共查询到20条相似文献,搜索用时 453 毫秒
1.
H. D. Inerowicz J. Chojnacki A. Merz T. Futterer 《Journal of inclusion phenomena and macrocyclic chemistry》2000,38(1-4):123-132
The complexation reactions between the macrocyclic polyethers dibenzo-18-crown-6, benzo-18-crown-6, benzo-15-crown-5 and polyethers bearing a stilbene unit with alkali metal and silver cations have been studied conductometrically in nitromethane. The formation constants of 1 : 1 and 1 : 2 (metal : ligand) complexes were determined and found to decrease with increasing cation diameter. The stability of the stilbene crown – metal cation complexes is lower than for complexes of other investigated crown ethers with analogous cations. There seem to be some effects of double bond-silver ion interactions. 相似文献
2.
Rahul M. KOTKAR 《Supramolecular chemistry》2013,25(6):545-552
The complexation behavior of nicotinamide with macrocyclic polyethers viz, 15-crown-5, benzo-15-crown-5, 18-crown-6, dicyclohexano-18-crown-6, dibenzo-18-crown-6, dibenzo-24-crown-8, 1,4,7,10,13,16-hexathiacyclooctadecane, monoaza-15-crown-5, 1,4,10-trioxa-7,13-diaza-cyclopentadecane, 5,6,14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadecane, 7,16-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, 1,4,7-tritosyl-1,4,7-triazacyclononane, 1,4,7,10-tetratosyl-1,4,7,10-tetraazacyclododecane and 1,4,8,11-tetraazacyclooctadecane has been studied in dimethylsulphoxide (DMSO) and 90% DMSO + water using differential pulse polarography and complexation constants have been reported. Nicotinamide forms stable complexes with six-membered coronand rings of the crown ethers. The nature of the atoms (oxygen, sulfur and nitrogen) in the coronand ring is observed to affect the stability of the complex. The stoichiometry and stability constants of the complexes were determined by monitoring the shifts in peak potentials of the polarograms of nicotinamide against the ligand concentration. The Gibbs free energy change turns out to be negative at 25°C, which indicates the spontaneity of the binding of nicotinamide with crown ethers. The mole ratio of nicotinamide to the macrocyclic compound was also determined and it was found that the complexes were of 1:1 type with respect to crown ethers. The tendency of nicotinamide to form complexes with macrocycles is found to be greater in DMSO than in DMSO + water. 相似文献
3.
Ljerka Tuek-Boi Christophe Pannecouque Erik De Clercq Jan Balzarini 《Polyhedron》2009,28(16):3449-3458
The eco-friendly synthesis, spectroscopic (IR, MS, 1H and 13C NMR) study and biological (cytostatic, antiviral) activity of sodium and potassium benzeneazophosphonate complexes, obtained by reaction in the solid state under microwave irradiation of the alkali salts of ethyl [α-(4-benzeneazoanilino)-N-benzyl]phosphonic acid and [α-(4-benzeneazoanilino)-N-4-methoxybenzyl]phosphonic acid with crown ethers containing 18-membered (dibenzo-18-crown-6 and bis(4′-di-tert-butylbenzo)-18-crown-6), 24-membered (dibenzo-24-crown-8) and 30-membered (dibenzo-30-crown-10) macrocyclic rings, have been described. The simple work-up solvent free reaction is an efficient green procedure for the formation of mononuclear crown ether complexes in which the sodium/potassium ion is bound to oxygen atoms of the macrocycle and the phosphonic acid oxygen. The free crown ethers, alkali benzeneazophosphonate salts and their complexes were evaluated for their cytostatic activity in vitro against murine leukemia L1210, murine mammary carcinoma FM3A and human T-lymphocyte CEM and MT-4 cell lines, as well as for their antiviral activity against a wide variety of DNA and RNA viruses. The investigated compounds showed no specific antiviral activity, whereas all the free crown ethers and their complexes demonstrated cytostatic activity, which was especially pronounced in the case of bis(4′-di-tert-butylbenzo)-18-crown-6 and its complexes. 相似文献
4.
