The association constant of macrocyclic ether–cation interactions in 1,4-dioxane/water mixtures. III. Effect of temperature on the binding

The association constant, K_a of Na⁺ with [12]crown-4, [15]crown-5 and [18]crown-6 crown ethers were determined in a binary mixture, 1,4-dioxane/water (50/50) using a Na⁺ ion selective electrode at different temperatures. K_a values were determined with the relationship, 1/K_a [L_o]^n+m–1 = (1–nP′)ⁿ(1–mP′)^m/P′, for various stoichiometries, (n:m), where P′ is the mole fraction of the complexed cation. The exothermic association constants and the thermodynamic data for cation–macrocycle complexes explained in terms of Eigen–Winkler binding mechanism are given. The binding power found for Na⁺, however, was the highest with [18] crown-6.     

Supramolecular assemblages from uranyl complexes of calixarenes and potassium complexes of 18-crown-6 or dibenzo-18-crown-6

Reaction of uranyl nitrate with p-tert-butyl[3.1.3.1]homocalixarene (L¹H₄) or p-tert-butylcalix[8]arene (L²H₈) has been carried out in the presence of KOH and 18-crown-6 (18C6) or dibenzo-18-crown-6 (db18C6), giving the supramolecular assemblages [K(db18C6)(H₂O)₂]₃ [{UO₂(L¹)}₂K(H₂O)₅] (1) and [K(18C6)(OH)₂][{(UO₂)₂(L²H₅)(OH)}{K(18C6)}] (2). Compound 1 comprises a sandwich, “complex-within-complex” assemblage in which two uranyl/calixarene complexes encompass a potassium/crown ether guest. A direct bond between uranyl and K(18C6) is present in 2, in which a columnar arrangement of alternate dimetallic calixarene complexes and potassium/crown ether species is formed.     

Coupling of cyclohexene oxide (CHO) and carbon disulfide (CS2) catalyzed by the asymmetric bis-Schiff-base Zn(II) complex

Based on the self-assembly of the asymmetric bis-Schiff-base ligand H₂L (H₂L = 4-((E)-(2-((E)-3,5-dibromo-2-hydroxybenzylideneamino)phenylimino)(phenyl)methyl-1-(4-chlorophenyl)-3-methyl-1H-pyrazol-5-ol) and Zn(OAc)₂·2H₂O, a new [Zn(L)] (1) was obtained and shown to efficiently catalyze the coupling of CHO (cyclohexene oxide) and CS₂ (carbon disulfide) in activation with [PPN]Cl (PPN⁺ = bis(triphenylphosphoranyidene)-ammonium), n-Bu₄NBr or n-Bu₄NI, where both poly[thio]carbonates and cyclic [thio]carbonates were produced, and the strong O/S exchange afforded the limited formation of trithiocarbonate in the cyclic [thio]carbonate byproducts.     

Coordination of a Schiff base as an iminium-phenone zwitterion in a double ligand-bridged fac-[Re(CO)3]+ dimer

The ligand-bridged dimers [Re(CO)₃(μ-H₂salet)]₂ (1) and [{Re(CO)₃}₂(μ-salpd)] (2) are formed by the reactions of [Re(CO)₅Cl] with the potentially heptadentate Schiff base 2,2′,2″-tris(salicylideneimino)triethylamine (H₃salet) and the hexadentate N¹-(3-(2-hydroxybenzylidene-amino)propylamino)ethyl)-benzylidenepropane-1,3-diamine (H₂salpd) respectively. In 1, the two H₂salet ligands bridge two fac-[Re(CO)₃]⁺ moieties. Mono-dentate coordination is by a neutral phenone oxygen atom, generated by the conversion of one salicylideneimine entity to an iminium zwitter-ion. In 2 each fac-[Re(CO)₃]⁺ core resides in a ‘3 + 0’ environment. In both complexes π–π interaction between the phenolate rings contribute to the stability. The crystal structures of 1 and 2 were determined by X-ray single crystal diffraction. Spectroscopic results are also reported.     

