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1.
Wen-Kui Dong Jun-Feng Tong Yin-Xia Sun Jian-Chao Wu Jian Yao Shang-Sheng Gong 《Transition Metal Chemistry》2010,35(4):419-426
Two new mono- and dinuclear Cu(II) complexes, namely [CuL1]·0.5H2O (1) and [(Cu2(L2)2)(DMF)]·0.5DMF (2) (H2L1 = 1,2-bis{[(Z)-(3-methyl-5-oxo-1-phenyl-1H-pyrazolidin-4(4H)-yl)(phenyl)]methylene-aminooxy}ethane; H2L2 = 1,3-bis{[(Z)-(3-methyl-5-oxo-1-phenyl-1H-pyrazolidin-4(4H)-yl)(phenyl)] methyleneaminooxy}propane), have been synthesized and characterized by X-ray crystallography. The unit cell
of complex 1 contains two crystallographically independent but chemically identical [CuL1] molecules and one crystalline water molecule, showing a slightly distorted square-planar coordination geometry and forming
a wave-like pattern running along the a-axis via hydrogen bonding and π···π stacking interactions. Complex 2 has a dinuclear structure, comprising two Cu(II) atoms, two completely deprotonated phenolate bisoxime (L2)2− moieties (in the form of enol), and both coordinated and hemi-crystalline DMF molecules. Complex 2 has square-planar and square-pyramidal geometries around the two copper centers, whose basic coordination planes are almost
perpendicular and form an infinite three-dimensional supramolecular network structure involving intermolecular C–H···N, C–H···O,
and C–H···π(Ph) hydrogen bonding and π···π stacking interactions of neighboring pyrazole rings. 相似文献
2.
Wen-Kui Dong Gang Wang Shang-Sheng Gong Jun-Feng Tong Yin-Xia Sun Xiong-Hou Gao 《Transition Metal Chemistry》2012,37(3):271-277
Two new Cu(II) complexes, [Cu(L1)2] (1) and [Cu(L2)2] (2) (HL1 = (E)-3-bromo-5-chloro-2-hydroxy benzaldehyde O-methyl oxime; HL2 = (E)-3-bromo-5-chloro-2-hydroxy benzaldehyde O-ethyl oxime), have been synthesized and characterized by physicochemical and spectroscopic methods. X-ray crystallographic
analyses show that complexes 1 and 2 have similar structures, consisting of one Cu(II) atom and two L− units. In both complexes, the Cu(II) atom, lying on an inversion center, is four-coordinated in a trans-CuN2O2 square-planar geometry by two phenolate O and two oxime N atoms from two symmetry-related N,O-bidentate oxime ligands. Moreover,
both complexes form an infinite three-dimensional supramolecular structure involving intermolecular C–H···Br hydrogen bonds
and π···π stacking interactions between the metal chelate rings and aromatic rings. Substituent effects in the two complexes
are discussed. 相似文献
3.
Qian Huang Wei-qiang Chen Xing Chen Xiao-bin Liu Jia-rong Zhou Hong-rong Zuo Lin-liang Yu Chun-lin Ni 《Transition Metal Chemistry》2009,34(7):765-771
Two new hybrid organic–inorganic salts, [BzDMAP]2[Cu(mnt)2](1) and [NO2BzDMAP]2[Cu(mnt)2] (2) ([BzDMAP]+ = 1-benzyl-4′-dimethylaminopyridinium, [NO2BzDMAP]+ = 1-(4′-nitrobenzyl)-4′-dimethylaminopyridinium, and mnt2− = maleonitriledithiolate) have been characterized structurally and magnetically. The [BzDMAP]+ or [NO2BzDMAP]+ cations (C) and the [Cu(mnt)2]2− anions (A) in 1 and 2 stack into a 1D alternating CC-A-CC-A-CC column. The Cu···N, π···π, C–H···N, C–H···O, and C–H···S weak interactions play
important roles in the molecular stacking and generate a 2D or 3D structure of 1 and 2. The magnetic susceptibilities of these salts measured in the temperature range 2.0–300 K show weak antiferromagnetic coupling
features with θ = −2.370 K for 1 and −0.222 K for 2. 相似文献
4.
