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1.
N-(ω-carboxyalkyl)morpholine hydrochlorides, OC 4H 8N(CH 2) nCOOH·HCl, n=1–5, were obtained and analyzed by 13C cross polarization (CP) magic angle spinning (MAS) NMR, FTIR and PM3 calculations. The structure of N-(3-carboxypropyl)morpholine hydrochloride ( n=3) has been solved by X-ray diffraction method at 100 K and refined to the R=0.031. The crystals are monoclinic, space group P2 1/ c, a=14.307(3), b=9.879(2), c=7.166(1) Å, β=93.20(3)°, V=1011.3(3) Å 3, Z=4. In this compound the nitrogen atom is protonated and two molecules form a centrosymmetric dimer, connected by two N +–HCl − (3.095(1) Å) and two O–HCl − (3.003(1) Å) hydrogen bonds. 13C CP MAS NMR spectra, contrary to the solution, showed non-equivalence of the ring carbon atoms. The PM3 calculations predict a molecular dimer without proton transfer for an HCl complex, while for an HBr complex an ion pairs with proton transfer, and reproduces correctly the conformation of both dimers but overestimates H-bond distances. Shielding constants calculated from the PM3 geometry of ion pairs gave a linear correlation with the 13C chemical shifts in solids. 相似文献
2.
When thienyl Schiff base 1, derived from 2-formylthiophene and hydrazine, reacted with Fe 2(CO) 9 in n-hexane, three major complexes were obtained: (1) a diironhexacarbonyl complex with two 2-thienylmethylideneamido bridging ligands 2, which resulted from the =N---N= bond cleavage of ligand 1; (2) a doubly cyclometalated di-μ-di-(η 1:η 2-thienyl; η 1:η 1( N))bis(hexacarbonyldiiron) complex (3); and (3) a cyclometalated (μ-η 1:η 2-thienyl; η 1:η 1( N))hexacarbonyldiiron complex (4). Molecular structures of compounds 1a, 1c, and 2a have been determined by single-crystal X-ray diffraction. 相似文献
3.
One-dimensional Co(dien) 2(VO 3) 3·(H 2O) was prepared from the hydrothermal reaction of NH 4VO 3, Co 2O 3, diethylenetriamine (dien) and H 2O at 130 °C. The compound crystallizes in the monoclinic system, space group P2 1/ c with a=16.1581(6) Å, b=8.7006(3) Å, c=13.9893(4) Å, β=103.1483(11)°, V=1915.13(11) Å 3, Z=4, and R1=0.0268 for 3060 observed reflections. Single crystal X-ray diffraction revealed that the structure is composed of infinite one-dimensional chains formed by corner-sharing VO 4 tetrahedra with Co(dien) 3+ complex cations and crystallization water molecules occupying the interchain positions, which are held together to a three-dimensional network via extensive hydrogen-bonding interactions. The compound, with a new zig-zag conformation of metavanadate chains, is the first example of vanadium oxides incorporating trivalent transition metal coordination groups. Other characterizations by elemental analysis, IR and thermal analysis are also described. 相似文献
4.
Oxazolone forms (1:1) complexes with Fe 2+, Co 2+, Ni 2+, Cu 2+ and Zn 2+ chlorides, as well as forms (1:1) complexes with Co 2+ and Cu 2+ acetates. All the complexes are found to be non-electrolytes in DMF; tetrahedral, square-planar and octahedral structures are assigned to them based on electronic and magnetic data. IR studies reveal that the complexes are formed by donating the lone-pair electron from O and N atoms to the metal ion. The thermal decomposition of the [ML· mX· nH 2O] y·H 2O chelates was studied by TG–DTA techniques. The mechanism of the decomposition has been established from TG–DTA data. The kinetic parameters, activation energy ( Ea) and pre-exponential factor ( A), were calculated from TG curves using Coats and Redfern method. Relative thermal stabilities of the chelates have been evaluated on the basis of these parameters. 相似文献
5.