Influence of guests and protonation on the conformation of N,N′-dipyridyl-bis-aza-18-crown-6

Crystallisation of the sodium perchlorate adduct of N,N^′-dipyridyl-bis-aza-18-crown-6 from acidic aqueous conditions yielded [(H₃O)(N,N^′-dipyridyl-bis-aza-18-crown-6)][ClO₄] and [Na·N,N^′-dipyridyl-bis-aza-18-crown-6]₂ [(H⁺)₂N,N^′-dipyridyl-bis-aza-18-crown-6][ClO₄]₄·2H₂O. The conformations of crown ethers were significantly influenced by incorporation of an H₃O⁺ or sodium ion, or protonation of the amino nitrogen atoms resulting in three different structures for the macrocycle.     

Synthesis and characterization of constrained-geometry half-sandwich sila- and germacarboranes derived from a trianionic C(cage)-appended alkyloxo-C2B9-carborane ligand

The reaction of the [nido-7-(OCH₂)-8-Me-7,8-C₂B₉H₉]³⁻ trianion with anhydrous MeMCl₃ (M=Si, Ge) in 1:1 molar ratio in dry toluene, followed by re-crystallization from a solution of toluene/heptane, resulted in the formation of the corresponding novel half-sandwich constrained-geometry group 14 metallacarboranes, closo-1-M(Me)-2-(1-η¹(σ)-OCH₂)-3-Me-η⁵-2,3-C₂B₉H₉ [M=Si (3), Ge (4)] in 48% and 56% yields, respectively.     

A strategy for controlling charge and conformation in 2,2′-bipyridine complexes for use in photonic applications

The complex [ⁿBu₄N][Cu(H1)₂]·H₂O (H₂1 = 3,3′-dihydroxy-6,6′-dimethyl-2,2′-bipyridine) is readily formed from the reaction of H₂1 with [Cu(MeCN)₄][PF₆] in the presence of [ⁿBu₄N]Br; in the solid state the anion comprises a discrete dinuclear {[Cu(H1)₂](H₂O)₂[Cu(H1)₂]}^2– unit in which two oxygen atoms of each [H1]^– ligand and two water oxygens form a chair shaped hydrogen-bonded six-membered ring.     

Synthesis of some 3-phenyl chromenone-crown ethers and equilibrium studies on complexation with ion-pair extraction of sodium and potassium dyes

6,7-Dihydroxy-3-phenyl-2H-chromenones and 7,8-dihydroxy-3-(methoxyphenyl)-2H-chromenones, o-dihydroxy-3-phenylcoumarins, were prepared from phenylacetic acid/2,4,5-trihydroxybenzaldehyde, methoxyphenylacetic acid/2,3,4-trihydroxybenzaldehyde in NaOAc/Ac₂O, respectively. 3-Aryl-6,7-dihydroxy-2H-chromenone and 3-aryl-7,8-dihydroxy-2H-chromenone reacted with the polyethylene glycol ditosylate in CH₃CN/Me₂CO₃ to afford 12-crown-4,15-crown-5, and 18-crown-6-chromenones. The purified products were identified with IR, ¹NMR, low and high resolution mass spectroscopy and elemental analysis. Liquid–liquid extractive-spectrophotometric studies of sodium and potassium ion complexes of 3a–c, 4a–h coumarin-crown ethers and anionic dyes [4-(2-pyridylazo)-resorcinol monosodium salt monohydrate (SPAR), and sodium picrate (SP), and potassium picrate (PP)], as the counter ion are described. The overall extraction equilibrium constants for the 1:1 complexes of the above coumarin-crown ethers with sodium and potassium ions, between the organic solvent and water, have been determined at 25 °C. They were conducted in various solvent–water systems maintaining an identical initial cation concentration in water, [M₀⁺]_w, and a macrocyclic ligand concentration in the organic phase, [L₀]_org, so that in all extractions [M₀⁺]_w:[L₀]_org ratios were 1:1. An ion association complex formed between the alkali-crown ether complex ion and a dye anion was extracted into the CH₂Cl₂ organic solvent, and then the dye concentration of the separated aqueous phase was measured with an ultraviolet–visible spectrophotometer. According to the study, SPAR is the best associated dye with all the coumarin-crown ethers and the extracted dye occurs as the ion-pair complex. The extraction selectivity was interpreted quantitatively by the constituent equilibrium constants, i.e. K_ext, the ion-pair extraction constant of ML⁺ and A⁻ in CH₂Cl₂.     

