Double-cavity calix[4]pyrrole derivative with enhanced capacity for the fluoride anion

A double-cavity calix[4]pyrrole derivative, meso-tetramethyl-tetra[N-(2-phenoxyethyl)-N'-phenylurea]calix[4]pyrrole, 1, with enhanced hosting ability for the fluoride anion has been designed and characterized. Its interaction with anions (fluoride, chloride, bromide, iodide, dihydrogen phosphate, hydrogen sulfate, perchlorate, nitrate, and trifluoromethane sulfonate) was qualitatively and quantitatively assessed through 1H NMR, conductance, and calorimetric studies. The outcome of these investigations demonstrates that 1 interacts only with fluoride and dihydrogen phosphate anions in dipolar aprotic media. However, the composition of these complexes differs in that two units of fluoride are taken per unit of 1, while a 1:1 anion/ligand complex is formed with the dihydrogen phosphate anion. Results from the 1H NMR studies are striking in that these not only provide information about the active sites of the ligand-anion interaction but also allow the establishment of the sequence of events taking place during fluoride complexation. Thus, hydrogen-bond formation between the pyrrolic hydrogen and the fluoride anion is followed by the uptake of a second anion through the same type of interaction, but with the phenyl urea. It is also the latter group that is responsible for the interaction of 1 with the dihydrogen phosphate anion. Finally, this paper illustrates the importance of structural information for the interpretation of the thermodynamics associated with these systems.     

New insights on anion recognition by isomers of a calix pyrrole derivative

Two isomeric structures of meso-tetramethyltetrakis(3-hydroxyphenyl)calix[4]pyrrole, 4-alphaalpha betabeta and 4-alphabeta alphabeta, have been isolated and characterized by 1H NMR in different solvents (CD3CN, CD3OD, and DMSO-d6) at 298 K. Standard Gibbs energies of solution derived from solubility data in various solvents were used to calculate the transfer Gibbs energy, delta(t)G(o), of these ligands using acetonitrile as the reference solvent. These results are consistent with the 1H NMR studies in different media that show chemical shift changes observed in the resonances of the NH and the OH protons of these ligands. Solvate formation was observed when these isomers were exposed to saturated atmosphere of N,N-dimethylformamide, dimethyl sulfoxide and propylene carbonate. Anion interaction involving 4-alphaalpha betabeta and 4-alphabeta alphabeta was investigated by 1H NMR in CD3CN while the complex composition was assessed through conductance measurements. Significant differences are observed in the affinity of these ligands for anions as well as in the composition of the fluoride complexes. Thus 4-alphaalpha betabeta shows selectivity for H2PO4(-) in acetonitrile while its isomer 4-alphabeta alphabeta is selective for the fluoride anion. Again the complex composition is altered for the fluoride anion when complexed with 4-alphaalpha betabeta in acetonitrile (1:1 complex) relative to 4-alphabeta alphabeta in the same solvent. The latter isomer shows an enhanced hosting ability for this anion. Thus two anions are taken up per unit of ligand. The thermodynamics of complexation of H2PO4(-) and these ligands in acetonitrile is discussed, and the results are compared with those involving calix[4]pyrrole and this anion in this solvent. It is shown that the isomers interact with two H2PO4(-) anions while one calix[4]pyrrole unit interacts with this anion. This paper demonstrates for the first time that the enthalpy parameter may be a suitable reporter of the number of hydrogen bonds formed when calix[4]pyrrole and its derivatives interact with the dihydrogen phosphate anion in acetonitrile. In moving from acetonitrile to N,N-dimethylformamide, 4-alphaalpha betabeta is unable to enter complexation with most anions, except fluoride, with which the formation of a 1:2 (ligand:anion) complex is demonstrated. The rather versatile behavior of these receptors for anions is explained on the basis of 1H NMR evidence and solvation effects. These investigations highlight the importance of the medium effect on the stability of the complex and reflect the inherent nature of the solvent and its highly significant involvement in the complexation process.     

