共查询到20条相似文献,搜索用时 15 毫秒
1.
Arzu Özek Çiğdem Albayrak Mustafa Odabaşoğlu Orhan Büyükgüngör 《Journal of chemical crystallography》2009,39(5):353-357
Abstract The crystal structure of C14H12ClNO2 was determined by X-ray analysis. It crystallizes in the triclinic space group Pc with a = 12.5346(10) ?, b = 4.5101(3) ?, c = 12.0534(11) ?, α = 90.00o, β = 113.669(6)o, γ = 90.00o, Z = 2, Dx = 1.393 mg/m3, μ (MoKα) = 0.298 mm−1. The title compound is photochromic and molecule is non-planar. It adopts a phenol–imine tautomeric form with a strong intramolecular
O–H···N hydrogen bond and a strong intermolecular C–H···O hydrogen bond. Minimum energy conformations AM1 were calculated
as a function of the three torsion angles θ1(C10–C9–N1–C8), θ2(C9–N1–C8–C1) and θ3(N1–C8–C1–C6), varied every 10°. As in the X-ray experiment results, molecule has an angle that makes it non-planar between
two aromatic rings in AM1 optimized geometry.
Graphical Abstract Molecular and crystal structure of [(E)-2-[(3-chlorophenylimino)methy])-4-methoxyphenol], C14H12ClNO2, have been determined by single crystal X-ray diffraction study, and conformational analysis of the title molecule with respect
to the selected torsion angle has been achieved by AM1 semi-empirical calculations.
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2.
Hüseyin Ünver Mustafa Yıldız Aşkın Kiraz Özen Özgen 《Journal of chemical crystallography》2009,39(1):17-23
Abstract The Schiff base (Z)-6-[(2-hydroxyphenylamino)methylene]-2-methoxycyclohexa-2,4-dienone has been synthesized from the reaction of 2-aminophenol
with 2-hydroxy-3-methoxybenzaldehyde. The title compound has been characterized by elemental analysis, FT-IR, 1H-NMR, 13C-NMR and UV–Visible techniques. The structure of the title compound also was determined crystallographically. The crystal
structure has been solved by direct methods and refined by full-matrix least squares. The title compound crystallize in the
monoclinic space group P21/c with a = 10.438(1), b = 8.851(1), c = 12.746(1) ?, β = 95.72(1)°, V = 1171.7(2) ?3, D
x
= 1.379 g cm−3, respectively (R1 = 0.0522 and wR2 = 0.126 for 1442 reflections [I > 2σ(I)]).
Index Abstract
N-salicylideneaniline derivatives have been shown to exist as tautomeric forms due to intramolecular proton shifts between
the phenol-oxygen and the imine-nitrogen, via intramolecular hydrogen bonding O–H···N or O···H–N.
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3.
Molecular and crystal structure of 2-methyl-3-(2-nitro-phenyl)-4-phenyl-[1,2,4]oxadiazolidin-5-one, C15H13N3O4, have been determined by single crystal X-ray diffraction study. The title compound is monoclinic, with a = 10.0313(8) Å, b = 9.0372(5) Å, c = 15.5964(14) Å, β = 96.926(7)∘, Z = 4, Dx = 1.42 g/cm3, μ (Mo-Kα) = 0.105 mm−1, and space group is P 21/c. The structure was solved by direct methods and refined to a final R = 0.036 for 1894 reflections with I > 4σ (I). The crystal structure is stabilized by C–H⋅sO type inter-molecular, C–H⋅sN and C–H⋅sO type intra-molecular, π–π stacking and edge to face (C–H⋅s π-ring) interactions. To enlighten conformational flexibility of the title molecule, selected two torsion angles are varied from −180∘ to +180∘ in every 10∘ separetely and then molecular energy profile is calculated and construed. 相似文献
4.