The XeOSeF 5+ cation has been synthesized for the first time and characterized in solution by 19F, 77Se and 129Xe NMR spectroscopy and in the solid state by X-ray crystallography and Raman spectroscopy with AsF 6− as its counter anion. The X-ray crystal structures of the tellurium analogue and of the Xe(OChF 5) 2 derivatives have also been determined: [XeOChF 5][AsF 6] crystallize in tetragonal systems, P4/ n, a=6.1356(1) Å, c=13.8232(2) Å, V=520.383(14) Å 3, Z=2 and R1=0.0453 at −60°C (Te) and a=6.1195(7) Å, c=13.0315(2) Å, V=488.01(8) Å 3, Z=2 and R1=0.0730 at −113°C (Se); Xe(OTeF 5) 2 crystallizes in a monoclinic system, P2 1/ c, a=10.289(2) Å, b=9.605(2) Å, c=10.478(2) Å, β=106.599(4)°, V=992.3(3) Å 3, Z=4 and R1=0.0680 at −127°C; Xe(OSeF 5) 2 crystallizes in a triclinic system,
, a=8.3859(6) Å, c=12.0355(13) Å, V=732.98(11) Å 3, Z=3 and R1=0.0504 at −45°C. The energy minimized geometries and vibrational frequencies of the XeOChF 5+ cations and Xe(OChF 5) 2 were calculated using density functional theory, allowing for definitive assignments of their experimental vibrational spectra. 相似文献
6.
X-Ray diffraction, IR and 1H NMR studies were performed on the 1:1 adduct of 1,8-bis(dimethylamino)naphthalene (DMAN) with 1,8-dihydroxy-2,4-dinitronaphthalene (DHDNN). The adduct crystallizes in the triclinic system, space group
, a = 9.911(2) Å, b = 11.212(2) Å, c = 11.194(2) Å, = 68.95(2)°, β = 79.72(2)°, γ = 73.78(2)°, Z = 2. Both [NHN] + and [OHO] − hydrogen bonds formed in the ion pairs are asymmetrical with lengths equal to 2.574(2) Å and 2.466(4) Å respectively. The [NHN] + bridge shows a typical behaviour in the IR spectrum, i.e. a low-frequency absorption between 300 and 700 cm −1. The coupling of [OHO] − hydrogen bonds with the naphthalene π-electron system is so strong that no absorption related to the proton stretching vibrations can be detected in the high- and low-frequency regions. The 1H NMR chemical shifts for the [NHN] + and [OHO] − bridge protons of 18.63 and 15.81 ppm respectively confirm the strong hydrogen bonds. 相似文献
7.
139La-NMR chemical shifts were measured for several anionic complexes of formulae Li(C 4H 8O 2) 3/2 [La(ν 3-C 3H 5) 4], [Li(C 4H 8O 2) 2][Cp′ nLa(ν 3-C 3]H 5) 4−n] (Cp′ = Cp(ν 5-C 5H 5); n = 1, 2 and Cp′ = Cp * (ν 5-C 5Me5); N = 1) and Li[R nLa(ν 3-C 3H 4) 4− n] (R = N(SiMe 3) 2; n = 1, 2 and R = CCsIMe 3; n = 4), as well as for neutral compounds for formulae La(ν 3-C 3H 5) 3L n (L = (C 4H 8O 2) 1.5, (HMPT) 2, TMED), Cp′ nLa(ν 3-C 3H 5) 3−n (Cp′= Cp(ν 5-Cp 5H 5), Cp *(ν 5-C 5Me 5); n = 1, 2) and La(ν 3-C 3H 2) 2X(THF) 2 X = Cl, Br, I). Typical ranges of the 139La-NMR chemical shifts were found for the different types of complex independent of number and kind of organyl groups directly bonded to lanthanum. Zusammenfassung139La-NMR-Spektroskopie wurde an einer Reihe anionischer Allyllanthanat(III)-Komplexe der Zusammensetzung
]- [La)ν3-C3H5)4, [Li(C4H8)2][Cp′nLa(ν3-C3H5)4−n(Cp′ = Cp(ν5-C5H5); n = 1, 2 und Cp′ = Cp * (ν5-C5Me5); N = 1) und Li[RnLa(ν3-C3H5)4−n (R = B(SiMe3)2; n = 1, 2 und R = CCSiMe3; n = 4 sowie neutraler Allyllanthan(III)-Komplexe der Zusammensetzung La(ν3-C3H5)3Ln (Ln = (C4H8O2)1.5, (HMPT)2, TMED), Cp′n, La(ν3-C3H5)3−n (Cp′ = Cp(ν5-C5H5), Cp * (ν5- Cp5Me5); n = 1, 2) und La(ν3-Cp3H5)2X(THF)2 (X = Cl, Br, I) durchgefürt. In Abhängikeit von der Anzahl und der Art der am Lanthan gebundenen Gruppen wurden für die verschieden Komplextypen charakteristische Resonanzbereiche ermittelt. 相似文献
8.
