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81.
K. M. Valikhanov M. G. Levkovich A. K. Tashmukhamedova 《Chemistry of Natural Compounds》2001,37(4):361-363
New derivatives of dibenzo-18-crown-6 were prepared by condensing 4,4(5)-dibenzo-18-crown-6-dicarboxylic acid dichloride with salsolidine and salsoline. The structures of these compounds were proved by PMR and IR spectral methods. 相似文献
82.
Till?R?hrich Bassam?Abu Thaher Nico?Manicone Hans-Hartwig?OttoEmail author 《Monatshefte für Chemie / Chemical Monthly》2004,135(8):979-999
Summary. (RS)-2-tert-Butyldimethylsilyl-1,2-thiazetidine-3-acetic acid 1,1-dioxide prepared from (RS)-S-benzyl--homocysteine was condensed via DCC/NHS with various L-amino acid esters or dipeptide esters yielding N-silylated -sultam peptides. A -sultam active ester was isolated as an intermediate. Desilylation with TBAF in THF yielded stable N-unsubstituted products, and deprotection of the benzyl esters was achieved by catalytic hydrogenation. (S)-S-Benzyl--homocysteine was obtained by fractional crystallization of the brucine salt of the racemate and transformed into benzyl (S)-1,2-thiazetidine-3-acetate, which was on the other hand synthesized by an enantiospecific route from -benzyl Boc-L-aspartate. Some -sultam peptides were prepared from the (S)-enantiomer, and finally some -sultam peptides containing D-Ala units were obtained. 相似文献
83.
A. N. Chekhlov 《Journal of Structural Chemistry》2007,48(6):1160-1163
The second crystal modification (II) of 1,10-diazonia-18-crown-6 dichloride [H2DA18C6]2+·2Cl?, where [H2DA18C6]2+ is the 1,10-diaza-18-crown-6 dication (DA18C6) with two protonated nitrogen atoms, was investigated by XRD. The monoclinic modification (II) (space group P21/n, a = 9.600 Å, b = 5.689 Å, c = 15.749 Å, β = 91.03°, Z = 2) was solved by direct methods and refined by full-matrix least squares analysis in an anisotropic approximation to R = 0.032 for all 2494 independent reflections collected (CAD-4 automatic diffractometer, λMoK α). In modification II, the conformation of the DA18C6 dication and the ion packing differ from those in triclinic modification I investigated previously. 相似文献
84.
The protonation constants of two nitro-Schiff bases SB1, SB2 and three asymmetric tetradentate diimines H2L1, H2L2 and H2L3 and the stability constants of their ML type binuclear Ni(II) and Fe(III) complexes have been determined potentiometrically. The asymmetric diimines are (2OH) RCHNC6H4CHNR′ (2OH) type compounds [where R = R′ = phenyl for H2L1; R = naphthyl, R′ = phenyl for H2L2 and R = R′ = naphthyl for H2L3]. The effect of tautomeric forms on the acid-base properties of the diimines has been investigated and discussed. In addition, dimeric and binuclear Ni(II) and Fe(III) complexes of the diimines have been synthesized and characterized by physical and spectroscopic techniques. Also, in vitro antimicrobial activities of the diimines and the complexes have been evaluated against three bacteria: Micrococcus luteus (NRLL B-4375), Bacillus cereus (RSKK 863), Escherichia coli (ATCC 11230) and the fungus: Candida albicans (ATCC 10239). 相似文献
85.
Ion-pair formation constants (KMLA mol−1 dm3) of Na+– and K+–18-crown-6 ether (18C6) complexes with MnO4− in water (w) were determined potentiometrically at 25 °C. Simultaneously, extraction constants (Kex mol−2 dm6) of the permanganates with 18C6 from w into 1,2-dichloroethane at 25 °C were obtained from the spectrophotometric determination of distribution ratios of the permanganates. These Kex values were divided into KMLA and other three component equilibrium constants and thereby extraction-selectivity and -ability were discussed in comparison with corresponding metal picrate–18C6 extraction systems reported before. 相似文献
86.
18-冠-6与Eu(fod)3+在CCl4中的化学平衡及其配合物的结构 总被引:1,自引:0,他引:1
在室温下测定了CCl_4溶液中,18-冠-6的亚甲基、Eu(fod)的t—丁基质子的PMR化学位移与溶液组成的相互关系。提出了生成配合物RS,R_2S,R_2,R_3(S为18-冠-6,R为Eu(fod)_3)的模式。求得了平衡常数值(升/摩):K_1=[RS]/([R][S])=2.O×10~5,K_2=[R_2S]/([R][RS])=1.0×10~3,Q_1=[R_2]/[R]~2=4.2×10~2,Q_2=[R_3]/([R_2][R])=4.0×10~1。并测得在配合物RS,R_2S中18-冠-6质子的平均化学位移分别为4.90,10.84(ppm,相对于纯18-冠-6); 在配合物R,R_2,R_3,RS,R_2中t-丁基质子平均化学位移分别为1.53,2.33,0.54,1.02,2.42(ppm,相对于TMS)。 根据配合物的化学位移值,并考虑分子及分子轨道的对称性、位阻等因素提出了配合物R_2,RS,R_2S的可能的结构模型。 相似文献
87.