Hüseyin Ünver Mustafa Yıldız Nazan Ocak Tahsin Nuri Durlu 《Journal of chemical crystallography》2008,38(2):103-108
Abstract Schiff base 3-[(2-morpholinoethylimino)methyl]benzene-1,2-diol has been synthesized from the reaction of 4-(2-aminoethyl)morpholine
with 2,3-dihydroxybenzaldehyde. The title compound has been characterized by elemental analysis, IR, 1H-NMR, 13C-NMR and UV–visible techniques. The structure of the compound also has been examined crystallographically. For the compound
exist as dominant form of enol-imines in both the solutions and solid state. The crystal structure has been solved by direct
methods and refined by full-matrix least squares. The title compound crystallize in the monoclinic space group P21/n with a = 12.085(1), b = 8.256(1), c = 13.650(1) ?, β = 108.56(1)°, V = 1291.1(2) ?3, D
x
= 1.288 g cm−3, respectively (R
1 = 0.0336 and wR
2 = 0.0922 for 2117 reflections [I > 2σ(I)].
Index abstract Intramolecular hydrogen bonding is important on the tautomeric properties and the type of aldehyde plays a vital role of the
enol-imine and keto-amine properties of the Schiff base ligand.
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5.
Brown block-shaped crystals of bis{2-methoxy-6-[(2-diethylaminoethylimino)methyl]phenolato}thiocyanatocobalt(III) perchlorate,
the first cobalt(III) complex derived from the Schiff base ligand HL, [CoIII(L)(HL)(NCS)].ClO4 (HL=2-methoxy-6-[(2-diethylaminoethylimino)methyl]phenol) have been obtained and characterized by elemental analysis and
X-ray single crystal determination. The complex crystallizes in the monoclinic space group P21/c with unit cell dimensions a=16.087(3) ?, b=12.354(3) ?, c=16.762(3) ?, β=93.77(3)°, V=3324.1(12) ?3, Z=4, R
1=0.0741 and wR2=0.1366. X-ray structure determination revealed that the complex consists of a [CoIII(L)(HL)(NCS)]+ cation and a disordered perchlorate anion. The Co atom in the cation is six-coordinate in an octahedral coordination. In
the crystal structure, the perchlorate anions are linked to the cations through intermolecular C–H⋯O hydrogen bonds, forming
zigzag chains running along the caxis. It is the first cobalt(III) complex derived from the Schiff base ligand HL. 相似文献
6.
The title compound C19H16N2O crystallize as either triclinic or monoclinic polymorph depending on the solvent used. Polymorph [1] crystallizes from methanol in the space group P \( \mathop 1\limits^ - \) with unit cell dimensions: a = 8.723(2), b = 9.344(2), c = 10.544(2) Å, α = 71.54(2), ß = 78.74(2), γ = 74.15(2)°, and Z = 2. Polymorph [2] crystallizes from benzene with space group P21/n with unit cell dimensions: a = 10.230(3), b = 20.536(7), c = 14.563(4) Å, ß = 97.14(3)°, and Z = 8. The only similarity between molecules of [1] and two independent molecules of [2] can be found in almost co-planar phenyl moiety with chelate ring. Both structures are characterized with strong intramolecular O-H···N hydrogen bond. Whereas the molecular interconnections in [2] are based on van der Waals attractions between discrete molecules, molecules of [1] associate in dimers via intermolecular N-H···O hydrogen bonding by the operation of crystallographic centre of inversion. 相似文献
7.
The metal complex, bis [2-(3-(2-((2-hydroxybenzylidene)amino)ethyl) oxazolidin-2-yl)phenol]cerium(IV) 1,4-dioxane monosolvate was synthesized and characterized by infrared, 1H NMR, elemental analysis, single-crystal, and powder X-ray diffraction. The coordination polyhedra of cerium shows a distorted square-antiprismatic geometry. No classical hydrogen bonds were observed. The crystal packing was influenced by weak C-H···O (intermolecular) and van der Waals interactions. 相似文献
8.
Tuncay Tunç Musa Sarı Murat Sadıkoğlu Orhan Büyükgüngör 《Journal of chemical crystallography》2009,39(9):672-676
Abstract A new Schiff-base complex 2-{(E)-[2-hydroxyphenyl)imino]methyl}phenol has been synthesized and characterized by elemental analyses, UV–VIS and IR spectroscopy
and single crystal X-ray determination. The structure comprises two independent and similar molecules. The two independent
molecules in the asymmetric unit are hydrogen bonded and have different conformations. In each molecule, C13H11NO2, adopt an E configuration about the azomethine C–N double bond. The complex crystallized in the triclinic space group P-1.
