Metal Hydroxide Layers Research Articles

Tin-Containing Layered Double Hydroxides

Hydrotalcite-like magnesium–aluminum and magnesium–cobalt–aluminum layered double hydroxides containing tin(II) in metal hydroxide layers have been obtained by the coprecipitation method. The maximal degree of substitution of tin for magnesium in hydrotalcite was 10%. The X-ray diffraction method confirmed the absence of the extraneous phases in samples synthesized using a tin chloride aqueous solution. The sample synthesized using an alcohol solution contained an impurity phase. It has been found that the samples have a characteristic layered structure and include cations of all metals incorporated during the synthesis.

Deterioration of anion-adsorption abilities of layered double hydroxides synthesized in agarose gel

With the goal of improving solid–liquid separability in wastewater treatment, Mg-Al layered double hydroxides (LDH) were synthesized in agarose gel, and the resulting LDH-containing hybrid hydrogels were dried. The anion-adsorption abilities of the dried hydrogels were compared with those of LDH synthesized by means of a conventional constant-pH coprecipitation method at low supersaturation. A surprising result was found: the adsorption abilities of the dried hybrid hydrogels decreased with storage time, whereas the adsorption abilities of the LDH synthesized by the conventional method remained essentially constant. Further investigation revealed that the adsorption abilities of LDH synthesized by rapid mixing of aqueous Mg-Al and aqueous NaOH at high supersaturation (i.e., a method similar to that used to prepare the hybrid hydrogel) also decreased over time. Therefore, only LDH synthesized by coprecipitation at high supersaturation showed deterioration during storage time in anion-adsorption abilities. Observed results that accompanied the deterioration suggest that the decrease was due to the formation of pockets of mutually adjacent Al-occupied cation sites in the metal hydroxide layers of the Mg-Al LDH as a result of rapid mixing of the starting solutions. The presence of mutually adjacent Al-occupied sites is thought to be in instability due to mutual repulsion. This instability may have led to gradual decomposition of hydroxide moieties containing mutually adjacent Al-occupied sites together with interlayer anions of OH– and Cl− to form aluminum hydroxide or basic aluminum chloride, as well as to separation of nearby Mg(OH)2 moieties from LDH structure.

Perchlorate‐Intercalated Layered Double Hydroxide of Ca and Al: Synthesis, Structure Refinement, and Reversible Dehydration

Hydrocalumite‐like layered double hydroxides are anionic clays comprising positively charged metal hydroxide layers of the composition [Ca2Al(OH)6(H2O)2]+. The water molecules provide the seventh coordination for the Ca2+ ion. Anions are intercalated in the interlayer space to balance the charge leading to a class of LDHs having the formula [Ca2Al(OH)6(H2O)2]·A (A = Cl, Br, I). Upon dehydration the Ca2+ ion gets coordinatively unsaturated, and crystal chemical considerations dictate that the layered structure should collapse. When A = ClO4–, the LDH dehydrates fully below 80 °C, but the layered structure is retained to well over 180 °C. Structure refinement shows that the ClO4– ion in the hydrated phase has one Cl–O bond parallel to the c‐axis, also the stacking direction (molecular symmetry C3v). Upon loss of water, the perchlorate ion not only diffuses to a different position, but also reorients in such way that one of its O atoms directly coordinates with the Ca2+ ion to provide for coordinative saturation of the Ca2+ ion. In the event, the local symmetry of the ClO4– ion is reduced. The hydrated phase is restored on cooling (temperature 27 °C, ambient humidity ca. 50 %).

Development of Highly Ion-Conductive Layered Double Hydroxide As Electrolyte for Solid-State Alkaline Fuel Cells

