Estimation of Li+, K+ and Ca2+ Complexation with [12] crown-4, [15] crown-5 and [18] crown-6 Using a Na+ ISE in Dioxane-Water, Part IV*

 The (1:1) Na⁺ equilibrium constants, Ke1, of macrocyclic ethers of [12]crown-4, [12]crown-5 and [18]crown-6 were determined with a Na⁺ ISE in the presence of a second cation e.g. Li⁺, K⁺ and Ca²⁺ in dioxane/water (50/50). We estimated the (1:1) equilibrium constants, K e2 of the macrocyclic ethers with Li⁺, K⁺ and Ca²⁺ by this way. The binding selectivity of a macrocyclic ether between two cations was estimated in the same binary solvent mixture where the water hydration role is diminished. Results showed clearly the effect of macrocyclic size and cation radii in a solution. Received October 27, 1998. Revision March 22, 1999.     

The Synthesis of Novel Crown Ethers, Part VII [1]. Coumarin Derivatives of Benzocrowns and Cation Binding from Fluorescence Spectra

4-[3-(1-benzopyran-2-one)] derivativesof benzo[12]crown-4, benzo[15]crown-5 andbenzo-[18]crown-6 were synthesized from4-[3-(1-benzopyran-2-one)]-1,2-dihydroxy-benzenereacting with bis-ethyleneglycol dihalides orpentaethylene glycol ditosylate in alkali carbonate/DMF/water. The original products were identified byhigh resolution EI-mass spectra as well as IR,¹H-NMR and ¹³C-NMR spectroscopy. The 1 : 1binding constants of Mg²⁺, Li⁺, Na⁺ andK⁺ with the coumarin-benzocrowns were estimated usingfluorescence emission spectroscopy in acetonitrile.The complexing enhanced quenching fluorescence spectra(CEQFS) and complexing enhanced fluorescence spectra(CEFS) exhibited the ion binding powers due tocationic recognition rules of the macrocycles.     

The Synthesis of Novel Crown Ethers. Part IV. Coumarin Derivatives of [18]crown-6 and Cation Binding from Fluorescence Spectra

4-H, 4-methyl and 4-phenyl-1-benzopyran-2-one derivatives of [18]crown-6 derivatives were synthesised from 6,7- and 7,8-dihydroxy-1-benzopyran-2-one reacting with pentaethylene glycol ditosylate in K₂CO₃/DMF/water. The products were identified by elemental analysis, EI-GC-mass spectra and ₁H-NMR spectroscopy. The Na⁺ association constants of some coumarin derivatives were determined with an ion selective electrode in water. The Na⁺ , K⁺, Ba²⁺ and Sr²⁺ binding role of such compounds were particularly observed as remarkable alterations in acetonitrile. The 1 : 1 associations constants of K⁺ and Na⁺ with some coumarin-[18]crown-6 derivatives estimated by this way in acetonitrile exhibited the utility of complexing enhanced quenching fluorescence spectra for the ion binding power of the such macrocycles.     

The cation binding of benzo crown ethers in acetonitrile using fluorescence spectroscopy

The effects of Na⁺, K⁺ and Li⁺ cations on the fluorescence spectra of benzo[15]crown-5, benzo[18]crown-6 and dibenzo[18]crown-6 were investigated in acetonitrile. The alkali cation role observed was usually the complexation-enhanced quenching fluorescence effect (CEQF) in acetonitrile due to the increased fluorescence quenching rate of the complexed fluoroionophore. The association constants for 1 :1 stoichiometry InK _a have been obtained using the relationship 1/K _a[L ₀] = (1 –P)²/P. It was shown that the preferential interaction rule of compatibility of cationic radii and macrocyclic ring size is in excellent agreement with the association constants obtained by fluorescence spectroscopy. The order of InK _a found for benzo[15]crown-5 complexation was Li⁺ > Na⁺ > K⁺ and K⁺ > Na⁺ > Li⁺ for benzo[18]crown-6 in acetonitrile.Presented at the Sixth International Seminar on Inclusion Compounds, Istanbul, Turkey, 27–31 August, 1995.     