Chromogenic sensing of Cu(II) by imino linked thiacalix[4]arene in mixed aqueous environment

Thiacalix[4]arene based imino receptors 4–5 carrying azophenol appendage have been synthesized and studied for their binding abilities towards different metal ions (Li⁺, Na⁺, K⁺, Cd²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ag⁺, Pb²⁺ and Hg²⁺). Receptor 4 showed selective chromogenic sensing for Cu²⁺ ions in mixed aqueous conditions (THF:H₂O, 9:1 v/v).     

Two Calix-Crown Based Stationary Phases. Synthesis,Chromatographic Performance and X-ray Photoelectron Spectroscopy Investigation

Two chromatographic stationary phases, obtained by covalently linking two suitably derivatized calix[4]crown-6 and calix[4]crown-5 receptors onto silica gel, are described here. A study of their chromatographic behaviour as well as their surface composition is reported. The packing materials exhibit high selectivity toward alkali metal ions. Complete separations of Cs⁺ from K⁺ and Na⁺ were obtained when using a water/methanol mixture (80:20) as the mobile phase. In these conditions, a selectivity factor Cs⁺/Na⁺=4.10 was achieved with the silica gel-bound calix[4]crown-6. The degree of coverage of the activated silica-gel surface following the covalent attachment of the macrocycle was estimated by mean of X-ray photoelectron spectroscopy (XPS). This technique allows the first few monolayers of the material to be analysed and thus is to be preferred to conventional Elemental Analysis for similar studies. Three methods for an adequate correction of the XP signals for the presence of organic contaminants are suggested and critically compared.     

Coordinatively unsaturated molybdenum complexes with chelating cycloheptatrienyl-phosphane ligands and their use in transition metal catalysis

The synthesis of the tetrahydroborate complex [(2-iPr₂PC₆H₄-η⁷-C₇H₆)Mo(η²-BH₄)(P–Mo)] 3 containing the linked cycloheptatrienyl-phosphane ligand [2-(diisopropylphosphanyl)phenyl]cycloheptatrienyl is described, which provides the possibility to generate the 14-electron complex [(2-iPr₂PC₆H₄-η⁷-C₇H₆)Mo(P–Mo)]⁺ (4) on treatment with dimethylanilinium salts such as [HNMe₂Ph][BPh₄]. Generation of (4)BPh₄ in the presence of 2,6-dimethylphenyl isocyanide, 2,5-norbornadiene or phenylacetylene affords the diisocyanide complex (5a)BPh₄, the diolefin complex (5b)BPh₄ and the alkyne complex (6)BPh₄, respectively. The latter complex can be used for the catalytic oligomerization of phenylacetylene affording predominantly the cyclotrimers 1,3,5- and 1,2,4-triphenylbenzene.     

Blue-green photoluminescent 5- and 10-connected metal 5-(4′-carboxy-phenyl)tetrazolate coordination polymers

Hydrothermal reaction of Zn/Cd salts, NaN₃ and 4-cyanobenzoic acid via in situ [2 + 3] cycloaddition generated two blue-green photoluminescent coordination polymers [Zn(cptta)(H₂O)] (1) and [Cd(cptta)(H₂O)] (2) (H₂cptta = 5-(4′-carboxy-phenyl)tetrazole). When only metal ions are considered as nodes, 1 shows rare 5-connected Shubnikov plane topological type and 2 has unprecedented 10-connected {3¹².4²⁴.5⁹} topological type.     

