Multinuclear Metal Carbonyl Alkoxide and Aryloxide Derivatives as Models for Metal Carbonyls Adsorbed on Metal Oxide Supports

The synthesis and characterization of two tungsten carbonyl dimers containing bridging alkoxide or aryloxide ligands are described. The crystal and molecular structures of [PPN]₂[W₂(CO)₈(OCH₂CF₃)₂], 1, and [Et₄N]₃[W₂(CO)₆-(OPh)₃]-CH₃CN, 2 , are reported and compared with the structures of tetranuclear tungsten derivatives previously described. The dimer 1 crystalizes in the triclinic space group P 1 with unit cell parameters a = 13.460(11) Å, b = 12.318(5) Å, c = 13.842(10) Å, α = 82.73(5)°, β = 59.11(5)°, γ= 80.09(5)°, V = 1938(2) ų, and Z = 1. The complex 2 crystalizes in the monoclinic space group P2₁/n with unit cell parameters a = 11.954(2) Å, b = 19.359(4) Å, c = 26.462(5) Å, β = 102.50(16)°, V = 5979(2) ų, Z = 4. Molecular modeling software was utilized to construct a tetranuclear derivative from 1 similar to the structurally characterized [W(CO)₃OH]₄₋⁴ tetramer. The two tetramers were found to possess similar molecular parameters. This supports the contention that dimers of type 1 are the precursors of the tetramers. Comparisons of the tungsten alkoxides and aryloxides with the behavior of W(CO)₆ on γ-alumina are provided.     

X-Ray crystal structure of the Dye 2,4,6-Tricyano-4'-N,N-diethylaminoazobenzene

The crystal structure and molecular conformation of 2,4,6-tricyano-4'-N,N-diethylaminoazobenzene (C₁₉H₁₆N₆, mol. wt. 328.4a.m.u.) has been determined from X-ray diffraction data: monoclinic P2₁/c, a = 9.302(7)Å, b = 8.733(5)Å, c = 20.98(1) Å, β = 94.93(6)°, V = 1699(2)ų, Z = 4, D_c = 1.284gem^?3, F(000) = 688, λ(MoKα) = 0-71069Å, μ(MoKα) = 0.76cm^?1. The structure was solved by MULTAN andrefined by full-matrix least-squares toR = 0.050 for 1358 independent observed reflections. The azobenzene skeleton is planar to within 0.12Å. Most significant bonding data are: NN, 1.286(4) Å; mean C-N (azo) 1.383(4) Å; mean C-C (cyano) 1.439(5) Å; mean CN 1.146(5)Å; NN-C, 112.8(2)° and 115.9(2)°; N-C-C (cis relative to NN) 127.6(2)° and 124.3(2)° ; N- C- C(trans) 115.2(2)° and 117.7(2)°.     

Reversible Carbon-Carbon Bond Cleavage of a 3-Vinyl-1-Cyclopropene by Rh(I). Molecular Structures of Two Sterically Crowded 1,2,3,5-η-Pentadienediyl Complexes of Rh(III)

1,2,3-Tri-tert-butyl-3-vinyl-1-cyclopropene 6a reacts with [RhCl(C₂H₄)]₂ to give the dimeric 1,2,3,5-η-pentadienediyl complex 7a . The cyclopentadienyl derivative of this complex, 8a , is obtained by reaction of 7a with T1(C₅H₅). Crystal structures of both 7a and 8a were determined: 7a ; orthorhombic, Pbcn, a = 28.136 (4) Å, b = 10.637 (2) Å, c = 12.154 (2) Å, V = 3637.6 (1.2) ų, and Z = 4 : 8a ; triclinic, P 1 -bar, a = 9.906 (2) Å, b = 9.736 (2) Å, c = 12.126 (2) Å, α = 76.07 (2)°, β = 78.21 (2)°, γ = 65.34 (2)°, V = 1024.6 (3) ų, and Z = 2. Treatment of 7a with one equivalent of PMe₃ per Rh center results in regeneration of the vinylcyclopropene, demonstrating the reversibility of the ring opening reaction. Deuterium labelling studies show that both the ring opening and closing reactions proceed with retention of configuration at the vinyl olefin. Thus the trans-deuterated vinylcyclopropene 6b reacts with [RhCl(C₂H₄)₂]₂ to give 7b in which deuterium is located exclusively in the syn position. Treatment of 7b with T1(C₅H₅) yields 8b . Treatment of 7b with one equivalent of PMe₃ per Rh center results in formation of 6b as the sole organic product. Unlike their triphenyl relative 2 , the tri-Bu complexes 7a , 7b, 8a , and 8b are stereochemically rigid in solution at room temperature, and do not undergo an η³ → η¹ → η³ isomerization on the NMR time scale. However, after prolonged heating, syn-anti site exchange of H and D slowly takes place with 8b .     

