Spectrophotometric studies of the thermodynamics of sitting-atop complexation between free base meso-tetraarylporphyrins and titanium(IV) chloride

Titanium(IV) chloride reacts with free base meso-tetraarylporphyrin and its ortho, meta and para-substituted derivatives (H₂T(X)PP; X: OCH₃, CH₃ and Cl) for formation of sitting-atop (SAT) complexes, [TiCl₄(H₂T(X)PP)]. The computer fitting of the variation of the absorbance versus mole ratio by KINFIT program was used for calculation of the formation constants of these complexes in chloroform. Thermodynamic parameters, ΔG°, ΔH°, ΔS°, have been determined and the influence of the temperature and the substituted aryl groups (electronic and steric effects) in the free base porphyrins on the stability of the SAT complexes was studied.     

Thermodynamic studies of sitting-atop (SAT) complexation of uranyl and free base meso -tetraarylporphyrins

The interaction of uranyl with meso-tetraphenylporphyrin and its para-substituted derivatives (H₂t(4-X)pp, X : H, Br, Cl, CH(CH₃)₂, OCH₃, CH₃) in chloroform produced 1 : 1 sitting-atop (SAT) complexes ((uranyl)H₂t(4-X)pp). Formation constants were calculated by computer fitting of complex absorbance versus mole ratio data to appropriate equations and found to decrease with temperature increase. Thermodynamic parameters, ΔG ⁰, ΔH ⁰ and ΔS ⁰ were obtained. The formation constants vary with changing of the substituent on the aryl rings of H₂t(4-X)pp in the following order: (uranyl)H₂t(4-OCH₃)pp?>?(uranyl)H₂t(4-CH₃)pp?>?(uranyl)H₂t(4-CH(CH₃)₂)pp?>?(uranyl)H₂tpp?>?(uranyl)H₂t(4-Br)pp?>?(uranyl)H₂t(4-Cl)pp.     

Thermodynamic studies of sitting-atop complexation between free base meso-tetraarylporphyrins and antimony(III) chloride in chloroform

Interaction of para, meta and ortho-substituted meso-tetraarylporphyrins, (H₂t(X)pp, X: OMe, Me, H and Cl) with SbCl₃ in chloroform solution afforded 1 : 1 sitting-atop (SAT) complexes ([(SbCl₃)(H₂t(X)pp)]). The formation constants were calculated by KINFIT and found to decrease with increasing temperature. The thermodynamic parameters, ΔH°, ΔS° and ΔG°, were obtained. Formation constants of these complexes change with changing substituent (X) on the aryl rings of H₂t(X)pp in the following order: (SbCl₃)H₂t(4-OMe)pp >?(SbCl₃)H₂t(4-Me)pp >?(SbCl₃)H₂tpp >?(SbCl₃)H₂t(4-Cl)pp >?(SbCl₃)H₂t(3-OMe)pp >?(SbCl₃)H₂t(3-Me)pp> (SbCl₃)H₂t(2-OMe)pp >?(SbCl₃)H₂t(2-Me)pp.     

Spectrophotometric Studies of the Thermodynamics of Molecular Complexation between Free Base Meso-Tetraarylporphyrins and Iodine(III) Chloride

A spectrophotometric method was used for the molecular complexation of ICl₃ with para-substituted meso-tetraarylporphyrins (H₂t(4-X)pp; X: OCH₃, CH(CH₃)₂, CH₃, H and Cl) in methanol/chloroform (2.5% v/v) solution. The equilibrium constants and the thermodynamic parameters were measured spectrophotometrically at various temperatures for 1:1 molecular complex formation of meso-tetraarylporphyrins as electron donors with ICl₃ as the electron acceptor. The formation constants for the molecular complexes change according to the following trend: [ICl₃(H₂t(4-OCH₃)pp)]>[ICl₃(H₂t(4-CH(CH₃)₂)pp)]>[ICl₃(H₂t(4-CH₃)pp)]>[ICl₃(H₂tpp)]>([ICl₃(H₂t(4-Cl)pp)]. Further, the thermodynamic parameters, ΔG ^o,ΔH ^o and ΔS ^o, for formation of the complexes were obtained.     

Sitting-atop complex formation of free base meso-tetraarylporphyrins with zirconium(IV) chloride

We have succeeded in the preparation and spectroscopic characterization of sitting-atop (SAT) complexes of meso-tetraarylporphyrins (H₂t(X)pp) with zirconium(IV) chloride under mild conditions and at room temperature, where two pyrrolenine nitrogens in the SAT complexes, [(H₂t(X)pp)ZrCl₄], coordinate to a zirconium atom and two protons still remain on the pyrrole nitrogens. UV–Vis and NMR (¹H and ¹³C) spectral data show that the porphyrin core of the SAT complexes is distorted and two pyrrolenine nitrogen atoms of the porphyrin act as electron donors to the zirconium atom of ZrCl₄.     

