Complex formation of dimeric cyclophane zinc diphenylporphyrinates with 1,4-diazabicyclo[2,2,2]octane and pyrazine

The formation of host-guest complexes between dimeric cyclophane zinc diphenylporphyrinates and bidentate ligands of different nature containing two nitrogen atoms has been studied by the spectrophotometric titration method and ¹H NMR spectroscopy in a toluene-methanol (2: 1) binary solvent. The complexation of these dimeric porphyrinates with 1,4-diazabicyclo[2,2,2]octane or pyrazine can lead to 1: 1 or 1: 2 complexes, depending on the metalloporphyrin-to-ligand molar ratio. The stability constants of the porphyrinate-ligand complexes and concentration ranges of their formation have been determined.     

Phosphoryl Containing Podands as Carriers in Plasticized Membrane Electrodes Selective to Quaternary Ammonium Surfactants

Open chain polyethers with phosphoryl-containing terminal groups have been studied as carriers in plasticized membrane electrodes that are selective towards cationic surfactants. Host–guest complexation has also been studied by means of batch extraction and bulk membrane transport experiments. For the various guests, the bulk membrane (chloroform) transport rate decreases in the series tetraalkyl ammonium > alkyl pyridinium > alkyl ammonium, while the series of solvent extraction efficiency is exactly opposite; an explanation for this behaviour is proposed. The performance of electrode membranes follows the series for bulk membrane transport. Among the ISE membranes of various composition, one containing the longest (seven oxygen atoms) podand, o-nitrophenyl octyl ether (plasticizer), and sodium tetraphenyl borate (anionic additive) performs the best. The slope of the electrode function equals 58.5 mV/decade, the detection limit for dodecyltrimethylammonium is 3.2 × 10^-6 M. ISE response time is 5–10 s, the working pH range is 2–11 and lifetime is at least 6 months. The electrode selectivity is significantly better than that of conventional ion-association and crown ether based electrodes.     

Ionic recognition by thiacalixarenes: binding of alkali and heavy metal ions by thiacalix[4]arene-bis-crown[n] ethers

The binding properties of two thiacalix[4]arene-bis-crown[n] derivatives (n = 5 and 6) were examined through extraction experiments. The stability constants of the resulting complexes in methanol were determined. The replacement of the bridging CH2 groups by sulfur atoms leads to a strong decrease in both extraction and complexation levels of alkali metal ions but does not affect the selectivity within the series of crown ethers. The stability of complexes with heavy metal ions does not change markedly on passing from thiacalix[4]arene-bis-crown[n] ethers to their calix[4]arene-bis-crown[n] counterparts; therefore no clear-cut conclusions about the possible interactions between these cations and the sulfur atoms can be drawn.     

Spectrophotometric Study of Complex Formation Between Iodine and Some Thiacrown Ethers in Chloroform Solution

Formation of the charge-transfer complexes betweenhexathia-18-crown-6, pentathia-15-crown-5,tetrathia-12-crown-4 and iodine in chloroform solution wasinvestigated spectrophotometrically. The molar absorptivities and formation constants of the resulting 1 : 1 molecularcomplexes were determined. The stability of the iodine complexes increased with the increasing number of donating sulfur atoms in thecrown ether ring. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. All molecular complexes formed were enthalpy stabilized, but entropy destabilized. From the thermodynamic data obtained, theT S° - H° plot shows a fairly good linear correlation, which indicates enthalpy-entropycompensation in the reactions.     

Complexation of iodine with macrocyclic polyethers and sulfides

The complexation of iodine with 12-, 15-, and 18-membered crown ethers containing two sulfur atoms in the macrocyclic ring was studied by the spectrophotometric method. It was shown that, in CCl₄, the stability constants of complexes with a 11 composition have a value of the order of magnitude of 10². The enthalpies of complexation are (22–34) kJ/mole, which is practically not different from the parameters of complexes of iodine with simple sulfides.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 747–750, November–December, 1988.     

Complexation of Li+, Na+ and K+ Ions by [222], [222D], [221], [221D] Cryptands in Acetonitrile at 25 °C: Conductometric Determination of the True Thermodynamic Formation Constants

A new method is presented for the analysis of precise conductance data to obtain the true thermodynamic formation constants of macrocyclic–cation complexes. The method, based on the Lee–Wheaton theory on mixed electrolytes, takes into consideration the ion pair formation of both the uncomplexed and complexed cations and avoids the use of the simple additivity assumption of the conductances of two electrolytic species present in salt/ligand/solvent systems. The method has been applied to determine the thermodynamic complexation constants of lithium, sodium and potassium ions with the cryptands [221], [222] and their decyl derivatives [221D], [222D] in acetonitrile. The results show that the presence of an alkyl chain in the molecular structure of the cryptands decreases the macrocyclic–cation complexation constant with respect to the values obtained for the parent compounds by almost an order of magnitude. Such a finding has been explained in terms of the asymmetric position in the space of the oxyethylenic bridges of the macrocyclic ligand promoted by the presence of the linked hydrocarbon chain. The above explanation has been confirmed by the anomalous behavior of both the ion-pair association constants of complexed salts and their limiting molar conductivity.     

