一维有机-无机杂化配聚物｛（BPE）3[Ag4Br4（SCN）6]｝n的合成与晶体结构

以1,2-亚乙基二吡啶鎓盐为结构导向剂合成了一维有机-无机杂化配聚物{(BPE)3[Ag4Br4(SCN)6]}n(BPE为1,2-亚乙基二吡啶鎓阳离子),通过元素分析、红外光谱和X-射线单晶衍射对其结构进行了表征.结构解析表明:该聚合物属单斜晶系,P21/n空间群,晶胞参数a=0.973 69(1)nm,b=0.909 07(1)nm,c=3.114 5(4)nm,β=91.659 0(1)°,Z=4.聚合物中有2类晶体学独立的Ag(Ⅰ)离子,每个Ag(Ⅰ)离子均为扭曲的四面体配位构型,通过Br原子和SCN-桥联形成一维聚阴离子链[Ag4Br4(SCN)6]n6n-,2类晶体学独立的BPE在bc平面分别贯穿链内的空腔和相邻链间的空隙之中。     

新型一维配位聚合物{[Cu(H2L)(HL)](ClO4)·3H2O}n的合成及其晶体结构

Cu(ClO4)2·6H2O与H2L{L=[2,3-f]-吡嗪[1,10]邻菲咯啉-2,3-二甲酸}反应合成了新型一维配位聚合物{ [Cu(H2L) (HL)] (C1O4)· 3H2O}n(1),其结构经UV,IR,XRD和元素分析表征. 1属单斜晶系,空间群C2/c,晶胞参数a=3.575 9(13) nm,b=0.962 7(3)nm,c=2.127 5(10)nm,β=116.106(8)°,V=6.577(5) nm3,Z=8,Dc=1.730 g·cm-3,Mr=856.56,F(000)=3 480,μ=0.837nm-1,R=0.082 6,wR=0.248.Cu2+分别与1个H2L的两个氮原子,2个不同μ2-HL的两个氮原子和一个羧酸氧原子配位,形成畸变四方锥的五配位构型.Cu(Ⅱ)通过HL桥联形成一维链,相邻一维链的芳环π-π堆积和分子间氢键作用使1构筑成三维超分子结构.     

亚乙基硫脲配位聚合物[Cu_3(etu)_3Br_3]_n的合成与晶体结构

CuB r2和亚乙基硫脲反应生成Cu(I)配位聚合物[Cu3(etu)3B r3]n(etu=亚乙基硫脲),单晶X射线衍射测得该晶体为三斜晶系,Pī空间群.晶胞参数:a=0.762 46(6)nm,b=1.198 48(10)nm,c=1.224 52(7)nm,α=68.202(5),°β=74.607(6),°γ=87.652(7)°,V=0.999 61(13)nm3,Z=2,Mr=736.82,Dc=2.448 g.cm-3,μ=9.477 mm-1,F(000)=708,偏差因子R1=0.030 6,wR2=0.071 0.配合物由环状[Cu(etu)B r]3单元聚合而成,形成Cu4S2B r2和Cu2S4B r2聚合体,两聚合体通过μ2-S桥键交替连接,形成平行于晶胞b轴的[Cu3(μ3-etu)(μ2-etu)2(μ2-B r)2B r]n一维链.Cu(I)均为变形四面体配位,亚乙基硫脲以S原子与Cu(I)结合,形成μ2-S和μ3-S两种配位方式.     

二维配位聚合物[Cu(anol)(μ1,3-N3)]n的合成、晶体结构及磁性

合成了一个结构新颖的二维Cu(Ⅱ)配位聚合物[Cu2(anol)2(μ1,3-N3)2]n(anol=2-氨基乙醇),通过X-射线单晶衍射确定了其晶体结构.晶体属单斜晶系,P21/n空间群,晶胞参数a=0.83806(17)nm,b=0.77355(15)nm,c=0.85349(17)nm,β=113.26(3)°.配体2-氨基乙醇以双齿模式配位,其配位原于包括醇羟基氧原子和氨基氮原子.在[Cu2(anol)2(μ1,3-N3)2]单元中,Cu(Ⅱ)离子通过2个μ1,1桥联方式配位的醇羟基氧原子相连,形成一个双核单元;单元之间以叠氮根离子EE桥联方式连接Cu(Ⅱ)离子形成二维网格状结构.变温磁化率测定结果表明,在配合物中,Cu(Ⅱ)离子之间存在反铁磁相互作用.     