Franz A. Mautner Febee R. Louka August A. Gallo Jörg H. Albering Mohamed R. Saber Nagua B. Burham Salah S. Massoud 《Transition Metal Chemistry》2010,35(5):613-619
Two thiocyanato-Cu(II) complexes including mononuclear dithiocyanato Cu(Me3dpt)(NCS)2 (1) and the polymeric 1D [Cu(d,l-Ala)(μN,S–NCS)(H2O)]
n
(2) were synthesized and structurally characterized (Me3dpt = bis(N-methyl-3-propyl)methylamine, Ala = alaninate anion). The IR spectrum of complex 1 confirmed the N-bonding coordination mode of the thiocyanate groups, and its visible spectrum revealed the square pyramidal
geometry around the central Cu2+ ion. Single X-ray crystallography of 1 showed that the Cu(II) center displays square pyramidal geometry with severe distortion toward trigonal bipyramidal environment. Complex 2 forms a 1-D polymeric chain with the NCS− acting as a μN,S-ligand. A distorted SP geometry around the Cu2+ centers was achieved by the O and N atoms of alaninato anion, the aqua ligand and by the N and S atoms of the bridging thiocyanate
groups. Hydrogen bonds of the type N–H···O, N–H···S and O–H···O are formed in this complex leading to the extension of the
1D chain to a supramolecular network. 相似文献
5.
Abstract
Four complexes of 3,3-diphenylpropanoate (L) and 4,4′-bipyridine as auxiliary bridging ligands were synthesized and characterized, namely [Zn(L)2(4bpy)(EtOH)2]∞ (1), [Co(L)2(4bpy)(EtOH)2]∞ (2), [Ni(L)2(4bpy)(EtOH)2]∞ (3), and [Cu(L)2(4bpy)(H2O)]∞ (4) (4bpy = 4,4′-bipyridine). X-ray single-crystal diffraction analyses show that complexes 1–4 all take one-dimensional (1D) fishbone-like structures incorporating bridging 4bpy ligands. The complexes show different supramolecular frameworks interlinked via intermolecular hydrogen bonds, π···π stacking, and/or C–H···π supramolecular interactions. Complex 3 only has a simple one-dimensional fishbone-like chain, whereas complexes 1 and 2 show two-dimensional supramolecular structures by interchain C–H···O hydrogen bonds. Complex 4 is assembled into two-dimensional layers and then an overall three-dimensional framework by a combination of interchain O–H···O hydrogen bonds and C–H···π supramolecular interactions. The luminescent properties of the ligands and their complexes were investigated. 相似文献6.
Two new 3,5-diaryl-1H-pyrazoles: 3(5)-(4-tert-butylphenyl)-5(3)-(naphthalene-2-yl)-1H-pyrazole (1) and 5-(4-(benzyloxy)phenyl)-3-(furan-2-yl)-1H-pyrazole (2) were synthesized and characterized. Two strong ions peaks [2M]+ and [2M + Na]+ observed in the ESI–MS spectra are attributed to the dimerization process in solution formed by intermolecular N–H···N hydrogen
bonds. The crystal structures have been determined by X-ray crystal structure analysis. Compound 1 exists as a pair of tautomers 1a and 1b, and its dimer [R
22(6) motif] is formed by the tautomers 1a and 1b. Compound 2 only exists as a 2a tautomer, and interesting intermolecular N–H···O and O–H···N hydrogen bonds link two pyrazoles and two methanol molecules,
leading to the formation of an R
44(10) dimer motif. 相似文献
7.
Chun-Sen Liu E. Carolina Sañudo Li-Fen Yan Ze Chang Jun-Jie Wang Tong-Liang Hu 《Transition Metal Chemistry》2009,34(1):51-60
Abstract To explore the influence of the anthracene ring skeleton, with a large conjugated π-system, on the structures and properties
of its complexes, two MnII complexes with anthracene-9-carboxylate ligand were synthesized and structurally characterized: {[Mn(L)2(H2O)2](H2O)}∞ (1) and [Mn2(L)4(phen)2(μ-H2O)](CH3OH) (2) (L = anthracene-9-carboxylate and phen = 1,10-phenanthroline). Complex (1) has a one-dimensional (1D) chain structure that is further assembled to form a two-dimensional (2D) sheet, and then an overall
three-dimensional (3D) network by π···π stacking and/or C–H···π interactions. Complex (2) makes a dinuclear structure by incorporating the chelating phen ligand, which is further interlinked via inter-molecular
π···π stacking and C–H···π interactions to generate a higher-dimensional supramolecular network along the different crystallographic
directions. The results reveal that the bulky anthracene ring skeleton in L, by virtue of intra- and/or inter-molecular π···π
stacking and C–H···π interactions, plays an important role in the formation of complexes (1) and (2). The magnetic properties of (1) and (2) were further investigated. As expected, the very long inter-metallic separations result in weak magnetic coupling, with
the corresponding coupling constant values of J = −10 cm−1 for (1) and J = −2.46 cm−1 for (2).