Layered Double Hydroxides (LDHs) have been studied by many researchers for their interesting properties such as ion exchangers, adsorbents, polymer stabilizer, catalyst, and so on. LDHs are well known as anionic clays include anion species and water molecules in the interlayer which consist of positively charged metal hydroxide layers. It was reported that some types of LDHs prepared by co-precipitated method have high OH- conductivity and high performance as electrolyte for Alkaline Fuel Cells (AFCs)1). On the other hand, it is necessary to develop a newly industrial LDH synthesis method which enables to synthesize the particle and the composition uniformly. Homogeneous precipitation method with Urea is one of the general and promising LDH synthesis method to prepare the uniform LDH, in which pH controlled by hydrolysis of Urea. However only CO3 2- type LDHs are formed by the method. Therefore, we developed the new type synthesis named “decarboxylation method” that enables to synthesize LDH with high crystallinity and selective anion species in inner layer from precursor compounds in one pot. Prepared samples were measured by ICP and XRD to determine the compositions and structures, respectively, and observed by FE-SEM. Several intercalated anion (CO3 2-, SO4 2-, NO3 -, and Cl-) type M(II) (Zn2+, Co2+, and Ni2+)-Al(III)LDHs were successfully prepared by the decarboxylation method with highly crystallinity and uniform particle size distribution. The ionic conductivities on prepared LDHs were measured by the AC impedance method. Each NO3 - type LDH has remarkably higher ionic conductivity than another type LDHs. The NO3 - type Zn-Al LDH has highest conductivity than another cation type LDHs, and its conductivity is via 16 mS/cm at 80 oC under R.H.80%. 1) Y. Furukawa, K. Tadanaga, A. Hayashi, and M. Tatsumisago, Solid State Ionics, 192, 185-187 (2011).

Enhancing Electrocatalytic Activity through Liquid-Phase Exfoliation of NiFe Layered Double Hydroxide Intercalated with Metal Phthalocyanines in the Presence of Graphene.

Earth‐abundant transition‐metal‐based catalysts are attractive for alkaline water electrolysis. However, their catalytic properties are often limited by their poor electrical conductivity. Here, we present a strategy for enhancing the electrical conductivity of NiFe layered double hydroxide (LDH) in order to further improve its properties as an electrocatalyst for the oxygen evolution reaction (OER) in alkaline media. We show that NiFe LDH containing metal tetrasulfonate phthalocyanine in the interlayers between the NiFe oxide galleries can be coupled with graphene during liquid‐phase exfoliation by taking advantage of their π‐π stacking capabilities. A substantial enhancement in the electrocatalytic activity of NiFe LDH with respect to the OER was observed. Moreover, the activity and selectivity of the catalyst materials towards the oxygen reduction reaction were investigated, demonstrating that both the metal hydroxide layer and the interlayer species contribute to the electrocatalytic performance of the composite material.

Why Do Carbonate Anions Have Extremely High Stability in the Interlayer Space of Layered Double Hydroxides? Case Study of Layered Double Hydroxide Consisting of Mg and Al (Mg/Al = 2).

Layered double hydroxides (LDHs) are promising compounds in a wide range of fields. However, exchange of CO32- anions with other anions is necessary, because the CO32- anions are strongly affixed in the LDH interlayer space. To elucidate the reason for the extremely high stability of CO32- anions intercalated in LDHs, we investigated in detail the chemical states of CO32- anions and hydrated water molecules in the LDH interlayer space by synchrotron radiation X-ray diffraction, solid-state NMR spectroscopy, and Raman spectroscopy. We found the rigidity of the network structure formed between the CO32- anions, hydrated water molecules, and the hydroxyl groups on the metal hydroxide layer surface to be a crucial factor underlying the stability of CO32- anions in the LDH interlayer space.

Influence of Varying Synthetic Routes on the Physicochemical Properties of Mg-Al-CO3 and Zn-Al-CO3 Hydrotalcite-Like Compounds: A Comparative Study

Magnesium-Aluminium Carbonate Hydrotalcite-like Compound (Mg-Al-CO3-HTlc) and Zinc-Aluminium Carbonate Hydrotalcite-like Compound (Zn-Al-CO3-HTlc) with Mg/Al and Zn/Al atomic ratio 2:1 was synthesized by co-precipitation and urea hydrolysis methods. Their physicochemical properties were studied using powder X-ray diffraction (PXRD), X-ray fluorescence spectrophotometry (XRF), Fourier transform infrared (FTIR) and Thermogravimetry (TG) and Differential Thermal Analysis (DTA) involving evolved gas analysis (EGA). The PXRD of the synthesized material showed that the crystallinity is influenced by the type of synthetic method and can affect the properties of the hydrotalcite-like compounds. The TG, DTA and EGA results showed that three steps of mass loss occurred corresponding to the release of gallery water, structural water and carbon dioxide (from carbonate decomposition) respectively. Thermal treatment up to about 500oC and beyond transforms them into nonstoichiometric metal stable oxides (MgO and ZnO) whose crystallinity is lower than that of the precursor and then into stable spinel with no further mass loss following the transformation. Derivatives of urea hydrolysis method gave better ordered and more crystalline Mg2AlCO3-HTlc but with smaller unit cell. Variation in synthesis route can influence the mode of stacking of the layers, order of the interlayer anions and water molecules in the gallery space and attraction between the interlayer anions and the hydroxyl ions of the metal hydroxide layers.

