mn, and Zn when using HCl 0.1 M as eluent.

Novel Non-Metal Cation (NMC) Pentaborate Salts of Some Amino Acids

Non-metal cation (NMC) pentaborate structures, in which some amino acids (valine, leucine, isoleucine, and threonine) were used as cations, were synthesized. The structural characterization of molecules was carried out by elemental analysis, FT-IR, mass, 11B-NMR, and thermal analysis (TGA/DTA) methods. The hydrogen storage capacity of molecules was also calculated by taking experimental results into consideration. The FT-IR spectra support the similarity of structures. The characteristic peaks attributable to pentaborate rings and amino acids were observed. When thermal analysis data were examined, it was observed that pentaborate salts gave similar degradation steps and degradation products. As a final degradation product of all thermal analysis experiments, a glassy form of B2O3 was observed. The valine pentaborate is the most thermally stable. Also, the amounts of hydrate water outside the coordination sphere of the compounds were determined by thermal analysis curves. The peaks of boric acid, triborate, and pentaborate structures were obtained in ppm with the 11B-NMR results of synthesized pentaborate compounds. With powder X-ray spectroscopy, all structures were found to be crystalline but not suitable for single-crystal X-ray analysis. The molecular cavities of the compounds detected by BET were found to be 3.286, 1.873, 2.309, and 1.860 g/cm3, respectively. A low number of molecular cavities can be interpreted in several existing hydrogen bonds in structures. The hydrogen storage capacities of the molecules were found to be in the range of 0.04 to 0.07% by mass.

Hydrated Zinc Borates and Their Industrial Use

Zinc borates are important chemical products having industrial applications as functional additives in polymers, bio-composites, paints and ceramics. Of the thirteen well documented hydrated binary zinc borates, Zn[B₃O₄(OH)₃] (2ZnO∙3B₂O₃∙3H₂O) is manufactured in the largest quantity and is known as an article of commerce as 2ZnO∙3B₂O₃∙3.5H₂O. Other hydrated zinc borates in commercial use include 4ZnO∙B₂O₃∙H₂O, 3ZnO∙3B₂O₃∙5H₂O and 2ZnO∙3B₂O₃∙7H₂O. The history, chemistry, and applications of these and other hydrated zinc borate phases are briefly reviewed, and outstanding problems in the field are highlighted.

Hexaborate(2−) and Dodecaborate(6−) Anions as Ligands to Zinc(II) Centres: Self-Assembly and Single-Crystal XRD Characterization of [Zn{κ3O-B6O7(OH)6}(κ3N-dien)]·0.5H2O (dien = NH(CH2–CH2NH2)2), (NH4)2[Zn{κ2O-B6O7(OH)6}2 (H2O)2]·2H2O and (1,3-pnH2)3[(κ1N-H3N{CH2}3NH2) Zn{κ3O-B12O18(OH)6}]2·14H2O (1,3-pn = 1,3-diaminopropane)

Two zinc(II) hexaborate(2−) complexes, [Zn{κ3O-B6O7(OH)6}(κ3N-dien)]·0.5H2O (dien = NH(CH2CH2NH2)2) (1) and (NH4)2[Zn{κ2O-B6O7(OH)6}2(H2O)2]·2H2O (2), and a zinc(II) dodecaborate(6−) complex, (1,3-pnH2)3[(κ1N-H3N{CH2}3NH2)Zn{κ3O-B12O18(OH)6}]2·14H2O (1,3-pn = 1,3-diaminopropane) (3), have been synthesized and characterized by single-crystal XRD studies. The complexes crystallized through self-assembly processes, from aqueous solutions containing 10:1 ratios of B(OH)3 and appropriate Zn(II) amine complex: [Zn(dien)2](OH)2, [Zn(NH3)4](OH)2, and [Zn(pn)3](OH)2. The hexaborate(2−) anions in 1 and 2 are coordinated to octahedral Zn(II) centres as tridentate (1) or bidentate ligands (2) and the dodecaborate(6−) ligand in 3 is tridentate to a tetrahedral Zn(II) centre.

Li2Na2[B12O19(OH)2]: a new open framework borate with a pcu-type net constructed from large cyclic dodeca-oxoboron units

A new open-framework borate with a pcu-type net has been made under solvothermal conditions by incorporating large cyclic dodeca-oxoboron clusters.

Two 1-D Coordination Polymers Containing Zinc(II) Hexaborates: [Zn(en){B6O7(OH)6}]·2H2O (en = 1,2-diaminoethane) and [Zn(pn){B6O7(OH)6}]·1.5H2O (pn = 1,2-diaminopropane)

The synthesis and characterization by single-crystal X-ray diffraction (XRD) studies of two new zinc(II) hexaborate(2−) complexes, [Zn(en){B6O7(OH)6}]·2H2O (en = 1,2-diaminoethane) (1) and [Zn(pn){B6O7(OH)6}]·1.5H2O (pn = 1,2-diaminopropane) (2), are reported. These complexes crystallize from aqueous solutions containing 10:1 ratios of B(OH)3 and the appropriate Zn(II) amine complexes ([Zn(en)3][OH]2 or [Zn(pn)3][OH]2) through self-assembly processes. The hexaborate(2−) anions in 1 and 2 are coordinated to two Zn(II) centers and form one-dimensional (1-D) polymeric coordination chains. R22(8) and R22(6) inter-chain H-bond interactions play an important role in these self-assembly processes and are discussed.

Linking 1D Transition-Metal Coordination Polymers and Different Inorganic Boron Oxides To Construct a Series of 3D Inorganic-Organic Hybrid Borates

Three inorganic-organic hybrid borates, M(1,4-dab)[B₅O₇(OH)₃] [M = Zn (1), Cd (2), 1,4-dab = 1,4-diaminobutane)] and Co(1,3-dap)[B₄O₇] (3, 1,3-dap = 1,3-diaminopropane), which integrated characteristics of 1D coordination polymers and 1D/3D inorganic boron oxides have been obtained under solvothermal conditions. Compounds 1 and 2 are isostructural and crystallize in a centrosymmetric space group P2₁/c; the 3D achiral structures of 1 and 2 consist of the nonhelical Zn/Cd-1,4-dap coordination polymers and 1D B-O chains. Compound 3 crystallizes in a chiral space group P4₃2₁2; the helical Co-1,3-dap coordination polymer chains are entrained within a 3D B-O network and finally form the chiral framework. Compounds 1-3 represent good examples of using coordination polymers to construct mixed-motif inorganic-organic hybrid borates. Compounds 1 and 2 display blue luminescence when excited with UV light.

Optical glucose sensing using ethanolamine–polyborate complexes

An optical glucose sensor based on polyborate–amine complexes with an aggregation-induced emission mechanism.