Micellization behavior of [C16-12-C16], 2Br gemini surfactant in binary aqueous-solvent mixtures

The micellization behavior of bis cationic gemini surfactant, N,N′-dihexadecyl-N,N,N′,N′-tetramethyl-1,12-dodecanediammonium dibromide [C₁₆H₃₃N⁺(CH₃)₂-(CH₂)₁₂-N⁺(CH₃)₂C₁₆H₃₃, 2Br⁻] has been studied in binary aqueous mixtures of dimethyl sulfoxide, methanol, 1,4-dioxane, glycerol and ethylene glycol by conductivity and surface tension measurements at 300 K. The critical micellar concentration, degree of micelle ionization (α), surface excess concentration (Г_max), minimum surface area per molecule of surfactant (A_min), Gibbs free energy of micellization (ΔG_m°), the surface pressure at cmc (π_cmc), and the Gibbs energy of adsorption (ΔG_ad°) of the gemini surfactant have also been determined. The cmc, α, A_min increases where as (ΔG_m°), Г_max, and π_cmc decreases with increasing volume percentage of the solvents in the solvent–water binary mixture. The interfacial properties of the gemini surfactant, solute–solute, solvent–solute interactions and the effectiveness of a surface-active molecule in binary solvent systems have been discussed.     

Dinitrogen and carbon monoxide hydrogen bonding in protonic zeolites: Studies from variable-temperature infrared spectroscopy

Adsorption (at a low temperature) of nitrogen on the protonic zeolite H-Y results in hydrogen bonding of the adsorbed N₂ molecules with the zeolite Si(OH)Al Brønsted-acid groups. This hydrogen-bonding interaction leads to activation, in the infrared, of the fundamental N–N stretching mode, which appears at 2334 cm⁻¹. From infrared spectra taken over a temperature range, the standard enthalpy of formation of the OH···N₂ complex was found to be ΔH⁰ = −15.7(±1) kJ mol⁻¹. Similarly, variable-temperature infrared spectroscopy was used to determine the standard enthalpy change involved in formation of H-bonded CO complexes for CO adsorbed on the zeolites H-ZSM-5 and H-FER; the corresponding values of ΔH⁰ were found to be −29.4(±1) and −28.4(±1) kJ mol⁻¹, respectively. The whole set of results was analysed in the context of other relevant data available in the literature.     

P NMR study of the stoichiometry, stability and thermodynamics of complex formation between palladium(II) acetate and bis(diphenylphosphino)ferrocene

The complexation reaction between palladium (II) acetate, and 1,1′-bis(diphenylphosphino)ferrocene, DPPF, was investigated in two different deuterated solvents CDCl₃ and DMSO at various temperatures using ³¹P NMR spectroscopy. The exchange between free and complexed DPPF is slow on the NMR time scale and consequently, two ³¹P NMR signals were observed. At metal ion-to-ligand mole ratio larger than 1, only one ³¹P NMR signal was observed, indicating the formation of a 1:1 Pd²⁺–DPPF complex in solution. The formation constant of the resulting 1:1 complexes was determined from the integration of two ³¹P signals. The values of the thermodynamic parameters (ΔH, ΔS and ΔG₂₉₈) for complexation were determined from the temperature dependence of stability constants. It was found that, in both solvents, the resulting complex is mainly entirely enthalpy stabilized and the ΔH compensates the TΔS contribution.     

Equilibrium, kinetics and thermodynamic aspects of Promethazine hydrochloride sorption by iron rich smectite

Equilibrium, kinetics and thermodynamic aspects of sorption of Promethazine hydrochloride (PHCl) onto iron rich smectite (IRS) from aqueous solution were investigated. The effect of pH on sorption of PHCl onto IRS was also found out. Experimental data were evaluated by using Langmuir, Freundlich and Dubinin–Raduschkevich (DR) isotherm equations. Freundlich and DR equations provided better compatibility than Langmuir equation. Besides, it was determined that the maximum sorption of PHCl takes place at about pH 5. From kinetic studies, it was obtained that sorption kinetics follow pseudo-second-order kinetic model for PHCl sorption onto IRS. When thermodynamic studies are concerned, the values of activation energy (E_a), ΔG°, ΔH° and ΔS° were obtained. ΔG° values are in the range of −8.84 and −9.45 kJ mol⁻¹ indicating spontaneous nature of physisorption. The negative value of the ΔH° (−3.20 kJ mol⁻¹) indicates exothermic nature of adsorption. FTIR analysis and SEM observations of IRS and PHCl adsorbed IRS were also carried out. Sorption experiments indicate that IRS may be used effectively for the adsorption of PHCl.     