Graphical abstract The constructions of two new MnII complexes comprising 1D chain (1) and dinuclear subunit (2) structures have been successfully achieved by using a bulky anthracene-9-carboxylic acid (HL), together with incorporating
the chelating 1,10-phenanthroline as a co-ligand for (2). The result reveals that the bulky anthracene ring skeleton of HL, by virtue of intra- and/or inter-molecular π···π stacking
and C–H···π interactions, plays an important role in the formation of the supramolecular architectures of (1) and (2). Moreover, magnetic properties of the complexes have been investigated.
相似文献
8.
Franc Perdih 《Monatshefte für Chemie / Chemical Monthly》2012,42(8):1011-1017
Abstract
Copper(II) bis(pentane-2,4-dionato-κ2 O,O′) compounds with 2-pyridone (1) and 3-hydroxypyridine (2) were prepared by the reaction of bis(pentane-2,4-dionato-κ2 O,O′)copper(II) with selected ligands. The coordination of Cu(II) in both compounds is square pyramidal with the fifth coordination site occupied by the carbonyl oxygen atom of the 2-pyridone ligand in 1 and by the nitrogen atom of 3-hydroxypyridine in 2. The X-ray crystallographic studies revealed different crystal aggregation influenced by the ability of the 2-pyridone ligand to act as a hydrogen bond donor and acceptor, and 3-hydroxypyridine acting only as a hydrogen bond donor. Intermolecular N–H···O hydrogen bonding forms dimers in 1 and infinite chains in 2. Three-dimensional aggregation is achieved by π–π interactions and C–H···π (arene) hydrogen bonding. 相似文献9.
Co-crystallization of melamine(MA) and sulfate results in crystalline product [(C3H7N6+)2(SO42−)] · 2H2O. The novel supramolecular complex has been characterized by elemental analysis, thermal analysis (TGA and DSC), nuclear
magnetic resonance (NMR), and single crystal X-ray diffraction. X-ray crystallographic studies of the complex reveal that
the title complex has a 3-D microporous structure which is linked by intense intermolecular hydrogen-bonding interactions
(N–H······O, N–H······N, O–H······O) and aromatic π-π interaction, which stabilize the whole crystal framework. The TGA curve
shows that the complex is stable up to 500 °C, above which its structure begins to collapse. 相似文献
10.
Xing Chen Wen-Tao Yin Qian Huang Hong-Rong Zuo Jia-Rong Zhou Lin-Liang Yu Chun-Lin Ni Xue-Lei Hu 《Transition Metal Chemistry》2010,35(2):143-149
Two new salts, [BzTPP]2[Cu(mnt)2] (1) and [4NO2BzTPP]2[Cu(mnt)2] (2) (BzTPP+ = benzyltriphenylphosphonium and mnt2− = maleonitriledithiolate) have been prepared and characterized by elemental analyses, UV, IR, molar conductivity and single-crystal
X-ray diffraction. The single-crystal structure analysis shows that 1 crystallizes in the monoclinic space group P21/n, while 2 crystallizes in the triclinic space group P−1. The effects of weak intramolecular interactions such as C–H···O, C–H···S, C–H···N, C–H···Cu hydrogen bonds and p···π, π···π stacking interactions in the solids generate a 3D network structure. It is noted that the change in the molecular
topology of the counteraction when the 4-substituted group in the benzyl ring is changed from H to NO2 results in differences in the crystal system, space group, weak interactions and the stacking mode of the cations and anions
of 1 and 2. The magnetic susceptibilities of these salts measured in the temperature range 2.0 to 300 K show weak ferromagnetic coupling
features with θ = 2.05 × 10−2 K for 1 and 5.13 × 10−3 K for 2. 相似文献
11.