4′-tert-Alkylbenzo[15]krone-5-ether. Synthesen und Kaliumthiocyanat-Komplexe

4′-tert-Alkylbenzo[15]Crown-5-Ether. Syntheses and Complexes with Potassium Thiocyanate The title compounds 4 are synthesized either by alkylation of pyrocatechole 1 in 4-position and followed by ring closure with 1,11-dichloro-3,6,9-trioxaundecane or by alkylation of benzo[15]-crown-5 3 . In most cases the way first mentioned gives better results. Analytical samples of the alkylated benzo[15]crown-5 ethers 4 are obtained through complexing with KSCN. Physical data and ¹H-n.m.r.-spectra of 5 new pyrocatecholes 2 and 6 new benzo[15]crown-5 ethers 4 are given.     

Cobaltacarboranes [closo-(9-R2N-1,7,9-C3B8H10)-commo-2,(3′)-Co-(1′,2′-C2B9H11)] (where R=H and Me) — crossover complexes between metallatricarbollides and metalladicarbollides

Reactions between 7-L-nido-7,8,9-C₃B₈H₁₀ compounds (where L=Bu^tNH₂ and Me₂NH) and [NMe₃H]⁺[7,8-C₂B₉H₁₂]⁻ in the presence of NaH, followed by the addition of anhydrous CoCl₂ and prolonged heating in diglyme at reflux, resulted in the isolation of mixed-ligand 12-vertex cobaltacarboranes [closo-(9-R₂N-1,7,9-C₃B₈H₁₀)-commo-2,(3′)-Co-(1′,2′-C₂B₉H₁₁)] (where R=H or Me). These represent neutral, crossover complexes between metallatricarbollides and metalladicarbollides and contain amino groups attached to p-positions with respect to the metal centre.     

Controlled synthesis of lanthanide–lithium inverse crown ether complexes

An ytterbium–lithium inverse crown ether complex stabilized by amine-bridged bis(phenolate) ligands (LYbBr)₂(μ₄-O)(μ₃-Li) (1) [L = Me₂NCH₂CH₂N{CH₂-(2-O- C₆H₂-Bu^t₂-3,5)}₂] was isolated as a byproduct from the reaction of LYbCl(THF) with CH₃Li in THF in a very low isolated yield. Further study revealed that the inverse crown ether complexes can be synthesized in a controlled manner by the reaction of bis(phenolate) lanthanide chloride with an in situ mixture of n-BuLi with water in THF. A second inverse crown ether complex (L′YbCl)₂(μ₄-O)(μ₃-Li) (2) [L′ = Me₂NCH₂CH₂N{CH₂-(2-O-C₆H₂-Bu^t-3-Me-5)}₂] was prepared in high isolated yield and well characterized.     

Synthesis and characterization of a novel cyclic tetranuclear CoII4 cluster consisting of a quadrilateral core

A novel cyclic tetranuclear cluster, [Co(H₂O)₆][Co₄(ccdp)₂(H₂O)₄]·8H₂O·2CH₃CN (1) with cobalt(II) ions sitting in a quadrilateral has been synthesized and fully characterized by exploiting the flexibility, chelating ability and bridging potential of a carboxylate rich dinucleating ligand, H₅ccdp [H₅ccdp = N,N^′-Bis[2-carboxybenzomethyl]-N,N^′-Bis[carboxymethyl]-1,3-diaminopropan-2-ol]. The crystal structure of 1 contains a [Co₄^II(H₂O)₄)]^2– core unit which is held together by two bridging benzoate potions of the ligands, ccdp^5–. Furthermore, the [Co₄^II(H₂O)₄)]^2– core unit is stabilized and charge neutralized by intermolecular hydrogen bonding and [Co(H₂O)₆]²⁺, respectively.     