Modified calix[4]pyrrole receptor: solution thermodynamics of anion complexation and a preliminary account on the phosphate extraction ability of its oligomer

A modified calix[4]pyrrole, namely meso-tetramethyl-tetrakis-(4-hydroxyphenyl) calix[4]pyrrole, 1, has been synthesized and characterized. (1)H NMR investigations in various deuterated solvents seems to indicate that this receptor interacts with acetone-d(6). The solution thermodynamics of 1 in various solvents is reported. Complexation studies in CD(3)CN show that the NH and OH functionalities of 1 are the active sites of its interaction with the fluoride and the dihydrogen phosphate anions. The composition of the anion complexes was established through conductance measurements. In all cases, 1:1 complexes are formed. The thermodynamics of anion complexation in acetonitrile and N,N-dimethylformamide is discussed comparatively with previous reported data for the parent calix[4]pyrrole, 2, and these anions in these solvents. The medium effect on anion complexation is discussed in terms of the solvation properties of the reactants and the product in acetonitrile and N,N-dimethylformamide. An oligomeric material containing 1 as anchor group was synthesized and characterized by mass spectrometry. Preliminary studies have been performed to assess the extracting properties of this oligomer for the removal of phosphates from aqueous solutions. The effects of pH, temperature on the extraction of this anion salt from water, as well as the kinetics of the process (fast) were investigated.     

Sulfur-containing hetero-calix[4]pyrroles as mercury(II) cation-selective receptors: thermodynamic aspects

Two sulfur-containing hybrid calix[4]pyrrole derivatives (III and IV) have been synthesized and fully characterized. Several analytical techniques (1H NMR, conductance measurements, UV-vis spectrophotometry, titration potentiometry, and titration calorimetry) have been used to assess the interaction between these hybrid calixpyrrole receptors and metal cations in acetonitrile and dimethylsulfoxide. The partition constants of calix[4]pyrrole, I, II, and IV in the acetonitrile-hexane solvent system and the solubilities of the ligands in various solvents at 298.15 K were determined. 1H NMR measurements reveal the sites of interaction of calixpyrrole ligands with metal cations in CD3CN. Conductance and UV-vis spectrophotometric measurements were performed to establish the composition of mercury(II) calixpyrrole complexes in acetonitrile at 298.15 K. Titration calorimetry was used to quantitatively assess Hg(II)-calixpyrrole interactions. Thus the thermodynamics of complexation of calixpyrrole ligands with the mercury(II) cation in acetonitrile at 298.15 K are reported. Potentiometric titrations were also used to establish the stepwise stability constants for the complexation of calix[3]thieno[1]pyrrole with the Hg(II) cation in acetonitrile at 298.15 K. The results show that replacement of one or more pyrrole units by thiophene rings in calix[4]pyrrole has tuned significantly the discrimination ability of these ligands between anions and enables the produced hybrid calixpyrroles to bind selectively with Hg(II) in acetonitrile. No interaction was observed between these ligands and other metal cations in acetonitrile.     

Cation/anion recognition by a partially substituted lower rim calix[4]arene hydroxyamide, a ditopic receptor

The complexation ability of a partially substituted lower rim calix[4]arene hydroxyamide derivative, 25,27-bis[N-(2-hydroxy-1,1-bishydroxymethylethyl)amino- carbonylmethoxy]calix[4]arene-26,28-diol, 1, for cations and anions was investigated through (1)H NMR, conductometry, spectrophotometry, and calorimetry in dipolar aprotic media. (1)H NMR studies of 1 in the deuterated solvents (acetonitrile, methanol, and dimethylsulfoxide) reflect ligand-solvent interactions in methanol and dimethylsulfoxide. As far as the cations are concerned, a selectivity peak is found when standard Gibbs energies of complexation of 1 with cations (alkaline-earth, zinc, and lead) are plotted against corresponding data for cation hydration. This finding reflects the key role played by the desolvation and binding processes in the overall complexation of this receptor and these cations in acetonitrile. This is also interpreted in terms of enthalpy and entropy data. Factors such as, the nature and the arrangement of donor atoms in the hydrophilic cavity of the ligand on cation complexation process, are discussed. This paper also addresses anion complexation processes. It is found that 1 interacts through hydrogen bond formation with fluoride, dihydrogen phosphate, and pyrophosphate in acetonitrile and N,N-dimethylformamide. The thermodynamics associated with these processes is fully discussed taking into account literature data involving calix[4]pyrroles and these anions in these solvents. Previous work regarding the water solubility of these ligands is discussed. It is concluded that 1 behaves as a ditopic ligand in dipolar aprotic media.     