配位聚合物{[Co2(HBTC)2(H2O)6]·C4H10N2·2H2O}n的水热合成、结构表征及荧光性质

采用水热法合成了配位聚合物[Co2(HBTC)2(H2O)6]·C4H10N2·2H2O}n(H3BTC为1,3,5-均苯三羧酸,C4H10N2为哌嗪),通过X射线单晶衍射、红外光谱和荧光光谱进行表征,并用TGA研究了该配位聚合物的热稳定性.晶体属三斜晶系,P1空间群,a=1.05437(9)nm,b=1.05485(9)nm,c=0.71482(5)nm,α=102.4623(28)°,β=91.3500(42)°,γ=111.0186(29)°,V=0.72018(10)nm3,Mr=764.37,Dc=1.762g·cm-3,Z=1,μ(MoKα)=1.25mm-1,F(000)=394,R=0.0307,wR=0.0815.晶体的基本构建单元中包含2个Co()中心、2个配位的HBTC分子和6个配位的水分子.基本构建单元通过相互链接形成具有“Z”型结构的一维配位聚合链,链间通过两种不同的氢键(O—H…O和N—H…O)相互作用,进而形成具有三维骨架结构的微孔晶体,微孔大小为0.71nm×0.82nm.荧光光谱表明,常温下用λex=312nm的光激发后,配位聚合物在329nm处出现强烈的荧光发射.     

二维配位聚合物[Cd(nicotinate)2(H2O)]n的水热合成、晶体结构及荧光性质

在中温水热条件下,用醋酸镉和烟酸自组装合成了二维配位聚合物[Cd(n icotinate)2(H2O)]n.对其进行了元素分析、红外光谱表征、热分析、荧光分析和X射线单晶衍射测定.该配位聚合物属正交晶系,Pbca空间群,晶胞参数为:a=1.144 6(7)nm,b=1.209 9(4)nm,c=1.742 2(4)nm,V=2.412 9(2)nm3,Z=8,Mr=374.62,Dc=2.062 g/cm3,F(000)=1 472,μ=1.832 mm-1,R1=0.023 4,wR2=0.061 0.     

一维链状配位聚合物[Cu(CH3COO)(C5H5N)2]n的合成与晶体结构

The coordination polymer [Cu(CH3COO)(C5H5N)2]n was synthesized and its crystal structure has been determined by X-ray diffraction technique.The crystal belongs to monoclinic,space group C2/c with a=1.183 2(1) nm,b=1.512 1(2) nm,c=1.3911(1) nm,β=97.137(3)°,V=2.469 6(4) nm3,C12H13CuN2O2,Mr=280.78,Z=8,Dc=1.510 g·cm-3,μ=1.759 mm-1,F(000)=1 152,R1=0.048 2 and wR2=0.122 5 for 1 515 observed reflections [1>2σ(Ⅰ)].In the crystal the copper(Ⅲ) atom is tetra-coordinated primarily by two oxygen atoms of two symmetry-related carbexyl groups of acetate anions and two nitrogen atoms of two pyridine ligands in a parallelogram fashion.All of the pyridine rings linked to Cu(1) and Cu(2) are arranged centrosymmetrically on Cu(1).The neighboring copper complex molecules are linked together by the carboxylate oxygen atom of acetate anions to form an infinite one-dimensional linear chain structure.Moreover,π-π stacking interactions between intrachain pyridine molecules play the crucial role in constructing of the supramolecular structure.CCDC:709977.     

一维链状[Mn(9-AC)2(4,4'-bpy)(H2O)2]n配位聚合物的合成及晶体结构

在水热条件下(120 ℃), 将醋酸锰、4,4'-联吡啶(4,4'-bpy)与9-蒽酸(9-HAC)反应, 得到了配位聚合物[Mn(9-AC)2(4,4'-bpy)(H2O)2]n, 通过元素分析、红外光谱、X射线单晶衍射对其进行了表征, 并用TGA研究了该配位聚合物的热稳定性. 结构解析结果表明, 该晶体属于正交晶系, Fdd2空间群, a=1.66772(12) nm, b=3.36471(16) nm, c=1.1687(4) nm, V=6.558(2) nm3, Z=8, Mr=689.60, Dc=1.397 Mg/m3, R=0.0356, wR2 = 0.0604. 在该配位聚合物中, 中心锰原子采取略微变形的八面体构型, 与两种配体共同构筑了一维直线形链结构, 链与链之间通过氢键相互作用构筑成三维超分子网络.     

