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 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.     

Thermodynamic investigation of the molecular interactions of 4-nitrophenol with free-bases meso-tetraarylporphyrins

The molecular interactions of 4-Nitrophenol (4NP) with free-base meso-tetraarylporphyrins (H₂T(4-X)PP; X = OCH₃, CH₃, H, Cl) have been studied. The formation constants and other thermodynamic parameters were calculated by using UV-Vis spectrophotometry titration results. The formation constants show the following trend relative to X substituent of porphyrins: H₂T(4-CH₃O)PP > H₂T(4-CH₃)PP > H₂TPP > H₂T(4-Cl)PP.     

A spectrophotometric and thermodynamic study of the sitting-atop complex formation from reaction between free base meso-tetraarylporphyrins and zirconyl nitrate in chloroform solution

The sitting-atop complexation of meso-tetraarylporphyrins and its para-substituted derivatives (H₂t(4-X)pp, X:H, Br, Cl, CH(CH₃)₂, OCH₃, CH₃), as electron donors, with zirconyl, as an electron acceptor, have been investigated spectrophotometrically in chloroform. The mole ratio studies based on physicochemical techniques were employed clearly and revealed the formation of 1:1 sitting-atop complexes which was confirmed by UV–vis, ¹H NMR and IR spectroscopic data. The value of the formation constant was estimated for each complex using a nonlinear optimization of the complex absorbance vs. mole ratio data by package KINFIT. The results showed that the stability of these complexes decreases with the temperature enhancement. Thermodynamic parameters, ΔG°, ΔH° and ΔS°, of the SAT complexes have been determined from the temperature dependence of formation constants by Van’t Hoff equation. Also, the influence of the substituents of the aryl rings in H₂t(4-X)pp on the stability of the SAT complexes is discussed.     

Interaction of methyltin(IV) compounds with carboxylate ligands. Part 1: formation and stability of methyltin(IV)–carboxylate complexes and their relevance in speciation studies of natural waters

Quantitative data on the stability of mono‐, di‐ and trimethyltin(IV)‐carboxylate complexes (acetate, malonate, succinate, malate, oxydiacetate, diethylenetrioxydiacetate, tricarballylate, citrate, butanetetracarboxylate and mellitate) are reported at t = 25 °C and I→ 0 mol l^?1. Several mononuclear, mixed proton, mixed hydroxo and polynuclear species are formed in these systems. As expected, the stability trend is mono‐ > di‐ > trimethyltin(IV) and mono < di < tri < tetra < hexa for the organotin moieties and carboxylate ligands investigated, respectively. Moreover, ligands containing, in addition to carboxylic,? O? and? OH groups show a significantly higher stability with respect to analogous ligands with the same number of carboxylic binding sites. The results obtained from all the systems investigated allowed us to formulate the following empirical predictive equation for correlation between complex stability and some simple structural parameters, (1) where n_carb and n_OH are the number of carboxylic and alcoholic groups in the ligand, respectively, r is the stoichiometric coefficient of H⁺ (positive) or OH^? (negative) and z_cat is the methyltin cation charge (CH₃)_xSn^z+ (z⁺ = 4 ? x). Distribution diagrams for some representative systems are also reported and are discussed in the light of speciation studies in natural waters. A literature data comparison is made with carboxylate complexes of other metal ions with the same charge as the organotin cations investigated here. Copyright © 2005 John Wiley & Sons, Ltd.     

Interaction of methyltin(IV) compounds with carboxylate ligands. Part 2: formation thermodynamic parameters,predictive relationships and sequestering ability

Thermodynamic data of mono‐, di‐ and tri‐methyltin(IV)‐carboxylate complexes (acetate, malonate, succinate, oxydiacetate, diethylenetrioxydiacetate, malate, citrate, 1,2,3‐tricarballylate, 1,2,3,4‐butanetetracarboxylate, 1,2,3,4,5,6‐benzenehexacarboxylate) in aqueous solution are reported at t = 25 °C and I = 0 mol l⁻¹. Thermodynamic parameters obtained were analysed to formulate empirical predictive relationships as a function of different parameters, such as the number of carboxylate groups of the ligand and the charge of the alkyltin(IV) cation. Sequestration diagrams of citrate and 1,2,3‐tricarballylate towards alkyltin(IV) cations at different pH values are also reported and discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

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.     