A new calix[4]pyrrole derivative and its anion (fluoride)/cation (mercury and silver) recognition

A new calix[4]pyrrole-based macrocycle, meso-tetramethyl-tetrakis{4-[2-(ethylthio)ethoxy]phenyl}calix[4]pyrrole, 7, has been synthesized and fully characterized. Unlike other calixpyrrole derivatives that show selective interaction with anions, calixpyrrole 7 described in the present work forms stable complexes with both metal cations and anions. The thermodynamics of complexation of this ditopic calixpyrrole derivative with metal cations (Hg2+ and Ag+) and the fluoride anion in nonaqueous solutions have been determined by titration calorimetry, and the host-guest composition has been investigated by using conductance measurements at 298.15 K. 1H NMR studies provide clear evidence about the sites of complexation of 7 with the ionic species, which show that the NH groups are taking part in the complexation of this ligand with the fluoride anion while the sulfur donor atoms are responsible for the interaction with metal cations. Using the present data on 7 and structurally related analogues (1-6), the complexation behavior is discussed comparatively from the thermodynamic point of view. Possessing four sulfur-containing pendent arms, 7 displays an enhanced hosting ability for Hg2+ in acetonitrile. As compared with 1, the calixpyrrole derivative, 7, shows a unique interaction with fluoride among the anions investigated in acetonitrile and dimethyl sulfoxide. As far as the fluoride complex is concerned, the medium effect is assessed in terms of the thermodynamics of the transfer of reactants and product from acetonitrile (reference solvent) to dimethyl sulfoxide.     

A partially substituted calix[4]resorcarene receptor and its selective recognition for soft metal cations (silver and mercury)

A partially substituted calix[4]resorcarene receptor, namely, 5,17-ethylthiomethylated calix[4]resorcarene, 1, has been synthesized and characterized by 1H NMR in CD3OD, CDCl3, and CD3CN and 13C NMR in CD3OD, as well as by 2D NMR. Partition data in the methanol-hexane and acetonitrile-hexane solvent systems show that the monomeric species are predominant in these solvents. The solubility of 1 in various solvents was determined at 298.15 K. These data were used to calculate the standard solution Gibbs energy of 1 in these solvents. Taking hexane as the reference solvent, the standard transfer Gibbs energy of 1 to various solvents was calculated. Good agreement is found between the DeltatG(o) values in the hexane-methanol and hexane-acetonitrile and the DeltapG(o) values of this ligand in these solvent systems. The higher partition constant of 1 in the hexane-methanol relative to the hexane-acetonitrile solvent system contrasts with corresponding data for the fully functionalized receptor, 2. This is explained in terms of the solvation differences of these receptors in these solvents as reflected in the DeltatG(o) values. The cation complexing properties of this receptor were investigated through 1H NMR, conductance, calorimetric, and potentiometric methods. Among the metal cations (alkali, alkaline earth, heavy, and transition), 1 interacts only with Ag+ in methanol and Hg2+ in propylene carbonate, acetonitrile, methanol, and N,N-dimethylformamide. While 1 forms a 1:1 complex with Ag+ in methanol, the hosting ability of the receptor for the mercury cation is enhanced in methanol, acetonitrile, and N,N-diethylformamide. Thus, Hg2+ complexes of 1:2 (ligand:metal cation) stoichiometry are found in these solvents. In moving to propylene carbonate, the composition of the mercury complex is altered from 1:2 to 1:1. The results are compared with corresponding data for 2 and these metal cations in the appropriate solvents. The lack of stability observed for 2 and Hg2+ in acetonitrile resulting from the departure of pendant arms from the resorcarene backbone greatly contrasts with the high stability observed for 1 and this metal cation in the various solvents. Preliminary results on the extraction of silver picrate by this ligand in the water-dichloromethane solvent system are reported. Final conclusions are given.     

Thermodynamics of ethyl p-tert-butylcalix[5]arene pentanoate and its cation complexes in nonaqueous media