A novel 18-metallacrown-6 complex: Synthesis, structural characterization and magnetic properties

The novel 18-metallacrown-6 complex, with the formula of [Mn₆(C₁₁H₁₁N₂O₃)₆(CH₃CH₂OH)₆]·3C₃H₇NO·2CH₃CH₂OH (1) (pmshz = N-propanoyl-3-methyl-salicylhydrazide), has been prepared and characterized. The self-assembled, manganese complex assumes a nearly planar cyclic structure with an [Mn–N–N]₆ backbone. Due to the coordination, the ligand enforces the stereochemistry of the Mn³⁺ ions as a propeller shape with alternating …ΔΛΔΛ… configurations. The magnetic properties of the metallacrown molecule are characterized by a weak antiferromagnetic exchange interaction between the Mn³⁺ ion spins with S = 2 in the cyclic system.     

Micelle Formation and Counterion Binding of Dodecylammonium Alkanesulfonates in Water at Different Temperatures

A temperature study was performed on micelle formation of a series of homologous cationic surfactants having organic counterions (alkanesulfonates) with carbon numbers ranging from 1 to 4: dodecylammonium salts of methanesulfonate (DAMS), ethanesulfonate (DAES), propanesulfonate (DAPS), and butanesulfonate (DABS) in water. The critical micelle concentrations (CMCs) and the degree of counterion binding (β) were determined at different temperatures ranging from 5 to 50°C by means of conventional electric conductance measurements. From the temperature dependence of β as well as CMC, Gibbs energy ΔG⁰_m, enthalpy ΔH⁰_m, and entropy ΔS⁰_m, on micelle formation, were estimated for the respective surfactants. As for the temperature dependence of CMC for these surfactants, the temperature-CMC curves have a minimum around 30°C and show that the CMC at each temperature is lowered by about 3 mmol dm^-3 per methylene group in the alkyl chain of the counterions. The relationship between β and temperature suggested that the counterion of MS^- behaves most similarly to common univalent ions such as halide ions. In contrast, PS^- and BS^-, having a stronger ability to lower CMC and to promote association of surfactant ions with counterions as well as of surfactant ions themselves, behave more like those of surfactant ions, and ES^- shows the most complicated character between those of common univalent ions and organic ions. However, the temperature dependence of enthalpy change, ΔH⁰_m demonstrates that these four surfactants are divided into two groups: (1) DAMS and DAES and (2) DAPS and DABS. In addition, the entropy change ΔS⁰_m as a function of alkyl chain length gives evidence that the contribution of the entropy term to the Gibbs energy on micelle formation clearly separates between DAES (m = 2) and DAPS (m = 3). A similar discontinuity is found even in the plot of ΔG⁰_m versus carbon atom number of alkyl chain, m, and in the plot of ΔG⁰_m versus estimated hydrodynamic radius of counterions. All the results obtained have indicated that lengthening the alkyl chains initially hinders micelle formation, but the longer chains are markedly effective in lowering the CMC and probably in increasing the aggregation number, owing to enhanced hydrophobic interaction between counterion and the micellar surface and/or core.     

Crown compounds for anions. The nature of chemical bonds in the complexes of halide anions with cyclic trimeric perfluoro-o-phenylenemercury and some of its analogs