Two benzene rings and azomethine group are practically coplanar, as a result of intramolecular hydrogen bonds involving the
hydroxy O atom and azomethine N atom. Also hydroxy group of the molecule is the presence intermolecular O–H···O hydrogen bonds
with the hydroxy group of the other molecule.
Index Abstract and Figure A new Schiff-base complex 2-{(E)-[2-hydroxyphenyl)imino]methyl}phenol has been synthesized and characterized by elemental analyses, UV–VIS and IR spectroscopy
and single crystal X-ray determination. The structure comprises two independent and similar molecules. The two independent
molecules in the asymmetric unit are hydrogen bonded and have different conformations. In each molecule, C13H11NO2, adopt
an E configuration about the azomethine C–N double bond. The complex crystallized in the triclinic space group P-1. Two benzene
rings and azomethine group are practically coplanar, as a result of intramolecular hydrogen bonds involving the hydroxy O
atom and azomethine N atom. Also hydroxy group of the molecule is the presence intermolecular O–H···O hydrogen bonds with
the hydroxy group of the other molecule.
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9.
De-Suo Yang 《Journal of chemical crystallography》2007,37(5):343-348
The Schiff base compounds, isonicotinic acid [1-(3-methoxy-2-hydroxyphenyl) methylidene]hydrazide (C14H13N3O3, 1) and isonicotinic acid [1-(4-dimethylaminophenyl) methylidene]hydrazide monohydrate (C15H16N4O·H2O, 2) have been synthesized by the condensation of equimolar 3-methoxysalicylaldehyde or 4-dimethylaminobenzaldehyde with isonicotinic
acid hydrazide in MeOH or EtOH. The compounds were characterized by elemental analysis, IR, 1HNMR spectra, and single crystal X-ray diffractions. Compound 1 crystallizes in the monoclinic space group P-1 with unit cell dimensions a = 7.662(1) ?, b = 16.249(2) , c = 10.874(2) ?, β = 110.426(3)°, V = 1268.7(3) ′3, Z = 4, R
1 = 0.0644, and wR
2 = 0.1283. Compound 2 crystallizes in the orthorhombic space group P212121 with unit cell dimensions a = 7.388(1) ?, b = 11.812(1) ?, c = 17.197(2) ?, V = 1500.7(2) ′3, Z = 4, R
1 = 0.0585, and wR
2 = 0.1143. X-ray structure determinations revealed that the molecules of both compounds display trans configurations with respect to the C=N double bonds. In the crystal structure of 1, molecules are linked through N–H···N intermolecular hydrogen bonds, forming layers parallel to the bc plane, while in the crystal structure of 2, molecules are linked through N–H···O, O–H···O, and O–H···N intermolecular hydrogen bonds, forming a network.
Supplementary material CCDC-615072 and 620235 contain the supplementary crystallographic data for this paper. These data can be obtained free of
charge at http://www.ccdccam. ac.uk/const/retrieving.html or from the Cambridge Crystallographic Data Centre (CCDC), 12 Union
Road, Cambridge CB2 1EZ, UK; fax: +44(0)1223–336033 or e-mail: deposit@ccdc.cam.ac.uk. 相似文献
10.
Yu. M. Chumakov V. I. Tsapkov E. Jeanneau G. Bocelli D. Luneau 《Crystallography Reports》2006,51(4):601-608
The crystal structures of 6-[(2-hydroxy-1,1-bishydroxymethylethylamino)methylene]-2,4-dinitrocyclohexa-2,4-dienone hydrate L · H2O (I), chloro-(2-hydroxymethyl-2-methylpropane-1,3-diol-2-iminomethyl-4,6-dinitrophenolo)aquacopper hydrate [Cu(H2O)(L-H)Cl] · H2O (II), and (2-hydroxymethyl-2-methylpropane-1,3-diol-2-iminomethyl-4,6-dinitrophenolo)aquacopper nitrate [Cu(H2O)(L-H)]NO3 (III) are determined using X-ray diffraction. It is established that the salicylidene fragment of azomethine L in the structure of compound I is in a quinoid tautomeric form. In the crystal, molecules L and water molecules are joined together by hydrogen bonds into two-dimensional layers aligned parallel to the (010) plane. The copper atom in the structure of compound II coordinates the singly deprotonated tridentate molecule L (whose salicylidene fragment is in a benzenoid form), the chlorine ion, and the water molecule. The coordination polyhedron of the central copper atom is a distorted tetragonal pyramid. In the structure of compound III, the polymer chains are formed through the coordination bonds of the copper atom with two oxygen atoms of the amino alcohol fragment of azomethine L of the neighboring complex, which is related to the initial complex by the translation along the x axis. The coordination polyhedron of the central atom is an elongated tetragonal bipyramid. Polymers and nitro groups form a three-dimensional framework through hydrogen bonds. 相似文献
11.
