Über quaternäre Oxoplumbate(IV). Zur Kenntnis von Rb2Li14[Pb3O14] und Cs2Li14[Pb3O14]

On Quaternary Oxoplumbates(IV). On the Knowledge of Rb₂Li₁₄[Pb₃O₁₄] and Cs₂Li₁₄[Pb₃O₁₄] For the first time, Rb₂Li₁₄[Pb₃O₁₄] and Cs₂Li₁₄[Pb₃O₁₄] have been prepared by heating of mixtures of Li₂O, β-?PbO₂”? and Rb₂PbO₃, Cs₂PbO₃ respectively with Li:Pb:A = 14:3:2, (A = Rb, Cs). [Ag-cylinders, sealed under vacuum in Duran-glass ampoule, 590 and 550°C, 40 d, powder (650°C, 200 d, single crystals of Rb₂Li₁₄[Pb₃O₁₄])]. Rb₂Li₁₄[Pb₃O₁₄] is nearly colourless with ivory nuance, Cs₂Li₁₄[Pb₃O₁₄] is pale yellow. According to powder and single crystal investigations, both are isotypic with K₂Li₁₄[Pb₃O₁₄]. Structure refinement of Rb₂Li₁₄[Pb₃O₁₄]: 1015 symmetry independent reflexions, four-circle-diffraktometer PW 1100 (Fa. Philips), ω-scan, MoKα, R = 5.73%, R_W = 5.33%, absorption not considered, space group Immm with a = 1284.71(9), b = 793.90(4), c = 727,35(5) pm, d_x-ray = 4.99 g · cm^?3, d_pyc = 5.01 g · cm^?3, Z = 2. Cs₂Li₁₄[Pb₃O₁₄]: a = 1295.28(12), b = 796.69(8), c = 732.44(7) pm, d_x-ray = 5.31 g · cm^?3, d_pyc = 5.28 g · cm^?3, Z = 2. The Madelung Part of Lattice Energy, MAPLE, Effective Coordination Numbers, ECoN, these via Mean Effective Ionic Radii, MEFIR, are calculated.     

“Fragmentierung” und “Aggregation” bei Bleioxiden Über das Oligooxoplumbat(IV) K2Li6[Pb2O8]

“Fragmentation” and “Aggregation” on Lead Oxides. On the Oligooxoplumbate(IV) K₂Li₆[Pb₂O₈] For the first time, the dinuclear Oxoplumbate(IV) K₂Li₆[Pb₂O₈] has been prepared as transparent colourless single crystals by heating mixtures of K₂PbO₃, Li₂O, and “PbO₂” with K:Li:Pb = 1:3:1 e. g. [Ag-cylinders, sealed under vacuum in Supremax-glass ampoule, 660°C, 120 d]. The structure determination verifies the space group P1 with a = 6.9720(9), b = 5.9252(6), c = 5.9312(7) Å, α = 88.05(1)°, β = 107.94(1)°, γ = 107.30(1)°; d_x = 4.95 g · cm^?3, d_pyk = 4.91 g · cm^?3; Z = 1, [2107 symmetry independent hkl, fourcircle-diffractometer Philips PW 1100, ω—2Θ—scan, MoKα, R = 5.07%, R_w = 4.59%, absorption not considered]. The structure is characterized by the group [Pb₂O₈] — two edge connected (equatorial/apical) trigonal bipyramids — that is observed for the first time. Several ways of synthesis are given. The Madelung Part of Lattice Energy, MAPLE, Effective Coordination Numbers, ECoN, these via Mean Effective Ionic Radii, MEFIR, are calculated.     