Geometries and electronic structures of the complexes of halide anions with cyclic trimerico-phenylenemercury, (o-C₆H₄Hg)₃, perfluoro-o-phenylenemercury, (o-C₆F₄Hg)₃, vinylenemercury, (C₂H₂Hg)₃, and perfluorovinylenemercury, (C₂F₂Hg)₃, were modelled by the MNDO method. Calculations were performed for [L-X]^– semisandwich complexes, [X-L-X]^2– bipyramidal complexes, and [L-X-L]^– sandwich complexes (where X=Hal,L is a mercury-containing macrocycle). Based on the results of calculations, we concluded that it was advantageous to describe the chemical bonding between halide anions and mercury-containing macrocycles in terms of generalized chemical bonds, which were successfully used for -complexes of transition metals. In the [L-X]^– semisandwich complexes, the halide anion and the metallacycle are involved in the formation of three generalized chemical bonds: one headlight-shaped -bond and two two-lobe -bonds. In the [X-L-X]^2– bipyramidal complexes, each halide anion forms three generalized chemical bonds with the macrocycle. It is possible because the macrocycleL has unoccupied molecular orbitals suitable for the formation of such bonds; these MOs consist mainly of the orbitals of mercury atoms directed toward both the upper and lower halogen atoms. In the [L-X-L]^– sandwich complexes, the halide anion cannot be bonded to each ringvia three bonds, and, hence, an unsymmetrical structure is formed, in which the rings are located at different distances from the central atom: the [L-X]^– semisandwich complex solvated by macrocycleL.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1035–1042, June, 1995.The authors are grateful to V. I. Faustov for valuable remarks.This work was supported by the Russian Foundation for Basic Research (Project No. 93-03-18342).     

Synthesis, characterizations and crystal structures of new organoantimony(V) complexes with various isomers of fluoromethylbenzoate ligands

Six new organoantimony(V) complexes containing various isomers of fluoromethylbenzoate ligands [RC₆H₃COO]₂SbPh₃ and [RC₆H₃COO]SbPh₄ [R = 3-F-4-(CH₃) (1, 4), 4-F-2-(CH₃) (2, 5), 5-F-2-(CH₃) (3, 6)] have been synthesized by the reactions of triphenylantimony(V) dichloride or tetraphenylantimony(V) bromide with various isomers of fluoromethylbenzoate ligands in 1:2 or 1:1 stoichiometries. All the complexes have been characterized by elemental analysis, IR and NMR [¹H, ¹³C and ¹⁹F] studies. The crystal structures of complexes 1, 3, 4, 5 and 6 have been determined by X-ray single crystal diffraction. The structure of complexes show that the five-coordinated antimony(V) atom adopts a distorted trigonal bipyramidal geometry. Furthermore, weak but significant intermolecular C–H···O, C–H···F hydrogen bonds, C–H···pi stacking lead to aggregation and assembly of these complexes into 1D and 2D supramolecular frameworks.     

Isotherm, kinetic and thermodynamic studies of lead and copper uptake by H2SO4 modified chitosan

The kinetic and thermodynamic adsorption and adsorption isotherms of Pb(II) and Cu(II) ions onto H₂SO₄ modified chitosan were studied in a batch adsorption system. The experimental results were fitted using Freundlich, Langmuir and Dubinin–Radushkevich isotherms; the Langmuir isotherm showed the best conformity to the equilibrium data. The pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models were employed to analyze the kinetic data. The adsorption behavior of Pb(II) and Cu(II) was best described by the pseudo-second order model. Thermodynamic parameters such as free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were determined; the adsorption process was found to be both spontaneous and exothermic. No physical damage to the adsorbents was observed after three cycles of adsorption/desorption using EDTA and HCl as eluents. The mechanistic pathway of the Pb(II) and Cu(II) uptake was examined by means of Fourier transform infrared (FTIR) and Energy dispersive X-ray (EDX) spectroscopy. The equilibrium parameter (R_L) indicated that chitosan–H₂SO₄ was favorable for Pb(II) and Cu(II) adsorption.     

Tetrameric O–HO hydrogen-bond systems accompanied by C–HO hydrogen-bonds in the crystal of 1,4-bis(hydroxymethyl)triptycene: an X-ray study

The crystal structure of the title compound was determined (crystal data at 143 K: triclinic, space group P−1, Z=4, a=9.538(2) Å, b=11.638(2) Å, c=14.473(2) Å, α=88.647(3)°, β=89.875(3)°, γ=83.835(3)°, V=1596.9(4) ų). In the crystal there exist two kinds of tetrameric O–HO hydrogen-bond (H-bond) systems that are quite similar to each other. The oxygen atoms accept also intermolecular C–HO H-bonds. The two types of the H-bonds connect the molecules to an infinite two-dimensional supramolecular unit, the stacking of which is aided by an intermolecular C–Hπ H-bond. A phase transition with ΔH_t=4.4±0.1 kJ/mol was found at around 420 K.     