Synthesis,spectral, thermal,potentiometric and antimicrobial studies of transition metal complexes of tridentate ligand

A series of metal complexes of Cu(II), Ni(II), Co(II), Fe(III) and Mn(II) have been synthesized with newly synthesized biologically active tridentate ligand. The ligand was synthesized by condensation of dehydroacetic acid (3-acetyl-6-methyl-(2H) pyran-2,4(3H)-dione or DHA), o-phenylene diamine and fluoro benzaldehyde and characterized by elemental analysis, molar conductivity, magnetic susceptibility, thermal analysis, X-ray diffraction, IR, ¹H-NMR, UV–Vis spectroscopy and mass spectra. From the analytical data, the stoichiometry of the complexes was found to be 1:2 (metal:ligand) with octahedral geometry. The molar conductance values suggest the non-electrolyte nature of metal complexes. The IR spectral data suggest that the ligand behaves as a dibasic tridentate ligand with ONN donor atoms sequence towards central metal ion. Thermal behaviour (TG/DTA) and kinetic parameters calculated by the Coats–Redfern and Horowitz–Metzger method suggest more ordered activated state in complex formation. To investigate the relationship between stability constants of metal complexes and antimicrobial activity, the dissociation constants of Schiff bases and stability constants of their binary metal complexes have been determined potentiometrically in THF–water (60:40%) solution at 25 ± 1 °C and at 0.1 M NaClO₄ ionic strength. The potentiometric study suggests 1:1 and 1:2 complexation. Antibacterial and antifungal activities in vitro were performed against Staphylococcus aureus, Escherichia coli and Aspergillus niger, Trichoderma, respectively. The stability constants of the metal complexes were calculated by the Irving–Rosotti method. A relation between the stability constant and antimicrobial activity of complexes has been discussed. It is observed that the activity enhances upon complexation and the order of antifungal activity is in accordance with stability order of metal ions.     

Rhodium complexation with phosphoryl-containing calix[4]resorcine

Complexation of rhodium compounds with phosphoryl-containing calix[4]resorcine in ethanol and acetone has been considered. The structure and properties of the synthesized complexes have been studied by IR and Raman spectroscopy, ¹H and ³¹P NMR, EPR, UV-Vis spectroscopy, and TG/DSC. The effect of the solvent nature and conformation of a macrocyclic ligand on the structure of the resulting complexes has been observed. It has been demonstrated that one of the key factors responsible for complexation in EtOH is self-association of the ligand without the participation of the solvent. Complex formation in acetone is determined by its high ionizing ability. In diamagnetic complexes, the macrocyclic ligand is coordinated to the central atom through the phosphoryl oxygen atoms. For triaquatrichlororhodium in an aprotic medium, coordination occurs through the oxygen atoms of resorcinol moieties, which is accompanied by the formation of resorcinol radical anion and conversion of the diethoxyphosphorylaryl groups into ethoxyhydroxyphosphorylaryl moieties.     

Synthesis, potentiometric and antimicrobial studies on metal complexes of isoxazole Schiff bases

The metal complexes of Cu(II), Ni(II) and Co(II) with Schiff bases of 3-(2-hydroxy-3-ethoxybenzylideneamino)-5-methyl isoxazole [HEBMI] and 3-(2-hydroxy-5-nitrobenzylidene amino)-5-methyl isoxazole [HNBMI] which were obtained by the condensation of 3-amino-5-methyl isoxazole with substituted salicylaldehydes have been synthesized. Schiff bases and their complexes have been characterized on the basis of elemental analysis, magnetic moments, molar conductivity, thermal analysis and spectral (IR, UV, NMR and Mass) studies. The spectral data show that these ligands act in a monovalent bidentate fashion, co-ordinating through phenolic oxygen and azomethine nitrogen atoms. Chelates of Co(II), Ni(II) appear to be octahedral and Cu(II) appears to be distorted octahedral. To investigate the relationship between formation constants of binary complexes and antimicrobial activity, the dissociation constants of Schiff bases and stability constants of their binary metal complexes have been determined potentiometrically in aqueous solution at 30+/-1 degrees C and at 0.1 M KNO3 ionic strength and discussed. Antimicrobial activities of the Schiff bases and their complexes were screened. The structure-activity correlation in Schiff bases and their metal(II) complexes are discussed, based on the effect of their stability constants. It is observed that the activity enhances upon complexation and the order of activity is in accordance with stability order of metal ions.     

Synthesis and metal ion complexation of acyclic Schiff base podands with lipophilic amide and ester end groups

A series of acyclic Schiff base podands 14?C19 with lipophilic amide and ester end groups were synthesized in good yield and in a simple way. Their transition metal ions complexation was studied using conductometric method in acetonitrile (AN) at 25 °C. Schiff base podands 14?C16 showed a continuous decrease in the molar conductances in their complexation with Hg²⁺, Pb²⁺, Cu²⁺, Zn²⁺ and Cd²⁺ which begins to level off at a mole ratio of 1:1 crown-to-metal indicating the formation of a stable 1:1 complexes. The order of the stability constants of the metal ions studied with the Schiff base podands 14, 15 and 16 is: Hg²⁺ > Pb²⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺ > Ag⁺. Metal ion complexation by acyclic diamide or diester podands involves presumably the oxygen atoms of the carbonyl groups in addition to the nitrogen atoms of the imino groups.     