Structure of the dye 2,6-dichloro-4′-N,N-diethylaminoazobenzene

The structure of 2,6-dichloro-4′-N,N-diethylaminoazobenzene has been determined from X-ray diffractometer data: C₁₆H₁₇Cl₂N₃, MW = 322·2, monoclinic, P2₁/n, a = 11·160 (2), b = 12·066 (2), c = 13·633 (3) Å, β = 116·46 (2)°, V = 1643·5 ų, Z = 4, D_c = 1·30 g cm^?3, F(000) = 672, λ(MoKα) = 0·71069 Å, μ(MoKα) = 3·94 cm^?1. The structure was solved by direct methods and refined to R = 0·073 for 1495 independent reflexions. The molecule is non-planar with a dihedral angle of 87·8° between the phenyl rings. The effects of substituents on the aromatic ring geometry are discussed. Significant molecular parameters are: NN, 1·164 (9) Å; mean ClC, 1·741 (6) Å; mean CN(azo), 1·487 (9) Å; NNC, 112·4 (2)° and 109·1 (2)°; NCC (cis relative to NN), 125·5 (3)° and 122·4 (2)°; NCC (trans relative to NN) 114·0 (3)° and 119·5 (3)°; mean CC(Cl)C, 122·3 (3)°.     

The 1:1 Mixed Stack Complex of Tetrathiafulvalene and 2,5-Dibenzyltetracyanoquinodimethane (TTF:DBTCNQ) at 115 K

Crystallographic constants for the title compound are as follows: M_r = 384.5 + 204.3, triclinic, PĪ, a = 6.878 (2), b = 10.309 (4), c = 11.159 (7) Å, α = 109.94 (4), β = 100.91 (4), γ = 105.64 (3)°, Z = 1, V = 680.8 ų, D_c = 1.46 g cm⁻³, D_m= 1.40 g cm⁻³ (flotation, aqueous KI), λ(MoKα) = 0.71069 Å, μ = 3.27 cm⁻¹, F(000) = 304, R_F = 0.085 for 1948 data with |F₀| > 2.5 σ(F₀). The complex crystallizes in mixed stacks of alternating donors and acceptors with a maximum of intrastack overlap and a minimum of interstack interactions. The degree of charge transfer is shown by a number of criteria to be essentially zero, in stark contrast to the complex of TTF with unsubstituted TCNQ. Comparison is made with the relatively few other complexes of derivatives of TTF and TCNQ which form mixed stack complexes.     

The Molecular and Crystal Structure of Photochemically Formed 1-H1 : 1,2-H2-Trans-2-Bromovinyl-μ-Bromobis(Tricarbonyliron) (Fe-Fe) A Carbonyliron-π-Complex of the 1-Ferra-Allylic System

The molecular structure of 1-h¹: 1,2-h²-trans-2-bromovinyl-μ-bromo-bis(tricarbonyliron) (Fe-Fe), Fe₂Br₂C₈O₆H₂, has been determined from 1970 absorption-corrected diffractometer intensity data by Patterson and Fourier methods and refined anisotropically by least-squares methods to a final R-value of 6.07%, including anomalous-dispersion corrections. The molecular framework consists of two distorted octahedral Fe(CO)₃ moieties linked together by a slightly asymmetric bromine bridge, an Fe-Fe bridge (2.525 Å) and a π-bonded bromovinyl group. The bonding features of the organic ligand suggest the formation of a 1-ferra-π-allyl system. Within the irontricarbonyl fragments, strong trans effects are observed. Cell data are: a = 9.373(4) b = 23.716(12) c = 6.671(4) Å β= 113.96(4)°, Z = 4. Space group Cc (No. 9). A mechanism for the formation of the compound is suggested.     