分别以2-(2-氨基苯基)菲并咪唑和2-(3-氨基苯基)菲并咪唑为原料,与5-硝基水杨醛反应合成了两个菲并咪唑-苯酚异构体衍生物(PI? o?OH和PI? m?OH)。在水相体系中( V(DMF)∶ V(HEPES) = 1∶1,pH = 7.4),两个异构体发射中等强度的荧光。Fe 3+存在下,两个异构体的荧光强度分别淬灭为原来的1/3和1/6,淬灭常数为4.8×10 3和4.6×10 3 L/mol,且淬灭效果不受其它干扰离子和pH值变化的影响。间位异构体PI? m?OH与Fe 3+的荧光识别在2 min之内完成,配合速度明显优于邻位基异构体,且配合稳定性高于邻位异构体,配合常数为3.82×10 4 L/mol。通过高分辨质谱和Job's曲线,确定了两个异构体与Fe 3+识别配合比为1∶1,并建议了PI? m?OH-Fe 3+ and PI? o?OH-Fe 3+两个配合物的结构。两个异构体均可实现实际水样中Fe 3+的定量检测,表明它们在实际水样的Fe 3+分析中具有一定的应用价值。 相似文献
9.
The synthesis, characterization, and thermal decomposition of the [Ni(SCN) 2(H +SCN) 2(4-mepy) 2] compound with an octahedral structure in polymeric chain were reported, in which SCN groups form bridges among Ni(II) ions. The compound decomposes in water resulting in a pH<4 solution. The FT-IR spectrum presented doublet bands at 2117; 2128 cm −1, 788; 773 cm −1 assigned to ν(C---N) and ν(C---S) stretching modes, respectively, and δ(SCN) deformation modes at 468; 476 cm −1. The Raman spectrum of the compound presented the ν(C---N) stretching as a strong doublet at 2122; 2128 cm −1, ν(C---S) at 783; 770 cm −1, and δ(SCN) at 468; 477 cm −1. No significant changes were observed in the 4-mepy ligand bands compared with the vibrational frequencies of the pure compound or the compound in aqueous solution 0.2 mol l −1. The crystal UV–vis reflectance spectrum presented two bands centered in 626 and 424 nm tentatively assigned to the d→d type transitions, 3A 2g→ 3T 1g and 3A 2g→ 3T 1g, for a symmetry close to O h. The TG curve showed a mass loss between 120 and 200 °C assigned to the loss of the two 4-mepy molecules; from 200 to 265 °C, the loss of the two H +SCN groups; and from 265 to 450 °C, the loss of the two SCN groups that formed the bridges among the nickel atoms. Based on these mass loss data, a mechanism of thermal decomposition for the compound was proposed. 相似文献
10.
The reactions of 2- trans-6-N 4P 4(NHPr n) 2Cl 6 (2), which was obtained from N 4P 4Cl 8 (1) and n-propylamine, with pyrrolidine and t-butylamine in different solvents have been studied. Compound (2) gave two different products, namely monocyclic (3 and 5) and bicyclic (4 and 6) phosphazenes. Compounds (2–6) have been characterized by elemental analysis, IR, 1H-, 13C-, 31P NMR, HETCOR and MS and the structure of compound (5) has been examined crystallographically. The bicyclic phosphazene (6) is the first exciting example of bicyclic phosphazenes containing chlorine atoms, in the literature. The formation mechanisms of bicyclic phosphazenes are re-considered by taking into account the synthesis of compound (6), which contains three stereogenic phosphorus atoms. Compound (5) crystallizes in the monocyclic space group P2 1/ n with a=13.974(2), b=17.836(5), and c=18.683(4) Å, β=98.50(1)°, V=4605.4(2) Å 3, Z=4 and Dx=1.051 g cm −3. It consists of a non-centrosymmetric, non-planar phosphazene ring in a saddle conformation, with two n-propylamino (in 2- trans-6 positions) and six bulky t-butylamino side groups. The bulky substituents are instrumental in determining the molecular geometry. 相似文献
11.
