Silbermercaptide und -mercaptokomplexe

The complex formation of silver(I) has been studied with the anions of simple mercaptans RSH which have been rendered soluble by replacing some H in the substituent R by OH. All equilibria constants refer to a solvent of ionic strength μ = 0,1 and 20°C. Monothioglycol HO? CH₂? CH₂? SH (pK = 9.48) forms an amorphous insoluble mercaptide {AgSR} (s), ionic product [Ag⁺] [SR^?] = 10^?19.7. The solution in equilibrium with the solid contains the molecule AgSR at a constant concentration of 10^?6.7 M which furnishes the formation constant of the 1:1-complex: K₁ = 10^{13. 0}. The solid is soluble in excess of mercaptide (AgSR+SR^? → Ag(SR)₂^?: K₂ = 10^{4. 8}) as well as in an excess of silver ion (AgSR + Ag⁺ → Ag₂SR⁺K ≈? 10⁶). With the bulky monothiopentaerythrite (HO? CH₂? )₃C? CH₂? SH (pK = 9.89) no precipitation occurs with silver when the mercaptan concentration is below 10^{?3. 2}M. A single polynuclear Ag₁₀(SR)₉⁺ (β_10.9 = 10¹⁷⁵) is formed in acidic solutions which breaks up with the formation of Ag₂SR⁺ (β_2.1 = 10^19.0) when an excess of silver ion is added. Below the mononuclear wall ([RS]_total < 10^?6) Ag₂SR⁺ is formed via the mononuclear AgSR (K₁ = 10¹³). At higher mercaptan concentrations ([RS]_tot > 10^?3.2) an amorphous precipitate is formed which has almost the same solubility product as silver thioglycolate ([Ag⁺] [SR^?] = 10^?19.1). Apparently silver(I) forms with mercaptans always the complexes Ag₂SR⁺, AgSR and Ag(SR)₂^?. Above the mononuclear wall, these species condense to chain-like polynuclears which are cations Ag(SRAg)_n⁺ in presence of an excess of Ag⁺, and anions SR (AgSR)_n^? when the concentration [RS^?] is larger than [Ag⁺]. Usually n becomes rapidly very large as soon as the condensation starts (n → ∞: precipitate). The decanuclear Ag(SRAg)₉⁺ formed with thiopentaerythrit is somewhat more stable than the shorter chains (n < 9) and larger chains (n > 9), because it can tangle up to a ball by coordination of bridging mercapto-sulfur to the terminal silver ions (figure 12, page 2179). This ball seems to be further stabilized by hydrogen bonds between the many alcoholic OH groups of the substituent R = (HO? CH₂)₃C? CH₂? . The stability of the bonds Ag? S, however, is little influenced by the substituent R which carries the mercaptide sulfure.     

Formation and Stability of Binary Complexes of Divalent Ecotoxic Ions (Ni, Cu, Zn, Cd, Pb) with Biodegradable Aminopolycarboxylate Chelants (dl-2-(2-Carboxymethyl)Nitrilotriacetic Acid, GLDA, and 3-Hydroxy-2,2′-Iminodisuccinic Acid, HIDS) in Aqueous Solutions

The protonation and complex formation equilibria of two biodegradable aminopolycarboxylate chelants {dl-2-(2-carboxymethyl)nitrilotriacetic acid (GLDA) and 3-hydroxy-2,2??-iminodisuccinic acid (HIDS)} with Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ ions were investigated using the potentiometric method at a constant ionic strength of I?=?0.10?mol·dm^?3 (KCl) in aqueous solutions at 25?±?0.1?°C. The stability constants of the proton?Cchelant and metal?Cchelant species for each metal ion were determined, and the concentration distributions of various complex species in solution were evaluated for each ion. The stability constants (log₁₀ K _ML) of the complexes containing Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ ions followed the identical order of log₁₀ K _CuL?>?log₁₀ K _NiL?>?log₁₀ K _PbL?>?log₁₀ K _ZnL?>?log₁₀ K _CdL for either GLDA (13.03?>?12.74?>?11.60?>?11.52?>?10.31) or HIDS (12.63?>?11.30?>?10.21?>?9.76?>?7.58). In each case, the constants obtained for metal?CGLDA complexes were larger than the corresponding constants for metal?CHIDS complexes. The conditional stability constants (log₁₀ $ K_{\text{ML}}^{'} $ ) of the metal?Cchelant complexes containing GLDA and HIDS were calculated in terms of pH, and compared with the stability constants for EDTA and other biodegradable chelants.     