配位聚合物[Zn(3-aba)2]n·nH2O和[Cd(3-aba)2]n的合成与晶体结构

用水热法合成了2个新的配位聚合物[Zn(3-aba)₂]_n·nH₂O (1)和[Cd(3-aba)₂]_n (2)(3-aba=间氨基苯甲酸阴离子)，对它们进行 了元素分析、热分析、红外光谱和X射线单晶衍射等表征。配位聚合物1晶体属正交晶系，Pca2₁空间群，晶体学数据为：a=0.926 26(8) nm，b=1.600 73(15) nm，c=1.885 22(17) nm，β=90°，V=2.795 2(4) nm³，Z=4，μ=1.783 mm^-1，D_c=1.690 g·cm^-3，R₁=0.027 9，wR₂=0.064 8；配位聚合物2晶体属单斜晶系，P2₁/n空间群，晶体学数据为：a=0.900 68(7) nm，b=0.452 03(4) nm，c=1.568 02(12) nm，β=106.075 0(10)°，V=0.613 43(9) nm³，Z=1，μ=1.799 mm^-1，D_c=2.082 g·cm^-3，R₁=0.019 8，wR₂=0.055 8。在配合物1中，配体分子以双齿配位模式与锌离子配位，而在配合物2中，它以三齿配位模式与镉离子配位。2个配合物均具有二维网状结构。     

多孔配位聚合物{[Cd2（tpom）（tpa）2]·（DMF）（H2O）3}n的合成及表征

由四(4-吡啶氧甲基)甲烷(tpom)和对苯二甲酸(tpa)与Cd(NO3)2.4H2O合成了配位聚合物{[Cd2(tpom)(tpa)2].(DMF)(H2O)3}n,通过元素分析、红外光谱、X-射线粉末衍射、热重、X-射线单晶衍射对配位聚合物的结构进行了表征。结果表明,标题化合物属于单斜晶系C2/c空间群,晶胞参数为a=3.4747(17)nm,b=2.0899(10)nm,c=1.4292(10)nm,β=111.642(5)°,V=9.647(9)nm3,Z=8,Dc=1.374 g.cm-3,F(000)=3984.0,μ=0.939 mm-1,其6586个可观测点的结构偏差因子R1=0.0566,wR2=0.1408。结构分析表明,对苯二甲酸连接镉离子形成含双核镉(CdCOO)2的平面,四(4-吡啶氧甲基)甲烷连接双核镉形成具有两重穿插pcu拓扑构型的三维骨架。     

Jahn-Teller-distorted dimeric anions in (cat)[Mn2F8(H2O)2]·2H2O (cat = pipzH2, dabcoH2) and (dabcoH2)2[Mn2F8(H2PO4)2]

Using biprotonated dabco (1,4-diazabicyclo[2.2.2]octane) or pipz (piperazine) as counter cations, mixed-ligand fluoromanganates(III) with dimeric anions could be prepared from hydrofluoric acid solutions. The crystal structures were determined by X-ray diffraction on single crystals: dabcoH₂[Mn₂F₈(H₂O)₂]·2H₂O (1), space group P2₁, Z = 2, a = 6.944(1), b = 14.689(3), c = 7.307(1) Å, β = 93.75(3)°, R₁ = 0.0240; pipzH₂[Mn₂F₈(H₂O)₂]·2H₂O (2), space group , Z = 2, a = 6.977(1), b = 8.760(2), c = 12.584(3) Å, α = 83.79(3), β = 74.25(3), γ = 71.20(3)°, R₁ = 0.0451; (dabcoH₂)₂[Mn₂F₈(H₂PO₄)₂] (3), space group P2₁/n, Z = 4, a = 9.3447(4), b = 12.5208(4), c = 9.7591(6) Å, β = 94.392(8)°, R₁ = 0.0280. All three compounds show dimeric anions formed by [MnF₅O] octahedra (O from oxo ligands) sharing a common edge, with strongly asymmetric double fluorine bridges. In contrast to analogous dimeric anions of Al or Fe(III), the oxo ligands (H₂O (1,2) or phosphate (3)) are in equatorial trans-positions within the bridging plane. The strong pseudo-Jahn-Teller effect of octahedral Mn(III) complexes is documented in a huge elongation of an octahedral axis, namely that including the long bridging Mn-F bond and the Mn-O bond. In spite of different charge of the anion in the fluoride phosphate, the octahedral geometry is almost the same as in the aqua-fluoro compounds. The strong distortion is reflected also in the ligand field spectra.     