The title complex [NH_3CH_2CH(NH_2)CH_3]_2 [M(Ⅵ)O_2(OC_6H_4O)_2](M= Mo_(0.6)W_(0.4))was synthesized via a simple solution-phase chemical route.The determination of single crystal X-ray diffraction revealed that the title compound is crystallized in a monoclinic system with P2(1)/n space group,a=1.0913(10)nm,b=1.0442(10)nm,c=1.8842(19)nm,α=90°,β=96.530(17)°,γ=90°,Z=4,and V=2.133(4)nm3.The mononuclear anionic unit [M(Ⅵ)O2(OC6H4O)2]2-displays chiral pseudo-octahedral [MO_6] coordination geometry and is linked by chiral cations via hydrogen bond and π…π stacking interaction.The transmission electron microscopy images show that the title complex is comprised of nano-particles with diameters ranging from 20 to 50 nm.The NMR study shows the 1H downfield chemical shifts of [NH_3CHaHbCH(NH_2)CH_3] cations in the title complex when it is mixed with adenosine-triphosphate(ATP),and the chemical shift difference between Ha and Hb is increased greatly,and most of the catecholate ligands dissociate from the central metal atoms.The DNA cleavage activity experiment reveals that DNA cleavage promoted by the title complex is lower than that by Na_2MoO_4 which possesses antitumor pro-perty,but higher than that by Na_2WO_4. 相似文献
12.
A new family of heteropolytungstate complexes (NH 4) 21[Ln(H 2O) 5{Ni(H 2O)} 2As 4W 40O 140]· xH 2O(Ln=Y, Ce, Pr, Nd, Sm, Eu, Gd) were prepared by the reaction of Na 27[NaAs 4W 40O 140]·60H 2O with NiCl 2·6H 2O and Ln(NO 3) 3· xH 2O at pH≈4.5. The crystal structures of (NH 4) 21[Gd(H 2O) 5{Ni(H 2O)} 2As 4W 40O 140]·51H 2O was determined by X-ray diffraction analysis and element analysis. The compound crystallizes in the monoclinic space group P2 1/ n with a=19.754(3), b=24.298(4), c=39.350(6) Å, β=100.612(3)°, V=18564(5) Å 3, Z=2, R1( wR2)=0.0544(0.0691). The central site S1 and two opposite sites S2 of the big cyclic ligand [As 4W 40O 140] 28− are occupied by one Ln 3+and two Ni 2+, respectively, each site supply four O d coordinating to metal ion, another one water molecule and other five water molecules coordinate, respectively, to Ni 2+and Ln 3+. Polyanion [Ln(H 2O) 5{Ni(H 2O)} 2As 4W 40O 140] 21− has C2v symmetry. IR and UV–vis spectra of [NaAs 4W 40O 140] 27− of the title compounds are discussed. 相似文献
13.
Six ternary lanthanide complexes formulated as [Ln(2, 4, 6-TMBA) 3(5, 5'-DM-2, 2'-bipy)] 2 (Ln = Pr 1, Nd 2, Sm 3, Eu 4, Gd 5, Dy 6; 2, 4, 6-TMBA = 2, 4, 6-trimethylbenzoate; 5, 5'-DM-2, 2'-bipy = 5, 5'-dimethyl-2, 2'-bipyridine) have been synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, etc. The results of crystal diffraction analysis show that complexes 1–6 are binuclear units, crystallizing in the triclinic Pī space group. Complexes 1–5 are isostructural, and each of the central metal ions has a coordination number of 9. The asymmetric unit of complexes 1–5 consists of one Ln 3+, one 5, 5'-DM-2, 2'-bipy ligand, and three 2, 4, 6-TMBA - moieties with three coordination modes: chelation bidentate, bridging bidentate, and bridging tridentate. The coordination geometry of Ln 3+ is distorted monocapped square antiprismatic. The binuclear units of complexes 1–5 form a one-dimensional (1D) supramolecular chain along the c-axis via π– π stacking interactions between the 2, 4, 6-trimethylbenzoic acid rings. The 1D chains are linked to form a supramolecular two-dimensional (2D) sheet in the bc plane via π– π stacking interactions between the pyridine rings. Although the molecular formulae of complex 6 and complexes 1–5 are similar, the coordination environment of the lanthanide ions is different in the two cases. The asymmetric unit of complex 6 contains a Dy 3+ ion coordinated by a bidentate 5, 5'-DM-2, 2'-bipy and three 2, 4, 6-TMBA - ligands adopting bidentate and bridging