Polyamines XV. Thermodynamics of Metal Complex Formation of Linear Tetraamines Containing Two Ethylenediamine Residues

The complex formation of Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Pb²⁺ and Hg²⁺ with three tetraamines of type H₂N? (CH₂)₂? NH? (CH₂)_n? NH? (CH₂)₂? NH₂ (= 2, n, 2-tet) for n = 2. 3 and 4, and with N-methylethylenediamine (= nmen) have been investigated at 25° and I = 1(KNQ₃). The stability constants and the heat evolved by formation of the (1:1)-complexes ML have been determined. It is shown that the more stable complexes are normally formed by 2,3,2-tet-ligands. These results are discussed relating the thermodynamic data obtained to the stereochemistry of the complexes and using the visible spectra of the complexes in solution. The change in enthalpy is found to be the dominant factor and the measure of the steric strain whereas the entropy of complex formation decreases slowly.     

Equilibrium investigation of complex formation reactions involving copper(II), nitrilo-tris(methyl phosphonic acid) and amino acids,peptides or DNA constitutents. The kinetics,mechanism and correlation of rates with complex stability for metal ion promoted hydrolysis of glycine methyl ester

The complex formation reactions of [Cu(NTP)(OH₂)]^4? (NTP?=?nitrilo-tris(methyl phosphonic acid)) with some selected bio-relevant ligands containing different functional groups, are investigated. Stoichiometry and stability constants for the complexes formed are reported. The results show that the ternary complexes are formed in a stepwise mechanism whereby NTP binds to copper(II), followed by coordination of amino acid, peptide or DNA. Copper(II) is found to form Cu(NTP)H _n species with n?=?0, 1, 2 or 3. The concentration distribution of the various complex species has been evaluated. The kinetics of base hydrolysis of glycine methyl ester in the presence of copper(II)-NTP complex is studied in aqueous solution at different temperatures. It is proposed that the catalysis of GlyOMe ester occurs by attack of OH^? ion on the uncoordinated carbonyl carbon atom of the ester group. Activation parameters for the base hydrolysis of the complex [Cu(NTP)NH₂CH₂CO₂Me]^4? are, ΔH^±?=?9.5?±?0.3?kJ?mol^?1 and ΔS^±?=??179.3?±?0.9?J?K^?1?mol^?1. These show that catalysis is due to a substantial lowering of ΔH^±.     

Gas-phase reactions of doubly charged alkaline earth and transition metal complexes of acetonitrile, pyridine, and methanol generated by electrospray ionization

Formation and low energy collision-induced dissociation (CID) of doubly charged metal(II) complexes ([metal(II)+L _n ]²⁺, metal(II)=Co(II), Mn(II), Ca(II), Sr(II) and L = acetonitrile, pyridine, and methanol) were investigated. Complexes of [metal(II)+L _n ]²⁺ where n≤7 were obtained using electrospray ionization. Experimental parameters controlling the dissociation pathways for [Co(II)+(CH₃CN)₂]²⁺ were studied and a strong dependence of these processes on the collision energy was found. However, the dissociation pathways appear to be independent of the cone potential, indicating low internal energy of the precursor ions. In order to probe how these processes are related to intrinsic parameters of the ligand such as ionization potential and metal ion coordination, low energy CID spectra of [metal(II)+L _n ]²⁺ for ligands such as acetonitrile, pyridine, and methanol were compared. For L = pyridine, all metals including the alkaline earth metals Ca and Sr were reduced to the bare [metal(I)]⁺ species. Hydride transfer was detected upon low energy CID of [metal(II)+L _n ]²⁺ for metal(II)=Co(II) and Mn(II) and L = methanol, and corroborated by signals for [metal(II)+H^?]⁺ and [metal(II)+H^?+CH₃OH]⁺, as well as by the complementary ion [CH₃O]⁺.     