Synthesis and structural investigation of the compounds containing HF2 anions: Ca(HF2)2, Ba4F4(HF2)(PF6)3 and Pb2F2(HF2)(PF6)

Three new compounds Ca(HF₂)₂, Ba₄F₄(HF₂)(PF₆)₃ and Pb₂F₂(HF₂)(PF₆) were obtained in the system metal(II) fluoride and anhydrous HF (aHF) acidified with excessive PF₅. The obtained polymeric solids are slightly soluble in aHF and they crystallize out of their aHF solutions. Ca(HF₂)₂ was prepared by simply dissolving CaF₂ in a neutral aHF. It represents the second known compound with homoleptic HF environment of the central atom besides Ba(H₃F₄)₂. The compounds Ba₄F₄(HF₂)(PF₆)₃ and Pb₂F₂(HF₂)(PF₆) represent two additional examples of the formation of a polymeric zigzag ladder or ribbon composed of metal cation and fluoride anion (MF⁺)_n besides PbF(AsF₆), the first isolated compound with such zigzag ladder. The obtained new compounds were characterized by X-ray single crystal diffraction method and partly by Raman spectroscopy. Ba₄F₄(HF₂)(PF₆)₃ crystallizes in a triclinic space group P1¯ with a=4.5870(2) Å, b=8.8327(3) Å, c=11.2489(3) Å, α=67.758(9)°, β=84.722(12), γ=78.283(12)°, V=413.00(3) Å³ at 200 K, Z=1 and R=0.0588. Pb₂F₂(HF₂)(PF₆) at 200 K: space group P1¯, a=4.5722(19) Å, b=4.763(2) Å, c=8.818(4) Å, α=86.967(10)°, β=76.774(10)°, γ=83.230(12)°, V=185.55(14) ų, Z=1 and R=0.0937. Pb₂F₂(HF₂)(PF₆) at 293 K: space group P1¯, a=4.586(2) Å, b=4.781(3) Å, c=8.831(5) Å, α=87.106(13)°, β=76.830(13)°, γ=83.531(11)°, V=187.27(18) Å³, Z=1 and R=0.072. Ca(HF₂)₂ crystallizes in an orthorhombic Fddd space group with a=5.5709(6) Å, b=10.1111(9) Å, c=10.5945(10) Å, V=596.77(10) Å³ at 200 K, Z=8 and R=0.028.     

Synthesis and characterization of methylpalladium(II) dithiolate complexes of the type [PdMe(SS)(ER3)] (SS = S2CNR 2, S2COEt, S2P(OR)2, S2 PPh2; ER3 = PMePh2, PPh3, AsPh3)

Methylpalladium(II) dithiolate complexes of the type [PdMe(SS)(ER₃] (SS = S₂ CNR₂ (R = Me or Et), S₂COEt, S₂P(OR)₂ (R = Et, ⁿPr, ⁱPr), S₂PPh₂; ER₃ = PMePh₂, PPh₃, AsPh₃) have been synthesized by the reaction of [Pd₂Me₂(μ-Cl)₂(PMePh₂)₂] with sodium/potassium/ammonium salts of the dithio acid or by treatment of [PdMeCl(cod)] with ER₃ followed by sodium/potassium/ammonium salts of the dithio ligand. All the complexes were characterized by elemental analysis, IR and nuclear magnetic resonance (¹H, ³¹P) data.     