The Synthesis of Dibenzo[3n]crown-n by Novel Methods and their Cation Binding Studied by Fluorescence Spectroscopy. Part IV

The dibenzo[3n]crown-n were synthesised from1,2-bis(o-hydroxyphenoxy)ethane obtained from 1,2-bis(o-formylphenoxy)ethane via Bayer-Willigeroxidations with H₂O₂/CH₃COOH in good yields. The cyclic condensation of 1,2-bis(o-hydroxyphenoxy)ethanewith dichlorides, and ditosylates of polyethylene glycols in DMF/Me₂CO₃ gave the macrocyclesdibenzo[15]crown-5, dibenzo[18]crown-6, dibenzo[21]crown-7 anddibenzo[24]crown-8. The structures were identified using IR, mass, ¹H and ¹³C NMR spectroscopy. Therecognition of the molecules for the cations, Li⁺, Na⁺, K⁺, Rb⁺ and Zn²⁺were conducted quantitatively with steady state fluorescencespectroscopy. The 1:1 association constants in acetonitrileshowed a good relation of the appropriate size of the macrocyclic ether towards the fitting cationradii. Namely, dibenzo[15]crown-5 was the best for Li⁺ binding and more than 100 times better thanNa⁺ and K⁺. Dibenzo[21]crown-7 was excellent for Rb⁺ binding while K⁺ is 100 timesless preferred. The largest crown ether studied, dibenzo[24]crown-8, exhibited the order of binding power,Rb⁺ > K⁺ > Na⁺. Zn²⁺ displayed, however, a marked binding with only dibenzo[18]crown-6.p>     

The association constants of Na(+) with dibenzo[3n]crown-n in THF/water using ISE

The Na⁺ association constants, K₁₁ and β₁₂, of 1/1 and 1/2 stoichiometry of macrocycles of (1,2)dibenzo[15]crown-5, (1,3)dibenzo[18]crown-6, (1,4)dibenzo[21]crown-7, (2,3)dibenzo[21]crown-7, (2,4)dibenzo[24]-crown-8 and dicyclohexano[24]crown-8 were determined in THF/water, (50/50), mixtures. We used a Methrom Na⁺ ISE for the potentiometric measurements and applied the 1/(β_nm[A_o⁺])^n+m−1=(1−nP_c)(1−mP_c)/P_c equation where the P_c=P/[1+(m−1)P] and P is the mole fraction of the complexed cation, [A_n⁺L_m] for association constants with linear best fit. Results were in well agreement with the macrocyclic size and cation radii relationships. Measurements showed the role of aromatic groups of macrocyclics in THF/water (50/50) which allowed the macrocyclic molecules more selectively bind Na⁺ compared to the associations those obtained in water.     

Novel Methods of Synthesis of Dibenzo[3n]crown-n and Their Cation Binding Studied by Fluorescence Spectroscopy. Part V

The dibenzo[3n]crown-n were synthesised starting from bis[2-(o-hydroxyphenoxy)ethyl]ether obtained from bis[2-(o-formylphenoxy)ethyl]ether via Baeyer-Villiger oxidation in H₂O₂/CH₃COOH in a good yield. The cyclic condensation ofbis[2-(o-hydroxyphenoxy)ethyl]etherwith tri- and tetraethylene glycol bisdichlorides andthe bisditosylate of pentaethylene glycol in DMF/Me₂CO₃ afforded the large cyclic ethers of dibenzo[21]crown-7, dibenzo[24]crown-8 and dibenzo[27]crown-9. The structures were analysed with IR, ¹H NMR, ¹³C NMR and low-resolution mass spectroscopy methods. The Na⁺, K⁺, Rb⁺ and Cs⁺ cations' recognition of the molecules were conducted withsteady-state fluorescence spectroscopy. The 1:1 association constants, K_a, in acetonitrile were estimated. Dibenzo[21]crown-7 was the best both for K⁺ and Rb⁺ binding but showed too small an effect on Cs⁺. Dibenzo[24]crown-8 exhibited the binding power in the order of Rb⁺ > K⁺ > Na⁺ > Cs⁺. However, dibenzo[27]crown-9 displayed marked binding with only K⁺ but not with Rb⁺ or with Cs⁺ cations probably due to the heavy atom effect of fluorescence quenching.     

Metal ion shuttling mechanism through thiacalix[4]crown: a computational study

The first computational study on the alkali metal ion shuttling mechanism through thiacalix[4]biscrown-5 has been performed using density functional theory (MPWB1K/6-31G(d)//B3LYP/6-31G(d)). The activation free energy for K⁺ ion shuttling through the calix tube of thiacalix[4]biscrown-5 is computed to be 12.7 kcal/mol which is in good agreement with the experimental value. Throughout the shuttling process, K⁺ ion maintains the maximum electrostatic interactions with ether oxygens of crown rings, which contributes to lower the activation barrier of the shuttling process.     