Thermodynamik der Metallkomplexbildung mit Polyoxadiazamacrocyclen

Ligands of the type H_3-nN(CH₂CH₂OCH₂CH₂OCH₂CH₂)_nNH_3?n with n values from 1 to 3 have been investigated. The stability constants and the heat evolved by formation of the 1:1 complexes of Na⁺, K⁺, Rb⁺, Tl⁺, Ca²⁺, Sr²⁺, Ba²⁺, Cd²⁺, Ag⁺, Hg²⁺ and Pb²⁺ have been determined. The complex formation is discussed in terms of ΔH and ΔS taking into consideration the radii of the cations. In contrast with the normal trend, for the A cations, complex formation is exothermic and almost exclusively favoured by the reaction enthalpy.     

Phenylmethoxybis(tetrazolium) ion-association complexes with an anionic indium(III) — 4-(2-pyridylazo)resorcinol chelate

Complex formation and liquid-liquid extraction were studied in systems containing indium(III), 4-(2-pyridylazo)resorcinol (PAR), phenylmethoxybis(tetrazolium) salt (MBT), water and chloroform. The following MBTs, which differ only by the number of -NO₂ groups in their cationic parts, were used: 3,3′-(3,3′-dimetoxy-4,4′-biphenylene)bis(2,5-diphenyl-2H-tetrazolium chloride) (Blue Tetrazolium chloride, BT), 3,3′-(3,3′-dimetoxy-4,4′-biphenylene)bis[2-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride] (Nitro Blue Tetrazolium chloride, NBT) and 3,3′-(3,3′-dimetoxy-4,4′-biphenylene)bis[2,5-di(4-nitrophenyl)-2H-tetrazolium chloride] (Tetranitro Blue Tetrazolium chloride, TNBT). The composition of the formed ternary complexes was determined, In:PAR:MBT=1:2:2, and the optimum conditions for their extraction found: pH, shaking time, concentration of the reagents and the sequence of their addition. Some key constants were estimated: constants of extraction (K_ex), constants of association (β) and constants of distribution (K_D). BT appears to be the best MBT for extraction of the In(III)-PAR species, [In³⁺(OH)₃(PAR)₂]^4?, (Log K_ex=10.9, Log β=9.8, Log K_D=1.12, R%=92.7%). Several additional characteristics concerning its application as extraction-spectrophotometric reagent were calculated: limit of detection (LOD = 0.12 μg cm^?3), limit of quantification (LOD = 0.40 μg cm^?3) and Sandell’s sensitivity (SS =1.58 ng cm^?2); Beer’s law is obeyed for In(III) concentrations up to 3.2 μg mL^?1 with a molar absorptivity coefficient of 7.3×10⁴ L mol^?1 cm^?1 at λ_max=515 nm.      

Aluminum-27 NMR studies of alcoholic (2-hydroxyethyl)trimethylammonium aluminate solutions

²⁷Al NMR spectroscopy is a power tool for investigation of the aluminate species existing in both aqueous and non-aqueous solutions. Aluminum-27 nuclear magnetic resonance (NMR) spectroscopy also can be used to determine thermodynamic properties of complexes in the solution. In this report, ²⁷Al NMR spectroscopy was used to characterize species present in alkaline alcoholic aluminate solutions. (2-Hydroxyethyl)trimethylammonium (2-EHTMA) hydroxide was used as base. In solution of CH₃OH and H₂O in a mole ratio of 64:1 it was possible to detect five signals by aluminum-27 NMR, indicating formation of [Al(OH)_4−n(CH₃OH)_n]⁽ⁿ⁻¹⁾⁺ (n = 0,1, 2, 3 and 4) species. Aluminum-27 NMR spectroscopy has also used for investigation of the species present in the ethanolic 2-HETMA aluminate solutions. The equilibrium constants for the formation of aluminate complexes were also determined for both methanolic and ethanolic aluminate solutions. Aluminum-27 NMR spectra of propanolic and butanolic 2-HETMA aluminate solutions were also studied.     