Preparation and structural characterization of [RuCl2(CO)2{Te(CH2SiMe3)2}2] and [RuCl2(CO){Te(CH2SiMe3)2}3]

The objective of the present work was to synthesize mononuclear ruthenium complex [RuCl₂(CO)₂{Te(CH₂SiMe₃)₂}₂] (1) by the reaction of Te(CH₂SiMe₃)₂ and [RuCl₂(CO)₃]₂. However, the stoichiometric reaction affords a mixture of 1 and [RuCl₂(CO){Te(CH₂SiMe₃)₂}₃] (2). The X-ray structures show the formation of the cis(Cl), cis(C), trans(Te) isomer of 1 and the cis(Cl), mer(Te) isomer of 2. The ¹²⁵Te NMR spectra of the complexes are reported. The complex distribution depends on the initial molar ratio of the reactants. With an excess of [RuCl₂(CO)₃]₂ only 1 is formed. In addition to the stoichiometric reaction, a mixture of 1 and 2 is observed even when using an excess of Te(CH₂SiMe₃)₂. Complex 1 is, however, always the main product. In these cases the ¹²⁵Te NMR spectra of the reaction solution also indicates the presence of unreacted ligand.     

Crystal and molecular structures of the Rh[(C2H5O)2PS2]3 and Co[(C6H5O)2PS2]3 chelate compounds

The crystal structures of the Rh[(EtO)₂PS₂]₃ (I) and Co[(PhO)₂PS₂]₃ (II) chelate compounds were determined from X-ray diffraction (XRD) data (CAD-4 diffractometer, MoK _β radiation, 1193 F _hkl , R = 0.0516 for I and 513 F _hkl , R = 0.0305 for II). Crystals I are monoclinic: a = 14.233(3) Å, b = 13.570(3) Å, c = 14.272(3) Å; β = 90.66(3)°, V = 2756.3(10) ų, Z = 4, ρ_calc = 1.587 g/cm³, space group C2/c. Crystals II are trigonal: a = 15.149(2) Å, c = 30.306(6) Å; V = 6023.2(16) ų, Z = 6, ρ_calc = 1.493 g/cm³, space group R3ˉ. Structures I and II consist of discrete mononuclear molecules. The coordination polyhedra of the M atoms (M = Rh, Co) are distorted octahedra formed by six sulfur atoms of three cyclic bidentate (RO)₂ PS₂⁻ ligands. Original Russian Text Copyright ? 2008 by R. F. Klevtsova, L. A. Glinskaya, and S. V. Larionov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 2, pp. 330–334, March–April, 2008.     

Two mixed valent molybdenophosphates with a tunnel structure closely related to K0.17MoP2O7: Pb2(PbO)2Mo8(P2O7)8 and PbK2Mo8(P2O7)8

Two new mixed valent Mo(III)/Mo(IV) diphosphates containing lead Pb₂(PbO)₂Mo₈(P₂O₇)₈ and PbK₂Mo₈(P₂O₇)₈ have been synthesized. The [Mo₈P₁₆O₅₆]∞ frameworks of these phosphates are closely related to that of K_0.17MoP₂O₇: the MoO₆ octahedra and P₂O₇ groups form two sorts of large eight-sided tunnels. They are occupied in an ordered way by PbO chains and Pb²⁺ cations in Pb₂(PbO)₂Mo₈(P₂O₇)₈ and by K⁺ and Pb²⁺ cations in PbK₂Mo₈(P₂O₇)₈. It results in different symmetries of these two structures, which are tetragonal and monoclinic, respectively, showing the great flexibility of these mixed frameworks, susceptible to accommodate various species with different sizes.     

Crystal structure, phase transitions and ferroelastic properties of [(CH3)2NH2]3[Bi2Cl9]

A sequence of structural phase transitions in [(CH₃)₂NH₂]₃[Bi₂Cl₉] (DMACB) is established on the basis of differential scanning calorimetry (DSC) and dilatometric studies. Four phase transitions are found: at 367/369, 340/341, 323/325 and 285/292 K (on cooling/heating). The crystal structure of DMACB is determined at 350 K. It crystallizes in monoclinic space group P2₁/n: a=8.062(2), b=21.810(4), c=14.072(3) Å, β=92.63(3)°, Z=4, R₁=0.0575, wR₂=0.1486. The crystal is built of the double chain anions (“pleated ribbon structure”) and the dimethylammonium cations. Dielectric studies in the frequency range 75 kHz-900 MHz indicate relatively fast reorientation of the dimethylammonium cations over the I, II, III and IV phases. Infrared spectra are recorded in the temperature range 40-300 K and analyzed in region assigned to the symmetric and asymmetric NC₂ stretching vibrations. Optical observations show the existence of the ferroelastic domain structure over all phases below 367 K. The possible mechanisms of phase transitions are discussed on the basis of presented results.     