Synthesis,Characterization, and Reactivity of trans-Ru(X)(Cl)(nbd)(dppb) (X = H,Cl; nbd = 2,5-norbornadiene; dppb = 1,4-bis(diphenylphosphino)butane), Including the X-ray Crystal Structure of the Dichloride

The ruthenium (II) diene complexes [Ru(X)(Cl)(nbd)(dppb)] (X = Cl, H; nbd = 2,5-norbornadiene; dppb = PPh₂(CH₂)₄PPh₂) have been prepared and characterized spectroscopically. The X-ray crystal structure of RuCl₂(nbd)(dppb) (crystal data at 22°C: space group P1, a = 10.896 (1) Å, b = 15.168(2) Å, c = 10.829 (1) Å, α = 103.02(1)°, β = 107.08(1)°, γ = 81.65(1)°, Z = 2, R = 0.054 for 6420 reflections) shows an octahedral geometry at Ru, with the chloro ligands slightly distorted from a trans configuration (Cl)(1)-Ru-C1(2) = 168.4°); the unit cell contains two molecules of the complex and one molecule of benzene. Reaction of this complex with H₂, in presence of Proton Sponge (PS, 1,8-bis(dimethylamino)naphthalene) as base, is complicated by initial dissociation of nbd, and [Ru₂Cl₅(dppb)₂]⁻-PSH⁺ is the major product. A minor product, the hydrido(diene) complex trans-RuCl(nbd)(dppb) 5 , characterized spectroscopically, is more effectively synthesized from (a) trans-Ru(H)Cl(nbd)(PPh₃)₂, 1 , and dppb, or (b) reaction of RuCl₂(dppb)-(PPh₃) with H₂ in presence of nbd and PS. Complex 5 is unreactive toward H₂ or CO while 1 has been shown previously to give η²-H₂ and norbornenoyl derivatives, respectively; the differences in reactivity are discussed.     

SHS of single crystals in the B-C-Mg system: Crystal structure of new modification of B25C4Mg1.42 = [B12]2[CBC][C2]Mg1.42

A new modification of B₂₅C₄Mg_1.42, [B₁₂]₂[CBC][C₂]Mg_1.42, was prepared by magnesiothermic SHS and characterized by XRD. This compound was found to have the following crystallographic parameters: a = 9.626(1), b = 11.329(1), c = 8.966(1) Å, β = 105.80(3)°, V = 940.8(2) ų, space group P2₁/b, Z = 4, R = 0.032. SHS-produced crystals exhibited high acid resistance and hardness and can be recommended as a starting compound for synthesis of other modifications of carboboride.     

X-ray crystal structure of the dye 2-bromo-4-cyano-4′-N,N-diethylaminoazobenzene

The crystal structure of 2-bromo-4-cyano-4′-N,N-diethylaminoazobenzene has been determined from X-ray diffraction data: C₁₇H₁₇N₄Br, mol. wt = 357·1. Triclinic, Pī (No. 2), α = 13·162(5) Å, b = 7·516(3) Å, c = 8·496(4) Å, α = 101·63(4)°, β = 95·79(4)°, γ = 91·49(4)°, V = 818·10 ų, Z = 2, D_c = 1·45 g cm^?3, F(000) = 378, λ(Mo_Kz) = 0·7107 Å, μ(Mo_Kα) = 26·70 cm^?1. The structure was solved by direct methods and refined by full-matrix least-squares to R = 0·053 for 2081 independent reflexions. The molecule possesses an essentially planar azobenzene skeleton. The effects of substituents on the geometry of the azo group are discussed. Significant molecular parameters are: NN, 1·264(6) Å; ₁BrC, 1·904(5) Å; mean NC, 1·410(7) Å; NNC, 115·7(2)° and 113·0(2)°; NCC (cis relative to NN), 125·4(3)° and 123·1(2)°; CC(Br)C, 123·0(2)°.     

Synthesis and crystal structure of a new oxohalide CdPb<Subscript>2</Subscript>O<Subscript>2</Subscript>Cl<Subscript>2</Subscript>

A new compound, CdPb₂O₂Cl₂, is synthesized by the method of solid-phase reactions. The compound has monoclinic symmetry, space group C2/m, a = 12.392(8) Å, b = 3.8040(14) Å, c = 7.658(5) Å, β = 122.64(5)°, and V = 304.0(3) ų. The structure contains one symmetrically independent position of the Pb²⁺ cation coordinated by three O^2? anions (Pb²⁺-O^2? = 2.29–2.34 Å) and five Cl^? anions (Pb²⁺-Cl^? = 3.35–3.57 Å). The Cd²⁺ cation has a symmetric coordination with the formation of two bonds Cd-O = 2.15 Å and four bonds Cd-Cl = 2.73 Å. The oxygen atom is tetrahedrally coordinated by three Pb²⁺ cations and one Cd²⁺ cation, which leads to the formation of oxo-centered heterometallic OPb₃Cd tetrahedra. The tetrahedra are linked together into chains through common Pb atoms and into layered complexes due to sharing of the equatorial Cd atoms. The chlorine atoms are located above the cavities of the oxo-centered layer.     