bidentate coordination modes. The Dy 3+ metal center has a coordination number of 8, with distorted square antiprismatic molecular geometry. The binuclear molecule of 6 is assembled into a six-nuclear unit by π– π weak staking interactions between two 5, 5'-DM-2, 2'-bipy ligands; then, adjacent six-nuclear units form a 1D chain via offset π– π interactions between 5, 5'-DM-2, 2'-bipy ligands on different adjacent units. The adjacent 1D chains are linked by C―H···O hydrogen bonding interactions to form a 2D supramolecular structure. The thermal stability and thermal decomposition mechanism of all the complexes are investigated by the combination of thermogravimetry and infrared spectroscopy (TG/FTIR) techniques under a simulated air atmosphere in the temperature range of 298–973 K at a heating rate of 10 K·min -1. Thermogravimetric studies show that this series of complexes have excellent thermal stability. During the thermal decomposition of the complex, the neutral ligand is lost first, followed by the acid ligand, and finally, the complex is decomposed into rare earth oxides. The three-dimensional infrared results are consistent with the thermogravimetric results. The photoluminescence spectra of complex 4 show the strong characteristic luminescence of Eu 3+. The five typical emission peaks at 581, 591, 621, 651, and 701 nm correspond to the 5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3, and 5D0 → 7F4 electronic transitions of Eu 3+, respectively. The emission at 621 nm is due to the electric dipole transition 5D0 → 7F2, while that at 591 nm is assigned to the 5D0 → 7F1 the magnetic dipole transition. The lifetime ( τ) of complex 4 is calculated as 1.15 ms based on the equation τ = ( B1τ12 + B2τ22))/( B1τ1 + B2τ2), and the intrinsic quantum yield is calculated to be 45.1%. Further, the magnetic properties of complex 6 in the temperature range of 2–300 K are studied under an applied magnetic field of 1000 Oe. 相似文献
14.
The compound [Zn(H 2O) 4] 2[H 2As 6V 15O 42(H 2O)]·2H 2O (1) has been synthesized and characterized by elemental analysis, IR, ESR, magnetic measurement, third-order nonlinear property study and single crystal X-ray diffraction analysis. The compound 1 crystallizes in trigonal space group R3, a= b=12.0601(17) Å, c=33.970(7) Å, γ=120°, V=4278.8(12) Å 3, Z=3 and R1( wR2)=0.0512 (0.1171). The crystal structure is constructed from [H 2As 6V 15O 42(H 2O)] 4− anions and [Zn(H 2O) 4] 2+ cations linked through hydrogen bonds into a network. The [H 2As 6V 15O 42(H 2O)] 6− cluster consists of 15 VO 5 square pyramids linked by three As 2O 5 handle-like units. 相似文献
15.
Reactions of the lithium salts of 3-substituted indenes 1, 2 with ZrCl 4(THF) 2 gave two series of nonbridged bis(1-substituted)indenyl zirconocene dichloride complexes. Fractional recrystallization from THF–petroleum ether furnished the pure racemic and mesomeric isomers of [(η 5-C 9H 6-1-C(R 1)(R 2)--- o-C 6H 4---OCH 3) 2ZrCl 2]· nTHF (R 1=R 2=CH 3, n=1, rac-1a and meso-1b; R 1=CH 3, R 2=C 2H 5; n=0.5 or 0, rac-2a and meso-2b), respectively. Complex 1a was further characterized by X-ray diffraction to have a C2 symmetrically racemic structure, where the six-member rings of the indenyl parts are oriented laterally and two o-CH 3O---C 6H 4---C(CH 3) 2--- substituents are oriented to the open side of the metallocene (Ind: bis-lateral, anti; Substituent: bis-central, syn). The four zirconocene complexes are highly symmetrical in solution as characterized by room temperature 1H-NMR, however 1H– 1H NOESY of meso-1b shows that some of the NOE interactions arise from the two separated indenyl parts of the same molecule, which can only be well explained by taking into account the torsion isomers in solution. 相似文献
16.