The solution behavior of ethyl p-tert-butylcalix[5]arene pentanoate, EtCalix(5), in various protic and aprotic solvents has been assessed from the standard Gibbs energies of transfer of this ligand from acetonitrile to other solvents. These data were derived from solubility measurements of EtCalix(5) in different media. It is concluded that in solvents in which metal cation salts are predominant as ionic species in solution (within a low concentration range), the solvation of the ligand will not contribute significantly to the thermodynamics of cation complexation as a result of the medium effect. Various analytical techniques were used to identify the sites of ligand-cation interaction (1H NMR) and the composition (conductance and calorimetric measurements) of the metal-ion complexes in the various solvents. Titration calorimetry (direct and competitive) was used to thermodynamically characterize the cation binding ability of EtCalix(5) and gain quantitative information on the complex stability and the factors controlling it. Given the large bulk of data reported in the literature wrongly placed under the thermodynamic umbrella, particular emphasis is made about the need of identifying the process taking place in solution prior to proceeding with its thermodynamic characterization. The results are compared with those for the ethyl ester derivative of the cyclic tetramer, EtCalix(4). It is concluded that in moving from EtCalix(4) to EtCalix(5), (i) the selectivity of the latter for cations is swallowed toward the larger cations and (ii) although the number of binding sites increases, these are not able to exert the efficient control upon the ligand-cation binding ability as that found for the tetramer ester and these cations in these solvents.     

Resorcarene-based receptor: versatile behavior in its interaction with heavy and soft metal cations

Standard solution Gibbs energies, DeltasG degrees, of the resorcarene-based receptor 5,11,17,23-ethylthiomethylated calix[4]resorcarene, (characterized by 1H NMR and X-ray diffraction studies) in its monomeric state (established through partition experiments) in various solvents are for the first time reported in the area of resorcarene chemistry. Transfer Gibbs energies of from hexane (reference solvent) to other medium are calculated. Agreement between DeltatG degrees (referred to the pure solvents) and standard partition Gibbs energies, DeltapG degrees (solvent mutually saturated) is found. Cation-ligand interactions were investigated through 1H NMR (CD3CN and CD3OD) and conductometric titrations in acetonitrile and methanol. 1H NMR data revealed the sites of interaction of with the metal cation. The composition of the metal-ion complexes (Ag+ and Pb2+ in acetonitrile and Ag+ and Cu2+ in methanol) was established through conductometric titrations. Thus, complexes of 1:1 stoichiometry were formed between and Ag+ and Pb2+ in acetonitrile and Cu2+ in methanol. However, in moving from acetonitrile to methanol, the composition of the silver complex was altered. Thus, two metal cations are hosted by a unit of the ligand. As far as Cu2+ and in acetonitrile is concerned, conductance data suggest that metalates are formed in which up to four units of Cu2+ are taken up per unit of resorcarene. The contrasting behavior of with Cu2+ in acetonitrile relative to methanol is discussed. As far as mercury (II) is concerned, the unusual jump in conductance observed in the titration of Hg2+ with in acetonitrile and methanol after the formation of a multicharged complex (undefined composition) is attributed to the presence of highly charged smaller units (higher mobility) resulting from the departure of pendant arms from the resorcarene backbone. Isolation of these species followed by X-ray diffraction studies corroborated this statement. The thermodynamic characterization of metal-ion complexes of Ag+ and Pb2+ in acetonitrile and Cu2+ and Ag+ in methanol is reported. Final conclusions are given.     

Selective interaction of lower rim calix[4]arene derivatives and bivalent cations in solution. Crystallographic evidence of the versatile behavior of acetonitrile in lead(II) and cadmium(II) complexes

The interaction of lower rim calix(4)arene derivatives containing ester (1) and ketone (2) functional groups and bivalent (alkaline-earth, transition- and heavy-metal) cations has been investigated in various solvents (methanol, N,N-dimethylformamide, acetonitrile, and benzonitrile). Thus, 1H NMR studies in CD3OD, C3D7NO, and CD3CN show that the interaction of these ligands with bivalent cations (Mg2+, Ca2+, Sr2+, Ba2+, Hg2+, Pb2+, Cd2+) is only observed in CD3CN. These findings are corroborated by conductance measurements in these solvents including benzonitrile, where changes upon the addition of the appropriate ligand (1 or 2) to the metal-ion salt only occur in acetonitrile. Thus, in this solvent, plots of molar conductance against the ligand/metal cation ratio reveal the formation of 1:1 complexes between these ligands and bivalent cations. Four metal-ion complex salts resulting from the interaction of 1 and 2 with cadmium and lead, respectively, were isolated and characterized by X-ray crystallography. All four structures show an acetonitrile molecule sitting in the hydrophobic cavity of the ligand. The mode of interaction of the neutral guest in the cadmium(II) complexes differs from each other and from that found in the lead(II) complexes and provides evidence of the versatile behavior of acetonitrile in binding processes involving calix(4)arene derivatives. The thermodynamics of complexation of these ligands and bivalent cations in acetonitrile is reported. Thus, the selective behavior of 1 and 2 for bivalent cations is for the first time demonstrated. The role of acetonitrile in the complexation process in solution is discussed on the basis of 1H NMR and X-ray crystallographic studies. It is suggested that the complexation of 1 and 2 with bivalent cations is likely to involve the ligand-solvent adducts rather than the free ligand. Plots of complexation Gibbs energies against the corresponding data for cation hydration show a selectivity peak which is explained in terms of the predominant role played by cation desolvation and ligand binding energy in complex formation involving metal cations and macrocycles in solution. A similar peak is found in terms of enthalpy suggesting that for most cations (except Mg2+) the selectivity is enthalpically controlled. The ligand effect on the complexation process is quantitatively assessed. Final conclusions are given highlighting the role of the solvent in complexation processes involving calix(4)arene derivatives and metal cations.     