How charging corannulene with one and two electrons affects its geometry and aggregation with sodium and potassium cations

Bowl-shaped mono- and dianions are prepared by reduction of corannulene (C(20)H(10), 1) with sodium and potassium metals in the presence of [18]crown-6 ether. Single-crystal X-ray diffraction studies of two sodium salts, [Na(THF)(2)([18]crown-6)](+)[1(-)] (2a) and [Na([18]crown-6)](+)[1(-)] (2b), reveal the presence of naked corannulene monoanions 1(-) in both cases. In contrast, the potassium adduct, [K([18]crown-6)](+)[1(-)] (3), shows an η(2)-binding of the K(+) ion to the convex face of 1(-). For the first time, corannulene dianions have been isolated as salts with sodium, [Na(2)([18]crown-6)](2+)[1(2-)] (4a) and [Na(THF)(2)([18]crown-6)](+)[Na([18]crown-6)](+)[1(2-)] (4b), and potassium counterions, [K([18]crown-6)](2)(+)[1(2-)] (5). Their structural characterization reveals geometry perturbations upon addition of two electrons to a bowl-shaped polyarene. It also demonstrates η(5)- or η(6)-binding of metals to the curved carbon surface of 1(2-), depending on the crystallization conditions. Both mono- and doubly-charged corannulene bowls show the preferential exo binding of Na(+) and K(+) ions in all investigated compounds. Various types of C-H···π interactions are found in the crystals of 2-5. The UV/Vis, ESR, and (1)H NMR spectroscopic studies of 2-5 indicate different coordination environment of corannulene anions in solution, depending on the metal ion.     

Association constants of dibenzo[3n + 2]crown-n ethers using steady-state fluorescence spectroscopy

The steady-state fluorescence spectra of cation complexes of fluorophore macrocyclic ethers have been studied for the estimation of 1:1 association constants, and perchlorate salts of Li⁺, Na⁺, K⁺ Rb⁺ and Pb²⁺ complexing with dibenzo[23]crown-9, dibenzo[26]crown-10, and sym-dibenzo[26]crown-10, were investigated. The fluorescence emission maximum of the free and the various ligand/cation mixtures of complexed crown ethers were measured at room temperature in AN. The concentrations of chromophore crown ether were obtained from nonlinear calibration plots. The 1:1 stoichiometry of association constants (K_ass) were calculated using the equation, 1/K_ass [L_o] = (1 − nP)ⁿ(1 − m)^m/P with linear best fit of plots depending on 1/[L_o] where P = P_C/[1 + (m − 1)P_C] and P_C is the mole fraction of n/m ratio of the complexed ligand. The association constants of cations, K_ass, displayed the cation selectivities depending on the cation radii and the macrocyclic ether size, and Pb⁺ was found to give the strongest association with such crown ethers.     

A Rational Approach to Selective Recognition of NH4+ over K+

An ion-selective electrode (ISE) based on receptor 1 is highly selective for binding NH₄⁺ over K⁺ (lg K=−2.6); the three imine nitrogen atoms in 1 are ideally positioned for hydrogen bonding with the tetrahedral NH₄⁺ ion. This selectivity is considerably greater than that found for commercial ISEs based on nonactin (lg K=−1.0).     

Synthesis of a Fullerene Derivative of Benzo[18]crown-6 by Diels-Alder Reaction: Complexation Ability,Amphiphilic Properties,and X-Ray Crystal Structure of a Dimethoxy-1,9-(methano[1,2]benzenomethano)fullerene[60] Benzene Clathrate

A fullerene derivative 1 of benzo[18]crown-6 was obtained by Diels-Alder addition of fullerene[60](C₆₀) to the ortho-quinodimethane prepared in situ from 4,5-bis(bromomethyl)benzo[18]crown-6 ( 3 ) with Bu₄NI in toluene. Extraction experiments show that the complexation of K⁺ ions strongly increases the solubility of 1 in protic solvents like MeOH. Using Langmuir-Blodgett techniques, monolayers of the highly amphiphilic fullerene-derived crown ether 1 and its K⁺ ion complex were prepared. An X-ray crystal structure was obtained from a benzene clathrate of comparison compound 2 , synthesized by Diels-Alder reaction of C₆₀ with the ortho-quinodimethane derived from 1,2-bis(bromomethyl)-4,5-dimethoxybenzene ( 4 ). Both the fullerene molecule 2 and the benzene molecule are fully ordered in a crystal packing which is stabilized by intermolecular van-der-Waals contacts between the benzene ring and the C-spheres, intermolecular C…?C contacts between the C₆₀ moieties, and intermolecular O…?C contacts between the O-atoms of the veratrole moieties and fullerene C-atoms.     