Neue Oxoterbate(IV) mit Lithium Rb2Li14[Tb3O14] und Li6Tb2O7

New Oxoterbates(IV) with Lithium: On Rb₂Li₁₄[Tb₃O₁₄] and Li₆Tb₂O₇ For the first time we prepared Rb₂Li₁₄[Tb₃O₁₄] as yellow single crystals from Li₈TbO₆ and Rb₂O (Tb:Rb = 1:2) [Ag-cylinder, 500°C, 30 d, then Au-tube, 700°C, 27 d]. The structure refinement [652 I₀ (h kl), four circle diffractometer Philips PW 1100, ω-scan, MoKα, R = 4.69%, R_w = 3.24%, absorption considered, Immm with a = 1 283.07(10), b = 790.87(7), c = 736.87(7)pm, Z = 2, d_x = 4.30 g · cm^?3] confirms that it is isotypic with K₂Li₁₄[Pb₃O₁₄]. Furthermore we got for the first time Li₆Tb₂O₇ as a bright yellow compound from Li₂O₂ and “Tb₄O₇*” [(Li:Tb = 3.4:1), Au-ube, 750°C, 13 d (powder), 850°C 22 d (single crystals)] and by thermal decomposition of Rb₂Li₁₄[Tb₃O₁₄] (Au-tube, 850°C, 25 d). Powder and single crystal data [1 327 I₀ (h kl), four circle diffractometer PW 1100, ω-scan, AgKα, R = 9.38%, R_w = 5.23%, absorption not considered, P2₁/a, a = 1 056.30(10), b = 613.50(4), c = 546.56(5) pm, β = 109.668(7)°, Z = 2, d_x = 4.67 g · cm^?3 d_pyc = 4.53 g · cm^?3] reveal a new type of structure that may be deduced by the NaCl-type of structure. The Madelung Part of Lattice Energy, MAPLE, Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated and discussed.     

Quaternäre Monoborate der Alkalimetalle: Na4Li5[BO3]3

Quaternary Monoborates of Alkali Metals: Na₄Li₅[BO₃]₃ We prepared hitherto unknown Na₄Li₅[BO₃]₃ in the shape of monoclinic, colourless-transparent and prismatic single crystals [a = 1238.8(5) pm, b = 729.6(3) pm, c = 973.8(3) pm, β = 107,29(4)°, Z = 4, d_x = 2,397 g/cm³, d_pyk = 2,37 g/cm³]. The crystal structure was solved by four-circle-diffractometer [PW 1100, MoKα , R = 9,02%, R_w = 5,29%, 1221 I₀(hkl)]I₀(hkl)]. Na₄Li₅[BO₃]₃ is sensitive against atmospheric moisture; hydrolysis takes place within 60 minutes. Effective Coordination numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, and the Madelung Part of Lattice Energy, MAPLE, are calculated and discussed.     

Ein neues Cobaltat mit Inselstruktur: Li6[CoO4]

A New Cobaltate with Isolated Anion Structure: Li₆[CoO₄] For the first time transparent, blue single crystals of Li₆[CoO₄] have been prepared (Li₂O/Na₂O/?CoO”? (Li:Na:Co = 1.3:1.3:1), Co-tube, 580°C, 22 d). Corresponding to Li₆□CoO; it is an ordered variant of the Li₂O-type of structure: P4₂/nmc; a = 653.6(1) pm, c = 465.4(1) pm; Z = 2; d_x = 2.75 g cm^?3, d_pyk = 2.71 g cm^?3 (4-circle-diffractometer-data (PW 1100), AgKα; 230 from 936 I₀(hkl); R = 9.58%, R_W = 5.25%). Parameters see text. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated and discussed. The magnetic properties are measured in the temperature range of 14–297 K.     

Zur Kenntnis von K4PbO4 und Rb4PbO4

On K₄PbO₄ and Rb₄PbO₄ For the first time single crystals of K₄[PbO₄] have been prepared by heating K₄PbO₃ in O₂. The structure has been refined [K₄[PbO₄]: 3029 I₀(hkl), four circle diffractometer PW 1100, ω-scan, MoKα, R = 6.73%, R_w = 6.64%, P1 ; a = 658.62(15), b = 658.41(12), c = 986.64(21) pm, α = 79.74(2)°, β = 108.45(2)°, γ = 112.49(2)°, d_x = 3.79 g · cm^?3, d_pyk = 3.78 g · cm^?3, Z = 2; Rb₄[PbO₄]: a = 686.94(18), b = 684.43(18), c = 1020.73(21) pm, α = 79.28(2)°, β = 108.40(2)°, γ = 113.02(2)°, d_x = 4.87 g · cm^?3, d_pyk = 4.85 g · cm^?3, Z = 2, (from Rb₂PbO₃ and Rb₂O)]. Both compounds are isotypic with K₄SnO₄. The Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated.     