Calix[6]pyrrole and hybrid calix[n]furan[m]pyrroles (n+m=6): syntheses and host-guest chemistry

Calix[6]pyrrole 2 and the "hybrid systems" calix[3]furan[3]pyrrole 12, calix[2]furan[4]pyrrole 13, and calix[1]furan[5]pyrrole 14, have been synthesized by increasing conversion of the furan units present in the readily accessible calix[6]furan 3 to pyrroles. The host-guest chemistry of these novel macrocycles towards a number of anions, including halogen ions, dihydrogen phosphate, hydrogen sulfate, nitrate, and cyanide has been investigated in solution by (1)H NMR titration techniques and/or phase transfer experiments. The solid-state structures of the free receptors 2, 12, and 13, the 1:1 complexes of calix[6]pyrrole 2 with chloride and bromide, and the 1:1 complex of 14 with chloride are also reported.     

Reaction of rhodium trichloride with oxyethylated calix[4]resorcinarene

Reaction of rhodium trichloride with a new ligand, oxyethylated calix[4]resorcinarene was examined in an inert atmosphere in different solvents (acetone, acetone + chloroform). The product was characterized by IR, Raman, ¹H NMR, ESR, ESCA spectroscopy, conductometry. Its composition was proved by the data of elemental and X-ray fluorescent analyses. The solvent used does not affect the composition of the product but only its yield. The structure of the coordination node and the type of coordination of the rhodium-containing fragment was investigated by calculating the model molecules of the ligand and the complex using the molecular mechanics method (MM+).     

Anion-free bambus[6]uril and its supramolecular properties

Methods for the preparation of anion-free bambus[6]uril (BU6) are presented. They are based on the oxidation of iodide anion, which is bound inside the macrocycle, utilizing dark oxidation by hydrogen peroxide or photooxidation in the presence of titanium dioxide. Anion-free BU6 was found to be insoluble in any of the investigated solvents; however, it dissolves in methanol/chloroform (1:1) or acetonitrile/water (1:1) mixtures in the presence of the tetrabutylammonium salt of a suitable anion. The association constants with halide ions, BF(4)(-), NO(3)(-), and CN(-), were measured by (1)H NMR spectroscopy. The highest association constant (8.9×10(5) M(-1)) was found for the 1:1 complex of BU6 with I(-) in acetonitrile/water mixture. A number of crystal structures of BU6 complexes with various anions were obtained. The influence of the anion size on the macrocycle diameter is discussed together with an unusual arrangement of the macrocycles into separate layers.     

Solvent control on the selective, nonselective, and absent response of a partially substituted lower rim calix(4)arene derivative for soft metal cations (mercury(II) and silver(I)). Structural and thermodynamic studies

The solvent control on the ability of a partially substituted lower rim calix(4)arene derivative 5,11,17,23,tetra-tert-butyl[25,27-bis(hydroxy)-26,28-bis(ethylthioethoxy)]-calix(4)arene, 1 to host soft metal cations (Hg(II) and Ag(I)) is demonstrated through 1H NMR, electrochemical (conductance measurements), and thermodynamic characterization of the complexation process in a wide variety of solvents. Solvent-ligand interactions were assessed from 1H NMR measurements involving 1 and various solvents in CDCl3. Thus, the formation of a 1:1 1-CH3CN adduct is reported. As far as metal cations are concerned, depending on the medium their complexation with 1 was only observed for Hg(II) and Ag(I). Thus, in acetonitrile, 1 is more selective for Hg(II) relative to Ag(I) by a factor of 2.2 x 10(3). In methanol the selectivity is reversed to an extent that the affinity of 1 for Ag(I) is 1.4 x 10(3) higher than that for Hg(II). However, 1 is unable to recognize selectively these cations in N,N-dimethylformamide while in propylene carbonate the ability of 1 to interact with these cations is lost. An outstanding feature of thermodynamics emerges when an assessment is made of the ligand effect on the complexation of these cations and analogues calix(4)arene derivatives. Thus, in acetonitrile the thermodynamics of cation complexation by the hydrophilic cavity of a calix(4)arene containing mixed pendant groups is built up from thermodynamic data for the same process involving derivatives with common functionalities at the narrow rim. This is a unique example of the additive contribution of pendant arms in the field of thermodynamics of calixarene chemistry.     

