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111.
Correia I Costa Pessoa J Duarte MT Henriques RT Piedade MF Veiros LF Jakusch T Kiss T Dörnyei A Castro MM Geraldes CF Avecilla F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(9):2301-2317
The Schiff base N,N'-ethylenebis(pyridoxylideneiminato) (H(2)pyr(2)en, 1) was synthesized by reaction of pyridoxal with ethylenediamine; reduction of H(2)pyr(2)en with NaBH(4) yielded the reduced Schiff base N,N'-ethylenebis(pyridoxylaminato) (H(2)Rpyr(2)en, 2); their crystal structures were determined by X-ray diffraction. The totally protonated forms of 1 and 2 correspond to H(6)L(4+), and all protonation constants were determined by pH-potentiometric and (1)H NMR titrations. Several vanadium(IV) and vanadium(V) complexes of these and other related ligands were prepared and characterized in solution and in the solid state. The X-ray crystal structure of [V(V)O(2)(HRpyr(2)en)] shows the metal in a distorted octahedral geometry, with the ligand coordinated through the N-amine and O-phenolato moieties, with one of the pyridine-N atoms protonated. Crystals of [(V(V)O(2))(2)(pyren)(2)].2 H(2)O were obtained from solutions containing H(2)pyr(2)en and oxovanadium(IV), where Hpyren is the "half" Schiff base of pyridoxal and ethylenediamine. The complexation of V(IV)O(2+) and V(V)O(2) (+) with H(2)pyr(2)en, H(2)Rpyr(2)en and pyridoxamine in aqueous solution were studied by pH-potentiometry, UV/Vis absorption spectrophotometry, as well as by EPR spectroscopy for the V(IV)O systems and (1)H and (51)V NMR spectroscopy for the V(V)O(2) systems. Very significant differences in the metal-binding abilities of the ligands were found. Both 1 and 2 act as tetradentate ligands. H(2)Rpyr(2)en is stable to hydrolysis and several isomers form in solution, namely cis-trans type complexes with V(IV)O, and alpha-cis- and beta-cis-type complexes with V(V)O(2). The pyridinium-N atoms of the pyridoxal rings do not take part in the coordination but are involved in acid-base reactions that affect the number, type, and relative amount of the isomers of the V(IV)O-H(2)Rpyr(2)en and V(V)O(2)-H(2)Rpyr(2)en complexes present in solution. DFT calculations were carried out and support the formation and identification of the isomers detected by EPR or NMR spectroscopy, and the strong equatorial and axial binding of the O-phenolato in V(IV)O and V(V)O(2) complexes. Moreover, the DFT calculations done for the [V(IV)O(H(2)Rpyr(2)en)] system indicate that for almost all complexes the presence of a sixth equatorial or axial H(2)O ligand leads to much more stable compounds. 相似文献
112.
Bassani DM Lehn JM Serroni S Puntoriero F Campagna S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(23):5936-5946
The absorption spectra, redox behavior, and luminescence properties (both at 77 K in rigid matrices and at room temperature in fluid solution) of a series of [2x2] molecular grids have been investigated. The latter were prepared either by means of sequential self-assembly, or by a stepwise protection/deprotection procedure, and are based on a ditopic hexadentate ligand 1 in which two terpyridine-like binding sites are fused together in a linear arrangement. The molecular grids studied include the homometallic species [[Fe(1)](4)](8+) (Fe(2)Fe(2)), and the heterometallic species [[Ru(1)](2)[Fe(1)](2)](8+) (Ru(2)Fe(2)) and [[Os(1)](2)[Fe(1)](2)](8+) (Os(2)Fe(2)). For comparison purposes, the properties of the mononuclear complexes [Ru(1)(2)](2+) (1-Ru) and [Os(1)(2)](2+) (1-Os) have been studied. All these compounds exhibit very intense absorption bands in the UV region (epsilon in the 10(5)-10(6) M(-1) cm(-1) range, attributed to spin-allowed ligand-centered (LC) transitions), as well as intense metal-to-ligand charge-transfer (MLCT) transitions (epsilon in the 10(4)-10(5) M(-1) cm(-1) range) that extend to the entire visible region. The mononuclear species 1-Ru and 1-Os exhibit relatively intense luminescence, both in acetonitrile at room temperature (tau=59 and 18 ns, respectively) and in butyronitrile rigid matrices at 77 K. In contrast, the tetranuclear molecular grids do not exhibit any luminescence, either at room temperature or at 77 K. This is attributed to fast intercomponent energy transfer from the Ru- or Os-based subunits to the low-lying metal-centered (MC) levels involving the Fe(II) centers, which leads to fast radiationless decay. The redox behavior of the compounds is characterized by several metal-centered oxidation and ligand-centered reduction processes, most of them reversible in nature (as many as twelve for Fe(2)Fe(2)). Detailed assignment of each redox process has been made, and it is apparent that these systems can be viewed as multilevel molecular electronic species capable of reversibly exchanging a number of electrons at accessible and predetermined potentials. Furthermore, it is shown that the electronic interaction between specific subunits depends on their location in the structure and on the oxidation states of the other components. 相似文献
113.