Dirk Steinborn Olaf Gravenhorst Clemens Bruhn Dusan Miklo Michal Dunaj-Jur
o Alfred Kolbe 《无机化学与普通化学杂志》1997,623(12):1954-1958
Synthesis and Characterization of Aquapentachloroplatinates(IV) – Structure of [K(18-crown-6)][PtCl5(H2O)] The crown ether complex of the aquapentachloroplatinic acid of the composition [H13O6][PtCl5(H4O2)] · 2(18-cr-6) ( 2 ) reacts with K2CO3 and [NnBu4]OH in aqueous solution to give [K(18-cr-6)][PtCl5(H2O)] ( 5 a ) and [NnBu4][PtCl5(H2O)] · 1/2 (18-cr-6) · H2O ( 5 b ), respectively. Both compounds were characterized by microanalysis, vibrational (IR, Raman) and NMR (1H, 13C, 195Pt) spectroscopy. The X-ray structure analysis of 5 a (orthorhombic, pnma; a = 16,550(4), b = 18,044(3), c = 7,415(1) Å; Z = 4; R1 = 0,0183; wR2 = 0,0414) reveals that the crystal is threaded by chains built up of [PtCl5(H2O)]? and [K(18-cr-6)]+ units. There are tight K …? Cl contacts (d(K? Cl1)) = 3,0881(9) Å and OW? H? Ocr hydrogen bridges (d(O1 …? O2) = 2,806(3) Å) between these units. The coordination polyhedron [PtCl5O] has approximately C4v symmetry. 相似文献
88.
Aboul-fetouh E. Mourad Friedrich-Wilhelm Raulfs Henning Hopf 《Monatshefte für Chemie / Chemical Monthly》1985,116(6-7):701-709
The charge-transfer (CT) spectra of the -complexes formed by a number of -acceptors with several indenophanes as well as indene as a model compound have been measured in methylene chloride at 20 °C. Association constants and transition energies of these complexes as well as ionization potentials of the -donors have been determined. The data obtained indicate the existence of transannular electronic interactions in the indenophane nucleus. Furthermore, the pseudo-para- andmeta[2.2]indenophane isomers (3 and4) show a large difference in their -base strength. A good linear relationship has been observed between the association constants and max of the long wavelength CT bands for the -complexes of these -donors with both tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ). All CT complexes studied have a 1:1 stoichiometry.
Charge-transfer-Komplexe aus Indenophanen und -Akzeptoren
Zusammenfassung Die Charge-transfer-Spektren (CT-Spektren) von -Komplexen aus Indenophanen bzw. der Modellverbindung Inden und verschiedenen -Akzeptoren wurden in Methylenchlorid bei 20 °C bestimmt. Die Assoziationskonstanten und Übergangsenergien dieser Komplexe sowie die Ionisationspotentiale der -Donatoren wurden ermittelt. Die Daten sprechen für das Vorliegen transannularer elektronischer Wechselwirkungen im Indenophan-System. Die isomeren pseudo-para- und -meta[2.2]indenophane3 und4 unterscheiden sich in ihrer -Basizität deutlich. Es besteht eine gute lineare Korrelation zwischen den Assoziationskonstanten und max der langwelligen CT-Banden der verschiedenen -Donatoren mit Tetracyanoethylen (TCNE) und 2,3-Dichlor-5,6-dicyano-p-benzochinon (DDQ). Alle untersuchten CT-Komplexe besitzen 1:1-Stöchiometrie.相似文献
89.
90.
Two new series of Nb6 bromides, CsRENb6Br18 (RE = all the lanthanides excepted Eu and Yb, + Y) (type H ) and M2RENb6Br18 (M = Cs, Rb, Tl; RE = Eu, Yb) (type R ) have been isolated. The crystal structures of CsErNb6Br18 and Cs2EuNb6Br18, isotypic with the corresponding chlorides, have been determined by single crystal X-ray diffraction data. The (Nb6Br18) intra-unit strength is related to the nature and the charge of the counter cation. A comparison between the corresponding chlorides and bromides series, based on the chemical properties and the size of the halogen is discussed. 相似文献