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101.
The kinetics of oxidation of three alpha beta-unsaturated compounds, CH2CHX (X=CN, CONH2 and CO2-) by bis(dihydrogentellurato)metallate(III) ions ([MIII-(H2TeO6)2]5-, M=Cu or Ag) have been studied in an alkaline medium. The reactions take place according to the rate expression: The k3 values are 2.42*10-2, 1.67*10-2 and 1.10*10-2mol6dm-2s-1 for oxidations of the respective substrate by the copper(III) complex and 1.49*10-2, 1.07*10-2 and 0.80*10-2mol6dm-2s-1, respectively, in the oxidations by silver(III), all at 303K. [CuIII(H2TeO6)2]5- reacts faster than the corresponding reactions with [AgIII(H2TeO6)2]5-. The oxidation rates follow the order: CN CONH2CO2-. The oxidations of the substrates by [CuIII(H2TeO6)2]5- take place by an outer-sphere mechanism, unlike [AgIII-(H2TeO6)2]5-, which reacts by an inner-sphere mechanism. The substrates are oxidized to diols under kinetic control and a tentative reaction mechanism leading to the formation of oxidation products is suggested. The activation parameters of the reactions have been evaluated. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
102.
A tetranuclear mixed ligand copper(II) complex of a pyrazole containing Schiff base and a hydroxyhexahydropyrimidylpyrazole and copper(II) and nickel(II) complexes of the Schiff base having N-donor atoms have been investigated. A 2 equiv amount of 5-methyl-3-formylpyrazole (MPA) and 2 equiv of 1,3-diamino-2-propanol (1,3-DAP) on reaction with 1 equiv of copper(II) nitrate produce an unusual tetranuclear mixed ligand complex [Cu4(L1)2(L2)2(NO3)2] (1), where H2L1 = 1,3-bis(5-methyl-3-formylpyrazolylmethinimino)propane-2-ol and HL2 = 5-methyl-3-(5-hydroxyhexahydro-2-pyrimidyl)pyrazole. In contrast, a similar reaction with nickel(II) nitrate leads to the formation of a hygroscopic intractable material. On the other hand, the reaction involving 2 equiv of MPA and 1 equiv each of 1,3-DAP and various copper(II) salts gives rise to two types of products, viz. [Cu(T3-porphyrinogen)(H2O)]X2 (X = ClO4, NO3, BF4 (2)) (T3-porphyrinogen = 1,6,11,16-tetraza-5,10,15,20-tetrahydroxy-2,7,12,17-tetramethylporphyrinogen) and [Cu(H2L1)X]X x H2O (X = Cl (3), Br (4)). The same reaction carried out with nickel(II) salts also produces two types of compounds [Ni(H2L1)(H2O)2]X2 [X = ClO4 (5), NO3 (6), BF4 (7)] and [Ni(H2L1)X2] x H2O [X = Cl (8), Br (9)]. Among the above species 1, 3, and 5 are crystallographically characterized. In 1, all four copper atoms are in distorted square pyramidal geometry with N4O chromophore around two terminal copper atoms and N5 chromophore around two inner copper atoms. In 3, the copper atom is also in distorted square pyramidal geometry with N4Cl chromophore. The nickel atom in 5 is in a distorted octahedral geometry with N4O2 chromophore, where the metal atom is slightly pulled toward one of the axial coordinated water molecules. Variable-temperature (300 to 2 K) magnetic susceptibility measurements have been carried out for complex 1. The separations between the metal centers, viz., Cu(1)...Cu(2), Cu(2)...Cu(2)A, and Cu(2)A...Cu(1)A are 3.858, 3.89, and 3.858 A, respectively. The overall magnetic behavior is consistent with strong antiferromagnetic interactions between the spin centers. The exchange coupling constants between Cu(1)...Cu(2) and Cu(2)...Cu(2A) centers have turned out to be -305.3 and -400.7 cm(-1), respectively, resulting in a S = 1/2 ground state. The complexes are further characterized by UV-vis, IR, electron paramagnetic resonance, and electrochemical studies.  相似文献   
103.
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106.
Two tetranuclear Ni(II) complexes: [Ni4(HL1)4] ⋅ H2O ( 1 ) and [Ni4(HL2)4] ⋅ 1.5 dmf ( 2 ) where dmf=dimethylformamide, H3L1=4-(tert-butyl)-2-(((2-hydroxy-5-nitrophenyl)imino)methyl)-6-(hydroxymethyl)phenol and H3L2=4-(tert-butyl)-2-(hydroxymethyl)-6-(((2-hydroxyphenyl)-imino)methyl)phenol, have been prepared and characterized by single crystal X-Ray diffraction, elemental analysis and FT-IR spectroscopy. The solid-state structures reveal the formation of highly symmetric and asymmetric [Ni4O4] cubane cores in complexes 1 and 2 , respectively. Extensive magnetic studies show that both complexes present ferromagnetic exchange interactions between the Ni(II) ions within the cubane core with g=2.113(3), J1=−7.89(8) cm−1, J2=13.3(1) cm−1 and |D|=11.3(4) cm−1 (for 1 ) and g=2.206(4), J1=1.0(1) cm−1, J2=7.8(1) cm−1 and |D|=8.7(2) cm−1 (for 2 ). The large anisotropy, high ground spin state (arising from the ferromagnetic coupling) and the good isolation of the clusters provided by the Schiff base ligands, give rise to the first examples of field-induced single-molecule magnets (FI−SMM) in Ni4O4 clusters and to the highest energy barrier reported to date in a Ni4O4 cluster.  相似文献   
107.