Héctor Novoa de Armas Norbert M. Blaton Oswald M. Peeters Camiel J. De Ranter Margarita Suárez Estael Ochoa Yamila Verdecia Esperanza Salfrán 《Journal of chemical crystallography》2000,30(4):237-243
The synthesis and structural characterization of Methyl 6-chloro-4-(2-chlorophenyl)-5-formyl-2-methyl-1,4-dihydropyridine-3-carboxylate is described. The structure was refined to R1 = 0.0470 for 2665 reflections (with I > 2(I)). Crystal data: C15H13C12NO3, monoclinic,space group P21/c, a = 11.163(9), b = 14.484(8), c = 9.422(7) Å, V = 1512.9(19) Å3, Z = 4. The results of crystallographic and molecular modeling (AM1) were compared. The Cl atom attached to the phenyl group has two possible orientations, having 75% (sp) and 25% (ap) occupancy, respectively. The molecules in the crystal are held together by means of intermolecular hydrogen bonds of the type N=H...O and by C=H...O interactions. 相似文献
12.
Hande Petek Çiğdem Albayrak Nazan Ocak İskeleli Erbil Ağar İsmet Şenel 《Journal of chemical crystallography》2007,37(4):285-290
The single crystal X-ray diffraction analysis of the title compound, C14H20N2O3, reveals that the structure is adapted to its zwitterionic form and centrosymmetric dimers are formed by N+–H···O− type ionic weak hydrogen bonds in the crystal structure. The title compound crystallizes in the triclinic space group P−1 with a = 5.9255(13) ?, b = 9.853(3) ?, c = 12.248(3) ?, α = 101.793(19)°, β = 94.941(17)°, γ = 104.36(2)°, Z = 2, Dx = 1.308 g/cm3, μ (Mo-Kα) = 0.092 mm−1. The structure was solved by direct methods and refined to a final R = 0.0371 for 2183 reflections with I > 2σ (I). The crystal structure is stabilized by N+–H···O− type intra-molecular hydrogen bonds and N+–H···O− type packing interactions referred to as weak hydrogen bonds. To elucidate conformational flexibility of the title molecule,
the selected torsion angle is varied from −180° to +180° in every 10° separately and then molecular energy profile is calculated
and construed. In addition, charge-population analysis of the crystallographically observed structure confirms its zwitterionic
form. 相似文献
13.
Crystal structure of [Mn2(III)(salpa)2Cl2(H2O)2] (H2salpa = 1-(salicylaldeneamino)-3-hydroxypropane)
Cun-Gen Zhang Jie Sun Xiang-Fu Kong Cheng-Xue Zhao 《Journal of chemical crystallography》1999,29(2):203-206
The manganese complex, (Mn2(III)(salpa)2Cl2(H2O)2], has been prepared and its structure determined using x-ray crystallography. The dimer is a di-2-alkoxo complex which is a six-coordinate manganese dimer with unsupported alkoxide bridges and a rare example of a chloride- and water-containing manganese dimer. The complex crystallizes in the monoclinic space group P21/c with a = 9.315(5), b = 11.130(4), c = 11.637(5) Å, = 104.33(3)°, V = 1169.0(9) Å3, and Z = 2. The structure comprises discrete binuclear clusters in which the metal atoms are bridged by two alkoxo oxygens of the salpa2– ligands. The Mn—O and Mn—N distances are in good agreement with those found for other manganese(III) Schiff base complexes. The Mn—Cl and Mn—O3 distances are 2.585(2) and 2.371(2) Å, respectively, and the Mn ··· Mn distance is 3.001(1) Å. In the crystal, there are two types of hydrogen bonding between the H2O molecule and the Cl atom with Cl ··· H(H2O) distance of 2.33(6) (intramolecule: –1 + x, y, –1 + z) and 2.68(6) Å (intermolecule: –1 + x, 0.5–y, –0.5 + z). 相似文献
14.
