共查询到20条相似文献,搜索用时 12 毫秒
1.
Rhodium(III) and iridium(III) octahedral complexes of general formula [MCl3{R2PCH2C(But)NNC(But)CH2PR2}] (M = Rh, Ir; R = Ph, c-C6H11, Pri, But; not all the combinations) were prepared either from the corresponding diphosphinoazines and RhCl3 · 3H2O or by the oxidation of previously reported bridging complexes [{MCl(1,2-η:5,6-η-CHCHCH2CH2CHCHCH2CH2)}2{μ-R2PCH2C(But)NNC(But)CH2PR2}] with chlorine-containing solvents. Depending on the steric properties of the ligands, complexes with facial or meridional configuration were obtained. Crystal and molecular structures of three facial and two meridional complexes were determined by X-ray diffraction. Hemilability of ligand in the complex fac-[RhCl3{(C6H11)2PCH2C(But)NNC(But)CH2P(C6H11)2}] consisting in reversible decoordination of the phosphine donor group in the six-membered ring was observed as the first step of isomerization between fac and mer isomers. 相似文献
2.
Shoichi Katsuta Yudai Iwabe Yayoi Kato Yoshihiro Kudo Yasuyuki Takeda 《Inorganica chimica acta》2008,361(1):103-108
The solvent extraction properties of macrocyclic trinuclear organometallic complexes, [(p-cymene)Ru(pyO2)]3 and [Cp∗Rh(pyO2)]3, for Li+, Na+, and K+ picrates have been investigated in a dichloromethane-water system at 25 °C. The extraction rates of the alkali metal picrates with these macrocyclic complex ligands are unusually slow; the shaking times required to attain equilibrium are at least 1 h for [(p-cymene)Ru(pyO2)]3 and 20-40 h for [Cp∗Rh(pyO2)]3. From analysis of the equilibrium data, the extraction constants (Kex = [ML+A−]o/[M+][L]o[A−]; M+ = alkali metal ion, L = macrocyclic ligand, A− = picrate ion, o = organic phase) have been determined. The log Kex value varies in the sequences, Li+ (5.72) > Na+ (4.50) > K+ (2.88) for [(p-cymene)Ru(pyO2)]3 and Li+ (4.79) > Na+ (2.70) ≈ K+ (2.69) for [Cp∗Rh(pyO2)]3. The Kex values of 6,6-dibenzyl-14-crown-4 (DBz14C4), which is one of the best Li+-selective crown ethers, have also been determined for comparison. It is revealed that [Cp∗Rh(pyO2)]3 is much superior to DBz14C4 both in the extractability for Li+ and the selectivity for Li+ over Na+. 相似文献
3.
Tina Osswald 《Inorganica chimica acta》2010,363(3):474-480
The synthesis, characterization, and application in asymmetric catalytic cyclopropanation of Rh(III) and Ir(III) complexes containing (Sa,RC,RC)-O,O′-[1,1′-binaphthyl-2,2′-diyl]-N,N′-bis[1-phenyl-ethyl]phosphoramidite (1) are reported. The X-ray structures of the half-sandwich complexes [MCl2(C5Me5)(1,κP)] (M = Rh, 2a; M = Ir, 2b) show that the metal-phosphoramidite bond is significantly shorter in the Ir(III) analog. Chloride abstraction from 2a (with CF3SO3SiMe3 or with CF3SO3Me) and from 2b (with AgSbF6) gives the cationic species [MCl(C5Me5)(1,2-η-1,κP)]+ (M = Rh, 3a; M = Ir, 3b), which display a secondary interaction between the metal and a dangling phenethyl group (NCH(CH3)Ph) of the phosphoramidite ligand, as indicated by NMR spectroscopic studies. Complexes 3a and 3b slowly decompose in solution. In the case of 3b, the binuclear species [Ir2Cl3(C5Me5)2]+ is slowly formed, as indicated by an X-ray study. Preliminary catalytic tests showed that 3a cyclopropanates styrene with moderate yield (35%) and diastereoselectivity (70:30 trans:cis ratio) and with 32% ee (for the trans isomer). 相似文献
4.