Self-assembly of the pre-formed inclusion complexes between cyclodextrins and alkanethiols on gold electrodes

A new kind of self-assembled monolayer (SAM) formed in aqueous solution through the pre-formed inclusion complexes (abbreviated CD · C_n) between α, β-cyclodextrins (CDs) and alkanethiols (CH₃(CH₂)_n−1)SH, n = 10, 14 and 18) was prepared successfully on gold electrodes. High-resolution ¹H NMR was used to confirm the formation of CD · C_n. X-ray photoelectron spectroscopy, cyclic voltammetry and chronoamperometry were used to characterize the resulting SAMs (denoted as M_CD·Cn). It was found that M_CD·Cn were more stable against repeated potential cycling in 0.5 M H₂SO₄ than SAMs of CH₃(CH₂)_n−1SH (denoted as M_Cn), with a relative sequence of M_β−CD·Cn > M_α−CD·Cn > M_Cn. In addition, an order of blocking the electron transfer between gold electrodes and redox couples (both Fe(CN)³₆ and Ru(NH₃)³⁴₆) in solution, M_CD·C10 > M_CD·C14 > M_CD·C18, was observed. A plausible explanation is provided to elucidate some of the observations.     

Hydrothermal Synthesis and Crystal Structure of [(CH3NH3)1.03K2.97]Sb12S20·1.34H2O

A novel thioantimonate(III) [(CH₃NH₃)_1.03K_2.97]Sb₁₂S₂₀·1.34H₂O was synthesized hydrothermally. It crystallizes in space groupP , witha=11.9939(7) Å,b=12.8790(8) Å,c=14.9695(9) Å,α=100.033(1)°,β=99.691(1)°,γ=108.582(1)°,V=2095.3(2) ų, andZ=2. The structure is determined from single crystal X-ray diffraction data collected at room temperature and refined toR(F)=0.037. In the crystal structure, each Sb(III) atoms has short bonds (2.37–2.58 Å) to three S atoms. The pyramidal [SbS₃] groups share common S atoms forming two types of centrosymmetric [Sb₁₂S₂₀] rings with the same topology. These rings are interconnected by weaker Sb–S bonds (2.92–3.29 Å) into 2-dimensional layers. Adjacent layers are parallel with K⁺and CH₃NH⁺₃ions and H₂O molecules located between them. Variation of bond valence sums calculated for the Sb(III) cations is found to be correlated with the coordination geometry. This is interpreted as due to the stereochemical activity of their lone electron pairs.     

A Thermodynamic Study Between 18-Crown-6 with Mg2+, Ca2+, Sr2+and Ba2+ Cations in Water–Methanol and Water–Ethanol Binary Mixtures Using The Conductometric Method

The complexation reactions between Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ cations with the macrocyclic ligand, 18-Crown-6 (l8C6) in water–methanol (MeOH) binary systems as well as the complexation reactions between Ca²⁺ and Sr²⁺ cations with 18C6 in water–ethanol (EtOH) binary mixtures have been studied at different temperatures using conductometric method. The conductance data show that the stoichiometry of all the complexes is 1:1. It was found that the stability of 18C6 complexes with Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ cations is sensitive to solvent composition and in all cases, a non-linear behaviour was observed for the variation of log K _f of the complexes versus the composition of the mixed solvents. In some cases, the stability order is changed with changing the composition of the mixed solvents. The selectivity order of 18C6 for the metal cations in pure methanol is: Ba²⁺ > Sr²⁺ > Ca²⁺ > Mg²⁺. The values of thermodynamic parameters (Δ H _c ° and Δ S _c °) for formation of 18C6–Mg²⁺, 18C6–Ca²⁺, 18C6–Sr²⁺ and 18C6–Ba²⁺complexes were obtained from temperature dependence of the stability constants. The obtained results show that the values of (Δ H _c ° and Δ S _c °) for formation of these complexes are quite sensitive to the nature and composition of the mixed solvent, but they do not vary monotonically with the solvent composition.This revised version was published online in July 2005 with a corrected issue number.     

Theoretical study of the influence of para- and meta-substituents on X-pyridineHF hydrogen bonding

The effects of O⁻, N (CH₃)₂, NH (CH₃), NH₂, C₂H₅, CH₃, OH, F, Cl, OF, Br, NO₂ and substituents in para- and meta-positions on X-pyridineHF hydrogen bond has been studied by HF, B3LYP and MP2 methods using 6-311++G(d,p) basis set. The relationship between hydrogen bond formation energy ΔE and electron donating (or withdrawing) of substituents has been investigated. In this respect, population analysis has been performed by atoms in molecules (AIM) and natural bond orbital (NBO) theories. The results of AIM and NBO analyses are in good agreement with calculated energy values. The relationship between Hammett coefficient and complexation energy has been established and the ρ constant has been calculated for hydrogen bonding. There is a relationship between σ and ΔE with a correlation coefficient equal to 0.94.