Effect of Hydration on Polytypism and Disorder in the Sulfate-Intercalated Layered Double Hydroxides of Li and Al

AbstractThe double hydroxide of Li+ and Al3+ is an anionic clay comprising positively charged metal hydroxide layers and intercalated anions. While the structure of the iono-covalently bonded metal hydroxide layer is well known, relatively less knowledge is available regarding the manner in which the anions and water molecules are packed in the interlayer region. The sulfate ion is of special interest as it can potentially intercalate in a multiplicity of orientations and grow an extended hydration sphere. The sulfate-intercalated double hydroxide was synthesized by the imbibition of Li2SO4 into both the gibbsite and bayerite forms of Al(OH)3 to obtain layered double hydroxides with the nominal formula Li2Al4(OH)12SO4·nH2O (n = 4–8). The as-prepared compounds were poorly ordered and did not yield any structural information. Temperature-induced partial dehydration yielded ordered phases of different structures in the two systems. Simulation of the powder patterns of different model structures, followed by structure refinement in both direct and reciprocal spaces, showed that the gibbsite-derived phase yielded a two-layer polytype of hexagonal symmetry (space group P63/m). The local symmetry of the sulfate ion was close to D2d with one of the C2 axes of the SO42− being nearly parallel to the c axis of the crystal. The bayerite-derived phase yielded a one-layer polytype of monoclinic symmetry (space group C2/m). The sulfate ion was oriented with its C3 axes tilted away from the stacking direction. Cooling and rehydration (relative humidity ~70%) resulted in a reversible expansion of the basal spacing due to the ingress of water molecules from the ambient humidity into the interlayer region. Hydration in both cases resulted in turbostratic disorder. The disorder in the bayerite-derived phase was a result of random intergrowth of motifs with rhombohedral and monoclinic symmetries.

Enhanced removal of Mn (II) from solution by thermally activated Bayer precipitates

This study assessed the ability of thermally activated Bayer precipitates (Bppt) for manganese remediation from acidic solutions, focusing on their application in acid mine drainage water. The Bayer precipitates were formed from the addition of seawater to Bayer liquor residues, and were primarily composed of hydrotalcite and calcium carbonate. Thermal activation of these materials at 320, 380 and 440 °C showed a reduction in Bayer hydrotalcite crystallinity and increased surface area due to the decarbonation and dehydroxylation of the mixed metal hydroxide layers in Bayer hydrotalcite. At higher thermal activation temperatures (380 and 440 °C), partial decarbonation of calcium carbonate were suspected of forming calcium oxide, which aided the neutralisation process. The removal capacities for manganese were found to increase with thermal activation temperature, which corresponded with increased maximum pH (pH > 10 for 380 and 440 °C heated sample). Treatment of acidic solutions with Bayer precipitates simultaneously removed manganese and aluminium, which is not achievable in lime neutralisation technologies currently used in acid mine drainage treatment. The optimum thermal activation temperature was found to be 380 °C, showing high manganese removal performance and a ten-fold reduction in material mass required when compared to Bayer precipitate. Removal mechanisms of manganese were found to be a combination of hydrotalcite reformation (determined by X-ray photoelectron spectroscopy, X-ray diffraction and infrared spectroscopy), surface precipitation and surface complexation, as well as the formation of hausmannite and rhodochrosite.

Enhanced catalytic performance of Cr-inserted hydrotalcites in the liquid oxidation of styrene

Chromium(III) ions were inserted in magnesium hydroxide layers via co-precipitation route. In the low-chromium content sample, Cr(III) ions are present mostly at octahedral sites of metal hydroxide layers, while some Cr(VI) species formed on the external surface of the high-chromium content catalyst. The Cr-doped metal hydroxide layer ions play as active sites for the oxidation of styrene with H2O2 at a low temperature. The insertion of chromium(III) in the brucite-like sheets enhanced catalytic stability of catalysts in the oxidation of styrene. The Cr-doped hydrotalcites showed a good activity (50–60%), and high selectivity to benzaldehyde (80–85%) at room temperature.