Reactions of Cp*M(MDMPP-P,O)Cl (1a: M=Rh, 1b: M=Ir; MDMPP-P,O=PPh2(2-O-6-MeOC6H3)) with tetracyanoethylene (tcne) in the presence of KPF6 gave Cp*MCl[PPh2{2-O-3-(C(CN)2CH(CN)2)-6-MeOC6H2}] (2), [{Cp*MPPh2{2-O-3-(C(CN)C(CN)2)-6-MeOC6H2}}2(CN)](PF6) (3), [{Cp*IrPPh2{2-O-3-(C(CN)C(CN)2)-6-MeOC6H2}}(CN){Cp*Ir(MDMPP-P,O)}](PF6) (4b) and [{Cp*Ir(MDMPP-P,O)}2(CN)](PF6) (5b), depending on the reaction conditions. Reaction of 2 with KPF6 or AgOTf in the absence and presence of xylyl isocyanide (XylNC) gave 3 or [Cp*MCl{PPh2(2-O-3-(C(CN)2-CH(CN)2)-6-MeOC6H2)}(XylNC)](OTf) (6). The structure of 3a (M=Rh) was confirmed by X-ray crystal analysis. 相似文献
5.
Marion Graf 《Inorganica chimica acta》2011,371(1):42-43
The synthesis of bis-cyclometalated aminocarboxylato complexes [M(α-aminocarboxylato)(ptpy)2] (M = Rh, 3, 4, 5; M = Ir, 6, 7, 8), ptpy = 2-(p-tolyl)pyridinato; aminocarboxylato = glycinato, l-alaninato, l-prolinato) from [{M(μ-Cl)(ptpy)2}2] (M = Rh, 1; M = Ir, 2) is described. The molecular structure of [Ir(l-alaninato)(ptpy)2] (7) was confirmed by a single-crystal X-ray diffraction study. Compound 7 crystallized from methanol-iso-hexane in the space group P21. For 7 the two diastereoisomers ΔIr, SC and ΛIr, SC were found crystallizing twice per unit. Absorption and emission spectra were recorded. The rhodium compounds are weak yellow-green and the iridium species strong green emitters. 相似文献
6.
The synthesis in high yields and the dissociative behaviour in the solid state and in solution of the mononuclear complexes [cis-M(CO)2Cl(pyz)] (M=Rh, Ir; PYZ=pyrazine) and [fac-M(CO)3Cl2(pyz)] (M=Ru, Os) are reported. The mononuclear complexes of Rh and Ir are relatively labile with respect to pyrazine release. Particularly in the case of rhodium they generate even in the solid state the corresponding dinuclear complexes [cis-Cl(CO)2M(pyz)cis-M(CO)2Cl] (M=Rh, Ir). The 1H NMR spectra of these mononuclear Rh and Ir complexes in CHCl3 solution show, at 25 and 60 °C, respectively, a fast and reversible dissociation of metal coordinated pyrazine, which is hindered by lowering the temperature. Crystallographic aspects of [cis-Ir(CO)2Cl(pyz)] have been investigated via single crystal X-ray diffraction. The mononuclear complexes of Ru and Os are more stable. In the solid state they do not rearrange, with release of pyrazine, to generate the related dimeric complexes with pyrazine as bridge. In solution, at room temperature, they do not dissociate quickly, although a mixture of monomeric and dimeric pyrazine complexes (ratio monomer to dimer 9:1 and 15:1 for Ru and Os, respectively) is slowly formed by a process which is reverted by addition of excess pyrazine, as expected for a dissociative equilibrium. 相似文献
7.
Nadera Haque 《Inorganica chimica acta》2010,363(4):723-728
The reactions of trans-[(PPh3)2M(CO)Cl] (M = Rh and Ir) with benzildiimine (H2BDI = 2) derived from benzil-bis(trimethylsilyl)diimine (Si2BDI) (1) in a 1:2 and 1:1 molar ratio afforded the cationic bis-benzildiiminato complexes [Rh(PPh3)2(HBDI)2]Cl (3) and the mono-benzildiimine complex [Ir(PPh3)2(CO)(H2BDI)]Cl (4), respectively. Both complexes are fully characterized using IR, FAB-MS, NMR spectroscopy and elemental analysis. The single crystal X-ray structure analysis reveals a distorted octahedral coordination geometry for the Rh(III) in 3 and a highly distorted square pyramidal geometry for Ir(I) in 4. In addition, the solid-state structure of Si2BDI is reported here for the first time showing the substituents highly twisted because of steric reasons. 相似文献
8.
