A Polarographic Study on Some Complexes of Pb2+ and Cd2+ with Macrocyclic Polyethers (Crown Ethers)

Abstract

Complexation constants of Pb²⁺ and Cd²⁺ nitrates with five crown compounds (18-crown-6, dicyclohexyl-18-crown-6, benzo-15-crown-5, dibenzo-24-crown-8 and 12-crown-4), have been determined by d.c. and a.c. polarographic measurements in aqueous medium using 0.1 M HNO₃ as supporting electrolyte. The complexes of lead with 18-crown-6 and dicyclohexyl-18-crown-6 are very stable which may be attributed to the partially covalent bonds formed by this metal ion.     

Synthesis and crystal structure of hexakis(isothiocyanato)erbium(III) thiocyanate bis(18-crown-6)dipotassium bis[(18-crown-6)ethanolpotassium]

A new complex compound, [K₂(18-crown-6)₂[K(18-crown-6)(EtOH)]₂[Er(NCS)₆](SCN) (I), was synthesized and its crystal structure was studied by X-ray diffraction. In this work, the synthes and X-ray difraction stady of the crystals of a new complex, hexakis (isothiocyanato) erbiu(III) thiocyanate bis(18-crown-6) dipotassium bis(18-crown-6) ethanolpotassium], [K₂(18-crown-6)₂][K(18-crown-6)(ETON)]₂[Er(NCS)₆(SCN)(I)] are described. In crystal I, the alternating [Er(NCS)₆]^3? anions and binuclear complex cation [K(18-crown-6)₂]²⁺ from infinite chains via the F-S bonds, while two complex cations [K(18-crown-6)(ETON)]⁺ and the statistically disordered SCN^? anion between them are linked by the hydragen bonds O-H…S and O-H…N. Complex I contains the host-guest complex cations [K₂(18-crown-6)₂)]²⁺ and [K(18-crown-6)(ETON)]⁺ [1]. The alternating octabedral [Er(NCS)₆]^3? anions and binuclear complex cations [K₂(18-crown-6)₂]²⁺of crystal I form infinite chains via the K-S bonds, while two complex cations [K(18-crown-6)(EtOH)]⁺ and the statistically disordered SCN^? anion lying between them are linked by interionic hydrogen bonds O-H…S and O-H…N. Complex I contains the host-guest complex cations [K₂(18-crown-6)₂]²⁺ and [K(18-crown-6)(EtOH)]⁺ [1].     

A Study of Formation Equilibria of the Complexes of Some Metal Cations with Polyoxa Macrocyclic Ligands

Abstract

The complexes formed by the Na⁺, K⁺, Rb⁺, Ca²⁺, UO²⁺ ₂, and Ag⁺ cations with the macrocyclic polyethers 18-crown-6, benzo-15-crown-5, and dicyclohexy1-18-crown-6 are investigated. The stability constants of these complexes have been determined potentiometrically in (90% vol.) ethanol-water solutions at 25[ddot]C and an ionic strength μ= 0.1 (achieved with tetrabuty lammonium perchlorate). The stablity of the investigated complexes was interpreted in terms of “caging” the metal cation into the cavity of the macrocyclic ligand, an effect which depends on the ratio of the diameter of the complexed cation over the diameter of the cavity of the complexing ligand.     

Synthesis and crystal structure of 18-crown-6 <Emphasis Type="Italic">E</Emphasis>-2-phenylethenylphosphonic acid diaqua(18-crown-6)sodium <Emphasis Type="Italic">E</Emphasis>-2-phenylethenylphosphonate

New complex compound, diaqua(18-crown-6)sodium E-2-phenylethenylphosphonate 18-crown-6 E-2-phenylethenylphosphonic acid, [Na(18-crown-6)(H₂O)₂]⁺·HO ₃ ^? PCH=CHPh·18-crown-6·H₂O₃PCH=CHPh, was obtained and its crystal and molecular structures were studied by the X-ray structural analysis. In this structure the complex cation [Na(18-crown-6)(H₂O)₂]⁺ is of guest-host type. The coordination polyhedron of its Na⁺ cation is a slightly screwed hexagonal bipyramid with the base consisting of all 6 O atoms of 18-crown-6 ligand and with two opposite apexes at two O atoms of two ligand water molecules. In the studied crystal structure the alternating complex cations and 18-crown-6 molecules as well as the molecules of acid and its anion HO ₃ ^? PCH=CHPh form by means of hydrogen bonds the infinite chains of two different types.     