114.
Hoebbel Dagobert Reinert Thomas Schmidt Helmut Arpac Ertugrul 《Journal of Sol-Gel Science and Technology》1997,10(2):115-126
The complexation degrees of Al-, Ti- and Zr-butoxide (M) with unsaturated and saturated -diketones (3-allylpentane-2.4-dione-APD, acetylacetone-ACAC) and -ketoesters (methacryloxyethyl-acetoacetate-MEAA, allylacetoacetate-AAA, ethylacetoacetate-EAA) as organic ligands (L) were examined by IR and 13 C NMR spectroscopy and were found to be L:M 1.5. The hydrolytic stability of the ligands of the metal alkoxide complexes (L:M = 1) during hydrolysis/condensation reactions at the molar ratio h (H2O : OR) = 0.5–2.0 decreases with increasing H
115.
Electronic structures of zinc and palladium tetraazaporphyrin derivatives controlled by fused benzo rings 总被引:1,自引:0,他引:1
Zinc and palladium tetracyclic aromatic complexes lying structurally between tetraazaporphyrin (TAP) and phthalocyanine (Pc), that is, monobenzo-, adjacently dibenzo-, oppositely dibenzo-, and tribenzo-fused TAPs, have been prepared, and their electronic structures investigated by electronic absorption, magnetic circular dichroism (MCD), fluorescence, phosphorescence, and time-resolved electron paramagnetic resonance (TREPR) spectroscopy, as well as cyclic voltammetry. The last-named indicated that the first oxidation potentials shift to more negative values with increasing number of the fused benzo rings, but also suggested that the first reduction potential apparently has no correlation with the size and symmetry of the pi-conjugated systems. However, this latter behavior is reasonably interpreted by the finding that the effect of the fused benzo rings on destabilization of the LUMO depends on the orbital to which they are fused (i.e., whether it is an egx or egy orbital), since the LUMOs of TAP complexes are degenerate with D4h symmetry. The energy splitting of the LUMOs, that is, DeltaLUMO, was evaluated experimentally for the first time by analyzing the relationship between the first reduction potential and the size and shape of the pi-conjugated system. Electronic absorption and MCD measurements indicate that the lowest excited singlet states are split in the case of the low-symmetry TAP derivatives, although these excited states are degenerate for Pc and TAP with D4h symmetry. These energy splittings DeltaE(SS) correlate well with the DeltaLUMO values. To investigate the electronic structures in the lowest excited triplet state, zero-field splitting (zfs) was analyzed by time-resolved EPR (TREPR) spectroscopy. The energy splitting in the lowest excited triplet state, DeltaE(TT) was quantitatively evaluated from the temperature dependence of the zfs or spin-orbit coupling of the Pd complexes. Consequently, it is demonstrated that DeltaLUMO, DeltaE(SS), and DeltaE(TT) values exhibiting a mutually good relationship can be determined experimentally. 相似文献
116.
Tsutomu Shiragami Katsunori Tanaka Yoshito Andou Shin-ichiro Tsunami Jin Matsumoto Hongxia Luo Yasuyuki Araki Osamu Ito Haruo Inoue Masahide Yasuda 《Journal of photochemistry and photobiology. A, Chemistry》2005,170(3):287-297
Tetraphenylporphyrinatoantimony(V) complexes, linked to boron-dipyrrin chromophores on axial ligands, were synthesized. The fluorescence spectra of 1a, 1b and 1c (3-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]propoxo(methoxo)antimony(V) tetraphenylporphyrin bromide (1a); 6-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]hexyloxo(methoxo)antimony(V) tetraphenylporphyrin bromide (1b); bis{3-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]propoxo}antimony(V) tetraphenylporphyrin bromide (1c)) were analyzed under the excitations of N,N′-difluorobornyl-5-dipyrrinylphenyl (Bdpy) and tetraphenylporphyrinatoantimony(V) (Sb(TPP)) chromophores. Under the irradiation of Bdpy chromophore, the excitation energy was transferred from Bdpy chromophore to the Sb(TPP) moiety at 0.13–0.40 of the quantum yields, even in a polar solvent. On the other hand, the emission of Sb(TPP) chromophores was quenched by Bdpy chromophores at rate constants of 108–109 s−1, independent of on the solvent polarity. Under the excitation of the Bdpy chromophore of 1d (3-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]propoxo(phenyloxo)antimony(V) tetraphenylporphyrin bromide) involving both the Bdpy and the phenoxy chromophores on the axial ligands, the excited singlet state of the Sb(TPP) chromophore generated by the energy transfer from the Bdpy chromophore was quenched by the phenoxy ligand via non-radiative processes involving electron transfer. However, rapid back electron-transfer may occur because no absorption of the anion radical of Sb(TPP) was observed by nanosecond laser photolysis. 相似文献
117.