Novel ion-pair receptors based on hexahomotrioxacalix[3]arene derivatives

A series of novel heteroditopic hexahomotrioxacalix[3]arene triamide receptors capable of binding an anion and cation simultaneously in a cooperative fashion has been prepared. The lower rim functionalized cone-hexahomotrioxacalix[3]arene derivatives cone-5a-5d bearing three amide groups were synthesized from cone-3 by a stepwise reaction. The crystal structures of 5c and 5d and (1)H NMR studies in nonpolar solvents strongly indicate that a number of interesting intramolecular hydrogen bonding interactions exist in these receptors. The binding abilities of these compounds towards n-butylammonium chloride and bromide salts have been investigated using (1)H NMR titration experiments in CDCl(3) solvent. Owing to the 'flattened cone' conformations and intramolecular hydrogen bonding involving the amide NH and neighbouring O atoms in cone-5a-5d, the affinities toward n-Bu(4)NX (X = Cl(-) and Br(-)) were weakened. However, it should be noted that triamides cone-5a-5d show a single selectivity for halide anions in the presence of n-BuNH(3)(+) through intermolecular hydrogen bonding with the amide NH hydrogen atoms in the receptors in CDCl(3) solution. Association constants were calculated from the chemical shift changes of the amide protons.     

杯[4]二吡咯与卤素阴离子相互作用的密度泛函理论研究

采用密度泛函B3LYP方法, 在6\|31G*/LANL2DZ水平上对杯[4]二吡咯主体分子及其与卤素阴离子形成的复合物进行研究.  结果表明, 杯[4]二吡咯可与卤素阴离子相互作用形成具有较高对称性的复合物, 其8个吡咯NH基团上的H原子均可以和卤素阴离子形成氢键; 杯[4]二吡咯与卤素阴离子结合能力大小的顺序为F- >Cl- >Br- > I-.  振动光谱、 电荷分布以及前线轨道计算结果表明, 杯[4]二吡咯与卤素阴离子相互作用的本质为氢键, 经BSSE校正的结合能与电荷转移程度、 N-H键键长和N-H伸缩振动频率变化呈线性关系.      

Autoionization of homogeneous nickel(II) diphosphane hydrogenation catalysts. An NMR study and crystal structures of [Ni(o-MeO-dppe)I2] and [Ni(o-MeO-dppe)I2](PF6)2

The synthesis of a number of nickel(II) complexes containing the didentate phosphane ligand 1,2-bis(di(o-methoxyphenyl)phosphino)ethane (o-MeO-dppe) is reported. Two types of complexes have been synthesized, i.e., the mono(chelate) complex (1) of the general formula [Ni(o-MeO-dppe)X2] (where X = Cl, Br or I) and the bis(chelate) complex (2) of the general formula [Ni(o-MeO-dppe)2]Y2 (where Y = PF6 or trifluoroacetate (TFA)). These complexes have been characterized using electronic absorption and NMR spectroscopy. The structures of the mono(chelate) complex [Ni(o-MeO-dppe)I2] (1c) and of the bis(chelate) complex [Ni(o-MeO-dppe)2](PF6)2 (2e) have been determined by X-ray crystallography. [Ni(o-MeO-dppe)I2] crystallizes in the monoclinic space group P2(1)/c with Z = 4, a = 12.1309(1) A, b = 16.5759(3) A, c = 17.6474(2) A, beta = 119.3250(10) degrees. [Ni(o-MeO-dppe)2](PF6)2 crystallizes in the monoclinic space group C2/c with Z = 4, a = 22.5326(3) A, b = 13.6794(2) A, c = 21.7134(3) A, beta = 107.1745(7) degrees. In both structures the nickel ion is in a square-planar geometry with a NiP2I2 and NiP4 chromophore, respectively. Using 1H and 31P[1H] NMR spectroscopy the behavior of the complexes in various solvents has been studied. It appears that in solution these nickel complexes are involved in an autoionization equilibrium: 2[Ni(o-MeO-dppe)X2] <==>[Ni(o-MeO-dppe)2](2+) + ["NiX(4)"](2-). The ionized complex (3) consists of a cationic unit in which a nickel atom is surrounded by two didentate phosphane ligands, and an anionic unit that stoichiometrically consists of a nickel atom and four anions. The position of the autoionization equilibrium is highly dependent on the anion and the solvent used. In a polar solvent in combination with weakly coordinating anions only the ionized complex is observed, whereas in an apolar solvent in combination with coordinating anions only the mono(chelate) complex occurs. A comparison of the behavior of o-MeO-dppe with its unsubstituted analogue dppe in combination with nickel(II) acetate using 31P[1H] NMR spectroscopy shows that the latter is more readily oxidized.     