Complex Formation of Potassium Hexachloroplatinate with 18-Crown-6 and Dibenzo-18-Crown-6 in Acetonitrile

The products of the reactions between potassium hexachloroplatinate {K₂PtCl₆} and 18-crown-6 or dibenzo-18-crown-6 in acetonitrile were studied. Pure crystalline compounds [2K·2(18-crown-6)· 2CH₃CN]²⁺·[PtCl₆]^2-·2H₂O, [2K·dibenzo-18-crown-6·CH₃CN]^{2 +}·[PtCl₆]^{2 -}, and [2K·dibenzo-18-crown-6·CH₃CN]^{2 +}·[Pt₂Cl₁₀]^{2 -} were obtained. Physicochemical properties of these compounds were studied, and their near- and far-IR IR spectra and thermogravimetric curves were considered. The composition of the complexes is determined by metal:ligand molar ratio and crown ether nature. It was found that acetonitrile is coordinated via the nitrogen atom.     

Ion-pair extraction of tetravalent plutonium from hydrochloric acid medium using crown ethers

Ion-pair extraction behaviour of plutonium (IV) from varying concentrations of HCl solution was studied employing crown ethers (benzo-l5-crown-5 (B15C5), 18-crown-6, (18C6), dibenzo-18-crown-6 (DB18C6), dicyclohexano-18-crown-6, (DC18C6), dibenzo-24-crown-8 (DB24C8) and dicyclohexano-24-crown-8 (DCH24C8)) in nitrobenzene as the extractant. Ammonium metavanidate was used as the holding oxidant in the aqueous phase and the conditions necessary for the quantitative extraction of the tetravalent ion were found. The co-extraction of species of the type [HL⁺].[HPu(Cl) ₆ ^– ] and [HL⁺]2·[Pu(Cl) ₆ ^2– ] as ion-pairs (where L represents the crown ether) is suggested.     

Synthesis and characterization of trans-di(nitrobenzo)- and di(aminobenzo)-18-crown-6 derivatives with high selectivity

The dibenzo-18-crown-6 derivatives such as di(nitrobenzo)-18-crown-6 and di(aminobenzo)-18-crown-6 were synthesized by nitration reaction and catalytic hydrogenation with high selectivity. The chemical structures were determined by FTIR, ¹H NMR, ¹³C NMR, and UV. Regarding the mixture of Ac₂O and HNO₃ as nitrating agent, the reaction exhibited commendable trans-isomer selectivity. Effects of nitrating agent ratio, reaction temperature and reaction time on yield of trans-di(nitrobenzo)-18-crown-6 were investigated. The yield of trans-di(nitrobenzo)-18-crown-6 was 62.9% for nitrating agent ratio of 1/1, reaction temperature of 50?°C and reaction time of 5?h. Moreover, effect of reaction time on trans-di(aminobenzo)-18-crown-6 was also studied.     

Ethers as ligands. Part VI. Transition metal(II) complexes with 18-crown-6

Summary Seven new coordination compounds are reported with the cyclicpolyether 18-crown-6 as the ligand,viz. [Mg(18-crown-6) (H₂O)₂](SbCl₆)₂, [M(18-crown-6)(MeNO₆)₂](SbCl₆)₂ with M is Ca²⁺ and Sr²⁺, [M(18-crown-6)(MeNO₂)](SbCl₆)₂ with M is Mn²⁺ and Co²⁺, and [M(18-crown-6)](SbCl₆)₂ with M is Ni²⁺ and Zn²⁺.     

Kinetics of Ion Transport by Macrocyclic Carriers in Liquid Membrane Systems

Abstract

The relationship between the extractability of a metal ion (K⁺ or Pb²⁺) and the rate of its transfer by neutral macrocyclic carriers (dibenzo-18-crown-6, dicyclo-hexano-18-crown-6, 18-crown-6, and polynactin) was investigated in chloroform membrane systems. The experimentally determined apparent rate constants are compatible with the diffusion-limited process. Both the rate of ion uptake and the rate of ion transport depend crucially on the extractability of the metal ion rather than on the apparent rate constant.     

Stability of Complexes of NH4 + with 18-Crown-6, Dicyclohexyl-18-Crown-6, Dibenzo-18-Crown-6 and Dibenzo-24-Crown-8 in Water Saturated Nitrobenzene

From extraction experiments with ²²Na tracer, the exchange extraction constants corresponding to the NH₄ ⁺(aq) + NaL⁺ (nb)NH₄L⁺(nb) + Na⁺ (aq) equilibrium taking place in the two-phase water-nitrobenzene system (L = 18-crown-6, dicyclohexyl-18-crown-6, dibenzo-18-crown-6 and dibenzo-24-crown-8; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the stability constants of the NH₄L⁺ complexes in nitrobenzene saturated with water were calculated; they were found to increase in the order dibenzo-24-crown-8 (DB24C8) < dibenzo-18-crown-6 (DB18C6) < dicyclohexyl-18-crown-6 (DCH18C6) < 18-crown-6 (18C6).     

