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51.
Electronic structures of the title complexes have been studied using quantum chemical computations by different methods. It is shown that the results of Xalpha calculations agree well with expectations from classical ligand-field theory, but both are far from being in agreement with the results given by ab initio calculations. The HOMO in the ab initio Hartree-Fock molecular orbital diagrams of all these complexes is a chalcogen p(pi) lone pair orbital rather than the metal nonbonding d(xy)() orbital previously proposed. Electronic transition energies were calculated by CASSCF and CI methods. The results suggest that in the cases when Q = S, Se, and Te the lowest energy transitions should be those from the p(pi) lone pair orbitals to the metal-chalcogen pi orbitals. The calculated and observed electronic spectra of the oxo complex are in good agreement and very different from the spectra of the other complexes, and the lowest absorptions were accordingly assigned to transitions of different origins. 相似文献
52.
A solid material consisting of dimethyl glyoxime (DMG), acenaphthenequinone dioxime (ANDO) or DMG-ANDO on naphthalene provides a very convenient, rapid and economical method for the preconcentration of palladium in synthetic samples. Pd-DMG, Pd-ANDO and Pd-DMG-ANDO are quantitatively retained on naphthalene in the column in the pH ranges 2.2–4.4, 1.8–5.6 and 1.7–6.8, respectively. The solid mixture consisting of the metal complex together with naphthalene is stripped from the column with 5 ml of dimethylformamide (DMF)-n-butylamine and the absorbance is measured at 247.6 nm with an atomic absorption spectrometer. Calibration graphs are linear over the palladium concentration range 5–25 μg per 5 ml of the final solution for all the three complexes. Ten replicate determinations of a sample solution containing 10 μg of palladium gave mean absorbances of 0.180, 0.225 and 0.230 with relative standard deviations of 1.8, 1.7 and 1.6% using the reagents DMg, ANDO and DMG-ANDO, respectively. The sensitivity of the method is better than the direct atomic absorption spectrometric determination of palladium. It is highest in case of the mixed ligands, i.e., DMG-ANDO (0.038 μg ml?1 for 1% absorption). The method can be applied to the trace determination of palladium in complex materials. 相似文献
53.
Reduction of ZrBr4 with HSnBu3 yielded a blue solid. When this blue solid was treated with PMe3, a hexanuelear cluster [Zr6Br14H4( PMe3)4] (2) was isolated. Reaction of the blue solid with [PPh4]Br in CH2Cl2 resulted in the formation of a paramagnetic and unstable cluster anion, [Zr6Br18H5]2– (3), which disproportionated to form a new cluster anion, [Zr6Br18H5]3– (4) and some Zr(IV) species. Compounds containing 4 can also be obtained from reaction of the blue solid with Br– in MeCN. Reduction of ZrCl4 with HsnBu3 gave a red–brown solid, and [Zr6Cl14H4(AsMe3)4] (9) and [Zr5Cl12H4(AsMe3)5](8) were obtained by reaction of the red–brown solid with AsMe3. No cluster compounds containing amine ligands were obtained in the reaction of the red–brown solid with amines; only compounds containing the [Zr6Cl18 H5]3– anion and ammonium cations were isolated. Altogether ten products were characterized by single crystal X-ray diffraction and where possible, by 1H NMR studies. 相似文献
54.
The molecular structure of gaseous CsReO4 has been studied by matrix isolation IR spectroscopy. The 18O substitution experiments indicate a bidentate structure of C2v symmetry in which the perrhenate anion is slightly distorted from the tetrahedral geometry. 相似文献
55.
Studies of the preparation of 1,8-dihydroazocines and transannular cyclization of hydroazocines to produce functionalized pyrrolizidines are described. Results are presented which demonstrate that unsymmetrically substituted acetylenes bearing at least one electron withdrawing groups undergo efficient cycloaddition to 1 - β - styryl - 1,2 - dihydropyridine producing in a regio-selective fashion 3,4 - disubstituted - 1,8 - dihydroazocines. The dihydroazocines generated in this manner can be converted to 1 - formyl - Δ4,5 - epoxyazocines which undergo interesting rearrangement reactions to form pyrrolizidines when subjected to methoxide deformylation followed by acid treatment. In addition, 1,6,7,8 - tetrahydroazocines can be converted to pyrrolizidines under bromination conditions. The intriguing chemical process which occur under the conditions outlined above are described. 相似文献
56.