Der erste röntgenstrukturanalytisch charakterisierte Cs+ – „in cavity”︁ – Komplex eines einundzwanziggliedrigen Coronanden: (Maleonitril-Dithio[21]krone-7)caesium-hexachloroantimonat

First X-ray Crystallographic Characterized Cs⁺ ‘‘in cavity”︁”︁ Complex of a Twenty-one Membered Coronand: (Maleonitrile-Dithio[21]crown-7)caesium Hexachloroantimonate A new maleonitrile-crown dithioether, the maleonitrile-dithio[21]crown-7 (mn–21 S₂O₅), was synthesized by high dilution cyclization of (Z)-1,2-disodium-1,2-dicyanoethene-1,2-dithiolate ( 1 ) with 1,17-dichloro-3,6,9,12,15-pentaoxaheptadecane ( 2 ) in ethanol/water mixtures. Mn–21 S₂O₅ forms with CsSbCl₆ in MeCN/MeNO₂ a 1 : 1 complex [Cs(mn–21 S₂O₅)]SbCl₆. X-ray crystal analysis revealed that the complex cation [Cs(mn–21 S₂O₅)]⁺ is an ‘‘in cavity”︁”︁ complex in which the Cs⁺ ion is coordinated by seven donor atoms (five O and two S atoms). This is the first X-ray crystallographic evidence of Cs⁺ coordination by seven donors in a hole of a twenty-one membered coronand.     

Synthesis and structure of the silylated benzene radical anion salts [K([18]crown-6){C6H4(SiMe3)2-1,4}] and [K([18]crown-6)(THF)2][C6H2(SiMe3)4-1,2,4,5]

The crystalline compound [K([18]crown-6){C₆H₄(SiMe₃)₂-1,4}] (1) was prepared by the low-temperature reduction of the para-disilylated benzene with K/[18]crown-6 in toluene followed by recrystallisation from the same solvent. Reduction of 1,2,4,5-tetrasilylated benzene with 2(K/[18]crown-6) in toluene produced a hydrocarbon-insoluble powder identified as the dianionic derivative [K([18]crown-6)]₂[C₆H₂(SiMe₃)₄-1,2,4,5)] (2), which upon crystallisation from THF/Et₂O yielded [K([18]crown-6)(THF)₂][C₆H₂(SiMe₃)₄-1,2,4,5] (3). An X-ray diffraction study revealed that 1 comprised a contact ion pair with the crown-encapsulated K cation η⁵-connected to the planar ring of the substituted benzene radical anion, while 3 contained a well separated cation and anion.     

Quantum simulation on donor and acceptor II calix[4]arene substrate and alkali metal ions: the driven inclusion

The energetic and structural optimized of a calix[4]arene with and without alkali-metal cations are presented with performance of various quantum chemical methods such as Hartree--Fock, second order Møller-Plesset perturbation theory, and density functional theory. The geometry optimizations have been carried out with the 3-21G (Li⁺--Cs⁺) and 3-21G(d,p) (Li⁺--K⁺) and the 3-21G basis sets for Cs⁺ and Rb⁺. Additional single-point energy ab initio calculations for Li⁺–K⁺ were carried out at HF/6--31G, HF/6-31G (d,p), HF/6--311G(d,p) for complexes of Li⁺ and Na⁺. The calculations were carried out to analyze the complexation of calix[4]arene with alkali metal cationic species (Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺). Assumption to isolate the effects of the aromatic core and cation-π interactions. Particular emphasis has been on conformational binding selectivity and the structural characterization of the complexes, the smaller cation as Li⁺ and Na⁺ has been placed in the lower rim's of the calix[4]arene's cavity. The large cations like K⁺, Rb⁺, and Cs⁺ take placed in upper rim and the endo (inclusive) complexation is driven by cation-π interactions, that reflect a superior interaction with two phenol rings. The endo complexation of Cs⁺ with calix[4]arene is in agreement with X-ray diffraction data. The binding modes of calixarene-cation systems are studied to involve cooperative effects between cation-π and electrostatic forces.     