Synergistic extraction of americium(III) with 2-thenoyltrifluoroacetone and crown ethers

Extracton, of Am³⁺ in benzene with 2-thenoyltrifluoroacetone (HTTA) and crown ethers (CEs) such as 15-crown-5, 18-crown-6, dicyclohexano-18-crown-6, dibenzo-18-crown-6, dicyclohexano-24-crown-8, and dibenzo-24-crown-8 was investigated. Synergistic effect by CE was observed regardless of the kind of CE examined. The extracted species was found to be Am(TTA)₃(CE), and adduct formation constants between Am(TTA)₃ and CE in the organic phase were determined. The sequence of constant could not be explained only by basicity of CE and the steric effect of CE should be taken into account to elucidate the adduct complex formation.     

HYBRID PHOSPHINE-CROWN ETHER LIGANDS: THE STUDY OF BENZO-15-CROWN-5 AND N-PHENYLAZA-15-CROWN-5 AND -18-CROWN-6 FUNCTIONALIZED WITH Ph2P-

Abstract

Methods for the preparation of the 4-diphenylphosphino derivatives of N-phenylaza-15-crown-5 and -18-crown-6 are described. The properties of these systems and the 4′-diphenylphosphino derivative of benzo-15-crown-5 have been examined by way of picrate ion extraction abilities and IR spectra of their Ni(CO)₃L (L = these phosphines) complexes. All three have abilities to extract Na⁺ and K⁺ that are comparable to benzo-15-crown-5. The IR studies (ν_CO, A₁ band) indicate that the azacrown systems have better ability than the benzocrown system to increase the electron density on the nickel center. Further, the addition of alkali metal ions, Na⁺ and K⁺, to the Ni(CO)₃L solutions results in maximum shifts of ca 1.5 cm^?1 for the former systems and 0.7 cm^?1 for the latter system. A rationale for this observation is presented in terms of Hammett substituent constants. Finally, an X-ray structure of the phosphine oxide of the phenylaza-15-crown-5 derivative is presented. A prominent feature of the structure is that the nitrogen atom is essentially planar with the result that the crown ether ring is large and not preorganized for coordination of spherical ions.     

Extraction of strontium from nitric acid solutions by selected crown ethers

The extraction of Sr from nitric acid solutions by the crown ethers, 12-crown-4, 15-crown-5, 18-crown-6 and DB 18-crown-6 dissolved in chloroform has been investigated. Sr is reasonably well extracted by 18-crown-6 compared to other crown ethers from different nitric acid solutions. The extraction is strongly dependent on the concentration of HNO₃ and nitrate salts. Preliminary studies indicate that¹³⁷Cs is also extracted to a limited extent by 18-crown-6 from nitrate medium. Stripping of Sr was achieved by an aqueous solution of low acidity, the crown ether being regenerated for subsequent extraction.     

Bis(4-benzhydryl-benzoxazol-2-yl)methane – from a Bulky NacNac Alternative to a Trianion in Alkali Metal Complexes

A novel sterically demanding bis(4-benzhydryl-benzoxazol-2-yl)methane ligand 6 (^4−BzhH2BoxCH₂) was gained in a straightforward six-step synthesis. Starting from this ligand monomeric [M(^4-BzhH2BoxCH)] (M=Na ( 7 ), K ( 8₁ )) and dimeric [{M(^4-BzhH2BoxCH)}₂] (M=K ( 8₂ ), Rb ( 9 ), Cs ( 10 )) alkali metal complexes were synthesised by deprotonation. Abstraction of the potassium ion of 8 by reaction with 18-crown-6 resulted in the solvent separated ion pair [{(THF)₂K@(18-crown-6)}{bis(4-benzhydryl-benzoxazol-2-yl)methanide}] ( 11 ), including the energetically favoured monoanionic (E,E)-(^4-BzhH2BoxCH) ligand. Further reaction of ^4−BzhH2BoxCH₂ with three equivalents KH and two equivalents 18-crown-6 yielded polymeric [{(THF)₂K@(18-crown-6)}{K@(18-crown-6)K(^4-BzhBoxCH)}]_n (n→∞) ( 12 ) containing a trianionic ligand. The neutral ligand and herein reported alkali complexes were characterised by single X-ray analyses identifying the latter as a promising precursor for low-valent main group complexes.     