A tetrasilver(I) phosphonitocavitand was synthesized and structurally characterized. The compound crystallizes in the monoclinic space group P2 1/ n with a=15.0151(13), b=39.832(4), c=15.2479(14) Å, β=95.1000(2)°, V=9083.3(14) Å 3 and Z=4. The structure contains four coplanar silver atoms bridged by four μ-Cl and one central trapped μ 4-Cl atoms in the inside of the closing bowl-shaped cavitand. Nonlinear optical properties of this metal-cavitand were investigated. Optical limiting effect with threshold of 0.6 J cm −2 was observed with the laser pulses of 7 ns at 532 nm. 相似文献
17.
The photophysics of three complexes of the form Ru(bpy) 3−(pypm) 2+ (where bpy2,2′-bipyridine, pypm 2-(2′-pyridyl)pyrimidine and P=1, 2 or 3) was examined in H 2O, propylene carbonate, CH 3CN and 4:1 (v/v) C 2H 5OH---CH 3OH; comparison was made with the well-known photophysical behavior of Ru(bpy) 32+. The lifetimes of the luminescent metal-to-ligand charge transfer (MLCT) excited states were determined as a function of temperature (between −103 and 90 °C, depending on the solvent), from which were extracted the rate constants for radiative and non-radiative decay and Δ E, the energy gap between the MLCT and metal-centered (MC) excited states. The results indicate that *Ru(bpy) 2(pypm) 2+ decays via a higher lying MLCT state, whereas *Ru(pypm) 32+ and *Ru(pypm) 2(bpy) 2+ decay predominantly via the MC state. 相似文献
18.
Through the oxidation-reduction combination procedure, the neutral tri-substituted {2Fe3S} complex 2 was synthesized by replacing the CO ligand in 1 with phosphine. This substitution leads to the Fe-Fe bonds in 1 and 2 with large Lewis basicity difference, i.e. △pK aMeCN~10. 相似文献
19.
Two nickel (imidazole) complexes, Ni(im) 6Cl 2·4H 2O (1) and Ni(im) 6(NO 3) 2 (2) (im=imidazole) have been synthesized and characterized by elemental analysis, IR, UV, TG and single crystal X-ray diffraction. 1 crystallizes in the triclinic space group P-1 with a=8.800(6) Å, b=9.081(6) Å, c=10.565(7) Å, =75.058(9)°, β=83.143(8)°, γ=61.722(8)°, V=718.3(8) Å 3, Z=1 and R1 ( wR2)=0.0469 (0.1497). 2 crystallizes in the trigonal space group R-3 with a=12.370(6) Å, b=12.370(6) Å, c=14.782(14) Å, =90.00°, β=90.00°, γ=120.00°, V=1959(2) Å 3, Z=3 and R1 ( wR2)=0.0358 (0.0955). 1 and 2 exhibit different supramolecular network due to their different counter anions and different hydrogen bonding connection. In compound 1, [Ni(im) 6] 2+ cation and counter anions Cl − alternatively array in an ABAB fashion via N–HCl hydrogen bonding. In compound 2, the plane of each NO 32− is almost parallel and each NO 32− connect three different [Ni(im) 6] 2+ cations via N–HO hydrogen bonding. 相似文献
20.
The reaction of 2-arylpyridinecarboxaldimine [RH 4C 6NC(H)Py, L (1)] with hydrated RuX 3 (X = Cl, Br) in boiling C 2H 5OH affords dark crystals of RuX 2L 2. Two geometrical isomers of the compound have been isolated and characterized by analytical and spectroscopic data. The trans isomer of RuCl 2L 2 shows a single sharp band for ν(Ru---Cl), whereas two bands are observed for the corresponding cis isomer. The highresolution 1H NMR spectra of the isolated complexes are reported and completely assigned. All the complexes have multiple t2→π *(L) transitions in the visible region. Each of the complexes display a quasi-reversible oxidative response due to an Ru III/Ru II couple in the range 0.25–0.40 V vs S.C.E. at a platinum working electrode. The formal potentials of this couple obey the Hammett relationship. The ligand-based irreversible oxidations are also briefly noted. 相似文献
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