Crystal chemistry of natural layered double hydroxides. 5. Single-crystal structure refinement of hydrotalcite, [Mg6Al2(OH)16](CO3)(H2O)4

AbstractHydrotalcite, ideally [Mg6Al2(OH)16](CO3)(H2O)4, was studied in samples from Dypingdal, Snarum, Norway (3Rand 2H), Zelentsovskaya pit (2H) and Praskovie–Evgenievskaya pit (2H) (both Southern Urals, Russia), Talnakh, Siberia, Russia (3R), Khibiny, Kola, Russia (3R), and St. Lawrence, New York, USA (3Rand 2H). Two polytypes, 3Rand 2H(both ‘classical’), were confirmed on the basis of single-crystal and powder X-ray diffraction data. Their chemical composition was studied by electron-microprobe analysis, infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. The crystal structure of hydrotalcite-3Rwas solved by direct methods in the space groupR$ {\bar 3} $mon three crystals (two data collections at 290 K and one at 120 K). The unit-cell parameters are as follows (290/290/120 K):a= 3.0728(9)/3.0626(3)/3.0617(4),c= 23.326(9)/23.313(3)/23.203(3) Å andV= 190.7(1)/189.37(4)/188.36(4) Å3. The crystal structures were refined on the basis of 304/150/101 reflections toR1= 0.075/0.041/0.038. Hydrotalcite-2Hcrystallises in theP63/mmcspace group; unit-cell parameters for two crystals are (data collection at 290 K and 93 K):a= 3.046(1)/3.0521(9),c= 15.447(6)/15.439(4) Å,V= 124.39(8)/124.55(8) Å3. The crystal structures were refined on the basis of 160/142 reflections toR1= 0.077/0.059. This paper reports the first single-crystal structure data on hydrotalcite. Hydrotalcite distribution in Nature, diagnostic features, polytypism, interlayer topology and localisation ofM2+–M3+cations within metal hydroxide layers are discussed.

Hydration-induced interpolytype transformations in the bayerite-derived nitrate-intercalated layered double hydroxide of Li and Al

The bayerite-derived layered double hydroxide of Li and Al crystallizes in a hexagonal structure (space group P3¯1m) on temperature induced dehydration. The metal hydroxide layers are stacked one above another [stacking vector (0, 0, 1)] in this crystal and the nitrate ion is intercalated with its molecular plane parallel to the metal hydroxide layer. On hydration, (i) there is an expansion in the basal spacing, and (ii) a translation of successive metal hydroxide layers by (1/3, 0, 1) relative to one another. Additionally numerous weak reflections emerge in the powder X-ray diffraction pattern possibly signifying a massive change in the packing of atoms in the interlayer. Partial structure refinement using only the major Bragg reflections suggests that the crystal adopts a structure of monoclinic symmetry (space group C2/m) with the nitrate ion oriented with its molecular plane perpendicular to the metal hydroxide layer. The complete pattern could be indexed to a cell of orthorhombic symmetry (space group P222) but the structure could not be refined for want of a structure model. The absence of a rational relationship between the cell parameters of the orthorhombic and monoclinic cells suggests that the hydrated phase crystallizes in either an incommensurate structure or in an entirely different crystal structure.

Synthesis of α- and β-CoNi binary hydroxides nanostructures and luminol chemiluminescence study for H2O2 detection

Herein, we firstly reported utilization of α- and β-CoNi hydroxides nanostructures as efficient catalyst for the luminol-H2O2 CL reaction. The catalysts were synthesized by hydrothermal method and characterized by XRD, FT-IR, FE-SEM/EDX, and UV–vis. The α-form had layered double hydroxide (LDH) structure witout trivalent cations in the metal hydroxide layer, while the structure of β-phase was similar to brucite. UV–vis spectra demonstrated that the partial oxidation of Co2+ and Ni2+ did not occur in the both catalysts. It was found that α- and β-CoNi could significantly enhance CL reaction of luminol-H2O2 at pH = 11. During study of experimental parameters the higher relative intensity of CL signal in the presence of α-Co-Ni hydroxide was observed. This may be due to the greater Co2+/Ni2+ ratio in this catalyst than β-phase. Therefore, a facile and rapid method was developed to assay H2O2 using α-CoNi binary hydroxide as catalyst. Under optimum conditions, in the range 0.1–12 μM of H2O2 concentrations the CL intensity was linear and a detection limit (S/N = 3) of 0.05 μM for H2O2 was obtained. The relative standard deviation for 6 repetitive determinations was less than 2.9%. The proposed method was successfully applied to detect H2O2 in river water samples with recoveries of 97.3% and 106%.