Ionic liquid crystals from β-diketonyl containing pyridinium cations and tetrachlorozincate anions

In this work, an approach towards ionic liquid crystals is strategically designed. A pyridine group has been attached to an 1,3-diketone containing an alkyloxyphenyl R substituent (R = C₆H₄OC_nH_2n+1; n = 10–18) and protonated with hydrochloric acid towards the formation of the chloride salts of 2-[3-(4-n-alkyloxyphenyl)propane-1,3-dion-1-yl]pyridinium cations [OO^R(n)py]Cl (I), which have been proved to be non-mesomorphic. Reaction of these organic–inorganic compounds (I) with ZnCl₂ yields to the ionic liquid crystals of the type bis{2-[3-(4-n-alkyloxyphenyl)propane-1,3-dion-1-yl]pyridinium}tetrachlorozincate [OO^R(n)py]₂[ZnCl₄] (II).The crystalline structure of compounds [OO^R(12)py]Cl and [OO^R(10)py]₂[ZnCl₄] as representative examples of both kinds of salts have been solved and discussed. Both compounds exhibit layered structures containing cationic and anionic sublayers. In addition for the tetrachlorozincate salt [OO^R(16)py]₂[ZnCl₄] structural relationships between the mesophases and the crystalline phase are proposed on the basis of the variable-temperature small-angle X-ray diffraction studies.     

Synthesis and characterization of potential NO donors: novel iron–sulfur nitrosyls containing the μ-N–C–S skeleton

Binuclear paramagnetic nitrosyl iron complexes of “g∼2.03 family” were first synthesized. Their structure and properties differ from those of “the red Roussin salt ethers”. The novel nitrosyl iron complexes: [Fe₂(μ₂-SR)₂(NO)₄]·nH₂O (η¹-S, η¹-N), n=1–2, R – 3-amino-1,2,4-triazolyl (1), 1,2,4-triazolyl (2), 1-methyl-tetrazolyl (3), benzothiazolyl (4) were obtained by the exchange reaction of Na₂Fe₂(S₂O₃)₂(NO)₄ with heterocyclic thiols and studied by methods of EPR, IR and Mössbauer spectroscopy. The molecular structure of complex 1 was determined by X-ray analysis.     

Synthesis,characterization and catalytic activity of a new sandwich-type tungstophosphate functionalized by carboxyethyltin

Reaction of the trivacant Keggin-type tungstophosphate (A-α-Na₉PW₉O₃₄⋅ 7H₂O, abbreviated as {PW₉}) with estertin (Cl₃Sn(CH₂)₂COOCH₃) in an acetate buffer solution leads to the formation of a new sandwich-type tungstophosphate functionalized by carboxyethyltin, Na₃K₈[K₃{Sn(CH₂)₂COO}₂(A-α-PW₉O₃₄)₂]·18H₂O (1). The title compound was characterized by single crystal X-ray diffraction, elemental analysis, IR, TG, PXRD, ¹³C, ³¹P and ¹¹⁹Sn NMR. Structural analysis reveals that the basic skeletal structure of 1 is made up of two [Sn(CH₂)₂COO]^2 + groups and three K⁺ ions sandwiched by two A-α-[PW₉O₃₄]^9 − building blocks, which shows the original estertin precursors hydrolyzed into carboxyethyltin. The catalytic activity of 1 has been investigated.     

Synthesis,structure and properties of a novel 3D pentanuclear [Zn5(OH)2]8 + cluster-based (3,4,11)-connected coordination polymer

A novel coordination polymer based on the multidentate N-donor ligand 1-((1H-1,2,4-triazol-1-yl)methyl)-3,5-bis(3-pyridyl)-1,2,4-triazole (3,3′-tmbpt) and 1,2,4,5-benzenetetracarboxylate anion (btec), namely, [Zn₅(3,3′-tmbpt)(btec)₂(OH)₂] (1), has been synthesized hydrothermally. Compound 1 displays a rare 3D (3,4,11)-connected framework based on a [Zn₅(OH)₂]^8 + cluster. The optical band gap and photoluminescent property of compound 1 have been studied.