David Wiedenfeld Mark Minton Vladimir Nesterov Christine Montoya 《Journal of chemical crystallography》2004,34(2):95-101
Hydrogen bonding parameters for the title materials are reported. 2-[(trifluoroacetyl)amino]benzoquinone crystallizes in the monoclinic space group P2
1/c, with a = 18.195(4), b = 5.110(1), c = 9.635(2), = 104.22(3)°, V = 868.4(3) Å3, and Z = 4. This compound exhibits two weak intramolecular hydrogen bonds. The first is between a hydrogen atom of the quinone ring and the carbonyl oxygen of the trifluoroacetamide group; it has a distance of 2.24 Å and a C—HsO angle of 122°. The second is between the hydrogen atom of the trifluoroacetamide group and a quinone carbonyl group; it has a distance of 2.26 Å and a N—HsO angle of 107°. 2-Aminohydroquinone hydrochloride crystallizes in the orthorhombic space group Pca21, with a = 16.220(3), b = 5.211(1), c = 8.719(2), V = 737.0(2) Å3, and Z = 4. 2-Aminohydroquinone perchlorate crystallizes in the orthorhombic space group P212121, with a = 7.110(1), b = 7.139(1), c = 18.043(4), V = 915.8(3) Å3, and Z = 4. All active hydrogens of the two salts exhibit intermolecular hydrogen bonds that serve to organize a three-dimensional framework for each case. 相似文献
15.
Synthesis and Crystal Structure of [2-(4-chlorobenzoyloxy)-5-methylphenyl]-(4-methylphenyl)methanone
S. Naveen T. D. Venu S. Shashikanth M. A. Sridhar J. Shashidhara Prasad 《Journal of chemical crystallography》2007,37(12):787-791
[2-(4-Chlorobenzoyloxy)-5-methylphenyl]-(4-methylphenyl)methanone was synthesized and characterized by spectroscopic and X-ray diffraction methods. The molecule crystallizes in the monoclinic space group P21/c with cell parameters a = 13.7530(19) Å, b = 10.0560(19) Å, c = 13.469(3) Å, β = 100.630(7)° and Z = 4. There is a large discrepancy between the carbonyl group bond lengths of ketone and the ester. The structure exhibits intermolecular hydrogen bonds of the type C–H···O. 相似文献
16.
The optically pure 2-(2′-methylbenzyl)succinic acid were obtained by the optical resolution of the racemates with the chiral
host 1-phenylethylamine. The structure of the salt complex between (S)-2-(2′-methylbenzyl)succinic acid and (R)-1-phenylethylamine was first elucidated by X-ray analysis: Monoclinic, Space group P21 with a=6.0781(12) ?, b=8.8224(18) ?, c=17.675(4) ?, β=97.64(3)°, V=939.4(3) ?3, Z=2, the absolute structure parameter is 0 (9). The crystal structure indicates that the hydrogen bonds are formed between
the acetate anions and the protonated amino group. The intermolecular hydrogen bond links the salt complex into a quasi-two-dimentional
netlike structure. 相似文献
17.
A. Elmali 《Journal of chemical crystallography》2000,30(7):473-477
The Schiff base, 1,3-bis(2-hydroxy-5-bromosalicylideneamine)propan-2-ol, has been studied by AM1 semiempirical quantum mechanical method and X-ray analysis. It crystallizes in the orthorhombic space group Pca21 with a = 8.458(3), b = 6.139(2), c = 32.957(4) Å, Dcalc = 1.770 g cm-3, V = 1711(1) Å3, Z = 4 and (MoK) = 0.476. The structure was solved by direct methods and refined to R = 0.041 for 1715 independent reflections [I > 2 (I)]. The title compound is not planar. Intramolecular hydrogen bonds are found between the hydroxyl and the amine nitrogen with O—H···N distances of 2.601(6) and 2.629(4) Å. There is also an intermolecular O—H···N hydrogen bond [3.176(6) Å] linking the neighbouring molecules. Minimum energy conformations from AM1 were calculated as a function of eight torsion angles varied every 5°. The optimized geometry of the crystal structure corresponding to the nonplanar conformation is the most stable conformation in all calculations. The results strongly indicate that the minimum energy conformation is primarily determined by nonbonded hydrogen—hydrogen repulsions. 相似文献
18.
