Thermodynamics and selectivity of complexation of lithium and sodium thiocyanates with phosphorus-containing podands and compounds modeling the terminal groups of these podands

A series of model compounds and heptadentate neutral phosphorus-containing podands that differ in the conformational rigidity of the terminal groups and in the coordination properties of the phosphoryl groups were synthesized. The thermodynamic parameters of complexation and the cationic selectivity of organophosphorus compounds and podands with respect to LiNCS and NaNCS were studied by calorimetric titration in acetonitrile at 298 K. The reasons for the high selectivity of certain phosphorus-containing podands to the Li⁺ cation are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1581–1587, September, 1994.This work was financially supported by the Russian Foundation for Basic Research (Grant No. 94-03-08848) and the International Science Foundation (Grant No. MTH000).     

Playing with podands based on cone-shaped cavities. How can a cavity influence the properties of an appended metal centre?

The potential of molecules that combine the properties of a conical cavity with those of a covalently-linked transition-metal centre is highlighted through the assessment of cyclodextrin- and calixarene-derived podands ("cavitand" ligands) in coordination chemistry and catalysis. Metallocavitands with coordination sites directed towards the interior of the generic cavity provide interesting systems for studying host-guest complexation processes, their enhanced strength of metal-ion binding allowing for regioselective catalysis in a confined environment, and stabilisation of coordination complexes of unusual forms. Where cavitands have exo-oriented podand arms, the intrinsic dynamics of the cavity can dramatically modify metal chelation behaviour and the catalytic properties of the complexes. Such functionalised cavities are also useful as metal-ion transporters.     

Chiral complex-forming and trans-phase transfer agents. 7. Complex forming properties of podands based on 1,4∶3,6-dianhydro-D-mannitol

In their complexation with alkali metal picrates, podands prepared from l,43,6-dianhydro-D-mannitol display affinity to Na and Li cations but virtually do not bind K ions. It was shown using the¹H NMR method that these podands form complexes with -phenylethylammonium perchlorate, the composition and strength of which depends on the nature of the side-chains of the podand. The podands studied are not capable of participating in the enantioselective transfer of the chiral substrate from the aqueous phase into chloroform.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2501–2504, November, 1989.     

Extraction of palladium with acyclic analogs of thiacalix[4]arenes from nitric acid solutions

p-tert-Butylcalix[4]arene was compared with its acyclic analogs in palladium extraction from nitric acid solutions as mononuclear and poly(bi)nuclear complexes with participation of protonated molecules of podands and macrocycle. The extraction ability of podands is similar to that of macrocycle because of the same character of complexation (Pd: S = 1: 1) without formation of new chelates and lower than that of monodentate analog owing to formation of a square complex (Pd: S = 1: 2).     

Synthesis, characterization and coordination properties of bis(alkyl)selenosalen ligands

New bis (alkyl) selenosalen podand ligands having Se2N2 donor sites have been synthesized by the condensation of unsymmetrical o-formylphenyl alkyl selenide (1-3) with ethylenediamine. The reaction of bis(alkyl)selenosalen podands with Pd(II) and Pt(II) afforded selenoether-selenolate coordination complexes 7-10via cleavage of one of the two Se-C(alkyl) bonds of bis(alkyl)selenosalen podands upon complexation. DFT calculations revealed that the cleavage of Se-C(alkyl) bonds occurred possibly via S(N)2 mechanism instead of a sequence of oxidative addition and reductive elimination reactions. The spectral data and elemental analyses confirmed the formation of selenoether-selenolate complexes. The structures of the podands N,N'-bis[(2-methylseleno)phenylmethylene]-1,2-ethanediamine (4), N,N'-bis[(2-decylseleno)phenylmethylene]-1,2-ethanediamine (5) and the selenoether-selenolate complex 8 have been determined by single crystal X-ray diffraction analysis. The crystal structure of 5 showed SeH interaction with a ladder like 3D supramolecular arrangement via interdigitation of long alkyl chains. Comparison of crystal packing of podands 4 and 5 indicates that the alkyl chain length has significant impact on the crystal packing. The platinum selenolate complex 8 shows a square planar arrangement around the Pt centre, where the Se atoms in the selenolate and the selenoether have nearly equal Pt-Se bond length.     

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.     