N Barik  RN Mishra 《Pramana》2001,56(4):519-536
Considering the nucleon as consisting entirely of its valence quarks confined independently in a scalar-vector harmonic potential; unpolarized structure functions F 1(x, μ 2) and F 2(x, μ 2) are derived in the Bjorken limit under certain simplifying assumptions; from which valence quark distribution functions u v(x, μ 2) and d v(x, μ 2) are appropriately extracted satisfying the normalization constraints. QCD-evolution of these input distributions from a model scale of μ 2=0.07 GeV2 to a higher Q 2 scale of Q 0 2 =15 GeV2 yields xu v(x, Q 0 2 ) and xd v(x, Q 0 2 ) in good agreement with experimental data. The gluon and sea-quark distributions such as G(x, Q 0 2 ) and q s(x, Q 0 2 ) are dynamically generated with a reasonable qualitative agreement with the available data; using the leading order renormalization group equations with appropriate valence-quark distributions as the input.  相似文献   
108.
Two mononuclear cobalt(III) complexes, namely [LCo(tmtp)(H2O)]ClO4?MeOH ( 1 ) (tmtp = tri(m‐tolyl)phosphine) and [LCo(PPh3)(H2O)]PF6 ( 2 ), have been prepared from a polydentate ligand, N,N′‐bis(3‐methoxysalicylidehydene)cyclohexane‐1,2‐diamine ( H 2 L ). Standard analytical techniques such as elemental analysis and UV–visible and Fourier transform infrared spectroscopies were used to characterize both complexes. The solid‐state molecular structures of both complexes were confirmed from single‐crystal X‐ray diffraction analysis. Structural analyses show that the Co(III) ion occupies the centre of a distorted octahedron in a complex cation: [LCo(tmtp)(H2O)]+ and [LCo(PPh3)(H2O)]+ for 1 and 2 , respectively. Phenoxazinone synthase activities of both complexes were screened. Kinetic studies and other experimental observations reveal that the reaction follows rate saturation kinetics and proceeds through the formation of a catalyst (complex)–substrate adduct. The turnover number (Kcat) of complex 2 is 54.07 h?1, exhibiting better catalytic activity compared to 1 (Kcat = 45.11 h?1).  相似文献   
109.
A new Mn (II)‐containing coordination polymer, [Mn6(Ipa)6(ad)?6H2O] ( 1 ; Ipa = isophthalate ligand; ad = adenine), was synthesized by reacting hydrated manganese nitrate with isophthalic acid and adenine under solvothermal reaction conditions. Polymer 1 was characterized using single‐crystal X‐ray diffraction analysis and other techniques such as Fourier transform infrared spectroscopy, elemental analyses and powder X‐ray diffraction. The solid‐state structure of 1 confirmed the formation of a three‐dimensional framework structure based on Mn6 secondary building units. Phase purity of bulk 1 and its thermal stability were investigated. Polymer 1 was evaluated for its performance as a heterogeneous catalyst for the Henry (nitroaldol) reaction of nitromethane with several aldehydes. The recyclability of 1 and heterogeneity of the reaction were also explored. A plausible mechanism for such reaction is proposed. To the best of our knowledge, polymer 1 represents the first example of a Mn (II)‐ and adenine‐containing coordination polymer as well as the first example of a Mn (II)‐containing coordination polymer that has been employed for the Henry reaction.  相似文献   
110.
Dioxomolybdenum(VI) complexes [MoO2(B1)H2O] (1), [MoO2(B2)EtOH] (2), [MoO2(B3)EtOH] (3) and [MoO2(B4)EtOH] (4) were synthesized using the Schiff base ligands H2B1(previously reported), H2B2, H2B3 and H2B4, respectively. These ligands were prepared by condensation of 1-(2-pyridyl) 5-methyl 3-pyrazole carbohydrazide with salicylaldehyde, o-hydroxy acetophenone, 5-bromo salicylaldehyde and 5-nitro salicylaldehyde respectively. Due to the presence of a substituted 1-(2-pyridyl) pyrazole unit, ligands H2B1, H2B2 and H2B3 exhibit fluorescent emissions, and the most intense emission was obtained for H2B3. H2B4 is incapable of showing fluorescence emission. As the ligands are capable of using different binding modes, according to the demands of the guest metal ions, their emission properties also change accordingly. The dioxomolybdenum(VI) complex of the ligand H2B1, i.e. complex 1, shows quenched emission compared to H2B1. Again when Cu2+, Co2+ or Ni2+ ions are added to a solution of 1, in each case a new complex of Cu2+ Co2+ or Ni2+ is formed in solution and further quenching was observed. However, with Zn2+ input to a solution of 1, fluorescence recovery was observed up to the level of the free ligand. The copper(II) complex of H2B1 (complex 5), produced by adding equivalent amount of Cu2+ salt to a solution of 1, was isolated and characterized. One of the dioxomolybdenum(VI) complexes, 3, when subjected to an oxo-transfer reaction with PPh3 produces complex [MoO(B3)CH3CN] (6). Complex 6 shows reduced fluorescence emissions compared to 3 in the solid phase. These observations open up the possibilities for these ligands to work as fluorescent signaling system with different metal ion inputs. All the complexes are characterized by elemental analyses, electronic spectra, IR, 1H NMR, magnetic measurements, EPR and by cyclic voltammetry. Complexes 1 and 5, as well as the ligands H2B2 and H2B3, have been crystallographically characterized.  相似文献   
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