Structures of the (4S, 14S)-4, 14-Dimethyl-3,6,9,12,15-pentaoxa-21-azabicyclo[15.3.1] heneicosa-1(21) 17,19-Triene-2,16-dione Complexes of R-and S-α-(1-Naphthyl)ethylammonium Perchlorate

Crystal data for the more stable (R) and less stable (S) 1:1 macrocycle-cation complexes are as follows: R cation: M_r = 625.08, orthorhombic P2₁2₁2₁, a = 8.47(1), b = 11.78(1), c = 31.19(6) A, V = 3112.0(123) ų, Z = 4, D_x = 1.333 kg m⁻³, λ(Mo Kα) = 0.71073 μ = 1.90 cm⁻¹, F(000) = 1320, T = 295 K, R = 0.17 for 1680 reflections. S Cation: M_r = 625.08, monoclinic, P2₁, a = 8.654(2), b = 11.954(3), c = 15.130(4) Å, β = 97.39(2)°, V = 1552.2(12) ų, Z = 2, D_x = 1.337 kg m⁻³, λ(Mo Kα) = 0.71073, μ = 1.91 cm⁻¹, F(000) = 660, T = 295K, R = 0.081 for 2751 unique reflections. Crystals of the complexes were prepared by the authors. The greater thermodynamic stability of the R cation complex is consistent with the observation that this cation experiences less steric interaction with the methyl substituent of the ligand than does the S cation.     

Structure of a biologically active binuclear palladium complex,bis(bis[(μ<Subscript>2</Subscript>-cysteine)(2,2′-dipyridyl)-palladium(II)]) · hexanitrates · novemhydrates

The structure of a biologically active binuclear palladium complex, namely, [(dipy)Pd(μ-cysH) (μ-cys)Pd(dipy)]³⁺ · 3NO ₃ ^? · 4.5H₂O (dipy = 2,2′-dipyridyl, C₁₀H₈N₂; cys = cysteine, C₃H₇NO₂S), has been determined from X-ray diffractometry data. The compound crystallizes in the triclinic system, symmetry space group P1, with the unit cell parameters a = 13.863(1) Å, b = 13.819(1) Å, c = 12.170(1) Å, α = 122.13(1)°, β = 103.61(1)°, γ = 91.40(1)°, V = 1887.02 ų, Z = 2, and ρ = 1.82 g/cm³. The final discrepancy factor is R1 = 0.0495 for 12884 symmetrically nonequivalent reflections with F ₀ ≥ 4σ(F ₀), wR2 = 0.1071, and GooF = 0.978. The unit cell contains two chemically equivalent but crystallographically independent positively charged binuclear palladium complexes, six NO ₃ ^? anions, and nine water molecules. The π-π stacking interaction between the nearest pyridyl rings of the neighboring layers takes place. Moreover, the interlayer and intralayer interactions occur through van der Waals interactions and a complex three-dimensional system of hydrogen bonds, which are formed by water molecules, NH ₃ ⁺ groups, and carboxyl groups.     

Use of HPLC in the identification of cis and trans-diaquabis(2,2′-bipyridine)ruthenium(II) complexes: crystal structure of cis-[Ru(H2O)2(bpy)2](PF6)2

[Ru(H₂O)₂(bpy)₂](PF₆)₂ complex was obtained by reacting HPF₆ in a [Ru(CO₃)(bpy)₂] aqueous solution. The complex can exist as cis and trans isomers and usually has been used in the preparation of several ruthenium–bipyridine species. Despite the possibility to have contamination of a specie in another, there is no analytical control involving the characterization of both complexes. Based on this we have proposed the use of high-performance liquid chromatography (HPLC) as an analytical technique to control the purity of cis and trans isomers. The separation was performed using a CLC-ODS column. The cis isomer eluted at 9.4 min while trans isomer eluted at 4.3 min. In aqueous solution the trans and cis isomer configurations were confirmed by NMR spectra (¹H). The attribution of cis isomer was also made based on the X-ray crystal structure (monoclinic, P2_1/c, a=12.320(2), b=13.852(2), c=34.220(3) Å, β=91.89(1)°, Z=8) which is reported. The six-coordinated ruthenium atom is chelated by two bipyridines and two molecules of H₂O.     