Crown-Ether Type Podands as Alkali Metal Cation Extractants: Influence of the Number of Oxygens in the Chain

Several polyether-type podands were synthesized that contained a variable number of potential donor oxygen atoms (four to twelve) and an aromatic ring in the chain. Extraction experiments were performed to elucidate the influence of the number of oxygen atoms on the extraction selectivity towards alkali metal picrates, from aqueous to dichloromethane phases. The results show that the extraction efficiency for lithium picrate is almost independent of the number of oxygen atoms in the podand. The extraction efficiency for sodium picrate was found to increase significantly with the number of oxygen atoms up to about seven, but for the potassium to cesium picrates the extraction efficiency increased up to about eight oxygen atoms. The increase in extraction efficiency may be rationalized in terms of the saturation of the cation’s first coordination sphere: after a critical number of oxygen atoms is reached and the first coordination sphere is saturated, the much smaller detected increases in the extraction efficiency may be seen as a statistical effect. The discrimination between sodium and potassium pirates is only achieved when the podands possess seven or more oxygen atoms. Under the experimental conditions used, the podands studied are unable to discriminate between potassium, rubidium and cesium picrates.     

Synthesis and Ionophoric Properties of α,ω-Diphosphorylated Aza Podands: II. Kabachnik-Fields Reaction as a Method for Design of α,ω-Diphosphorylated Aza Podands and Their Use for Determination of Metal Ions

Methods of the design of podands with α-aminomethylphosphine oxide terminal groups with the purpose of investigation of the ionophoric properties of the podands and their use as components of ion-selective electrodes are analyzed. The most convenient procedure is a one-pot synthesis based on the Kabachnik-Fields reaction in a system comprising a dialkyl(aryl)phosphinous acid, formaldehyde, and a diamine. An alternative procedure is two-stage and involves the reaction of a primary amine with a phosphinous acid and formaldehyde to form an α-aminomethyldialkyl(aryl)phosphine oxide in the first stage and cross-linking of two molecules of this compound via reaction with a dihalooligoether of the corresponding length in the second. Advantages and disadvantages of both procedures are considered. Electrode-active properties of the prepared aza podands are studied to show that ion-selective electrodes on their basis can be used for selective determination of low concentrations of alkali and alkaline-earth metal ions.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 2, 2005, pp. 244–252.Original Russian Text Copyright © 2005 by Garifzyanov, Vasil’ev, Cherkasov.For communication I, see [1].     

De novo structure-based design of bisurea hosts for tetrahedral oxoanion guests

This paper presents a computational approach to the deliberate design of improved host architectures. De novo molecule building software, HostDesigner, is interfaced with molecular mechanics software, GMMX, providing a tool for generating and screening millions of potential structures. The efficacy of this computer-aided design methodology is illustrated with a search for bisurea podands that are structurally organized for complexation with tetrahedral oxoanions.     

Synthesis and properties of podands with 4-antipyryliminomethine groups

Novel podands with 4-antipyryliminomethine groups on benzenes and various numbers of ethers are prepared. According to UV spectroscopy, these compounds form complexes with alkali, alkaline earth, and transition metals. Extraction of metal picrates demonstrated that the podands selectively form extractable complexes with these salts. A lead-selective electrode with an electrode function 22–24 mV/pPb is based on 1,8-bis[2-(4-antipyryliminomethine)phenoxy]-3,6-dioxaoctane. This enables 1·10^–6–1·10^–2 M Pb to be determined in the pH range 3.5–5.5. The electrode is highly selective for Pb in the presence of alkali and alkaline earth metals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2099–2102, September, 1990.     

Novel podands and macrocycles with diacetal (tetraoxadecalin) cores: synthesis, structure, stereochemistry and cation inclusion

A series of functionalized 2,6-dialkyl-cis-1,3,5,7-tetraoxadecalin podands (3-10, alkyl = hydroxy-, mesyloxy-, halo-, azido- and aminomethyl and -ethyl) were prepared, characterized, and used as precursors for a new and interesting class of macrocycles and cryptands (12-21), with the aim to use these as host-guest inclusion systems. Extensive spectroscopic work was performed, structural endorsement was obtained from X-ray diffraction analyses and further insight into the structures was obtained from theoretical/computational studies. A number of macrocycles in the series exhibited good complexation with alkaline-earth metal ions.     

Sulfonamides as ionophores for ion-selective electrodes. IV. New secondary sulfonamide podands and cryptands

New compounds — podands and cryptands with two secondary sulfonamide groups —have been synthesized and are described. They were tested as ionophores for guanidinium ions in PVC-membrane electrodes with bis (2-ethylhexyl)sebacate (DOS) as plasticizer.     

New Tripodal Ligands Containing Aza-Thioethers as Selective Extractants for Silver(I)

A new series of tripodal receptors bearing imine and thioether units, have been synthesized in high yields by simple condensation method. The binding properties of these ligands towards alkali, alkaline earth and transition metal ions have been established by extraction and transport experiments. These podands have highest extraction and transport rate for Ag(I). The complexation of Ag(I) with the receptors has been established using ¹H-and ¹³C-NMR spectroscopy.This revised version was published online in July 2005 with a corrected issue number.     