Daniel Totev Daniel Carmona Luis A Oro Isabel T Dobrinovitch 《Inorganica chimica acta》2004,357(10):2889-2898
The synthesis of arene-ruthenium(II) and C5Me5-rhodium(III) and -iridium(III) complexes of chiral arene-chromium-tricarbonyl-based P∧P and P∧N ligands is described. Three complexes were characterized in the solid state by X-ray structural analysis. The complexes were tested in the catalytic hydrogen transfer reactions as well as in the kinetic resolution of racemic alcohols, where some complexes showed good conversion, but low enantioselectivity. 相似文献
9.
Thomas Dirnberger 《Inorganica chimica acta》2007,360(4):1339-1343
The reaction of the dihydrido iridium(III) precursor [IrH2(Cl)(PiPr3)2] (5) with internal alkynes RCC(CO2Me) (R = Me, CO2Me) afforded the five-coordinate hydrido(vinyl) complexes [IrH(Cl){(E)-C(R)CH(CO2Me)}(PiPr3)2] (6, 7), via insertion of the alkyne into one of the IrH bonds. Compounds 6 and 7 are also accessible by careful hydrogenation of the alkyne iridium(I) derivatives trans-[IrCl{RCC(CO2Me)}(PiPr3)2] (9, 10), the latter being prepared from in situ generated trans-[IrCl(C8H14)(PiPr3)2] and RCC(CO2Me). UV irradiation of 6 (R = CO2Me) led to the formation of the isomer [IrH(Cl){κ2(C,O)-C(CO2Me)CHC(OMe)O}(PiPr3)2] (3) having the vinyl ligand coordinated in a bidentate fashion. While 6 reacted with acetonitrile and CO to afford the six-coordinate iridium(III) compounds [IrH(Cl){(E)-C(CO2Me)CH(CO2Me)}(L′)(PiPr3)2] (11, 12), treatment of 6 with LiC5H5 gave the half-sandwich-type complex [(η5-C5H5)IrH{(E)-C(CO2Me)CH(CO2Me)}(PiPr3)] (13) by, the loss of one PiPr3. The reaction of 3 with CO under pressure resulted in the formation of [IrH(Cl){(Z)-C(CO2Me)CH(CO2Me)}(CO)(PiPr3)2] (14) in which, in contrast to the stereoisomer 12, the two CO2Me substituents are trans disposed. 相似文献
10.
Raimund W. Lass 《Inorganica chimica acta》2011,369(1):288-291
The labile iridium(I) precursor trans-[IrCl(C8H14)(PiPr3)2] (2), prepared in situ from [IrCl(C8H14)2]2 (1) and PiPr3, reacted with equimolar amounts of 1,4-C6H4(CCSiMe3)2 (3) at 60 °C to give the mononuclear vinylidene complex trans-[IrCl(CC(SiMe3)C6H4CCSiMe3)(PiPr3)2] (4). From 2 and 3 in the molar ratio of 2:1, the dinuclear compound trans,trans-[(PiPr3)2ClIr(CC(SiMe3)C6H4C(SiMe3)C)IrCl(PiPr3)2] (5) was obtained. Reaction of 4 with [RhCl(PiPr3)2]2 (6) at room temperature afforded the heterodinuclear alkyne(vinylidene) complex trans,trans-[(PiPr3)2ClIr(CC(SiMe3)C6H4CCSiMe3)RhCl(PiPr3)2] (7), which on heating at 45 °C was converted to the bis(vinylidene) isomer trans,trans-[(PiPr3)2ClIr(CC(SiMe3)C6H4C(SiMe3)C)RhCl(PiPr3)2] (8). 相似文献
11.
