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 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.     

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.     

Synthesis of intermediate sitting-atop complexes (i-SAT) from the reaction between free base meso-tetraarylporphyrins and phosphorus(III) chloride in solvent free media

The reaction of meso-tetraarylporphyrins (H₂tap) with phosphorus(III) chloride has been studied in the solid state. The reaction products are intermediate sitting-atop (i-SAT) complexes in which two pyrrolenine nitrogen atoms of the porphyrins act as electron donors to the phosphorus(III) atoms and two protons on the pyrrole nitrogen atoms remain. These new complexes have been characterized by (¹H, ³¹P, ¹³C) NMR, FT-IR and UV–Vis spectroscopy, elemental analysis and electrical conductometry.     

Synthesis and thermodynamic studies of the dinuclear adducts between dimethyltin(IV) dichloride with SalenH2 and MII(Salen) complexes in chloroform

A UV-Vis spectrophotometric study of adduct formation of SalenH₂ (1) and M^II(Salen), where M?=?Mn (2), Fe (3), Co (4), Ni (5) and Cu (6) as donors with Me₂SnCl₂ as acceptor have been investigated in chloroform. Adducts (1a–6a) have been characterized by ¹H, ¹³C and ¹¹⁹Sn NMR, IR and electronic spectroscopy and microanalysis. Formation constants and thermodynamic parameters were measured for 1 : 1 and 2 : 1 adducts at various temperatures (T?=?278 to 308 K). The data refinement was carried out with the SQUAD 84 program. The trend of formation constants of M^II(Salen) complexes with Me₂SnCl₂ follows the order: Mn>Fe>Cu>Co>Ni. The formation constants for the free 1 and M^II(Salen) with Me₂SnCl₂ changes according to the following trend: M^II(Salen)>SalenH₂     

A thermodynamic and spectrophotometric study of the complex formation of copper(II) ions with sulphide-containing α,ω-aminopyridines in aqueous solution

The complexation in aqueous solution of ligands of the type

(CH₂)_n?1 S(CH₂)_mNH₂ (n and m = 2 or 3) with Cu(II) has been investigated. The thermodynamic functions ΔG, ΔH and ΔS of complex formation have been determined at 25°C in 0.5 M KNO₃ solution by means of potentiometric and direct calorimetric titrations. They revealed that the ligands studied act as tridentates towards Cu(II).It was found that the CuL²⁺ complexes having one or two six-membered chelate rings are more distorted than their analogues with only five-membered chelate rings.The CuL²⁺₂ complex with L =

CH₂SCH₂CH₂NH₂ was found to be a strong covalent complex, in which both ligand molecules were completely coordinated.     

A spectrophotometric investigation into the complex formation between bismuth(III) and 2-mercaptoethanol in aqueous solution

Complex formation between bismuth(III) and 2-mercaptoethanol was studied at 25°C and I = 1.0 mol dm^?3 HClO₄. The results were used to test the validity of an empirical equation for the calculation of formation constants.     

The thermodynamic characteristics of complex formation between calcium ions and L-leucine in aqueous solution

Complex formation of L-leucine with calcium ions in aqueous solution was studied by potentiometric titration at 298.15 K and ionic strength values I = 0.5, 1.0, and 1.5 (KNO₃). The formation of the CaL⁺ and CaHL²⁺ complex particles was established and their stability constants were determined. The enthalpies of protolytic equilibria of leucine and formation of calcium ion complexes with leucine were determined calorimetrically at 298.15 K and I = 0.5 (KNO₃). The thermodynamic characteristics of complex formation between calcium ions and L-leucine were calculated.     

Standard thermodynamic functions of complex formation between Cu2+ and glycine in aqueous solution

Heat effects of the interaction of copper(II) solutions with aminoacetic acid (glycine) are measured by the direct calorimetry at 298.15 K and ionic strengths of 0.5, 1.0, and 1.5 against a background of potassium nitrate. Standard enthalpy values for reactions of the formation of aminoacetic acid copper complexes in aqueous solutions are obtained using an equation with a single individual parameter by extrapolating it to zero ionic strength. The standard thermodynamic characteristics of complex formation in the Cu²⁺-glycine system are calculated. It is shown that glycine-like coordination is most likely in Cu(II) complexes with L-asparagine, L-glutamine, and L-valine.     

A spectrophotometric study of the colour reaction between chloranil and aromatic amines

The colour reaction between aromatic amines and chloranil was studied spectrophotometrically. A 1 : 1 adduct formed in solution, with some dissociation. The effects of solvents, acid and alkali were examined. The adducts exhibited intense, and characteristic, broad absorption bands, which could be used for the detection and estimation of an aromatic amine, in the absence of substances of similar light absorption characteristics. A correlation between the basicities of an amine and the ight absorption of the adduct was established.     