Novel large heteropolymetalate complexes formed from Ni(II) and cryptate [As<Subscript>4</Subscript>W<Subscript>40</Subscript>O<Subscript>140</Subscript><Superscript>28-</Superscript>

The heteropolytungstate (NH4)₂₀[Na2(H₂O)₂Ni(H₂O)₅{Ni(H₂O)}₂As₄W₄₀O₁₄₀] · 61H₂O is obtained by the reaction of Na₂₇[NaAs₄W₄₀O₁₄₀] · 60H₂O with NiCl₂ · 6H₂O and NH₄Cl in pH≈4.0. The structure and chemical composition are determined by X-ray diffraction analysis and element analysis. The crystal data and main structure refinement are: a = 1.33135(18) nm, b = 1.9722(3) nm, c = 3.6430(5) nm, α = 78.010(2)°, β = 82.145(2)δ, γ = 74.385(2)°, V = 8.978(2) nm³, triclinic crystal system, space group: P1, Z = 2, R1 = 0.0512, and wR2 = 0.0684(I >2σ). The four S2 sites of the big cyclic ligand [As₄W₄₀O₁₄₀]^28- are occupied by two Na⁺ and two Ni²⁺ respectively, and each site supplies four O_d coordinating to metal ion. The coordination number of Ni²⁺ is six, and that of two Na⁺ is five and six respectively. The third Ni²⁺ locates outside the cyclic [As₄W₄₀O₁₄₀]^28- and connects with one O_d, and its coordination number is six.     

Über Oxoosmate(VII) Na5[OsO6] und Li5[OsO6]

On Oxoosmates(VII). Na₅[OsO₆] and Li₅[OsO₆] For the first time bluish black single crystals of Na₅[OsO₆] have been prepared. The structure was determined according to four-circle-diffractometer data. According to powder samples Li₅[OsO₆] is isotypic to Na₅[OsO₆]. Both are of the NaCl-type like Na₅[ReO₆] (space-group C2/m (No. 12, I.T.), Z = 2): Na₅[OsO₆]: a = 568.10(4), b = 975.00(6), c = 559.65(5) pm, β = 111.00° (1), 436 hkl, 4° ? Θ ? 30°, MoK, R = 2.7%, R_W = 2.6%. Li₅[OsO₆]: a = 568.10(4), b =975.00(6), c = 559,65(5) pm, β = 111.00° (1). Effective Coordination Numbers, ECoN, and the Madelung Part of Lattice Energy, MAPLE, are calculated and discussed.     

Preparation,Structure and Properties of the One-Dimensional Polymeric Complex Na2[AlW3O4(O2CEt)8]2

Abstract

The heterometallic polymeric cluster Na₂[AlW₃O₄ (O₂CEt)₈]₂ (1) has been prepared by reaction of W(CO)₆ and NaWO₄·2H₂O with AlCl₃ at 120°C in propionic anhydride and characterized by X-ray crystallography, with the following crystal data: triclinic, space group P1, a = 12.205(5), b = 13.032(4), c = 13.925(3) Å, α = 90.21(3)°, β = 109.53(5)°, γ = 117.26(6)°, V = 1822.8(1)ų, Z = 1, R = 0.038 and R_w = 0.101. The structure consists of two triangular [W₃O₄(O₂CEt)₈]^4? cluster unit, which act as polydenate ligands to link Al³⁺ and Na⁺ ions forming a one–dimensional chain structure. IR spectra show characteristic [W₃O₄]⁴⁺ bands at 746–815 cm^?1. Thermal analysis reveals that the complex is air stable up to 250°C. Cluster 1 decomposes in hot aqueous 2 M HCl solution to produce discrete [W₃O₄]⁴⁺ units.     