Kinetics and mechanism of vanadium(IV) oxidation by tetrabutylammonium tribromide

The reaction between tetrabutylammonium tribromide(TBATB) and vanadium(IV) has been studied in 50% (v/v) acetic acid under second order conditions. The overall order of reaction is found to be two, unity in each reactant. The reaction involves two single-electron transfer steps generating bromine free radical in the first rate determining step. The test for the formation of free radicals in presence of added acrylonitrile was negative while added toluene increases the rate of the reaction considerably due to its conversion into benzyl bromide. The reaction is retarded by hydrogen ions as a result of protonation prior equilibria of the active reductant, vanadyl acetate. The oxidation of the vanadylsalen complex by TBATB proceeds more rapidly than that of vanadyl acetate but follows the similar kinetic behaviour. Considerable decrease in the entropy of activation of the reaction indicates formation of an ordered transition state between the two reactants and since the kinetic behaviour remains unaltered, even after the change in the ligand attached to the reductant, indicates an interaction between the reactants through the oxygen atom on the vanadyl ion.     

Nickel(II) salophen-type complexes characterization and their thermodynamic studies with diorganotin(IV) dichlorides in chloroform

A u.v.–vis spectrophotometric study of the adduct formation of the nickel(II) Schiff base complexes,([NiL]) where L = [3-methoxysalophen, N,N′-bis(3-methoxysalicylidene)-1,2-phenylenediimine] (1), [4-methoxysalophen, N,N′-bis(4-methoxysalicylidene)-1,2-phenylenediimine] (2), [5-methoxysalophen, N,N′-bis(5-methoxysalicylidene)-1,2-phenylenediimine] (3) and [Salophen, [N,N′-bis(salicylaldehydo)-1,2-phenylenediimine] (4) as donors with R₂SnCl₂ (R = methyl, phenyl and n-butyl) as acceptors have been investigated in chloroform, as solvent. Adducts have been characterized by ¹H, ¹³C and ¹¹⁹Sn NMR, IR and electronic spectroscopy and CHN elemental microanalysis. The formation constants and the thermodynamic free energies were measured using u.v.–vis spectrophotometry titration for 1:1 adduct formation at various temperatures (T = 278 to 308 K). The trend of the adduct formation of the nickel Schiff base complexes with a given tin acceptor decreases as follows:

The molecular and ionic sublimation of holmium tribromide

The molecular and ionic composition of vapor over holmium tribromide was studied by high-temperature mass spectrometry under the conditions of sublimation from a Knudsen effusion cell and from the open single crystal surface. The partial pressures of HoBr₃ and Ho₂Br₆ in saturated vapor and the ratio between their sublimation coefficients under free vaporization conditions were determined. The intensities of lines in the electron impact mass spectra and their temperature dependences were different under Knudsen and Langmuir conditions, which was evidence of superthermal vibrational-rotational excitation of molecules sublimed from the open surface. The enthalpies and activation energies of sublimation of HoBr₃ crystals as monomers and dimers were calculated. The emission of HoBr ₄ ^? and Ho₂Br ₇ ^? negative ions was observed under both sublimation conditions. Ion-molecular equilibria in the LaBr₃-HoBr₃ system were studied. The enthalpies of formation of the HoBr₃ and Ho₂Br₆ molecules and HoBr ₄ ^? and Ho₂Br ₇ ^? negative ions in the gas phase were calculated.     

Schiff base derivatives of titanium(IV) and zirconium(IV)

The reactions of a few bifunctional and tridentate Schiff bases with titanium-(IV) and zirconium(IV) isopropoxides in equimolar and bimolar ratios are described. The resulting compounds have been obtained in almost quantitative yields and are of the general formulae M(SB)_x(OPrⁱ)_4?2X (where M = Ti or Zr; SB- = anion of the Schiff base SBH₂ and x = 1 or 2). Their molecular weights have been determined ebullioscopically and IR spectra recorded.     