Lokman Torun 《Tetrahedron》2005,61(35):8345-8350
Lariat ether carboxylic acids of structure CECH2OCH2C6H4-2-CO2H with crown ether (CE) ring sizes of 12-crown-4, 15-crown-5 and 18-crown-6 are prepared and converted into alkali metal-lariat ether carboxylate complexes. Absorptions for the diastereotopic benzylic protons in the 1H NMR spectra of the complexes in CDCl3 are utilized to probe the extent of side arm interaction with the crown ether-complexed metal ion as a function of the crown ether ring size and identity of the alkali metal cation. 相似文献
5.
Jerald S. Bradshaw Hua-Can Song Guo-Ping Xue R. Todd Bronson Joseph A. Chiara Krzysztof E. Krakowiak 《Supramolecular chemistry》2013,25(3):499-508
Abstract Sixteen new diazadi(or tri)thiacrown ethers containing two 5-substituent(or 2-methyl)-8-hydroxyquino-lin-2-ylmethyl side arms have been prepared by a three-step process. First, the appropriate bis(α-chloroamide)s were treated with five dimercaptans in base to form macrocyclic di(or tri)thiadiamides. The macrocyclic diamides were reduced by BH3-THF to form 1,7-diaza-4-oxa-10,13-dithia-cyclopentadecane (11); 1,7-diaza-4,13-dioxa-10,16-dithiacyclooctadecane (12); 1,7-diaza-4-oxa-10,13,16-trithiacyclooctadecane (13); 1,7-diaza-4,13,16-trioxa-10,19-dithiacycloheneicosane (14); and 1,10-diaza-4,7-dioxa-13,16-dithiacyclooctadecane (15). The diazadi(or tri)thiacrown ethers were then treated with 8-hydroxyquinoline, 8-hydroxy-5-methylquinoline, 5-chloro-8-hydroxyquinoline, and 8-hydroxyquinaldine in the presence of paraformal-delyde in refluxing benzene to form the bis(8-hydroxy-5-substituent(or 2-methyl)quinolin-7-ymethy)-substituted diazadi(or tri)thiacrown ethers 16-31. The crown ethers containing two 8-hydroxyquinoline or 8-hydroxyquinaldine side arms proved to be mixtures of about 90% bis(8-hydroxyquinolin-7-ylmethyl)-substituted crown ethers; 9% mixed (8-hydroxyquinolin-7-ymethyl)-substituted and (8-hydroxyquinolin-5-ylmethyl)-substituted crown ethers; and 1% bis(8-hydroxyquinolin-5-ylmethyl)-substituted crown ethers. 相似文献
6.
Crown ethers as size-selective synergists in solvent extraction systems: A new selectivity parameter
《Journal of Inorganic and Nuclear Chemistry》1981,43(11):2947-2953
Mixtures of macrocyclic polyethers (crown ethers) and organic-phase-soluble liquid cation exchangers have been found to produce a synergistic effect in the extraction of metal ions. The synergistic effect is size selective; that is, it tends to be greatest for those ions that best fit the crown ether cavity. The mixtures of a liquid cation exchanger and a crown ether also allow metal ion extraction from common mineral-acid anion systems (NO3−, Cl−, SO42−) that would be impossible with the crown ether alone, because of the difficulty of solubilizing those anions in nonpolar solvents. This cooperation makes the use of crown ethers as size-selective coordinators available for process applications. Size selectivity of compounds such as crown ethers may thus become a useful new parameter in designing selective solvent extraction systems. 相似文献
7.
The crown ethers dibenzo-16-crown-4 and dibenzo-18-crown-5 and a diaryl polyether were complexed by the chromium tricarbonyl group for the purpose of selective functionalization. This complexation did indeed permit exclusive functionalization of the complexed ring. CHO and CH2OH functionalities were introduced ortho to the ether group. It was noted that the nature of the two ether chains had a strong influence on the regioselectivity of the functionalization, which occurred preferentially on the side with the polyether chain. Photochemical decomplexation produced functionalized organic crown ethers. 相似文献
8.