Eu(fod)(3) binding on the (1)H-NMR spectra of some benzo[3n]crown-n and dibenzo[3n+2]crown-n

The complexing of Eu(fod)₃ with macrocyclic ethers, benzo[15]crown-5, benzo[12]crown-4, dibenzo[20]crown-6, dibenzo[23]crown-7 and dibenzo[26]crown-8 was observed on their ¹H-NMR spectra and the selective binding constants at 400 MHz and 305 K in CDCl₃ were reported. The Eu(fod)₃ interaction displayed the selective binding role of oxygen on macrocyclic, H₂COCH₂, backbones with o- or m-dioxyphenyl groups referring the ¹H chemical shifts. The estimated equilibrium constants, K_a of 1:1 ratio of interactions were in accordance with the Eu³⁺ ionic radii to bind the oxygen sites depending on the macrocyclic size and conformation of the ethers. The minimum lanthanide-macrocyclic ether distance displayed the maximum stability so that benzo[3n]crown-n (n=4, 5) group was found to bind the Eu(fod)₃ moderately whilst dibenzo[3n+2]crown-n (n=6-8) oligomer chemical shifts were induced largely since the such Eu³⁺ complexes are more stable with larger ethyleneoxy groups.     

Alkaline Earth Metal Template (Cross-)Coupling Reactions with Hybrid Disila-Crown Ether Analogues

Alkaline earth metal iodides were used as templates for the synthesis of novel silicon-based ligands. Siloxane moieties were (cross-)coupled and ion-specific, silicon-rich crown ether analogues were obtained. The reaction of 1,2,7,8-tetrasila[12]crown-4 ( I ) and 1,2-disila[9]crown-3 ( II ) with MgI₂ yielded exclusively [Mg(1,2,7,8-tetrasila[12]crown-4)I₂] ( 1 ). The larger Ca²⁺ ion was then employed for cross-coupling of I and II and yielded the complex [Ca(1,2,7,8-tetrasila[15]crown-5)I₂] ( 2 ). Cross-coupling of I and 1,2,4,5-tetrasila[9]crown-3 ( III ) with SrI₂ enables the synthesis of the silicon-dominant 1,2,4,5,10,11-hexasila[15]crown-5 ether complex of SrI₂ ( 3 ). Further, the compounds [Sr(1,2,10,11-tetrasila[18]crown-6)I₂] ( 4 ), [Sr(1,2,13,14-tetrasila[24]crown-8)I₂] ( 5 ), and [Sr(1,2,13,14-tetrasila-dibenzo[24]crown-8)I₂] ( 6 ) were obtained by coupling I , 1,2-disila[12]crown-4 ( IV ) or 1,2-disila-benzo[12]crown-4 ( V ), respectively. Using various anions, the (cross-)coupled ligands were also observed in an X-ray structure within the mentioned complexes. These template-assisted (cross-)couplings of various ligands are the first of their kind and a novel method to obtain macrocycles and/or their metal complexes to be established. Further, the Si−O bond activations presented herein might be of importance for silane or even organic functionalization.     

Ab initio calculations of electronic interactions in inclusion complexes of calix- and thiacalix[n]arenes and block s cations

Ab initio calculations at the HF/6-31G(d) level of theory were performed on a series of thiacalix[4]arenes and calix[6]arenes in presence and in absence of monovalent (Li⁺, Na⁺ and Cs⁺) and divalent cations (Ca²⁺ and Ba²⁺) respectively, in order to evaluate their particular bonding properties as host systems towards electrically charged species. NBO, as well as NBO deletion calculations were undertaken to evaluate the energy difference in the circular hydrogen bonding at the lower rim once an ion was placed inside the cavity. Disruption of this H-bonded system is dependent on the position of the ion within the guest and not on its ionic ratio. The basis set superposition error and the NBO deletion energy between the host and guest species were calculated in order to assess the interaction energy between them.     

Novel Macrocycles. Part 6. Synthesis, Structures and Cation Binding from Optical Spectroscopy of 9,10-Anthraquinone-crown Ethers

The 9,10-anthraquinone-[12]crown-4, [15]crown-5 and [18]crown-6 derivatives were synthesized from 1,2-dihydroxy-9,10-anthraquinone and 1,8-dihydroxy-9,10-anthraquinone which were condensed with dihalides or ditosylates of polyethylene glycols in alkali carbonate/DMSO. The 9,10-anthraquinone derived polyoxacyclo-alkanes were characterized with IR, mass spectrometry, ¹H, ¹³C spectroscopy and elemental analysis. The cation binding properties were studied with UV-vis spectroscopy. The association constants found in acetonitrile were selectively dependent on the cation radius and macrocycle size as well as the molecular structures. The observed results from UV-vis studies, however, showed the stronger complexing role of 1,2-derived macrocycles compared to those of 1,8-derivatives. The theoretical conformational analysis and the energy optimisations of the 9,10-anthraquinone-macrocycles carried out with MM+ method explained the binding results.