Complexes of Mercury(II) Cyanide with Crown Ethers in Dimethylsulfoxide

The complexation of mercury(II) cyanide with macrocyclic ligands 15-crown-5,18-crown-6 and dibenzo-24-crown-8 in dimethylsulfoxide was studied using¹⁹⁹Hg NMR measurements. No significant complexation with 15-crown-5was observed. The stability constants K_s for 1 : 1 complexes with two other ligands were determined and found to be similar, in contrary to the results reported in nitrobenzene. Solvent effects on K_s values obtained are discussed in comparison with the literature data. X-ray crystal structure of Hg(CN)₂.A18-crown-6 was also determined.     

Synthesis and crystal structure of bis[(18-crown-6)oxonium]tetrabromomanganese(II)

A new complex compound, bis[(18-crown-6)oxonium]tetrabromomanganese(II), 2[(H₃O)⁺(18-crown-6)]·[MnBr₄]^2–, was prepared and studied by X-ray diffraction to reveal its unusual cubic crystal structure, space group Fd $ \bar 3 A new complex compound, bis[(18-crown-6)oxonium]tetrabromomanganese(II), 2[(H₃O)⁺(18-crown-6)]·[MnBr₄]^2–, was prepared and studied by X-ray diffraction to reveal its unusual cubic crystal structure, space group Fd, a 20.424 ?, and Z 8. In this crystal structure, the complex cation [(H₃O)⁺(18-crown-6)] the point symmetry position and the anion [MnBr₄]²⁻ with the point symmetry 23. The complex cation [(H₃O)⁺(18-crown-6)] has a guest-host structure, and, unlike metal complexes by hydrogen bonds between H₃O⁺ hydrogens and 18-crown-6 oxygens, rather than by coordination bonds. The pyramidal cation H₃O⁺ in this crystal structure is statistically disordered, and the tetrahedral anion [MnBr₄]²⁻ is reorientationally disordered. Original Russian Text ? A.N. Chekhlov, 2008, published in Zhurnal Obshchei Khimii, 2008, vol. 78, No. 10, pp. 1622–1626.     

Synthesis and crystal structure of bis[(18-crown-6)potassium] bis(μ2-bromo)tetrabromodicopper(II)

A new complex bis[(18-crown-6)potassium] bis(μ₂-bromo)tetrabromodicopper(II), [{K(18-crown-6)}₂Cu₂Br₆] (I), is synthesized and studied by X-ray diffraction analysis (space group P2₁/n, a = 9.137 Å, b = 34.860 Å, c = 13.414 Å, β = 99.53°, Z = 4). The structure is solved by a direct method and refined by the fullmatrix least-squares method in the anisotropic approximation to R = 0.083 for 5850 independent reflections (CAD-4 automated diffractometer, λMoK _α radiation). Complex molecule I consists of the central binuclear anion [Cu₂Br₆]^2? and two peripheral cations K(18-crown-6)]⁺ of the host-guest type bound to the [Cu₂Br₆]^2? anion through two and one K-Br coordination bonds. In the [Cu₂Br₆]^2? anion, the coordination polyhedra of two Cu atoms can be described as strongly flattened tetrahedra. In two [K(18-crown-6)]⁺ fragments, the coordination polyhedra of their K⁺ cations (coordination numbers 8 and 7) are distorted hexagonal pyramids with a base of six O atoms of the 18-crown-6 ligand and a bifurcated or ordinary vertex: the Br atoms of the [Cu₂Br₆]^2? anion. Two 18-crown-6 ligands have a standard crown conformation.     

Crown Ether As The Phase-Transfer Catalyst for Free Radical Polymerization of Hydrophobic Vinyl Monomers

Various crown ethers were used as phase-transfer catalysts for free radical polymerizations of some water-insoluble vinyl monomers such as acrylonitrile, methylmethacrylate and styrene with persulfate as initiator. The catalytic abilities of these crown ethers for free radical polymerization of acrylonitrile with S₂O₈^2?ion as an initiator were in the order: 18-crown-6 > 15-crown-4 > 12-crown-4 > benzo-15-crown-5 > dibenzo-18-crown-6. Among various persulfates such as Na₂S₂O₈ K₂S₂O₈ and (NH₄)₂S₂O₈, ammonium persulfate was the optimum initiator for the polymerization of acrylonitrile catalyzed by 18-crown-6 or 15-crown-5. Among the organic solvents used, chloroform seems to be the best solvent for the catalytic polymerization of acrylonitrile. An apparent activation energy of 72.9 kJ mol^?1 was observed for the polymerization of acrylonitrile. The catalytic reaction rates of free radical polymerization for these hydrophobic vinyl monomers were in the order: acrylonitrile > methylmethacrylate > styrene > isoprene. Effects of concentrations of crown ether, initiator, and nitrogen on the polymerization of these vinyl monomers were investigated.     