A spectrophotometric and thermodynamic study of the charge-transfer complexes of iodine with 2-aminomethyl-15-crown-5 in chloroform and 1,2-dichloroethane solutions

Interaction of 2-aminomethyl-15-crown-5 (AM15C5) with iodine has been investigated spectrophotometrically in chloroform and 1,2-dichloroethane (1,2-DCE) solutions. The observed time dependence of the charge-transfer band and subsequent formation of I(3)(-) in solution were related to the slow transformation of the initially formed 1:1 AM15C5.I(2) outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The pseudo-first-order rate constants were evaluated from the absorbance- and conductivity-time data. The stoichiometry and formation constants of the resulting EDA complexes have also been determined. Thermodynamic parameters, Delta H degrees and Delta S degrees , of the complexes have been determined from the temperature dependence of stability constants by Van't Hoff equation. The results indicate that iodine complexes of AM15C5 in both solvents are enthalpy stabilized but entropy destabilized. The influence of solvent properties on the kinetics and stability of the resulting charge-transfer complexes are discussed.     

光谱法研究CTAB与PAN复合过程的热力学性质

近年来,表面活性剂胶束和微乳液增溶光度法的应用及机理已作了较为深刻的研究[1-3],本文将通过紫外分光光度法考察十六烷基三甲基溴化铵CTAB与有机显色剂PAN复合反应的热力学性质,从而为光度比色分析条件的选择提供一定的理论依据。1　实验方法ShimadzuUV 240型紫外分光光度计(北京市通用仪器设备公司);CS 501型超级恒温器(重庆试验设备厂);AE204电子天平(梅特勒 托利多仪器〈上海〉有限公司)。0 02%的1 (2 吡啶偶氮) 2 萘酚(PAN)乙醇溶液;0 0200mol·dm-3的Sigma公司生产的十六烷基三甲基溴化铵(CTAB)水溶液,HAc NaAc缓冲溶…     

A solution study of complex formation between iron(III) and oxalate in dimethylsulphoxide

Summary The complex formation between iron(III) and oxalic acid (ethanedioic acid, H₂ox) has been studied by potentiometry in dimethylsulphoxide (dmso) solution. H₂ox behaves as a weak diprotic acid in such a solvent, with overall association constants: log _j1=8.551(3) and log _j2=14.242(3) at 25°C and 0.1 Mn-Bu₄NClO₄. A reliable set of overall stability constants for the iron(III)-oxalato complexes, log ₁₁=13.16(4), log ₁₂=23.66(4) and log ₁₃=30.75(4), have been obtained for the first time under identical conditions. The electrochemical behaviour of such complexes was studied in dmso at a platinum electrode. The coordination ability of oxalate towards iron(III) in dmso and water media is compared and discussed in the light of thermodynamic and structural parameters.     

Characterization and determination of the thermodynamic and kinetic properties of p-CP adsorption onto organophilic bentonite from aqueous solution

The characterization of tetraethylammonium bentonite and the adsorption of p-chlorophenol (p-CP) onto organophilic bentonite (tetraethylammonium bentonite) was studied as a function of the solution concentration and temperature. The observed adsorption rates were found to fit first-order kinetics. The rate constants were calculated for temperatures ranging between 15.0 and 35.0 degrees C at constant concentration. The adsorption energy E and adsorption capacity q(m) for the phenolic compound adsorbing on organophilic bentonite were estimated using the Dubinin-Radushkevic equation. Thermodynamic parameters (Deltag(a), Deltah(a), Deltas(a)) were calculated by a new approximation from the isotherms of p-CP adsorption on organophilic bentonite. These isotherms were modeled according to Freundlich and Dubinin-Radushkevic adsorption isotherms. The amount of adsorption of p-chlorophenol on organophilic bentonite was found to be dependent on the relative energies of adsorbent-adsorbate, adsorbate-solvent, and adsorbate-adsorbate interactions.     

A study of polyamine complex formation with H+, Cu(II), Zn(II), Pb(II), and Mg(II) in aqueous solution

Summary The composition and stability of the following biogenic amine complexes have been investigated: 1,4-diaminobutane(Put), 4-azaoctane-1,8-diamine(Spd), 4,9-diazadodecan-1, 12-diamine(Spm) as well as homologues such as 1,3-diaminopropane(Put3), 4-azaheptane-1, 7-diamine(Spd3,3) and 4,8-diazaundecan-1,11-diamine(Spm3,3,3) with H⁺, Cu(II), Zn(II), Pb(II) and Mg(II). A potentiometric method was used. The VIS technique enabled the determination of coordination mode in copper/amine systems. It was found that Mg(II) does not form coordination compounds with any of the studied polyamines in solution. An increase in the concentration of ligand and metal was found to result in a stronger tendency towards the formation of protonated compounds accompanied by a decrease in the concentration of hydroxocomplexes. At physiologicalpH (7.4) an increase in the concentration of protonated compounds by approximately 15% was observed within the ligand concentration range from 0.001 mol dm^–3 to 0.0001 mol dm^–3 at a Cu(II) concentration of 0.000177 mol dm^–3.