Hasan Karabıyık M. Emin Günay Muhittin Aygün Bekir Çetinkaya Canan Kazak 《Journal of chemical crystallography》2006,36(4):243-248
The molecular and crystal structures of the title compound, C19H22N2O4S, were determined by single crystal X-ray diffraction technique. The title compound crystallizes in space group F d d 2, with a = 30.785(3) ?, b = 10.6455(9) ?, c = 11.0036(8) ?, Z = 8, D
calc = 1.379(2) g cm−3, μ(Mo-Kα) = 0.207 mm−1, and its crystal system is orthorhombic. The structure was solved by direct methods and refined to a final R = 0.042 for 1530 reflections with I > 2σ (I). There is a half-independent molecule in the asymmetric unit. The title molecule has twofold rotational symmetry along with the C–S bond. Classically no hydrogen bond is found in the crystal structure. The crystal structure is stabilized by π–π stacking and edge to face (C–H…π-ring) interactions. To elucidate conformational features and steric hindrances of the title molecule, selected torsion angle is varied from −180° to +180° in every 10° and thus molecular energy profile is calculated by PM3 semi-empirical method.Supplementary materials CCDC 261789 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, by emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: $+$44 1223 336033. 相似文献
19.
De- Suo Yang 《Journal of chemical crystallography》2007,37(6):429-432
A nitrate salt of bis[4-bromo-2-(pyridin-2-ylmethyliminomethyl)phenolato]iron(III), [Fe(C13H10BrN2O)2].NO3, has been obtained and characterized by elemental analysis and X-ray single crystal determination. The complex crystallizes
in the tetragonal space group P42/n with unit cell dimensions a = b = 17.608(3) ?, c = 17.199(3) ?, V = 5332.4(15) ?3, Z = 8, R
1 = 0.0444 and wR2 = 0.0902. The complex consists of a [Fe(C13H10BrN2O)2]+ cation and a nitrate anion. The Fe atom in the cation is six-coordinated in an octahedral geometry. In the crystal structure,
molecules are linked through weak C–H⋯O intermolecular hydrogen bonds, forming chains running along the c axis.
Supplementary material CCDC-607149 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge at
http://www.ccdccam.ac.uk/const/retrieving.html or from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge
CB2 1EZ, UK; fax: +44(0)1223-336033 or e-mail: deposit@ccdc.cam.ac.uk. 相似文献
20.
Yu. M. Chumakov V. I. Tsapkov G. Bocelli S. A. Palomares-Sanchez R. S. Ortiz A. P. Gulea 《Crystallography Reports》2007,52(1):102-107
The crystal structures of bis{2,4-dibromo-6-[(2-hydroxyethylamino)-methyl]phenolato}copper (I), bis{2,4-dichloro-6-[(2-hydroxyethylamino)-methyl]phenolato}copper (II), and bis{2-[(2-hydroxyethylamino)-methyl]-4,6-dinitrophenolato}copper (III) in which the metal atom is located at the center of symmetry are determined using X-ray diffraction. Crystals of compounds I and II are isostructural. The copper atom in the structures of compounds I and I coordinates two singly deprotonated bidentate molecules of the ligand through the phenol oxygen atoms and the azomethine nitrogen atoms with the formation of a distorted planar square. In the crystals, complexes I and II form one-dimensional infinite chains along the b axis. In the structure of compound III, the coordination polyhedron of the central atom is an elongated tetragonal bipyramid with the base formed by the azomethine nitrogen atoms and the phenol oxygen atoms. Both vertices of the bipyramid are occupied by the oxygen atoms of the amino alcohol groups of the neighboring complexes, which are related to the initial complex through the center of symmetry. In turn, the oxygen atoms of the alcohol groups of the initial complex are located at the vertices of the coordination bipyramids of the metal atoms of the neighboring centrosymmetric complexes, thus forming infinite polymer chains along the a axis. 相似文献