Neue Oxozincate der Alkalimetalle: Rb2[ZnO2] und Cs2[ZnO2]

New Oxozineates of Alkali Metals: Rb₂[ZnO₂] and Cs₂[ZnO₂] Colorless single crystals of the hitherto unknown Rb₂[ZnO₂] (a = 9.55₈, b = 6.33₅, c = 15.91 Å, β = 118.6°, z = 8, d_pyk = 4.11, d_rö = 4.21 g · cm^?3) and Cs₂[ZnO₂] (a = 9.85₁, b = 6.61₉, c = 16.26 Å, β = 116.8°) have been prepared, which crystallize monoclinic, P2₁/c – D. (For parameters see text.) Unexpected there are “isolated” groups [Zn₄O₈]. Half of the Zn atoms exhibit the unusual coordination number 3 towards O^2?. The Madelung Part of Lattice Energy, MAPLE, and the Effective Coordination Number, ECoN, the latter by means of Mean Fictive Ionic Radii, MEFIR, are calculated and discussed.     

Zur Konstitution von ‚KPbO2’︁

On the Constitution of ‘KPbO₂’ Transparent, orangered single crystals of K₂Pb₂O₄ have been obtained by heating mixtures of K₂O₂ and PbO (K:Pb = 1:1) [Ag-cylinders, 560°C, 40 d, after cooling (15°C/h)]. The space group is P1 , a = 1295.94(9), b = 753.35(7), c = 697.12(8) pm, α = 118.00(1)°, β = 106.15(1)°, γ = 93.44(1)°, Z = 4, d_x = 6.573 und d_pyk = 6.54 g · cm³. The structure is characterized by rutilanalogous chains of edge-connected [PbO₆] octahedra along [001] according to [PbO_4/2O_2/1] = PbO₄. On both sides of such a chain there are respectively three O^2?, which belong to two octahedra, alternating capped with Pb²⁺ or not capped, corresponding to [PbO₄]Pb₂[PbO₄]□₂… = Pb₂O₄. Those capped chains are held together by K(1)…K(4), each of them with C.N. 6. The order of the chains corresponds to the motive of a closest packing. The Madelung Part of Lattice Energy, MAPLE, Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated and discussed.     

Ternäre Hydroxide. I. Synthese,Struktur und Eigenschaften von Li2[Sn(OH)6] · 2 H2O

Ternary Hydroxides. I. Synthesis, Structure, and Properties of Li₂[Sn(OH)₆] · 2 H₂O Colourless crystals of Li₂[Sn(OH)₆] · 2 H₂O were synthesized by reaction of SnCl₄ with LiOH in aqueous solution. The crystal structure was determined from single crystal data. Li₂[Sn(OH)₆] · 2 H₂O: monoclinic, P2₁/n (Nr. 14), a = 502.3(1), b = 692.3(1), c = 1020.2(3) pm, β = 99.78(1)°, V = 349.6(2) · 10⁶ pm³, Z = 2, R/Rw = 0.0192/0.0472, N(I) > 2σ(I) = 1527, N(Par.) = 54. Within the crystal structure only slightly distorted octahedrally [Sn(OH)₆]^2? ions are bonded via hydrogen bonds with water molecules forming layers, which themselve are linked by tetrahedrally coordinated Li ions; the structure is in accordance with the IR-data and the results of the ¹¹⁹Sn solid state NMR-spectroscopy; the hydrat water is eliminated at 117.1°C, the condensation reaction – forming the ternary oxide – takes place at 257.7°C.     

Ein anionischer Oxohydroxo‐Komplex mit Bismut(III): Na6[Bi2O2(OH)6](OH)2 · 4H2O

An Anionic Oxohydroxo Complex with Bismuth(III): Na₆[Bi₂O₂(OH)₆](OH)₂ · 4H₂O Colourless, plate‐like, air sensitive crystals of Na₆[Bi₂O₂(OH)₆](OH)₂ · 4H₂O are obtained by reaction of Bi₂O₃ or Bi(NO₃)₃ · 5H₂O in conc. NaOH (58 wt %) at 200 °C followed by slow cooling to room temperature. The crystal structure (triclinic, P 1¯, a = 684.0(2), b = 759.8(2), c = 822.7(2) pm, α = 92.45(3)°, ß = 90.40(3)°, γ = 115.60(2)°, Z = 1, R1, wR2 (all data), 0, 042, 0, 076) contains dimeric, anionic complexes [Bi₂O₂(OH)₆]^4— with bismuth in an ψ¹‐octahedral coordination of two oxo‐ and three hydroxo‐ligands. The thermal decomposition was investigated by DSC/TG or DTA/TG and high temperature X‐ray powder diffraction measurements. In the final of three steps the decomposition product is Na₃BiO₃.     