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Untersuchungen zur Komplexbildung von Polyaminen mit H⁺, Cu(II), Zn(II), Pb(II) und Mg(II) in wäßriger Lösung

Zusammenfassung Anhand einer Analyse von potentiometrischen Daten wurden Zusammensetzung und Beständigkeit folgender biogener Aminkomplexe untersucht: 1,4-Diaminobutan(Put), 4-Azaoktan-1,8-diamin(Spd), 4,9-Diazadodekan-1,12-diamin(Spm), sowie auch deren Homologen 1,3-Diaminopropan(Put3), 4-Azaheptan-1,7-diamin(Spd3,3) und 4,8-Diazaundekan-1,11-diamin(Spm3,3,3) mit H⁺, Cu(II), Zn(II), Pb(II) und Mg(II). Mit Hilfe der VIS-Technik wurde die Koordinationsweise in Kupfer/Amin-Systemen bestimmt. Es wurde festgestellt, daß Mg(II) keine Koordinationsverbindungen mit den untersuchten Polyaminen bildet. Eine höhere Konzentration von Ligand und Metall führte zu stärkerer Tendenz der Bildung protonierter Verbindungen, wobei die Konzentration von Hydroxokomplexen kleiner wurde. Bei physiologischempH (7.4) wurde im Bereich der Ligand-Konzentration von 0.001 mol dm^–3 bis 0.0001 mol dm^–3 bei einer Cu(II)-Konzentration von 0.000177 mol dm^–3 ein Anstieg der Konzentration protonierter Verbindungen um etwa 15% beobachtet.

     

Synthesis,complex formation kinetics and thermodynamic study of some acyclic polyamine and N2O2 ligands with copper(II)

The polydentate ligands, 3-(2-aminocyclohexylamino)-2-(2-aminocyclohexyl aminomethyl) propionic acid (L¹ ), 4,7,10-triazatridecanedinitrile trihydrochloride (L² ), and 2,2′-(ethane-1,2-diyl) bis(methylazanediyl) diethanol (L³ ) were prepared and their structures investigated by FT-IR, NMR, and MS. The kinetics of complex formation between Cu(II) and L¹, L², and L³ were investigated in acidic aqueous solutions using the stopped-flow method. The stability constants of the complexes were determined by spectrophotometric titration (T?=?293?K, μ?=?0.1?mol?L^?1 NaClO₄), using a diode array UV-Vis spectrophotometer equipped with peristaltic pump and pH meter. The stability constants for the complexes were CuL^1?>?CuL^2?>?CuL³. Activation enthalpies (ΔH#) of these complexes were 55?kJ?mol^?1 for CuL¹, 61?kJ?mol^?1 for CuL², and 36?kJ?mol^?1 for CuL³, respectively.     

Enhancing reactivity of carbonyl compounds via hydrogen-bond formation. A DFT study of the hetero-Diels-Alder reaction between butadiene derivative and acetone in chloroform

To examine how hydrogen-bond (HB) formation involving chloroform solvent molecules influences the chemical reactivity of ketones, the hetero-Diels-Alder reaction of N,N-dimethyl-1-amino-3-methoxy-1,3-butadiene and acetone has been studied by using density functional theory (DFT) at the B3LYP/6-31G level. The effects of the chloroform on the activation energies have been modeled by means of discrete-continuum models. In the gas phase, the formation of specific HB between acetone and one and two chloroform molecules decreases the activation barriers from 19.3 to 13.6 and 8.5 kcal/mol, respectively. Inclusion of solvent effects by means of combined discrete and polarizable continuum models yields a change of molecular mechanism from a concerted to a two-step mechanism, and the first nucleophilic step is the rate-limiting step. The corresponding values of activation barriers in chloroform are 18.6 kcal/ mol (no HB), 13.5 kcal/mol (one HB), and 9.6 kcal/mol (two HBs). These theoretical results account for the experimental observation that chloroform accelerates the reaction more markedly than more polar aprotic solvent such as acetonitrile. A DFT analysis of the global electrophilicity power of the reagents provides a sound explanation about the catalytic effects of chloroform.     

Studies on complex formation between curcumin and Hg(II) ion by spectrophotometric method: A new approach to overcome peak overlap

Complex formation between curcumin and Hg(II) ion MeOH/H₂O (1: 1 v/v) was investigated and monitored by the spectrophotometric method. The absorption peak of unreacted curcumin which was close and overlapped with that of the complex, was removed by calculation using Microsoft Excel, thereby, allowing determination of the stoichiometry of the complex by the mole-ratio and the Job’s continuous variation methods. Both methods indicated that a 1:1 complex of curcumin and Hg(II) was formed in solution. The formation constant of the 1:1 Hg(II) complex was obtained from two methods, the equilibrium concentration calculation and the linear plot of Benesi-Hildebrand equation, as log K = 4.44 ± 0.16 and 4.83 ± 0.02, respectively. The structure is proposed as a tetrahedral complex of Hg(II) with one curcumin and two chloride ions as ligands. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

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.