Freidzon A. Ya. Bagatur"yants A. A. Gromov S. P. Alfimov M. V. 《Russian Chemical Bulletin》2003,52(12):2646-2655
Photoinduced recoordination of Ca2+ complexes of the photochromic azacrown ethers is studied by the density functional method. The study included model arylazacrown ethers containing various acceptor groups in the aromatic ring in the para position to the azacrown ether moiety and a real azacrown-containing styryl dye. It is found that both free azacrown ethers and their complexes can adopt two types of conformations: (1) axial conformations, in which the aromatic ring axis passing through the crown ether nitrogen Ncr and the opposite atom of the aromatic ring is perpendicular to the root-mean-square (RMS) plane of the crown ether (least-squares fitted plane for all the crown ether atoms), and (2) equatorial conformations, in which the aromatic ring axis only slightly deflects from the RMS plane of the crown ether. In the equatorial conformers, the metal cation is coordinated only to the O atoms of the azacrown ether cycle, the metal—nitrogen bond is broken, and Ncr is conjugated with the aromatic ring. In the axial conformers, the metal cation is additionally coordinated to Ncr. It is found that the presence of an acceptor group bearing a formal positive charge decreases the relative energy of the equatorial conformer and favors metal—nitrogen bond dissociation, which results in the recoordination of the metal cation. However, a long distance between the charged group and Ncr has the reverse effect. The photoinduced recoordination observed in the alkaline-earth metal complexes of the photochromic azacrown ethers is explained by the transitions between the axial and equatorial conformers facilitated by the charge transfer in the excited state of the complex. 相似文献
9.
Monika Wysocka-?o?opa Krzysztof Winkler Suresh Gadde Francis D’Souza 《Journal of Solid State Electrochemistry》2012,16(1):65-74
Redox active films have been generated via electrochemical reduction in a solution containing palladium(II) acetate and fulleropyrrolidine
with covalently linked crown ethers, viz., benzo-15-crown-5 and benzo-18-crown-6. In these films, fullerene moieties are covalently
bonded to palladium atoms to form a polymeric network. Films show ability to coordinate alkali metal cations from the solution.
Therefore, in solutions containing salts of alkali metal cations, benzo-15-crown-5-C60/Pd and benzo-18-crown-6-C60/Pd films are doped with cations coordinated by crown ether moiety and anions of supporting electrolyte which enter the film
to balance positive charge. These films are electrochemically active in the negative potential range due to the reduction
of the fullerene moiety. Reduction of the polymer is accompanied by the transport of supporting electrolyte ions between solution
and solid phase. In solution containing alkali metal salts, the process of film reduction is accompanied by the transport
of anions from the film to the solution. In the presence of tetra(alkyl)ammonium salts, transport of cations from the solution
to the film takes place during the polymer reduction. 相似文献
10.
A simple and efficient synthetic protocol for an easy access of carbohydrate-linked crown ethers from cheap and readily available D-glucose in good yields has been devised. The base-mediated cyclization of sugar-linked bis-iodo podands in CH3CN with amines, including ethylamine and furfurylamine afforded the novel chiral monoaza-15-crown-5-type macrocyclic crown ethers anellated to 3-O-benzyl-1,2-O-isopropylidene-α-D-glucofuranose and 3-O-benzyl-1,2-O-isopropylidene-α-D-allofuranose. The glucose-based crown ethers have been characterized by spectroscopy techniques including IR, 1H NMR, and 13C NMR. 相似文献
11.
《Tetrahedron》1987,43(3):617-624
The complexation of uronium perchlorate with crown ethers of different ringsizes (18–33 ring atoms) has been studied by using two-phase extraction experiments. Crown ethers with 27 or more ring atoms are the best hosts to transfer uronium salts from an aqueous phase to an organic phase. The amount of uronium perchlorate transferred was measured by coulometric titration of the stoichiometric amount of ammonia produced by enzymatic degradation of urea. The crystal and molecular structure of the 1:1 complex of uronium perchlorate with benzo-27-crown-9 has been determined by X-ray crystallography. The uronium cation is encapsulated in the crown ether cavity with all its hydrogen atoms bonded to the macrocyclic host. A 1:1 complex of uronium picrate with benzo-21-crown-7 was isolated and is assumed to be a perching complex. 相似文献
12.