Über Perrhenate. 3 Zum Aufbau des Mesoperrhenates Na3[ReO5]

About Perrhenates. 3 On the Structure of the Mesoperrhenate Na₃[ReO₅] By tempering powder samples (prepared from mixtures of binary oxides: Na₂O₂/ReO₂ and Na₂O/ReO₃ respectively, Na : Re = 3 : 1, Ar and O₂ atmosphere respectively, 400–450°C, corundum boat) in a closed Ag cylinder (500–550°C, 10 d) yellow single crystals of Na₃ReO₅, sensitive to moisture, were grown. The compound crystallizes trigonal, space group P3₁, P3₂ respectively, with a = 5.544(1), c = 13.580(7) Å, Z = 3, d_rö. = 4.62 g/cm³. The crystal structure [4-circle diffractometer data, 1091 I₀(hkl), AgKα, R = 6.14, R_w = 6.08%] is characterized by “isolated” bipyramids ReO₅. Na⁺ ions are occupying all the tetrahedral (Na2, Na3) and octahedral (Na1) holes of the pseudocubic face centred (c/a = 2.441) Re part of the lattice; resulting in a Na₃Re kation framework corresponding to the Li₃Bi type of structure. Effective Coordination Numbers (ECoN), the Madelung Part of Lattice energy (MAPLE) and the charge distribution (CHARDI) are computed and discussed.     

Synthesis and crystal structure of Na2[RuNOCl5] · 6H2O

A procedure for the synthesis of Na₂[RuNOCl₅]·6H₂O is described. The complex was studied by IR spectroscopy and by thermal, X-ray phase, and X-ray diffraction analyses. Crystal data: a = 26.740(7), b = 31.581(7), c= 6.918(3) Å, V = 5842(3) ų space group Fdd2. Z = 16, d_calc= 2.103, d_exp = 2.112 g/cm³. The structure consists of [RuNOCl₅]^2? complex cations, Na⁺ cations, and crystallization water molecules. The compound is stable in conditions of high humidity of atmosphere but irreversibly loses up to four water molecules when stored in dry atmosphere. Removal of two water molecules is accompanied by crystal decay and changes in the crystal structure. Heating the substance above 100°C leads to a hygroscopic anhydrous complex Na₂[RuNOCl₅], which is stable below t = 375°C.     

Notiz über Li2PdO2

Note on Li₂PdO₂ For the first time we prepared ruby-red single crystals of Li₂PdO₂ by reaction with the wall 3 Na₂O + Li₂O₂ + ?Tb₄O₇”?(+ Pd) = 3 Na₂TbO₃ + Li₂PdO₂ + ?TbO₂”?, Pd-tube, 1100°C, 7 d. Single crystal data confirm the Li₂CuO₂-type of structure [a = 375.34(5), b = 298.18(4), c = 931.58(10) pm; spacegroup Immm; d_x = 4.85 g · cm^?3; 144 I₀(hkl); R = 3.54%, Rw = 3.19%; MoKα ; four-circle diffractometer Philips PW 1100] and reveal clearly different parameters compared with those deduced by powder data. The Madelung Part of Lattice Energy, MAPLE, corresponds now to the sum of the MAPLE values of the binary oxides.     

Neue Oxoferrate(III). Na2Li3[FeO4] und K2Li3[FeO4]

New Oxoferrates (III). Na₂Li₃[FeO₄] and K₂Li₃[FeO₄] . Na₂Li₃[FeO₄] and K₂Li₃[FeO₄] (transparent, pink or light yellow single crystals) have been prepared by heating mixtures of the oxides (Na:Li:Fe = 2.2:3.3:1; Ag-tube, 720°C, 27 d or K:Li:Fe = 2.2:3.3:1; analogous, 700°C, 40 d). Na₂Li₃[FeO₄] is isotypic with Na₂Li₃[GaO₄] (a = 832.2(1), b = 796.0(1), c = 656.3(1)pm, Pnnm) and K₂Li₃[FeO₄] with K₂Li₃[GaO₄] (a = 557.7(1), b = 880.6(1), c = 1101.8(2)pm, β = 111.51(2)°, P2₁/c). Four cycle diffractometer data: MoK_α, 525 out of 686 I₀(hkl), R = 9.36%, R_w = 5.97% or 1424 out of 1424 I₀(hkl), R = 8.45%, R_w = 5.66%. Parameters see text. The structures are characterized by calculations of the Madelung Part of Lattice Energy, MAPLE. The Effective Coordination Numbers, ECoN, which are calculated by means of Mean Fictive Ionic Radii, MEFIR, are compared with the analogous gallates.     