Anion-dependent binding of zinc calix[4]pyrrole-bisporphyrinate triethylenediamine

The complexation properties of zinc 10,20-bis[5-(2,3,7,8,12,13,17,18-octaethylporphyrinate)ethynylphenyl]-5,5′,10′,15,15′,20′-hexamethylcalix[4]pyrrole toward halide ions, triethylenediamine, and 4,4′-bipyridyl were studied by spectrophotometric titration and ¹H NMR spectroscopy. The influence of binding of anions (F⁻ and Cl⁻) by the calix[4]pyrrole fragment of zinc calixpyrrole-bisporphyrinate on the complexation properties of its interporphyrin cavity toward the bidentate organic ligand triethylenediamine.     

A thermodynamic study of complexation process between <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-dipyridoxylidene(1,4-butanediamine) and Cd<Superscript>2+</Superscript> in some binary mixed solvents using conductometry

Complexation of the Cd²⁺ ion with N,N′-dipyridoxylidene(1,4-butanediamine) Schiff base was studied in pure solvents including acetonitrile (AN), ethanol (EtOH), methanol (MeOH), tetrahydrofuran (THF), dimethylformamide (DMF), water (H₂O), and various binary solvent mixtures of acetonitrile–ethanol (AN–EtOH), acetonitrile–methanol (AN–MeOH), acetonitrile–tetrahydrofuran (AN–THF), acetonitrile–dimethylformamide (AN–DMF), and acetonitrile–water (AN–H₂O) systems at different temperatures using the conductometric method. The conductance data show that the stoichiometry of complex is 1: 1 [ML] in all solvent systems. A non-linear behavior was observed for changes of log K_f of [Cd(N,N′-dipyridoxylidene(1,4-butanediamine)] complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions. The results show that the thermodynamics of complexation reaction is affected by the nature and composition of the mixed solvents.     

Thermodynamics of Complexation of Alkali Metal Cations by a Lower-Rim Calix[4]arene Amino Acid Derivative

Complexation of alkali metal cations with 5,11,17,23-tetra-tert-butyl-26,28,25,27-tetrakis(O-methyl-d-α-phenylglycylcarbonylmethoxy)calix[4]arene (L) in methanol and acetonitrile was studied by means of direct and competitive microcalorimetric titrations at 25 °C. The thermodynamic parameters of complexation reactions showed that all the reactions investigated were enthalpically controlled. In both solvents the reaction enthalpy was most favorable for Na⁺ binding with L leading to the highest affinity of the examined calix[4]arene derivative towards this cation. The solubilities (and consequently the solution Gibbs energies) of the ligand were determined, as were the corresponding solution enthalpies and entropies. No significant difference was observed between the solution thermodynamic quantities of L in the two solvents, whereas the transfer of complex species from methanol to acetonitrile was found to be quite favorable. The interactions of solvent molecules with the free and the complexed ligand were investigated by ¹H NMR spectroscopy. It was concluded that in both cases inclusion of an acetonitrile molecule into the hydrophobic cavity of L occurred, which significantly affected the cation complexation in this solvent. The thermodynamic data were discussed regarding the structural properties of the ligand, the free and the complexed cations as well as the solvation abilities of the solvents examined. In this respect, the specific solvent-solute interactions and the intramolecular NH⋅⋅⋅O=C hydrogen bonds at the lower rim of L were particularly addressed.