Heterometallic Molecular Architectures Based on Fluorinated β-Diketone Ligands

This review summarizes the data on the synthesis of coordination compounds containing two or more different metal ions based on fluorinated β-diketonates. Heterometallic systems are of high interest in terms of their potential use in catalysis, medicine and diagnostics, as well as in the development of effective sensor devices and functional materials. Having a rich history in coordination chemistry, fluorinated β-diketones are well-known ligands generating a wide variety of heterometallic complexes. In this context, we focused on both the synthetic approaches to β-dicarbonyl ligands with additional coordination centers and their possible transformations in complexation reactions. The review describes bi- and polynuclear structures in which β-diketones are the key building blocks in the formation of a heterometallic framework, including the examples of both homo- and heteroleptic complexes.     

Efficient Routes for the Synthesis of Dinaphthosulfide (BINOL Derivatives) and Dibenzosulfide Aza Podands Containing Ethanolamine

Four new dinaphthosulfide and dibenzosulfide aza podands were synthesized. The synthesis of these podands was performed under three different reaction conditions: 1) diester, K ₂ CO ₃ , methanol, and RT; 2) diester, ethanolamine, and microwave (MW); and 3) diacid dichloride, ethanolamine, Et ₃ N, CH ₂ Cl ₂ , RT. Two kinds of diester (dinaphthosulfide and dibenzosulfide) were used for the preparation of dihydroxy podands. These dihydroxy podands were reacted with thionyl chloride to afford dichloro podands. The second route gave excellent yields of dihydroxy podands. Dichloro podands are more soluble than dihydroxy podands in conventional solvents such as methanol, chloroform, and acetonitrile.     

The role of copper ions in Tb(III) luminescence sensitization in heterometallic complexes with podands

It has been demonstrated that copper-induced terbium(III) luminescence sensitization in heterometallic complexes with hydrazine-containing podands is caused by the ligand ring closure and joint coordination of both metal ions to the carbonyl oxygen atoms as well as, mainly, by the reduction with the hydrazine substituents of Cu(II) to Cu(I), which is able to sensitize terbium luminescence.     

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.     

Controllable DNA strand displacement by independent metal–ligand complexation

Introduction of artificial metal–ligand base pairs can enrich the structural diversity and functional controllability of nucleic acids. In this work, we revealed a novel approach by placing a ligand-type nucleoside as an independent toehold to control DNA strand-displacement reactions based on metal–ligand complexation. This metal-mediated artificial base pair could initiate strand invasion similar to the natural toehold DNA, but exhibited flexible controllability to manipulate the dynamics of strand displacement that was only governed by its intrinsic coordination properties. External factors that influence the intrinsic properties of metal–ligand complexation, including metal species, metal concentrations and pH conditions, could be utilized to regulate the strand dynamics. Reversible control of DNA strand-displacement reactions was also achieved through combination of the metal-mediated artificial base pair with the conventional toehold-mediated strand exchange by cyclical treatments of the metal ion and the chelating reagent. Unlike previous studies of embedded metal-mediated base pairs within natural base pairs, this metal–ligand complexation is not integrated into the nucleic acid structure, but functions as an independent toehold to regulate strand displacement, which would open a new door for the development of versatile dynamic DNA nanotechnologies.

This metal-mediated artificial base pair can function as an independent toehold based on metal–ligand coordination and exhibit flexible and reversible controllability to manipulate the dynamics of strand displacement.     

Switching Ca2+/Ba2+ to Ba2+/Ca2+ Potentiometric Selectivities of Podands with Phosphoryl-containing Terminal Groups: A Molecular Modelling Study

It has been shown experimentally that theCa²⁺/Ba²⁺ potentiometric selectivity ofphosphoryl-containing podandR–-O–-(CH₂–-CH₂–-O)_nndash;-R,R = –-C₆H₄–-P(O)Ph₂, n = 3 (I),switches to Ba²⁺/Ca²⁺ when the ligand containsthe longer polyether chain, n = 5 (II). Here, we reportmolecular dynamics and free energy perturbation simulationsperformed using the amber 4.1 program on the complexesL ^.M²⁺ (M²⁺ = Ca²⁺, Sr²⁺ andBa²⁺, L = I and II) in the gas phase inorder to gain a microscopic insight into structural and energy bindingproperties of podands as a function of n. Mixed QM/MM (PM3/ amber) calculations were performed toanalyse the role of polarisation effects on the complexation selectivityof podands. It isshown that an increase of n does not affect the interactions ofM²⁺ with phosphine oxide groups,but leads to less efficient interactions of small cations with the polyether chain. Calculatedpotentiometric selectivities of I (Ca²⁺ > Ba²⁺)and II (Ba²⁺ > Ca²⁺) are in agreement with the experimental data.