Spectra and structure of iron(III) complexes with carbamide derivatives containing an acetyl group

Equilibria of complex formation reactions of Fe^III in aqueous solutions with CH₃CONHCONH₂ and CH₃CONHCONHCH₃ were investigated by the UV spectral method. The formation of complexes of [Fe(H₂O)_6-nL_n]⁺³ (where n = 1, 2) has been established and their stability constants determined. The following crystalline complexes have been obtained: [Fe(CH₃CONHCONH₂ )₃ ]Cl₃ and [Fe(CH₃CONHCONHCH₃)₃]Cl₃, and their structures investigated using IR and NMR spectra. Results suggest that they are six-membered ring structures. The influence of the polar effects of substituents on the stability of iron(III) complexes with acetylcarbamides has been discussed and mesomeric effects have been shown to dominate inductive effects and work in opposite directions.     

KINETICS OF FORMATION AND STABILITY CONSTANTS OF MONO AND BIS l-TYROSINE COMPLEXES OF Cu(II), Co(II), AND Ni(II)

Abstract

The kinetics and stability constants of l-tyrosine complexation with copper(II), cobalt(II) and nickel(II) have been studied in aqueous solution at 25° and ionic strength 0.1 M. The reactions are of the type M(HL)^(3-n)+ _n-1 + HL- ? M(HL)^(2-n)+_n(k_n, forward rate constant; k_-n, reverse rate constant); where M=Cu, Co or Ni, HL^? refers to the anionic form of the ligand in which the hydroxyl group is protonated, and n=1 or 2. The stability constants (K_n=k_n/k_-n) of the mono and bis complexes of Cu²⁺, Co²⁺ and Ni²⁺ with l-tyrosine, determined by potentiometric pH titration are: Cu²⁺, log K₁=7.90 ± 0.02, log K₂=7.27 ± 0.03; Co²⁺, log K₁=4.05 ± 0.02, log K₂=3.78 ± 0.04; Ni²⁺, log K₁=5.14 ± 0.02, log K₂=4.41 ± 0.01. Kinetic measurements were made using the temperature-jump relaxation technique. The rate constants are: Cu²⁺, k₁=(1.1 ± 0.1) × 10⁹ M ^?1 sec^?1, k_-1=(14 ± 3) sec^?1, k₂=(3.1 ± 0.6) × 10⁸ M ^?1 sec^?1, k^?2=(16 ± 4) sec^?1; Co²⁺, k₁=(1.3 ± 0.2) × 10⁶ M ^?1 sec^?1, k_-1=(1.1 ± 0.2) × 10² sec^?1, k₂=(1.5 ± 0.2) × 10⁶ M ^?1 sec^?1, k_-2=(2.5 ± 0.6) × 10² sec^?1; Ni²⁺, k₁=(1.4 ± 0.2) × 10⁴ M ^?1 sec^?1, k_-1=(0.10 ± 0.02) sec^?1, k₂=(2.4 ± 0.3) × 10⁴ M ^?1 sec^?1, k_-2=(0.94 ± 0.17) sec^?1. It is concluded that l-tyrosine substitution reactions are normal. The presence of the phenyl hydroxyl group in l-tyrosine has no primary detectable influence on the forward rate constant, while its influence on the reverse rate constant is partially attributed to substituent effects on the basicity of the amine terminus.     

Complex formation of mono-and binuclear dimeric cyclophane zinc diphenylporphyrinates with pyridine

The formation of host-guest complexes between zinc diphenylporphyrinates of dimeric diphenylporphyrins and pyridine in toluene has been studied by the spectrophotometric titration method and ¹H NMR spectroscopy. The zinc porphyrinates with pyridine form “internal” or “external” 1: 1 or 1: 2 complexes, depending on the length of binding ether O(CH₂)_nO bridges (n = 2, 3) of the cyclophane dimers and the reactant concentration. The stability constants of the porphyrinate-ligand complexes and concentration ranges of their formation have been determined.     