Thorium(IV) complexes with tetradentate Schiff base ligands

Summary Some thorium(IV) complexes were synthesized with the tetradentate Schiff base ligands (N₂O₂ donor set) obtained by the condensation of ethylenediamine with salicylaldehyde (H₂salen) or acetylacetone (H₂ acacen). In all cases the neutral Schiff bases and not their anions are coordinated to the central thorium(IV) atom. The complexes have the general formula: ThL₂Xa (L = H₂ salen; X = Cl, Br, 1, NCS and L = lie acacen; X = Cl, 1, NCS, ClO₄) or ThLX₄ (L = H₂ salen; X = NO₃, ClO₄ and L = H₂ acacen; X = Br, NO₃). The stoichiometry and coordination number of the complexes was determined on the basis of elemental analysis, conductivity measurements, i.r. spectra and t.g.a./d.t.a. data. The coordination number of the complexes is either 12 or 8 for the bisor monocomplexes respectively.     

Schiff base complexes of silicon(IV)

Reactions of silicon tetraacetate with different types ofSchiff bases have been investigated in anhydrous benzene. Monofunctional bidentate, C₆H₅CHNXOH and HORCHNC₆H₅ [whereX=CH₂CH₂, CH₂CH(CH₃) or o-C₆H₄ and R=o-C₆H₄ or 2,1-C₁₀H₆], bifunctional tridentate, o-HOC₆H₄CHNYOH [whereY=CH₂CH₂ or CH₂CH(CH₃)] and bifunctional tetradentateSchiff bases, o-HOC₆H₄C(CH₃)N(CH₂) _n NC(CH₃)C₆H₄OH-o (wheren=2 or 3) have been shown to yield derivatives of the type, Si(OAc)_4– m L _m, Si(OAc)_4–2 n L _n and Si(OAc)₂ L (wherem=1,2 or 3;n=1 or 2 and HL, H₂ L and H₂ L represent the molecules of monofunctional bidentate, bifunctional tridentate and bifunctional tetradentateSchiff bases resp.) and have been found to be monomeric in boiling benzene. Tentative structures based on IR and in a few cases PMR spectra have been indicated for the resulting derivatives.With 2 Figures     

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     

Synthesis, characterization and structural studies of diorganotin(IV) complexes with Schiff base ligand salicylaldehyde isonicotinylhydrazone

Eight diorganotin(IV) complexes of salicylaldehyde isonicotinylhydrazone (H₂SalN) R₂Sn(SalN) R = t-Bu 1, Ph 2, PhCH₂3, o-ClC₆H₄CH₂4, p-ClC₆H₄CH₂5,m-ClC₆H₄CH₂6,o-FPhCH₂7, p-FC₆H₄CH₂8 were prepared. All complexes 1-8 have been characterized by elemental, IR, ¹H, ¹³C and ¹¹⁹Sn NMR analyses. The crystal structures of H₂SalN and complex 1 were determined by X-ray crystallography diffraction analyses. Studies show that H₂SalN is a tridentate planar ligand. For complex 1, the tin atom lies in this plane and forms a five- and six-membered chelate ring with the tridentate ligand. A comparison of the IR spectra of the ligand with those of the corresponding complexes, reveals that the disappearance of the bands assigned to carbonyl unambiguously confirms that the ligand coordinate with the tin in the enol form.     

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.     

Study of weak molecular interactions through thermodynamic mixing properties

The electron donor-acceptor abilities of some cyclic ethers (tetrahydropyran or tetrahydrofuran), benzene, and halobenzenes (fluorobenzene or chlorobenzene) and the molecular interactions between these compounds have been investigated through a wide set of thermodynamic mixing properties of their mixtures. The mixing properties have been derived from experimental measurements of density, speed of sound, refractive index, surface tension, heat of mixing, and vapor-liquid equilibrium at the temperature of 298.15 K.     

Tetradentate Schiff base oxovanadium(IV) complexes

Summary Eleven oxovanadium(IV) complexes of tetradentate Schiff bases, obtained by condensating two moles of an o-hydroxycarbonyl compound with a diamine, have been prepared and characterized by elemental analysis, m.p., and i.r. and electronic spectra. The i.r. and electronic spectra of the free ligand and the complexes are compared and discussed. The Gaussian analysis of the vis. spectra of the complexes, normally C₁ or C_s, in MeCN yielded four peaks at ca. 12000, 15000, 17700 and 20000–23000cm^–1, assigned to the four d-d transitions.