Conductance and Thermodynamic Study of the Complexation of Ethyl p-Tert-butylcalix[4]arene Tetraacetate with Alkali Metal and Silver Ions in Various Solvents

The first conductometric studies for the complexation reactions between alkali metaland silver cations with ethyl p-tert-butylcalix[4]ester in the cone conformation using acetonitrile and methanol in the temperature range 278–303 K are reported. The observed molar conductivities were found to decrease significantly for mole ratios less than unity. The conductivity data were analysed using a computer program based upon 1 : 1 stoichiometry. Stability constants of the resulting 1 : 1 complexes were determined, indicating that the sequence of stability in acetonitrile is Na⁺ > Li⁺ > K⁺. The H⁰ and S⁰ values of the calix[4]ester complexation reactions were determined from the temperature dependence of the complexation constants, and their significance are discussed.     

Structural control of Schiff base ligands for selective extraction of copper(II).

Structural control of Schiff base ligands for selective extraction of copper(II) was investigated by changing pendant arms and the distance between two imine-N donor atoms in ligands. Di-Schiff base ligands, N,N'-bis(2-quinolylmethylidene)-1,2-diiminoethane (BQIE), N,N'-bis(2-pyridylmethylidene)-1,3-diimino-2,2-dimethylpropane (BPMP) and N,N'-bis(2-quinolylmethylidene)-1,3-diimino-2,2-dimethylpropane (BQMP), were used as complexation reagents for ion-pair extraction of divalent transition metal cations into nitrobenzene with picrate anion. The pendant arms affected the lipophilicity of ligand to nitrobenzene, due to their polarity. The distance between two imine-N atoms, on the contrary, was a factor of controlling the extraction selectivity. BQMP has both 2-quinolyl pendant arms and trimethylene backbone structure; use of BQMP as a complexation reagent led to the selective extraction of Cu2+ in the system.     

Design of Extractants for F-Block Elements in a Series of (2-(Diphenylphosphoryl)methoxyphenyl)diphenylphosphine Oxide Derivatives: Synthesis,Quantum-Chemical,and Extraction Studies

With the aim to find new efficient extractants for recovery of f-block elements from processing wastes of different origin, we have compared a series of phosphoryl-containing podands, including (2-(diphenylphosphorylmethoxy)phenyl)diphenylphosphine oxide 1 and its analogues 5–7, where the ArP(O)Ph₂ group of phosphine oxide type is replaced by phosphonic fragments. Quantum-chemical modelling of the structures of phosphoryl-containing podands 1 and 5–7 has been performed, which was later confirmed by the data of X-ray diffraction. The features of extraction of nitric acid, as well as U(VI), Th(IV), Nd(III), and Ho(III) with compounds 1 and 5–7 from nitric acid media into 1,2-dichloroethane have been studied. The compositions of extracted complexes have been determined.     

Nature of Brønsted acid–noble atom contacts: A reevaluation of hydrogen bonding criteria

Xenon atoms interact weakly and reversibly with different molecular systems and human body. In this report, we consider their participation in hydrogen bonding in relation to analogous interactions of Ne, Ar, and Kr. Acid–noble atom dimers, A? H···Rg, are examined by the quantum theory of atoms in molecules and the results are discussed using several independent parameters. Different factors of this complexation are recognized: (i) the AH acidity and the Rg basicity, (ii) the AH structure, (iii) the electronegativities of atoms A and Rg, and (iv) the charge transfer from Rg to the complex critical point and to the acidic H atom. A? H···Ne contacts are qualitatively different from the remaining complexes. Koch and Popelier's criteria of hydrogen bonding, developed for classic complexes, are usually fulfilled for these very weak systems with one main exception: the charge on the acidic H increases upon the complexation to bigger Rg atoms. © 2014 Wiley Periodicals, Inc.     

Rigidified Macrocyclic Phosphoramides a New Family of Preorganized Ligands

Abstract

Macrocyclic molecules capable of selective recognition of ionic or neutral guests are of considerable current interest. The design and synthesis of host molecules that contain phosphorus have been developed recently. Typically, the model compound A is modified to the more rigid molecule B which can exist as two exo/endo isomers. B represents a new family of preorganized ligands that can involve the phosphorus group during complexation of various guests. The exo/endo isomerisni was investigated by NMR studies. The complexing properties of B were studied by NMR and extraction method with alkaline and ammonium cations. The complexation constants mainly depend on the molecular geometry and the size of the cavity. The highest Ka constants are obtained with the endo isomer where the P=O bond is directed toward the center of the macrocycle. Complex formation and detailed stereochemical data for A and B will be presented.