The preparation and reactions of group IIB metal chloride stabilized complexes of (chlorofluoromethylene)tris(dimethylamino)phosphorane

A facile dechlorination reaction occurs between [((CH₃)₂N)₃⁺PCFCl₂]Cl^? and Group IIB metals to form addition complexes of the type [((CH₃)₂N)₃P⁺ CFCl-(MCl)]Cl^? where M = Zn, Cd, or Hg. These complexes exhibit surprising stability in ethereal solvents, and serve as effective 1-chloro-1-fluorovinyl transfer agents via the Wittig reaction by dissociation into [(CH₃)₂N]₃PCFCl and the metal chloride. ¹⁹F and ³¹P NMR, as well as derivative formation, substantiate that these complexes are indeed quaternary phosphonium compounds which contain covalent carbonmetal bonds.     

Gleichgewichte der Protonenaddition an 1, 1-Bis-(4′, 4″-dimethylaminophenyl)-äthylen in Methanol und in Dimethylsulfoxid

The first and second proton addition equilibrium constants of 1,1-bis-(4′, 4″-dimethylaminophenyl)-ethylene ( 1 ) have been measured by the spectrophotometric method in methanol and in dimethylsulfoxide. Defined as acid dissociation constants of the mono- and diprotonated adduct they are: K₁ (CH₃OH) = 8.3 (± 0.9) · 10^?6M, K₂ (CH₃OH) = 1.22 (± 0.06) · 10^?4M, K₁ (DMSO) = 2.3 (± 0.9) · 10^?3M, K₂ (DMSO) ≥ 1M. The evaluation of the electronic and the NMR. spectra demonstrates that the equilibrium of the two monoprotonated tautomers 2 (methyl-carbenium ion) and 3 (ammonium ion) is, in methanol to about 96% on the side of the ammonium ion (tautomeric equilibrium constant K₂₃ = [3]/[2] ? 23). The tautomer 2 cannot be detected in dimethylsulfoxide. The possible causes of these solvent effects are discussed.     

Supramolecular assembler based on cucurbit[8]uril: Photodimerization of a styryl dye in water

Photolysis of aqueous solutions of styryl dye 1 in the presence of cucurbit[8]uril (CB[8]) has been studied by optical spectroscopic methods for the molar ratios n = c _CB[8]/c ₁ in the range of 0 ≤ n ≤ 6. It has been found that the inclusion complexes (1)₂@CB[8] dominate in the solution at n ≤ 0.5, whereas the complexes 1@CB[8] dominate at n ≥ 1. The stability constants have been determined for the 1: 1 (log K ₁ = 6.2 (L mol^?1)) and 2: 1 (log β = 11.9 (L² mol^?2)) complexes. The fluorescence decay kinetics of dye 1 in the presence of CB[8] is two-exponential, with the average lifetime increasing substantially at n ≥ 1. It has been shown that the system can operate in the cyclic mode as an assembler (or supramolecular catalyst) in the photodimerization reaction of dye 1 to form cyclobutane derivative 2. The stability constant of the complex 2@CB[8] (log K ₃ = 5.9 (L mol^?1)) and the quantum yield of cycloaddition (? ≈ 0.07 at n ≈ 0.5) have been determined.     

Complex Formation of PdII Ion with the Tripodal Ligand Tris[2-(dimethylamino)ethyl]amine

The complex formation of Pd^II with tris[2-(dimethylamino)ethyl]amine (N(CH₂CH₂N(CH₃)₂)₃, Me₆tren) was investigated at 25° and ionic strength I = 1, using UV/VIS, potentiometric, and NMR measurements. Chloride, bromide, and thiocyanate were used as auxiliary ligands. The stability constant of [Pd(Me₆tren)]²⁺ in various ionic media was obtained: log β([Pd(Me₆tren)] = 30.5 (I = 1(NaCl)) and 30.8 (I = 1(NaBr)), as well as the formation constants of the mixed complexes [Pd(HMe₆tren)X]²⁺ from [Pd(HMe₆tren)(H₂O)]³⁺:log K = 3.50 = Cl^?) and 3.64 (X^? = Br^?) and [Pd(Me₆tren)X]⁺ from [Pd(Me₆tren)(H₂O)]²⁺: log K = 2.6 (X^? = Cl^?), 2.8(Br^?) and 5.57 (SCN^?) at I = 1 (NaClO₃). The above data, as well as the NMR measurements do not provide any evidence for the penta-coordination of Pd^II, proposed in some papers.     