Salvador Conejero 《Inorganica chimica acta》2011,369(1):165-172
Complexes TptolRh(C2H4)2 (1a) and TptolRh(CH2C(Me)C(Me)CH2) (1b) have been prepared by reaction of KTptol with the appropriate [RhCl(olefin)2]2 dimer (Tptol means hydrotris(3-p-tolylpyrazol-1-yl)borate). The two complexes show a dynamic behaviour that involves exchange between κ2 and κ3 coordination modes of the Tptol ligand. The iridium analogue, TptolIr(CH2C(Me)CHCH2) (2) has also been synthesized, and has been converted into the Ir(III) dinitrogen complex [(κ4-N,N’,N’’,C-Tptol)Ir(Ph)(N2) (3) by irradiation with UV light under a dinitrogen atmosphere. Compound 3 constitutes a rare example of Ir(III)-N2 complex structurally characterized by X-ray crystallography. Its N2 ligand can be easily substituted by acetonitrile or ethylene upon heating and denticity changes in the Tptol ligand, from κ4-N,N’,N’’,C (monometallated Tptol, from now on represented as Tptol′) to κ5-N,N′,N″,C,C″ (dimetallated Tptol ligand, represented as Tptol″) have been observed. When complex 3 is heated in the presence of acetylene, dimerization of the alkyne takes place to yield the enyne complex [(κ5-N,N′,N′′,C,C′-Tptol)Ir(CH2CHCCH), 7¸ in which the unsaturated organic moiety is bonded to iridium through the carbon-carbon double bond. 相似文献
12.
Mai Kotera 《Inorganica chimica acta》2010,363(13):3602-3605
A reaction of [Cp*IrCl2]2 {Cp* = η5-C5(CH3)5} and 2-mercaptobenzimidazole (H2bimt) in methanol in a 1:2 molar ratio gave a yellow complex of [Cp*IrCl2(H2bimt)]·CH3OH (1). In compound 1 the H2bimt acts as a monodentately S-donating (κS) ligand. A similar reaction of [Cp*IrCl2]2 and H2bimt in the presence of NaOCH3 (molar ratio of 1:2:2) gave an orange product (2) on addition of excess amount of NH4PF6. Compound 2 was composed of an unsymmetrical dinuclear complex cation, [(Cp*IrCl)2(μ-Hbimt)(μ-H2bimt)]+, a PF6− anion, and water molecules of crystallization. In the complex cation, H2bimt bridges two IrIII centers by S atom in the μ-κS:κS mode, while the monodeprotonated Hbimt− ligand bridges via S and N atoms in the μ-κS:κN1 mode. 相似文献
13.
Density functional theory (DFT) calculations have been performed for understanding the linkage isomerism of [RuII/III(NH3)5(dmso)]2+/3+ (dmso = dimethylsulfoxide) from a theoretical point of view. In particular, we focus on the interchange between O-bonded and S-bonded structures of the dmso ligand by oxidation/reduction. We have examined five different exchange-correlation functionals (SVWN, BP86, mPWPW91, B3PW91, and B3LYP) in our DFT calculations and found that the relative stabilities of the O-bonded and S-bonded structures are largely dependent on the functional employed. From detailed analyses of atomic charge distributions, it has been found that the calculated atomic charges on the central metal ions are strongly correlated with the relative energies. We also studied the effect of solvation on the linkage isomerism using continuum solvation models. 相似文献
14.
A series of ruthenium and rhodium complexes with a urea-disubstituted pyridine ligand are reported. The X-ray crystal structures of three of these species, RuCl2(L1)(PPh3) (1), [Ru(MeCN)2(L1)(PPh3)][BF4]2 (3) and Rh(CH2Cl)Cl2(L1) (9) (where L1 = N,N′-(2,2′-(1E,1′E)-(1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))bis(azan-1-yl-1-ylidene)bis(ethane-2,1-diyl))diacetamide) have shown that the disubstituted pyridine acts as a tridentate ligand and its urea substituents engage in hydrogen bonding interactions with species coordinated to the metal centres. The reactivity of the ruthenium complexes towards coordination of other anions such as NCS− has been investigated, as well as the oxidative-addition of alkyl chlorides to rhodium(I) centres (to yield species such as 9). 相似文献
15.