$$\hbox {NO}_{2}^{-}$$ NO 2 - and $$\hbox {SCN}^{-}$$ SCN - -intercalated layered double hydroxides: structure and orientation of anions in the interlayer gallery

\(\hbox {NO}_{2}^{-}\) and \(\hbox {SCN}^{-}\) are two common small inorganic anions. The former is a common industrial pollutant. The latter is linear and is a good mimic for the toxic \(\hbox {CN}^{-}\) ion. The structures of these two anions are refined within the gallery of the [Zn–Al]-layered double hydroxide (LDH). Both LDHs crystallize as mixed anion phases. The nitrite is found to co-exist with the nitrate ion. The nitrite ion is intercalated with its molecular plane inclined to the metal hydroxide layer. In the case of the \(\hbox {SCN}^{-}\) intercalated LDH, no other anion was detected by ion chromatography, suggesting that the \(\hbox {SCN}^{-}\) deficiency is compensated by intercalated hydroxyl ions. In this case, the \(\hbox {SCN}^{-}\) ion is found to be intercalated with its molecular axis inclined to the metal hydroxide layer.

Chemistry below graphene: Decoupling epitaxial graphene from metals by potential-controlled electrochemical oxidation

While high-quality defect-free epitaxial graphene can be efficiently grown on metal substrates, strong interaction with the supporting metal quenches its outstanding properties. Thus, protocols to transfer graphene to insulating substrates are obligatory, and these often severely impair graphene properties by the introduction of structural or chemical defects. Here we describe a simple and easily scalable general methodology to structurally and electronically decouple epitaxial graphene from Pt(111) and Ir(111) metal surfaces. A multi-technique characterization combined with ab-initio calculations was employed to fully explain the different steps involved in the process. It was shown that, after a controlled electrochemical oxidation process, a single-atom thick metal-hydroxide layer intercalates below graphene, decoupling it from the metal substrate. This decoupling process occurs without disrupting the morphology and electronic properties of graphene. The results suggest that suitably optimized electrochemical treatments may provide effective alternatives to current transfer protocols for graphene and other 2D materials on diverse metal surfaces.

Synthon Approach to Structure Models for the Bayerite-Derived Layered Double Hydroxides of Li and Al

The Br- ion intercalated layered double hydroxide (LDH) of Li and Al obtained from the bayerite-Al(OH)3 precursor crystallizes in a structure different from that of the gibbsite-Al(OH)3 derived counterpart. Additionally, it undergoes temperature- and humidity-induced reversible interpolytype transformations. The dehydrated LDH (T ≈ 120 °C) adopts a structure of hexagonal symmetry (space group P3̅1m) and comprises a stacking of the metal hydroxide layers arranged one above another. On cooling and rehydration, the LDH adopts a structure of monoclinic symmetry with a stepwise increase in the stacking angle, β. Using the structural synthon approach, based on the systematic elimination of the principal symmetry elements of the hexagonal crystal, structure models were generated for each of the two hydration steps (relative humidity ∼50%, >70%) and the structures refined (space group C2/m). The refined structures show that the interpolytype transitions are a result of rigid translations of successive metal hydroxide layers relative to one another by translation vectors (1/6, 0, 1) and (1/3, 0, 1), respectively.

Reappraisal of Polytypism in Layered Double Hydroxides: Consequences of Cation Ordering in the Metal Hydroxide Layer

Recent diffraction studies on layered double hydroxides have shown that the three-layer polytypes that were thought to crystallize in rhombohedral symmetry are actually one-layer polytypes of monoclinic symmetry. However, the prevailing Bookin and Drits (1993) scheme of polytypism, which is based on the widely accepted cation-disordered structure model, fails to predict the occurrence of low symmetry (monoclinic and orthorhombic) polytypes among the layered double hydroxides. In this work, a cation-ordered metal hydroxide layer (layer group p312/m or c12/m1) is chosen as the basic building block. Application of the structural synthon approach enables the description of the complete universe of polytypes comprising 1H, 1M1–7, 2H, 2O, 3R, 3H, 6H, and 6R among others (M: monoclinic; O: orthorhombic). These polytypes are characterized by their unique stacking vectors. The polytypes of large unit cell volume are obtained by a combination of two or more stacking vectors. This work has relevance to the understa...