新型一维链状配位聚合物[Cd2(C23H14O6)2(C10H9N3)2(H2O)]n的研究

配位超分子聚合物的设计合成与应用研究一直是配位化学、超分子化学、生物无机化学及材料科学等领域的热点研究课题之一,具有微孔结构的配位聚合物吸引了许多科学家的目光,这不仅因为该类配合物具有新颖的结构,展现出多种诱人的拓扑结构,更主要的 是因为它们在离子交换、催化、磁性材料、光学材料及气体贮存领域的应用潜力[1～3].     

Some further studies of estertin compounds. crystal structures of [NEt4][MeO2CCH2CH2Sn(dmio)2] (dmio = 1,3-dithiole-2-one-4,5-dithiolato) and (MeO2CCH2CH2)2SnX2[X2 = I2, (NCS)2 or Cl, Br]

Estertn compounds, (MeO₂CCH₂CH₂)₂SnX₂ [X₂ = I₂ (2); X₂ = Br₂ (9); X₂ = Cl, Br (4)) or X₂ = (NCS)₂ (3)] have been obtained by halide exchange reactions of (MeO₂CCH₂CH₂)₂SnCl₂. Crystal structure determinations of 2–4 revealed chelating MeO₂CCH₂CH₂ units with distorted octahedral geometries at tin. The Sn---O bond lengths in the isothiocyanato complex, 3, are shorter [2.390(11) to 2.498(12), mean 2.439 Å], with the chelate bite angles, C---Sn---O, larger [74.3(7) to 78.2(6), mean 76.0°] than those in the halide analogues 2 and 4 [Sn---O = 2.519(2) to 2.541(8), mean 2.530 Å; C---Sn---O 72.8(3) to 73.9(4), mean 73.3°]. ¹H, ¹³C and ¹¹⁹Sn NMR and IR spectra of 2–4 and 9 were determined in CDCl₃ solution: the NMR spectra of (MeO₂CCH₂CH₂)₂SnX₂ show the following trends: (i) both δ¹H and δ¹³C, increase and (ii) both ²J (Sn---H) and ¹J(Sn---C) decrease in the sequence X₂ = (NCS)₂, Cl₂, ClBr, Br₂ and I₂. The MeO₂CCH₂CH₂ and dmio groups (dmio = 1,3-dithiole-2-one-4,5-dithiolato) are all chelating groups in (MeO₂CCH₂CH₂)₂Sn(dmio) (5). As shown by X-ray crystallography, the tin atom in the anion of solid [Q][MeO₂CCH₂CH₂Sn(dmio)₂] 6 (Q = NEt₄) forms 5 strong bonds [to C and the 4 thiolato S atoms, Sn---S 2.459(2) to 2.559(2) Å], arranged in a near trigonal bipyramidal array. There is an additional Intramolecular but weaker, interaction with the carbonyl oxygen atom [Sn---O = 3.111(5) Å]; v(C=O) = 1714 cm⁻¹ in solid 6 (Q = NEt₄). NMR spectra of 5 and 6 are also reported.     

One-step synthesis of pentavalent triphenylantimony derivatives Ph3Sb(OSiR3)2, Ph3Sb(OCH2CH2)2NH and Ph3Sb(OCH2CH2NMe2)2: X-ray molecular structure of Ph3Sb(OSiMe3)2

Pentavalent bis(triorganosiloxy)triphenylantimony derivatives, Ph₃Sb(OSiR₃)₂ (R = Me, Ph), were synthesized by reaction of triphenylantimony with trimethyl- or triphenylsilanol in the presence of tert-butylhydroperoxide by the mild reaction conditions (0-5 °C, 2 h). The reaction of triphenylantimony with diethanolamine in the presence of tert-butylhydroperoxide gave the cyclic compound Ph₃Sb(OCH₂CH₂)₂NH. The mixture of Ph₃SbO and Ph₃Sb(OCH₂CH₂NMe₂)₂ was obtained by the reaction of triphenylantimony with 2-(N,N-dimethylamino)ethanol in the presence of tert-butylhydroperoxide.