A. I. Vedernikov S. N. Dmitrieva L. G. Kuz’mina N. A. Kurchavov Yu. A. Strelenko J. A. K. Howard S. P. Gromov 《Russian Chemical Bulletin》2009,58(5):978-1001
Benzoaza-15-crown-5 ethers containing one or two nitrogen atoms in different positions of the macrocycle and bearing different
substituents at these atoms were synthesized. The structures of azacrown ethers and their metal complexes were studied by
X-ray diffraction. The stability constants of the complexes of azacrown ethers with Na+, Ca2+, Ba2+, Ag+, Pb2+, and EtNH3
+ ions were determined by 1H NMR titration in MeCN-d3. In free benzoazacrown ethers containing secondary nitrogen atoms bound to the benzene ring, as well as in N-acetyl derivatives, the N atoms are sp2-hybridized and have a planar geometry. The nitrogen lone pairs on the p orbitals are efficiently conjugated to the benzene
ring or the carbonyl fragment of the acetyl group, which is unfavorable for the complex formation. In addition, the formation
of complexes with benzoazacrown ethers containing secondary nitrogen atoms is hindered because the hydrogen atoms of the NH
groups are directed to the center of the macrocyclic cavity. In benzoazacrown ethers bearing N-alkyl substituents or secondary nitrogen atoms distant from the benzene ring, the N atoms show a substantial contribution
of the sp3-hybridized state and have a pronounced pyramidal configuration, which promotes the complex formation. The lead and calcium
cations form the most stable complexes due to the high affinity of Pb2+ ions for O,N-containing ligands, a high charge density on these ions, and the better correspondence of the cavity size of
the 15-membered macrocycles to the diameter of the Ca2+ ion. An increase in the stability of the complexes is observed mainly in going from monoazacrown ethers to diazacrown ethers
containing identical substituents at the N atoms and in the following series of substituents: C(O)Me < H < Me < CH2CO2Et. In the case of the CH2CO2Et substituents, the carbonyl oxygen atom is also involved in the coordination to the cation. The characteristic features
of the complexing ability of N-alkylbenzomonoaza-15-crown-5 ethers bearing the nitrogen atom conjugated to the benzene ring show that macro-cyclic ligands
having this structure are promising as selective and efficient complexing agents for metal cations. 相似文献
13.
Inokuchi Y Boyarkin OV Kusaka R Haino T Ebata T Rizzo TR 《The journal of physical chemistry. A》2012,116(16):4057-4068
Electronic and vibrational spectra of benzo-15-crown-5 (B15C5) and benzo-18-crown-6 (B18C6) complexes with alkali metal ions, M(+)?B15C5 and M(+)?B18C6 (M = Li, Na, K, Rb, and Cs), are measured using UV photodissociation (UVPD) and IR-UV double resonance spectroscopy in a cold, 22-pole ion trap. We determine the structure of conformers with the aid of density functional theory calculations. In the Na(+)?B15C5 and K(+)?B18C6 complexes, the crown ethers open the most and hold the metal ions at the center of the ether ring, demonstrating an optimum matching in size between the cavity of the crown ethers and the metal ions. For smaller ions, the crown ethers deform the ether ring to decrease the distance and increase the interaction between the metal ions and oxygen atoms; the metal ions are completely surrounded by the ether ring. In the case of larger ions, the metal ions are too large to enter the crown cavity and are positioned on it, leaving one of its sides open for further solvation. Thermochemistry data calculated on the basis of the stable conformers of the complexes suggest that the ion selectivity of crown ethers is controlled primarily by the enthalpy change for the complex formation in solution, which depends strongly on the complex structure. 相似文献
14.
The influence of substituents in close proximity to crown ether cavities, on the stability of complexes of the crown ethers with t-butylammonium salts, has been investigated. Crown ethers with intra-annular donor substituents (2–4) were prepared by the reaction of 2-acetylresorcinol (1) with polyethylene glycol ditosylates and subsequent modification of the acetyl group. Crown ethers with substituents above and below the plane of the crown ether 0 atoms were synthesized by the reaction of 2,2'-dihydroxy-1,1'-biphenyls with polyethylene glycol ditosylates. Chloromethylation of 5,5'-dimethyl-1,1'-biphenyl crown ethers (6) yielded 4,4'-bis(chloromethyl)-1,1'-biphenyl crown ethers (10). 3,3'-Disubstituted-1,1'-biphenyl crown ethers (13–24) were synthesized by the reaction of 3,3'-diallyl-2,2'-dihydroxy-1,1'-biphenyl (12) with polyethylene glycol ditosylates. The allyl groups of 13 were isomerized with sodium hydride to propen- 1-yl groups. Ozonolysis of 13 and 14 gave the corresponding dialdehydes (15 and 18) which were converted into other 3,3'-disubstituted biphenyl-20-crown-6 derivatives (RCH2COOMe, CH2COOH, CH2OH, CH2Cl, CH2OMe, OH and Me) by standard operations. The thermodynamic stability of the complexes of these functionalized crown ethers with t-butylammonium hexafluorophosphate has been studied in deuterochloroform in competition experiments with m-xyleno-18-crown-5 and benzo-15-crown-5 as the reference compounds. The nature of the 2-substituents in the crown ethers 2 and 3 has little effect on the stability of the complexes. The stability of the complexes of 3,3'-disubstituted biphenyl crown ethers depends of ringsize and the size and nature of the substituents. The most stable complexes are those of 24 (R = Me) and 14 (R=CH=CHMe).The Me groups in 24 represent the optimum between relief of O-O repulsion in the polyether ring and steric hindrance of complexation. The propen-1-yl substituents of 14 stabilize the complex because they provide extended π-electron donor stabilization. Substitution at the 4- and 4'-positions of the aryl groups has little effect on the stability of the complexes. 相似文献
15.