Zhi Qiang Shi Ning Ning Ji Ren Gao Zhao Ji Kun Li Zhi Feng Li 《Structural chemistry》2011,22(1):225-233
Two new copper(II) complexes, [Cu(p-FBA)2(2,2′-bpy)]·(H2O) (1) and [Cu(p-FBA)(2,2′-bpy)2]·(p-FBA)2 (2) {p-FBA = p-fluorobenzoic acid, 2,2′-bpy = 2,2′-bipyridine} have been obtained from an identical starting mixture using temperature as
the only independent variable and characterized by X-ray single crystal diffraction as well as with infrared spectroscopy,
elemental analysis, and thermogravimetric analysis. The results reveal that 1 has 1D infinite chain structure formed by O–H···O hydrogen bonds, while 2 features a 0D structure. Additionally, there exist C–H···O hydrogen bonds and π–π stacking interactions in 1, forming 2D supramolecular structure. Furthermore, density functional theory (DFT) calculations of the structures, stabilities,
orbital energies, composition characteristics of some frontier molecular orbitals and Mulliken charge distributions of the
[Cu(p-FBA)2(2,2′-bpy)] of 1 and [Cu(p-FBA)(2,2′-bpy)2]+ cation of 2 were performed by means of Gaussian 03W package and taking B3LYP/lanl2dz basis set. 相似文献
12.
Güneş Süheyla Kürkçüoğlu Tuncer Hökelek Okan Zafer Yeşilel Sabiha Aksay 《Structural chemistry》2008,19(3):493-499
The cyano-bridged heteronuclear polymeric complex, [Cd(teta)Ni(μ-CN)2(CN)2] · 2H2O (1), (teta = triethylenetetraamine) was synthesized and characterized by FT-IR spectroscopy, thermal analysis and single crystal
X-ray diffraction techniques. It crystallizes in the orthorhombic system, space group Pccn. The asymmetric unit also contains two uncoordinated water molecules. The coordination geometry around the Cd(II) centre
is a highly distorted octahedral. In the crystal structure, intramolecular N–H···O and intermolecular N–H···O, O–H···O and
O–H···N hydrogen bonds, beside the cyano-bridged chains made up of tetracyanonickelate ions coordinated to Cd(II) ions, where
the Ni(II) ion is coordinated by four cyanoligands in a square-planar arrangement, link the molecules into polymeric networks
parallel to (001) plane, where the hydrogen bonded water molecules occupy the cavities between the layers. The FT-IR spectrum
was reported in the 4,000–400 cm−1 region. Vibration assignments were given for all the observed bands and the spectral feature also supported the structure
of the polymeric complex. The decomposition reaction takes place in the temperature range 20–1,000 °C in the static air atmosphere. 相似文献
13.
Tulika Ghosh Abhik Mukhopadhyay Kummari S. C. Dargaiah Samudranil Pal 《Structural chemistry》2010,21(1):147-152
Reactions of Ni(O2CCH3)2·4H2O and Cu(O2CCH3)2·H2O with biacetyl bis(benzoylhydrazone) (H2babh) in alcoholic media afford mononuclear nickel(II) and copper(II) complexes of general formula [M(babh)]. The complexes
have been characterized by microanalysis (C, H, N), magnetic susceptibility, and various spectroscopic measurements. X-ray
structures of both complexes have been determined. The metal centre in [Ni(babh)] is in square-planar N2O2 environment provided by the tetradentate babh2−. On the other hand, [Cu(babh)] crystallizes as distorted square-pyramidal [Cu(babh)(CH3OH)] from methanol. Here the tetradentate babh2− constitutes the N2O2 square-base and the O-coordinating methanol occupies the apical site. In the crystal lattice, the molecules of [Ni(babh)]
form a one-dimensional π-stacked structure. The [Cu(babh)(CH3OH)] molecules also form a one-dimensional structure with alternating long and short Cu···Cu distances via intermolecular
O–H···N hydrogen bonding and π–π interaction. 相似文献
14.