The novel phosphinite PPh(2)(3-OCH(2)C(5)H(4)N) (1) has been synthesized, and its coordination properties to Ag(I) have been studied. When reacted in a 1:1 ratio with Ag(I), coordination polymers with different coordination numbers about the Ag are found depending on the anion. For PPh(2)(3-OCH(2)C(5)H(4)N)AgBF(4) (2), a two-coordinate Ag is observed with a P-Ag-N angle of 167 degrees. Mixed three and four coordination about Ag is observed for PPh(2)(3-OCH(2)C(5)H(4)N)AgOTf (3), and for the trifluoroacetate derivative, PPh(2)(3-OCH(2)C(5)H(4)N)Agtfa (4), only a four-coordinate Ag is produced. X-ray crystal-structure determinations for compounds 2-4 have been carried out. The X-ray structures show a wide range of Ag-Ag distances in the polymers, which are dependent on the conformation of the bridging ligand. 相似文献
57.
Fackler JP 《Inorganic chemistry》2002,41(26):6959-6972
Inorganic chemistry became a passion for me as a graduate student in the 1950s. It was exciting to be part of the renaissance of the discipline, and I am pleased to have contributed to its strength. Physical concepts applied to the understanding of the properties of transition metal compounds guided our work initially. In the 1970s, probably as a direct result of the world abandoning the gold standard, the chemistry of gold was awakened after a long sleep. Much of the chemistry covered in this review of our work relates to novel compounds of gold and the properties they display which have been uncovered during the last 25 years of the 20th century. Stable metal-metal bonded Au(II) and organometallic Au(III) compounds, bi- and trimetallic oxidative addition, phosphorescent species with microsecond lifetimes, gold chains resulting from aurophilic bonding stronger than H-bonding, and recently, gold binding to organic pi acids have intrigued my group and other gold chemists during this period. 相似文献
58.
De La Rosa Luis B. Reshamwala Sultan Latimer Vivian M. Shawky Bahaa T. Dale Bruce E. Stuart Earnest D. 《Applied biochemistry and biotechnology》1994,(1):483-497
The herbaceous crops that may provide fermentable carbohydrates for production of fuels and chemicals also contain 10–20%
protein. Protein coproduction with biomass-derived fuels and chemicals has important advantages: (1) food and fuel production
can be integrated, and (2) protein is a high-value product that may significantly improve overall process economics. We report
the results of an integrated approach to producing protein and fermentable sugars from one herbaceous species, Coastal Bermudagrass
(CBG). The ammonia fiber explosion (AFEX) process makes possible over 90% conversion of cellulose and hemicellulose to simple
sugars (about 650 mg reducing sugars/g dry CBG) at 5 IU cellulase/g vs < 20% conversion for untreated CBG. The AFEX treatment
also improves protein extraction from CBG; over 80% protein recovery is possible from AFEX-treated CBG vs about 30% recovery
from untreated CBG. 相似文献
59.
Photosynthetic suspension cultures of higher plants offer an alternative approach to biomass production, potentially yielding
cellulosic material and protein on a continuous year-round basis. A bench-top hybrid photobioreactor was developed to study
photomixotrophic and photoautotrophic growth of Glycine max as a model system. Maximum biomass doubling times for photomixotrophic
and photoautotrophic growth were 1.87 and 3.92 d, respectively. The presence of exogenous sugars resulted in photomixotrophic
growth, reduced chlorophyll levels, and a reduction in photosynthetically-evolved oxygen. Depletion of carbohydrates from
the medium coincided with the beginning of stationary phase and an increase in oxygen evolution by the cells. A second growth
phase, prolonging cell viability, could be initiated by increasing the carbon dioxide from 2 to 5%, just before the onset
of stationary phase. Biomass from bioreactor cultured cells proved resistant to enzymatic attack without pretreatment. Composition
of the biomass was 7.8% lignin, 20.7% α-cellulose, 23% hemicellulose, 5.5% starch, 14.5% protein and 6.5% nucleic acids. 相似文献
60.
Aspen wood substrates with varying degrees of deacetylation, xylan, and lignin removal have been prepared and submitted to
enzymatic hydrolysis with a cellulase/hemicellulase preparation for an extended constant period of hydrolysis. Controlled
deacetylation has been achieved by treating wood with various alkali metal hydroxide solutions, at various alkali/wood ratios.
It has been found that samples with the same extent of deacetylation produce the same sugar yields upon enzymatic hydrolysis.
Increased degree of deacetylation increases the yield of sugars obtained from enzymatic hydrolysis, all other compositional
parameters held constant. The acetyl group removal is proportional to the stoichiometric relation between added base and wood
acetyl content, i.e., the same number of milliequivalents of base/weight of wood remove the same extent of acetyl groups,
regardless of the concentration of the base solution. No cation effects are found among Li, Na, and K alkali hydroxide solutions,
suggesting that swelling is not as important a parameter as is the removal of the acetyl groups from the xylan backbone in
determining the extent of hydrolyzability of the resulting sample. 相似文献