Michel F Thomas F Hamman S Saint-Aman E Bucher C Pierre JL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(17):4115-4125
Galactose oxidase (GO) is an enzyme that catalyzes two-electron oxidations. Its active site contains a copper atom coordinated to a tyrosyl radical, the biogenesis of which requires copper and dioxygen. We have recently studied the properties of electrochemically generated mononuclear Cu(II)-phenoxyl radical systems as model compounds of GO. We present here the solution chemistry of these ligands under various copper and dioxygen statuses: N(3)O ligands first chelate Cu(II), leading, in the presence of base, to [Cu(II)(ligand)(CH(3)CN)](+) complexes (ortho-tert-butylated ligands) or [(Cu(II))(2)(ligand)(2)](2+) complexes (ortho-methoxylated ligands). Excess copper(II) then oxidizes the complex to the corresponding mononuclear Cu(II)-phenoxyl radical species. N(2)O(2) tripodal ligands, in the presence of copper(II), afford directly a copper(II)-phenoxyl radical species. Addition of more than two molar equivalents of copper(II) affords a Cu(II)-bis(phenoxyl) diradical species. The donor set of the ligand directs the reaction towards comproportionation for ligands possessing an N(3)O donor set, while disproportionation is observed for ligands possessing an N(2)O(2) donor set. These results are discussed in the light of recent results concerning the self-processing of GO. A path involving copper(II) disproportionation is proposed for oxidation of the cross-linked tyrosinate of GO, supporting the fact that both copper(I) and copper(II) activate the enzyme. 相似文献
118.
Daniel Canseco-González 《Journal of organometallic chemistry》2003,679(1):101-109
The complexes cis-[M(Ph2PC6H4-2-S)2] M=Ni, Pd, Pt were stereoselectively synthesized by transmetallation reactions of [M(Cl)2(NCC6H5)2] M=Pd, Pt or NiCl2·6H2O with [Sn(R)2(Ph2PC6H4-2-S)2] R=Ph, nBu or tBu. The conformation of the Pd and Pt derivatives being unequivocally confirmed by single crystal X-ray diffraction studies showing both metal centers to be into a slightly distorted square planar environment, the main distortion being due to the steric hindrance caused by the aromatic rings in the phosphine moiety. 相似文献
119.
A hydrothermal reaction of a mixture of ZnCO3, phosphoric acid, 1, 10‐phenanthroline in H2O gave rise to large plates of a new zinc phosphate, [(C12H8N2Zn)2(HPO4)(H2PO4)2], I . The structure consists of ZnO3N2 distorted trigonal‐bipyramidal and PO4 tetrahedral units linked through their vertices to give rise to a zero‐dimensional molecular solid (monomer). The structure of the monomer appears to be similar to the secondary building unit (SBU) 4 = 1, commonly found in many fibrous zeolites. To our knowledge, this is the first time this building unit has been isolated. The structure, with a unique composition, is stabilized by hydrogen bond interactions between the terminal —OH groups forms a one‐dimensional molecular wire and also by strong π…π interactions between the 1, 10‐phenanthroline units. Photoluminescence studies show that there is a ligand‐to‐metal charge transfer (LMCT). Crystal data: orthorhombic, space group = Fdd2 (no. 43), a = 40.4669(1), b = 7.4733(2), c = 17.4425(5)Å, V = 5274.9(2)Å3, Z = 8. 相似文献
120.
Two polymorphs of zero-dimensional zinc phosphate with the formula, 0∞[Zn(2,2′-bipy)(H2PO4)2], have been synthesized employing hydrothermal technique and their structure determined by single crystal X-ray diffraction. Both the structures consists of ZnO3N2 distorted trigonal-bipyramidal and PO2(OH)2 tetrahedral units linked through their vertices giving rise to a zero-dimensional molecular zinc phosphate. The structures are stabilized by extensive hydrogen bond interactions between zero-dimensional monomers. The structures display subtle differences in their packing created by hydrogen bond interactions. Crystal data: polymorph I, triclinic, space group (No. 2), , , , α=67.32(3)°, β=81.67(3)°, γ=69.29(3)°, , Z=2; polymorph II, triclinic, space group (No. 2), , , , α=97.37(2)°, β=100.54(2)°, γ=100.98(2)°, , Z=2. 相似文献