Ionische Kronenetherkomplexe von Zinn(II) und Zinn(IV): [Sn(15-Krone-5)] [SnCl6] und [SnCl3(18-Krone-6)]2[Sn2Cl10]; Synthesen,IR-Spektren und 119Sn-Mößbauer-Spektren

Ionic Crown Ether Complexes of Tin(II) and Tin(IV): [Sn(15-Crown-5)][SnCl₆] and [SnCl₃(18-Crown-6)]₂[Sn₂Cl₁₀]; Syntheses, IR Spectra, and ¹¹⁹Sn-Mössbauer Spectra [Sn(15-crown-5)][SnCl₆] ( 1 ,) has been prepared by the reaction of SnCl₂, SnCl₄, and 15-crown-5 in the molar ratio of 1 : 1 : 1 in acetonitrile solution, forming a white insoluble crystal powder. [SnCl₃(18-crown-6)]₂[Sn₂Cl₁₀] ( 2 ,) as well as [SnCl₃(18-crown-6)][BiCl₄] · CH₃CN ( 3 ,) are prepared by the reaction of SnCl₄ with 18-crown-6 (molar ratio 2 : 1), and of SnCl₄, 18-crown-6, and BiCl₃ (molar ratio 1 : 1 : 1), respectively. According to IR-spectroscopy and ¹¹⁹Sn-Mössbauer-spectroscopy 1–3 , have ionic structures; the cation of 1 , being polymeric via a sandwich-like structure.     

Kronenetherkomplexe von Blei(II). Die Kristallstrukturen von [PbCl(18-Krone-6)][SbCl6], [Pb(18-Krone-6)(CH3CN)3][SbCl6]2, and [Pb(15-Krone-5)2][SbCl6]2

Crown Ether Complexes of Lead(II). The Crystal Structures of [PbCl(18-Krone-6)][SbCl₆], [Pb(18-Krone-6)(CH₃CN)₃][SbCl₆]₂ und [Pb(15-Krone-5)₂][SbCl₆]₂ . [PbCl(18-crown-6)][SbCl₆] has been prepared in low yield besides [Pb(CH₃)₂(18-crown-6)][SbCl₆]₂ by the reaction of Pb(CH₃)₂Cl₂ with antimony pentachloride in acetonitrile solution in the presence of 18-crown-6, forming pale-yellow crystals. The other two title compounds are formed as colourless crystals by the reaction of PbCl₂ with antimony pentachloride in acetonitrile solutions in the presence of 18-crown-6 and 15-crown-5, respectively. The complexes were characterized by IR spectroscopy and by crystal structure determinations. [PbCl(18-crown-6)][SbCl₆]: Space group P2₁/c, Z = 8, 5 003 observed unique reflections, R = 0.046. Lattice dimensions at - 80°C: a = 1 386.9; b = 1 642.7; c = 2 172.1 pm, β = 92.95°. The lead atom in the cation [PbCl(18-crown-6)]⁺ is surrounded in an almost hexagonal-planar construction by the six oxygen atoms of the crown ether and an axially oriented Cl atom. [Pb(18-crown-6)(CH₃CN)₃][SbCl₆]₂: Space group P1 , Z = 2, 6 128 observed unique reflections, R = 0.076. Lattice dimensions at - 70°C: a = 1 228.0; b = 1 422.9; c = 1 463.2 pm, α = 69.08°; β = 65.71°; γ = 64.51°. In the cation [Pb(18-crown-6)(CH₃CN)₃]²⁺ the lead atom is coordinated by the six oxygen atoms of the crown ether and by the three nitrogen atoms of the acetonitrile molecules. The structure determination is restricted by disorder. [Pb( 15-crown-5)₂][SbCI₆]₂: Space group P6₃/m, Z = 6, 5 857 observed unique reflections, R = 0.059. Lattice dimensions at -70°C: a = b = 2 198.5; c = 1499.4 pm, α = β = 90°, γ = 120°. In the cation [Pb(l5-crown-5)₂]² the lead atom is sandwich-like coordinated by the ten oxygen atoms of the two crown ether molecules. The structure determination is restricted by disorder.