Shyamapada Shit Joy Chakraborty Brajagopal Samanta Alexandra M. Z. Slawin Volker Gramlich Samiran Mitra 《Structural chemistry》2009,20(4):633-642
Three new coordination complexes, 2{[Co(L1)2]ClO4} · 0.5CH3OH (1), [Mn(L2)2] (2), and [Cu(HL2)(L2)]ClO4 · 2H2O (3) have been synthesized from two tridentate N,N,O-donor hydrazone ligands HL1, 2-acetylpyridine-salicyloylhydrazone, and HL2, 2-benzoylpyridine-salicyloylhydrazone, respectively and thoroughly characterized by elemental analysis, FT-IR, UV–Vis, electrochemical,
and room temperature magnetic susceptibility measurements. Structures of the complexes have been unequivocally established
by single crystal X-ray diffraction technique. Structural analysis reveals that 1 consists of two chemically similar but crystallographically independent cationic [Co(L1)2]+ units and 2 consists of a neutral [Mn(L2)2] molecule while 3 consists of a cationic [Cu(HL2)(L2)]+ unit. Metal ions display distorted octahedral geometry in 1 and 2 while in 3 it shows a distorted square pyramidal geometry. Ligand conformations around the metal ions are stabilized by the presence
of intra-ligand hydrogen bonding in all the complexes. Structure of 3 reveals that a perchlorate ion linked to the complex by hydrogen bonding via a water molecule. 相似文献
15.
Magdalena Ma?ecka 《Structural chemistry》2010,21(1):175-184
The intramolecular N–H···O hydrogen bonds in 3-aminomethylene-2 methoxy-5,6-dimethyl-2-oxo-2,3-dihydro-2λ5-[1,2]oxaphosphinin-4-one and its derivatives (F, H, Li, -BeH) were studied by DFT (density functional theory) methods. The
results of calculations were obtained at B3LYP/6-311++G(d,p) level on model species, with the resonance-assisted hydrogen
bonds (RAHB). Topological parameters such an electron density, its Laplacian, kinetic electron energy density, potential electron
energy density, and total electron energy density at the bond critical points (BCP) of H···O/N–H contact bonds from Bader’s ‘Atoms in molecules’ (AIM) theory were analyzed in details. The energy of the N–H···O interactions studied here was found rather weak (E
HB = 2.53–12.08 kcal/mol). The results of AIM ellipticity indicated π-delocalization over all six atoms within ring. 相似文献
16.
Tushar S. Basu Baul Khrawborlang Nongsiej Augustine Lamin Ka‐Ot Santa Ram Joshi Irn Rojas Len Herbert Hpfl 《应用有机金属化学》2019,33(7)
A series of six new Zn (II) compounds, viz., [Zn(HLASA)2(Py)2] ( 1 ), [Zn(HLMASA)2(Py)2] ( 2 ), [Zn(HLMASA)2(4‐MePy)2] ( 3 ), [Zn(HLCASA)2(4‐MePy)2] ( 4 ), [Zn(HLBASA)2(Py)2] ( 5 ), [Zn(HLBASA)2(4‐MePy)2] ( 6 ) and representative Cu (II) and Cd (II) complexes, viz., [Cu(HLASA)2(Py)2(H2O)] ( 7 ) and [Cd(HLBASA)2(Py)3] ( 8 ) [(HLXASA)? = para‐substituted 5‐[(E)‐2‐(aryl)‐1‐diazenyl]‐2‐hydroxybenzoate with X = H (ASA), Me (MASA), Cl (CASA) or Br (BASA); Py = pyridine; 4‐MePy = 4‐methylpyridine] have been synthesized and characterized by spectroscopic techniques and single‐crystal X‐ray diffraction analysis. The structural characterization of the compounds revealed distorted tetrahedral ( 1 – 6 ), square‐pyramidal ( 7 ) and pentagonal‐bipyramidal ( 8 ) coordination geometries around the metal atom, in which the aryl‐substituted diazosalicylate ligands are coordinated only through the oxygen atoms of carboxylate groups, either in an anisobidentate or isobidentate mode; meanwhile, the 2‐hydroxy groups of the monoanionic ligand (HLXASA)? are involved only in intramolecular O‐H···O hydrogen bonds with the carboxylate function. In the crystal structures of 1 – 8 , the complex molecules are assembled by π‐stacking interactions giving mostly infinite 1D strands. The intermolecular binding in the solid state structures is accomplished by diverse additional non‐covalent contacts including C‐H···O, C‐H···N, C‐H···π, C‐H···Br, O···Br, Br···π and van der Waals contacts. Although the primary and secondary ligands in the Zn (II) complex series 1 – 6 carry different substituents at the periphery (X = H, Me, Cl, Br for (HLXASA)? and R = H, Me for 4‐Py‐R), five of the crystal structures were isostructural. Additionally, the antimicrobial activity of the pro‐ligands H2LXASA and their Zn (II), Cu (II) and Cd (II) compounds were studied in a comparative manner, showing high sensitivity (IZD ≥ 20) against Bacillus subtilis. 相似文献
17.