Effects of reduced dimensionality on the properties of magnesium hydroxide and calcium hydroxide nanostructures.

Metal hydroxides are a class of layered materials that contain two-dimensional metal hydroxide layers that can be isolated to form layered nanostructures. In this work, density functional theory (DFT) and self-consistent-charge density-functional tight-binding (SCC-DFTB) methods have been used to investigate the properties of magnesium hydroxide and calcium hydroxide nanostructures. The properties of single layer and multi layer structures with up to 10 metal hydroxide sheets and nanoparticles containing more than 2000 atoms have been calculated and compared with the bulk properties of these systems. The accuracy of the DFT methods employed and SCC-DFTB parameters developed in this study were validated against available experimental data. The results of the calculations indicate that significant differences exist between the properties of the nanostructures and the corresponding bulk values. In particular, the interlayer binding energies, electronic band gaps, and spectroscopic features are size-dependent and tend to converge to the bulk values as the size of the nanosystem is increased. The calculated binding energies and shear moduli show that all nanostructures are mechanically stable, in agreement with the experimental reports; although, their stabilities may be affected by the presence of intercalated species. Energy decomposition analyses reveal that the intralayer interactions in the investigated systems are predominantly electrostatic in nature, while the interlayer interactions are dominated by dispersion and polarization components. The results presented here quantify various properties of magnesium hydroxide and calcium hydroxide nanostructures, and could be used to understand the properties of other nanosystems containing layers of metal hydroxides in their structure.

Design and synthesis of ternary-component layered double hydroxides for high-performance supercapacitors: understanding the role of trivalent metal ions

To understand the insightful mechanics of the effects of the trivalent metal ions on the electrochemical performance of ternary-component layered double hydroxides (LDH), the ternary LDH composed by NiCoAl-LDH, NiCoAl0.5Fe0.5-LDH and NiCoFe-LDH are designed, synthesized and characterized. Despite bivalent metal ions (Ni2+, Co2+) having been demonstrated to play a highly specialized role in surface redox chemistry, the role of the trivalent metal ions within the metal hydroxide layer has not been elucidated yet in supercapacitor applications. Here we demonstrated that Al3+ has a positive effect on the stabilization of host layers of LDH, which leads to the improvement of the electrochemical performance. It was also found that Al3+ could regulate the crystallinity, hydrophilicity and nanosheets stacking of LDH. Further, comparative studies show that NiCoAl-LDH exhibited superior specific capacitance of 1153Fg−1 at 6Ag−1, and excellent cycling stability (ca. 92.97% capacitance retention after 3000 cycles). We attribute such remarkable enhancement in cyclic performance to the framework stability of Al3+ in the multi-metal LDH matrix layer. These results highlight the importance of trivalent metal ions in ternary-component LDH for high-performance supercapacitors and may guide future design and synthesis of LDH.

A Crystal Chemical Approach to a Cation-Ordered Structure Model for Carbonate-Intercalated Layered Double Hydroxides

Layered double hydroxides comprise a stacking of positively charged metal hydroxide layers with anions and water molecules included in the interlayer galleries. Among the anions, the carbonate ion is the most ubiquitous in both mineral and laboratory synthesized phases. Taylor (1973) suggested that the carbonate ion (molecular symmetry D3h) prefers a trigonal prismatic interlayer site (local symmetry D3h), whereby the hydrogen bonding with the metal hydroxide layer is maximized. However, the cation ordered structure models of hexagonal symmetry include interlayer sites which are exclusively trigonal antiprisms (local symmetry D3d). In keeping with Taylor’s criterion, a hexagonal stacking of metal hydroxide layers does not permit the inclusion of carbonate ions in the interlayer. In this work, a crystal chemical approach is adopted based on the translationgleiche subgroups of hexagonal and cubic summits to arrive at a structure model based on the space group C2/m. In this structure, not only is the 3-fold ...