X‐ray crystal structure analysis for CI Disperse Orange 61

The synthesis, crystal structure analysis and characterisation of a monoazo dye, CI Disperse Orange 61, are reported. The dye crystallised in the triclinic system, space group P‐1 with a = 8.859(2), b = 9.899(2), c = 11.417(3)Å, α = 78.51(4)°, β = 70.37(3)°, γ = 80.46(4)°, V = 918.8(4)ų and Z = 2. There is only one molecule in the asymmetric unit. The two phenyl rings are oriented at a dihedral angle of 57.87(20)°. In the crystal structure, intermolecular C–H…N hydrogen bonds link the molecules into centrosymmetric dimers, forming R₂²(30) ring motifs, in which they may be effective in the stabilisation of the structure. The π…π stacking (interactions) between the phenyl rings may further stabilise the structure, with a centroid–centroid distance of 3.741(4)Å.     

Structure of a biologically active binuclear palladium complex in the compound bis(bis[(μ<Subscript>2</Subscript>-2-chloroethylammonium) (1,10-phenanthroline)-palladium(I)]) · octanitrates · dihydrates

The structure of a biologically active binuclear palladium complex, namely, [(1,10-phenanthroline) Pd(μ₂-2-chloroethylammonium) ₂ ⁴⁺ · 4NO ₃ ^? · H₂O, has been determined using X-ray diffraction analysis. The compound crystallizes in the monoclinic system, space group of symmetry Cc, with the unit cell parameters a = 24.527(3) Å, b = 13.097(1) Å, c = 22.651(3) Å, β = 104.23(1)°, V = 7052(2) ų, Z = 8, and ρ = 1.88 g/cm³. The final discrepancy factor is R1 = 0.0316 for 15581 symmetrically nonequivalent reflections with I ≥ 2σ(I), wR2 = 0.0513, and GooF = 1.047. The palladium atoms reside in the oxidation state of 1+, which is rarely encountered in organometallic compounds. The asymmetric part of the unit cell contains two chemically equivalent but crystallographically independent positively charged binuclear palladium complexes, eight NO ₃ ^? anions, and two water molecules. The π-π stacking interaction between the nearest 1,10-phenanthroline rings of the neighboring layers takes place. Moreover, the interlayer and intralayer interactions occur through electrostatic interaction forces and a complex three-dimensional system of hydrogen bonds, which are formed by water molecules and N ₃ ⁺ groups.     

X-Ray Analysis of trans-9, 10-Dihydroxy-9,10-diphenyl-9,10-dihydroanthracene and Its 1:2 Molecular Complex with Methanol,and Structural Comparison with the Related 1:1 Ethanol and 1:1 1,4-Butanediol Adducts

trans-9,10-Dihydroxy-9,10-diphenyl-9,10-dihydroanthracene (2) and its 1:2 molecular complex (3) with methanol have been subjected to X-ray analysis. The crystal structure of 2 is built of discrete molecules held by π interactions between neighboring parallel phenyl rings and van der Waals forces, whereas that of 3 features virtually rhombic hydrogen-bonded (OH)₄ rings, each comprising two methanol fragments and two hydroxy groups, linking the molecular moieties into a chain-and-layer arrangement. The molecular stereochemistry, hydrogen bonding, and packing modes in these two compounds are compared with those in the 1:1 adducts of 2 with ethanol and 1,4-butanediol. Crystal data: for 2, space group P1, a = 6.814(1), b = 8.119(1), c = 9.053(1)Å, α = 103.66(1), β = 96.30(1), γ = 106.55(1)°, and Z = 1 : for 3, space group C2/c, a = 12.165(3), b = 12.484(3), c = 16.349(4)Å, β = 110.33(2)° and Z = 4. Based on observed MoKα data, the structures of 2 and 3 have been refined to R_F = 0.069 for 1139 reflections and R_F = 0.070 for 1412 reflections, respectively.     