Cyril Rajnák Ján Titi? Roman Bo?a Ján Moncol’ Zdeňka Padělková 《Monatshefte für Chemie / Chemical Monthly》2011,36(4):789-795
Abstract
A mononuclear complex [CoL2Cl2]·3.5H2O (L = 2-[(2,2-diphenylethylimino)methyl]pyridine-1-oxide) has been synthesized and characterized by X-ray structure analysis. The crystal structure confirms the formation of an interesting porous framework with channel diameters of about 8 ? through weak C–H···π and C–H···Cl interactions. The magnetic properties of this complex have also been studied, and the susceptibility and magnetization data were analyzed in terms of the spin Hamiltonian formalism. They confirm substantial zero-field splitting, D/hc = 75 cm−1. 相似文献18.
A new ligand N′-(pyridin-2-ylmethylene)nicotinohydrazide (HL2) and two Ni(II) complexes of stoichiometry NiL1·H2O [L1-2-benzoylpyridine nicotinoylhydrazone] and NiL2·H2O have been synthesized and characterized by elemental analyses, IR and UV–Vis spectral studies. Structures of HL2 and Ni(II) compounds have been determined by single crystal X-ray diffraction studies which reveal a distorted octahedral
geometry around the two Ni(II) centers.
Graphical abstract A new ligand N¢-(pyridin-2-ylmethylene)nicotinohydrazide (HL2) and two Ni(II) complexes of stoichiometry NiL1·H2O [L1-2-benzoylpyridine nicotinoylhydrazone] and NiL2·H2O have been synthesized and characterized by elemental analyses, IR, UV–Vis spectral studies and single crystal X-ray analysis.相似文献
19.
Nanthawat Wannarit Viwat Hahnvajanawong Chaveng Pakawatchai Sujittra Youngme 《Transition Metal Chemistry》2012,37(1):79-84
Two multiple-layer heterometallic MnII–AgI coordination polymers, {MnII(ampyz)(H2O)[Ag2I(CN)3][AgI(CN)2]·ampyz}
n
(1) and {[MnII(benzim)2[AgI(CN)2]2][(benzim)AgI(CN)]·H2O}
n
(2) where ampyz = 2-aminopyrazine and benzim = benzimidazole, have been prepared and structurally characterized. Compound 1 reveals a multiple-layer two-dimensional network with strong hexanuclear argentophilic interactions leading to an infinite
three-dimensional framework. Compound 2 has an unprecedented double-layer two-dimensional squared grid-type network with (4,4) topology through AgI···AgI and π–π interactions between two adjacent squared layers. These double-layer networks of 2 are linked to others by π–π interactions, leading to a three-dimensional framework. 相似文献
20.
Yong Hou Jiarong Zhou Xiaoping Liu Linliang Yu Chunlin Ni 《Transition Metal Chemistry》2008,33(4):411-416
Two new salts, [oClBzTPP]2+[Ni(mnt)2]2−(1) and [oClBzTPP]+[Ni(mnt)2]−(2) ([oClBzTPP]+ = 1-(2′-chlorobenzyl)triphenylphosphonium and mnt2− = maleonitriledithiolate) have been prepared and characterized by elemental analyses, UV, IR, MS spectra, single crystal
X-ray diffraction, and magnetic susceptibility. The Ni ions of the Ni(mnt)2 anions for 1 and 2 exhibit the square-planar coordination geometry. The Ni(III) ions of 2 form a 1D zigzag alternating magnetic chain within a Ni(mnt)2− column through Ni···S, S···S, or Ni···Ni interactions. The C–H···N, C–H···S, C–H···π hydrogen bonds or π···π stacking interactions
play important roles in the molecular stabilizing and stacking of 1 and 2. Magnetic susceptibility measurements in the temperature range 1.8−300 K show that 2 exhibits diamagnetic behavior. 相似文献