Synthesis of pyridine N-imine complexes of methylcobaloxime and reactions of bis(dimethylglyoximato)methyl(Pyridine N-imine)cobalt with acid anyhydrides and acetylenedicarboxylic acid dimethyl ester

Pyridine N-imine complexes of methylcobaloxime, CH₃Co(Hdmg)₂(R¹— C₅H_nN⁺N^?H) (n = 4; R¹ = H, 2-CH₃, 3-CH₃, 4-CH₃: n = 3; R¹ = 2,6-CH₃), have been synthesized by the reaction of CH₃Co(Hdmg)₂S(CH₃)₂ with a pyridine N-imine which is generated from a pyridine, hydroxylamine-O-sulfonic acid and K₂CO₃. The reactions of CH₃Co(Hdmg)₂(C₅H₅N⁺N^?H) with acid anhydrides form new methylcobaloxime complexes with N-substituted pyridine N-imines, CH₃Co(Hdmg)₂(C₅H₅N⁺N^?R²) R² = COPh, COMe, COEt). With maleic anhydride, (pyridine N-acryloylimine)carboxylic acid is formed. With acetylenedicarboxylic acid dimethyl ester, 1,3-dipolar cycloaddition of the ligand gives pyrazolo[1,5-a]pyridine-2,3-dicarboxylic acid dimethyl ester.     

α, ω-Alkan-bis-dimethylarsansulfide und -selenide,eine neue Klasse von Liganden

α ω-Alkane-bis-dimethylarsine Sulfides and Selenides, a Novel Class of Ligands The reaction of α,ω-alkane-bis-dimethylarsanes (CH₃)₂As? (CH₂)_n? As (CH₃)₂ with sulfur and selenium results in formation of the sulfides and selenides, respectively, (CH₃)₂As(X)? (CH₂)_n? As(CH₃)₂ or (CH₃)₂As(X)? (CH₂)_n? As(X)(CH₃)₂ (X = S, Se), which form chelat-complexes with the salts CoX₂ · 6 H₂O (X = Cl^?, Br^?, I^?, NO₃^?). The UV-spectra of the complexes are presented and discussed.     

Study on the Binding of Chloride Ion to Hemoglobin Using Electromotive Force Method

The electromotive force of the concentration cell, in which both half‐cells contain the same concentration of sodium chloride, and one of which also contains hemoglobin (Hb), was measured on the isoelectric point of Hb (pH = 6.70). On the basis of Scatchard equation, a stepwise binding model and an improved calculation method were presented. Using the new calculation method, the number of the chloride‐binding sites on Hb molecule and the corresponding binding constants were calculated. The results show that there are three classes of binding groups on a Hb molecule, the number of the binding sites and the corresponding binding constants are n₁ = 1, K⁰₁ = 245; n₂ = 8, K⁰₂ = 3.50; n₃ = 8, K⁰₃ = 1.91, respectively. The factors of influencing the interaction between Cl^? and Hb molecule were clarified, and that the differences between our results and the results of computer modeling, as well as the results of molecular dynamics simulation were also discussed.     

Kinetics of substitution on chloro-1,1,7,7-tetraethyldiethylene-triaminegold(III) in methanol-water mixtures

Summary Rate constants are reported for the replacement of chloride by bromide in the complex [Au(Et₄dien-H)⁺ in methanol-water mixtures. This reaction follows the usual two-term rate law = (k_obs = k₁ + K₂[Br^–1]) for square planar complexes in all the mixtures studied. The logarithms of the rate constants correlate with Grunwald-Winstein solvent Y values and yield slopes of 0.32 (k₁) and 0.15 (k₂). The results suggest that both reaction paths are associative.Dien complexes of gold(III) yield conjugate base species at low pH; Et₄dien-H = Et₂NCH₂CH₂NCH₂CH₂NEt₂.     

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.