Structural characterization and conformational analysis of (aqua)(ethylenediamine-N,N,N′-triacetato)chromium(III) monohydrate complex. Crystal structure of the cis-equatorial isomer of [Cr(ed3a)(H2O)] · H2O

The structure of the cis-equatorial isomer of [Cr(ed3a)(H₂O)] · H₂O (ed3a=ethylenediamine-N,N,N^′-triacetate ion) was determined by X-ray diffraction method. The complex crystallizes in the monoclinic space group P2₁/n, a=7.004(1) Å, b=15.958(2) Å, c=11.046(1) Å, β=97.16(1)°, and Z=4. Conformational analysis of the three possible geometrical isomers, trans(H₂O,N^′), trans(H₂O,N_H), and trans(H₂O,O) of [Cr(ed3a)(H₂O)] moiety, performed using the consistent force field (CFF) program with the recently developed parameters for EDTA-type complexes, yielded structural details and energies of the minimized form for each of the isomers. Calculated energies showed that the cis-eq isomer is the most stable one, with the geometry in a very good agreement with the crystallographic structure. Comparison of the molecular mechanics calculations with those for the analogous [Cr(ed3p)(H₂O)] · H₂O (ed3p=ethylenediamine-N,N,N^′-tripropionate ion) revealed some general patterns for the conformational preference of EDTA-type complexes.     

Structure of a biologically active binuclear palladium complex in the compound (bis[(μ<Subscript>2</Subscript>-2-chloroethylammonium)(1,10-phenanthroline)-palladium(I)]) · tetranitrates · hydrate

The structure of a biologically active palladium complex [(1,10-phenanthroline)Pd(μ₂-2-chloroethylammoniu)] ₂ ⁴⁺ · 4NO ₃ ^? · H₂O has been determined from the diffractometric data. The compound crystallizes in the triclinic crystal system, space group of symmetry P \(\bar 1\), with the unit cell parameters a = 12.8352(8) Å, b = 14.4040(8) Å, c = 12.1668(9) Å, α = 116.16(1)°, β = 115.72(1)°, γ = 91.09(1)°, V = 1756.3 ų, Z = 2, and ρ = 1.892 g/cm³. The final reliability factor is R ₁ = 0.0351 for 7357 nonequivalent reflections with I ≥ 2σ(I), wR ₂ = 0.0970, and S = 1.044. The asymmetric part of the unit cell contains one positively charged binuclear palladium complex, four NO ₃ ^?1 anions, and one water molecule. The nanocomplexes are involved in the stacking π-π interaction by pairs: each complex forms a stacking with only one adjacent complex. The interaction between layers and inside each layer occurs through the van der Waals interactions and a three-dimensional system of hydrogen bonds, which are formed by the N ₃ ⁺ groups and water molecules.     

Molecular Packing Modes. Part X. The Crystal and Molecular Structures of Trans,Trans-Muconic Acid

trans, trans-Muconic acid C₆H₆O₄ crystallises in the space group , with a = 8.982, b = 9.895, c = 3.787 Å, α = 103.68, β=75.27, γ= 101.58°, and two centrosymmetric molecules per unit cell. The structure was solved from 1671 reflections measured by an ω/2θ scan with Mo Kα radiation on an IBM 1800 computer-controlled Siemens diffractometer, and refined anisotropically (on F²) to R = 0.078. The geometries in the carbon chains of the two independent molecules are essentially identical; their bond lengths match to within 0.003 Å. The carboxyl group of one molecule is statistically disordered (C-O 1.257, 1.275 Å) whereas in the second molecule the bond lengths differ significantly (1.236, 1.294 Å), indicating a greater degree of order. A careful consideration of the packing mode allows us to interpret the difference between the two molecules.     

Synthesis of iron aluminates and a new modification of aluminum oxide under shock waves from explosives (Review)

The results of an x-ray diffraction investigation of iron aluminate with unit cell parameter a = 8.090(4) Å, cation-defective iron aluminate Fe_0.5Al_2.23O₄ with a = 8.002 Å, and a new modification of aluminum oxide synthesized under shock waves from explosives containing aluminum are presented. Aluminum oxide can crystallize in the hexagonal system in a primitive lattice with a = 9.151(1) Å, c = 7.945(2) Å, V = 576 ų or in a tetragonal system in a primitive lattice with one-half the volume — a = 7.941(2) Å, c = 4.575(1) Å, V = 288 ų.