Über die komplexen Hydroxide des Chroms: Na9[Cr(OH)6]2(OH)3 · 6 H2O und Na4[Cr(OH)6]X · H2O (X = Cl, (S2)1/2) – Synthese,Kristallstruktur und thermisches Verhalten

Complex Hydroxides of Chromium: Na₉[Cr(OH)₆]₂(OH)₃ · 6 H₂O and Na₄[Cr(OH)₆]X · H₂O (X = Cl, (S₂)_1/2) – Synthesis, Crystal Structure, and Thermal Behaviour Green plate‐like crystals of Na₉[Cr(OH)₆]₂(OH)₃ · 6 H₂O (triclinic, P1, a = 872.9(1) pm, b = 1142.0(1) pm, c = 1166.0(1) pm, α = 74.27(1)°, β = 87.54(1)°, γ = 70.69(1)°) are obtained upon slow cooling of a hot saturated solution of Cr^III in conc. NaOH (50 wt%) at room temperature. In the presence of chloride or disulfide the reaction yields green prismatic crystals of Na₄[Cr(OH)₆]Cl · H₂O (monoclinic, C2/c, a = 1138.8(2) pm, b = 1360.4(1) pm, c = 583.20(7) pm, β = 105.9(1)°) or green elongated plates of Na₄[Cr(OH)₆](S₂)_1/2 · H₂O (monoclinic, P2₁/c, a = 580.8(1) pm, b = 1366.5(3) pm, c = 1115.0(2) pm, β = 103.71(2)°), respectively. The latter compounds crystallize in related structures. All compounds can be described as distorted cubic closest packings of the anions and the crystal water molecules with the cations occupying octahedral sites in an ordered way. The thermal decomposition of the compounds was investigated by DSC/TG or DTA/TG and high temperature X‐ray powder diffraction measurements. In all cases the final decomposition product is NaCrO₂.     

Crystal structure and thermal properties of Na2[ReCl6]·6H2O

The crystal structure of Na₂[ReCl₆]·6H₂O is determined. The crystallographic characteristics are as follows: a = 6.6955(2) ?, b = 7.0926(2) ?, c = 8.3667(3) ?; α = 102.567(1)°, β = 98.853(2)°, γ = 107.236(1)°; V = 360.08(2) ?³, P-1 space group, Z = 1, d _x = 2.550 g/cm³. The thermal properties of Na₂[ReCl₆]·6H₂O are studied in the hydrogen atmosphere. During the thermolysis of Na₂[ReCl₆]_0.50[PtCl₆]_0.50·6H₂O double complex salt in the hydrogen atmosphere, Re _x Pt_1−x nanocrystalline solid solutions were obtained.     

Über Oxotitanate der Alkalimetalle. Zur Kenntnis von Na4Ti5O12

On Oxotitanates of the Alkaline Metals: On Na₄Ti₅O₁₂ Colourless single crystals of the new titanate Na₄Ti₅O₁₂ (starting from mixtures Na₂O/TiO₂, 1000°C, 6 d, Au-crucible, open system) crystallize in the monoclinic system, space group C2/m, a = 26.544(9), b = 2.952(1), c = 6.322(3) Å, β = 95.79(3)°, Z = 2, d_rö = 3.45 and d_pyk = 3.38 g · cm^?3 (four-cycle-diffractometer data, PW 1100, 2?-scan, MoKα). R = 5.09% and R_w = 4.87% for 1178 independent I₀(hkl) with 3° ≤ 2? ≤ 34°. Corrugated layers of Ti₅O₁₂, held together by Na⁺, are stacked along [001]. Details about partially occupied positions of Na⁺, Effective Coordination Numbers (ECoN), the Madelung part of lattice energy (MAPLE), and the structural differences to Na₂Ti₃O₇ are discussed.