Robert M. Chin Devin Maurer Neysa Allworth Daniel Sullivan William Brennessel 《Inorganica chimica acta》2009,362(2):389-3875
The dimerization of 6,6-dimethylfulvene with Ni(cod)2 yields the 4,4,8,8-tetramethyl-3a,4,7a,8-tetrahydro-s-indacene isomer (1a). Heating a solution of 1a converts it to the 1,4,5,8 (1b) and 1,4,7,8 (1c) tetrahydro-s-indacene isomers. The activation energy for the isomerization is 23(1) kcal/mol. 1b and 1c can be deprotonated with n-BuLi and the reaction of the dianion with [ClIr(C2H4)2]2 gives two isomers, cis-[(η5-C5H3)(CMe2)Ir(C2H4)2]2 (cis-2) and trans-[(η5-C5H3)(CMe2)Ir(C2H4)2]2 (trans-2). Reaction of 1b and 1c with RhCl3 · xH2O in refluxing methanol yields a red-orange solid, which was consistent with the empirical formula, [(C5H3)(CMe2)RhCl2]n (3). Reaction of 3 with C2H4 in a Na2CO3/ethanol mixture afforded cis-[(η5-C5H3)(CMe2)Rh(C2H4)2]2 in 5% yield. 相似文献
16.
Reduction of RuQ3 (1a, Q = 8-quinolinolato) with Zn/Hg in the presence of various π-acceptor ligands in ethanol affords RuQ2L2 (L2 = (dimethylsulfoxide)2 (2); (4-picoline)2 (3); N,N′-dimethyl-1,4-diazabuta-1,3-diene, dab (4); cyclooctadiene, COD (5); norborna-2,5-diene, nbd (6)). Compound 6 is isolated as an equimolar mixture of cis,trans (6a) and trans,cis (6b) isomers, which can be separated by column chromatography. DFT calculations have been performed on 6a and 6b. Oxidation of 3 and 6b affords the corresponding ruthenium(III) species 7 and 8, respectively. The structures of 2, 3, 4 and 6 have been determined by X-ray crystallography. 相似文献
17.
Kim R. Dunbar Steven C. Haefner Calvin E. Uzelmeier Anthony Howard 《Inorganica chimica acta》1995,240(1-2):527-534
Rh(I) and Ir(I) complexes of the type [Rh(cod)(η2-TMPP)]1+ (1) and M(cod)(η2-TMPP-O) (M = Rh (2), Ir (3); cod = cyclooctadiene; TMPP = tris(2,4,6-trimethoxyphenyl)phosphine; TMPP-O = mono-demethylated form of TMPP) have been isolated from reactions of [M(cod)Cl]2 with M′BF4 (M′ = Ag+, K+, Na+) followed by addition of the tertiary phosphine ligand. This chemistry is dependent on the identity of the metal, as both the cationic phosphine complex and the neutral phosphino-phenoxide compound are stable for Rh(I), whereas only the latter is stable for Ir(I). The three complexes have been characterized by IR and NMR (1H and 31P) spectroscopies as well as by cyclic voltammetry. The 1H NMR spectrum of [Rh(cod)(η2-TMPP)]1+ (1) is in accord with the formula and reveals that the TMPP phenyl rings are undergoing rapid exchange between coordinated and non-coordinated modes; the corresponding spectra of 2 and 3 support free rotation about the P---C bonds of the unbound phenyl rings with no fluxionality of the bound demethylated ring. The 31P{1H} NMR spectrum of the neutral species 2 exhibits a significant upfield shift with respect to the analogous cationic compound 1. This shielding is the result of improved electron donation to the metal from a phenoxide group as compared to an ether substituent. In situ addition of CO to the reaction between TMPP and [Rh(cod)Cl]2 or [Ir(cod)Cl]2 in the presence of M′BF4 results in the isolation of the monocarbonyl species [Rh(TMPP)(η2-TMPP)(CO)][BF4] (5) and the stable dicarbonyl compound [Ir(TMPP)2(CO)2][BF4] (4), respectively. Single crystal X-ray data for . The geometry of 4 is square planar, with essentially ideal angles for the mutually trans disposed phosphine and carbonyl ligands, as found in earlier studies for the analogous Rh dicarbonyl compound. The 1H NMR spectrum of 4 supports the assignment of magnetically equivalent phosphorus nuclei in solution. The results of this study indicate that cyclooctadiene is a particularly strong ligand for monovalent late transition metals ligated by TMPP, to the extent that it is inert with respect to substitution in the absence of π-acceptor ligands such as carbon monoxide. 相似文献
18.