In this paper, the nitrogen position isomers of diaza-18-crown-6, diaza-15-crown-5, diaza-12-crown-4, and their complexes with Na+ ion are studied by the density functional theory. Their stable structures are identified by geometry optimization without strict for their geometry. The binding capability that reflects the selectivity of these diazacrown ethers to metallic ions is estimated by the binding energy. The position effects of nitrogen on the stability of these complexes are also investigated by the explicit natural bond orbital and atoms-in-molecule analysis. It is found that different nitrogen position in crown ring will result in different relative energy. To those diazacrown ethers under consideration, the calculation results show that 1,10-diaza-4,7,13,16-tetraoxacyclooctadecane, 1,4-diaza-7,10,13-trioxacyclopentadecane, and 1,7-diaza-4,10-dioxacyclododecane exhibit higher metal binding selectivity than their corresponding nitrogen position isomers, respectively. Clearly, the position of nitrogen plays an important role in the selectivity of diazacrown ethers to metal ions in the system involved. This work will be help for the material design of ionic recognition and other related fields. 相似文献
16.
Sadik Elshani Randal Noriyuki Chien M. Wai N. R. Natale Richard A. Bartsch 《Journal of heterocyclic chemistry》1998,35(4):875-885
Twenty-six new lariat ether carboxylic and hydroxamic acids based upon dibenzo-13-crown-4, dibenzo-14-crown-4, dibenzo-16-crown-5 and dibenzo-19-crown-6 ring systems are synthesized and the solid-state structure for a dibenzo-19-crown-6 lariat ether hydroxamic acid is determined. The efficiency and selectivity for lanthanide ion extraction into chloroform by these proton-ionizable lariat ethers is strongly influenced by the crown ether ring size, lipophilic group attachment site and identity of the acidic function. In general, the lariat ether hydroxamic acids were more efficient and selective lanthanide ion extractants than the corresponding lariat ether carboxylic acids. The 1H nmr and ir binding studies indicate that both the macrocyclic polyether unit and the proton-ionizable group are involved in lanthanide ion complexation. 相似文献
17.
利用等温滴定微量热法测定了298.15 K时12-冠-4、15-冠-5、18-冠-6和4,13-二氮杂-18-冠-6四种冠醚在纯水及不同质量分数(w=0-0.3)的N,N-二甲基甲酰胺(DMF)+H2O混合物中的稀释焓, 根据McMillan-Mayer理论计算得到相应的焓对作用系数(hxx). 实验发现, hxx均为较大的正值, 表明在冠醚-冠醚自相互作用中疏水性成分占绝对优势, 主要表现为两种机制: (1) 当疏水-疏水作用发生时, 共球交盖使得水结构形成减少, 对hxx有正的贡献; (2) 当疏水-亲水作用发生时, 共球交盖使得水结构破坏增加, 对hxx有正的贡献. 此外, 四种冠醚hxx的大小关系为: hxx(18-冠-6)>hxx(4,13-二氮杂-18-冠-6)≈hxx(15-冠-5)>hxx(12-冠-4), 表明冠醚环越大, 疏水-疏水作用越强, 存在显著的大环疏水效应. 相似文献
18.
Teng W Allis DG Ruhlandt-Senge K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(4):1309-1319
The preparation of a series of crown ether ligated alkali metal (M=K, Rb, Cs) germyl derivatives M(crown ether)nGeH3 through the hydrolysis of the respective tris(trimethylsilyl)germanides is reported. Depending on the alkali metal and the crown ether diameter, the hydrides display either contact molecules or separated ions in the solid state, providing a unique structural insight into the geometry of the obscure GeH3? ion. Germyl derivatives displaying M? Ge bonds in the solid state are of the general formula [M([18]crown‐6)(thf)GeH3] with M=K ( 1 ) and M=Rb ( 4 ). The compounds display an unexpected geometry with two of the GeH3 hydrogen atoms closely approaching the metal center, resulting in a partially inverted structure. Interestingly, the lone pair at germanium is not pointed towards the alkali metal, rather two of the three hydrides are approaching the alkali metal center to display M? H interactions. Separated ions display alkali metal cations bound to two crown ethers in a sandwich‐type arrangement and non‐coordinated GeH3? ions to afford complexes of the type [M(crown ether)2][GeH3] with M=K, crown ether=[15]crown‐5 ( 2 ); M=K, crown ether=[12]crown‐4 ( 3 ); and M=Cs, crown ether=[18]crown‐6 ( 5 ). The highly reactive germyl derivatives were characterized by using X‐ray crystallography, 1H and 13C NMR, and IR spectroscopy. Density functional theory (DFT) and second‐order Møller–Plesset perturbation theory (MP2) calculations were performed to analyze the geometry of the GeH3? ion in the contact molecules 1 and 4 . 相似文献
19.
S. N. Dmitrieva M. V. Churakova N. A. Kurchavov A. I. Vedernikov L. G. Kuz’mina A. Ya. Freidzon A. A. Bagatur’yants Yu. A. Strelenko J. A. K. Howard S. P. Gromov 《Russian Chemical Bulletin》2010,59(6):1192-1206
A number of N-alkylnitrobenzoaza-15-crown-5 with the macrocycle N atom conjugated with the benzene ring were obtained. The structural and
complexing properties of these compounds were compared with those of model nitrobenzo- and N-(4-nitrophenyl)aza-15-crown-5 using X-ray diffraction, 1H NMR spectroscopy, and DFT calculations. The macrocyclic N atom of benzoazacrown ethers are characterized by a considerable
contribution of the sp3-hybridized state and a pronounced pyramidal geometry; the crownlike conformation of the macrocycle
is preorganized for cation binding, which facilitates complexation. The stability constants of the complexes of crown ethers
with the NH4
+, EtNH3
+, Na+, K+, Ca2+, and Ba2+ ions were determined by 1H NMR titration in MeCN-d3. The most stable complexes were obtained with alkaline-earth metal cations, which is due to the higher charge density at
these cations. The characteristics of the complexing ability of N-alkylnitrobenzoaza-15-crown-5 toward alkaline earth metal cations are comparable with analogous characteristics of nitrobenzo-15-crown-5
and are much better than those of N-(4-nitrophenyl)aza-15-crown-5. 相似文献
20.
Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali Cations
Yu Liu Jian-Rong Han Zhong-Yu Duan Heng-Yi Zhang 《Journal of inclusion phenomena and macrocyclic chemistry》2005,52(3):229-235
A series of double-armed benzo-15-crown-5 lariats (3–8) have been synthesized by the reaction of 4′, 5′-bis(bromomethyl)-benzo-15-crown-5 (2) with 4-hydroxybenzaldehyde, phenol, 4-chlorophenol, 4-methoxyphenol, 2-hydroxybenzaldehyde, and 4-acetamidophenol in 43 ~ 82% yields, respectively. The complex stability constants (K
S) and thermodynamic parameters for the stoichiometric 1:1 and/or 1:2 complexes of benzo-15-crown-5 1 and double-armed crown ethers 3–8 with alkali cations (Na+, K+, Rb+) have been determined in methanol–water (V/V=8:2) at 25 °C by means of microcalorimetric titrations. As compared with the parent benzo-15-crown-5 1, double-armed crown ethers 3–8 show unremarkable changes in the complex stability constants upon complexation with Na+, but present significantly enhanced binding ability toward cations larger than the crown cavity by the secondly sandwich complexation. Thermodynamically, the sandwich complexations of crown ethers 3-8 with cations are mostly enthalpy-driven processes accompanied with a moderate entropy loss. The binding ability and selectivity of cations by the double-armed crown ethers are discussed from the viewpoints of the electron density, additional binding site, softness, spatial arrangement, and especially the cooperative binding of two crown ether molecules toward one metal ion. 相似文献