Bradley T. Loughrey Michael L. Williams Peter C. Healy Alessio Innocenti Daniela Vullo Claudiu T. Supuran Peter G. Parsons Sally-Ann Poulsen 《Journal of biological inorganic chemistry》2009,14(6):935-945
Cationic ruthenium(II) pentamethylcyclopentadienyl benzenesulfonamide sandwich complexes have been synthesized and screened
for enzymatic inhibition of the physiologically dominant carbonic anhydrase (CA) isozymes: human CA I and II, mitochondrial
isozymes VA and VB, and the cancer-associated isozyme IX. The complexes demonstrated weaker binding to CAs compared with typical
aromatic sulfonamides, inhibiting the enzyme at high nanomolar concentrations. An in vitro cytotoxic evaluation of the complexes
was also undertaken against a range of tumorigenic cell lines and a healthy human cell line. Complexes inhibited the growth
of cancerous cells at low micromolar concentrations while expressing lower levels of toxicity towards the normal human cell
line. Factors influencing the synthesis, cytotoxicity, and enzyme affinity for this series of organometallic complexes are
discussed. 相似文献
19.
Spillane CB Dabo MN Fletcher NC Morgan JL Keene FR Haq I Buurma NJ 《Journal of inorganic biochemistry》2008,102(4):673-683
The substituted tris(bipyridine)ruthenium(II) complexes {[Ru(bpy)(2)(4,4'-bbob)](2+) and [Ru(bpy)(2)(5,5'-bbob)](2+) [where bpy=2,2'-bipyridine and bbob=bis(benzoxazol-2-yl)-2,2'-bipyridine] have been prepared and compared to the previously studied complex [Ru(bpy)(2)(4,4'-bbtb)](2+) [where bbtb=bis(benzothiazol-2-yl)-2,2'-bipyridine]. From the UV/VIS titration studies, Delta-[Ru(bpy)(2)(4,4'-bbob)](2+) displays a stronger association than the Lambda-isomer with calf-thymus DNA (ct-DNA). For [Ru(bpy)(2)(5,5'-bbob)](2+), there appears to be minimal interaction with ct-DNA. The results of fluorescence titration studies suggest that [Ru(bpy)(2)(4,4'-bbob)](2+) gives an increase in emission intensity with increasing ct-DNA concentrations, with an enantiopreference for the Delta isomer, confirmed by membrane dialysis studies. The fluorescent intercalation displacement studies revealed that [Ru(bpy)(2)(4,4'-bbob)](2+) and [Ru(bpy)(2)(5,5'-bbob)](2+) display a preference for more open DNA structures such as bulge and hairpin sequences. While Lambda-[Ru(bpy)(2)(4,4'-bbtb)](2+) has shown the most significant affinity for all the oligonucleotides sequences screened in previous studies, it is the Delta isomer of the comparable benzoxazole ruthenium(II) complex (Delta-[Ru(bpy)(2)(4,4'-bbob)](2+)) that preferentially binds to DNA. 相似文献
20.
Kathryn J. Arm 《Inorganica chimica acta》2006,359(4):1222-1232
A series of iridium(III) bis-terpyridine complexes have been prepared which incorporate pendent pyridyl groups at the 4′-positions of one or both of the terpyridine (tpy) ligands. These include: three mutually isomeric homoleptic complexes, in which the nitrogen atom of the pendent pyridyl is para, meta or ortho to the C-C bond to the terpyridine; their heteroleptic analogues in which the second ligand is 4′-tolyl-terpyridine (ttpy); analogous complexes of the new ligand, 4′-(2,6-dimethylpyrid-4-yl)-terpyridine; and related complexes incorporating an additional phenyl ring interposed between the terpyridine and the pendent pyridyl group. All of the complexes are luminescent in air-equilibrated aqueous solution at room temperature. The homoleptic complexes display structured emission resembling that of unsubstituted [Ir(tpy)2]3+, with luminescence lifetimes of around 1 μs under these conditions. The heteroleptic analogues give broader, red-shifted emission spectra, similar to that of [Ir(ttpy)2]3+, indicating that emission in these complexes arises primarily from a lower-energy excited state associated with the 4′-tolyl-terpyridine ligand. A further red-shift for the complexes incorporating the additional phenyl ring suggests that the emissive state involves the more conjugated phenylpyridyl-appended ligand in these cases. The luminescence of all of the heteroleptic complexes investigated, except the meta-substituted system, is sensitive to the protonation state of the pendent pyridyl group, and the structure of the ligand can have a significant influence on both the magnitude of the response and the pH region over which it occurs. 相似文献