Molecular complexes of iodine with metal acetylacetonates

The ability of metal acetylacetonates to act as electron donors and form molecular complexes with I₂ was studied by examining the electronic, vibrational, and NMR spectra of the complexes. The specific compounds used in the study were Al(acac)₃ Sc(acac)₃ Zr(acac)₄, and Th(acac)₄. The electronic spectra of mixtures of the metal acetylacetonates with I₂ in CHCl₃ had, in addition to the absorption peaks characteristic of the free components, two peaks that were due to the charge transfer complexes. For each complex, the highest wavelength peak (near 360 nm) was assigned to the blue shifted I₂ band, while the lower peak (between 270 nm and 305 nm) was attributed to the intermolecular charge transfer. In the i.r. spectra of each complex, the major effect of complexation was to cause the I₂ stretching frequency to appear between 145 cm⁻¹ and 160 cm⁻¹. The positions of the absorption peaks in both the electronic and vibrational spectra led to the conclusion that in these complexes, I₂ had received a large amount of charge from the donors. Complex formation had little effect on the NMR spectra of the donors. Association constants of 1:1 complexes were determined from the concentration dependence of the absorbance of the blue shifted I₂ bands. Values of ΔHdg and ΔS°₂₉₈ for the complex formation were obtained from the temperature variation of the association constants. The data indicate that the complexes are extremely stable species. Both the stability of the complexes and the high degree of charge transfer were rationalized by considering a model for the intermolecular interactions that involved two M(acac) rings simultaneously transferring charge from one donor to an I₂ molecule.     

Untersuchungen an molekülkomplexen von n-σ-TYP MITT. I. über freie enthalpie—kraftkonstantenkorrelationen von molekülkomplexen des jods m

Linear correlations have been found between the ΔG⁰ values of the molecular complexes R₁R₂R₃PO/I₂, R₁R₂SO/I₂ and R₁R₂SeO/I₂ and the PO, SO and SeO valence force constants, respectively. The nature of the correlation is determined by the ZO donor bond and not by the donor atom, where Z is P, S or Se. The change on ΔG⁰ values for an equal change in the ZO valence force constants increases in the order R₁R₂SO/I₂?R₁R₂R₃PO/I₂ < R₁ R₂SeO/I₂. Seleninyl complexes with I₂ are more stable than the analogous thionyl complexes. From ΔG⁰—f_zo correlation deductions can be made about the nature of the ZO donor bond and ΔG⁰ values can be evaluated from vibrational spectra. A linear correlation exists between the ΔG⁰ values of corresponding thionyl and seleninyl complexes which is of the same form as the correlation between the valence force constants of analogous thionyl and seleninyl compounds.     

Calcium—malonate complexes in aqueous solution. Thermodynamic parameters and their ionic strength dependence

Formation constants of calcium complexes with malonate (mal^2?), in the ranges 10 ? t ? 50°C and 0.05 ? I ? 0.9 mol dm^?3, were determined by means of alkalimetric titrations in aqueous solution. The species found in this system were [Ca(mal)]⁰ and [Ca(Hmal)]⁺; also, the hydrolysis of Ca²⁺ was taken into account. The effect of ionic medium on the formation constants was studied by using different background salts (KNO₃, NaNO₃, Et₄NI and Et₄NBr); the parameters defining ionic strength dependence were calculated from the values of stability constants obtained at different ionic strengths. ΔH and ΔS values were obtained from temperature coefficients of stability constants.A general equation, useful for correlating the formation constants in the studied temperature and ionic strength ranges, has been found. It has also been found that, by considering all the significant interactions in the solution, the formation constants are dependent on temperature and ionic strength only.Literature data are discussed and compared with those obtained in this work.     

Thermodynamische Untersuchungen zur Chelatbildung zwischen Aminoterephthalsäure-N,N-diessigsäure und 3 d- bzw. Erdalkalimetallionen. Eine Betrachtung zum Einfluß einer koordinativ inaktiven Carboxylgruppe auf die komplexe Bindung von Metallionen durch Aminopolycarbonsäuren

N-(2-Carboxyphenyl)iminodiacetic acid (H₃A) and N-(2,5-dicarboxyphenyl)iminodiacetic acid (H₄B) are tetradentate ligands and form complexes of the composition MA- and MB^2? with M^II ions. These compounds differ by the additional charge of the second carboxylic group only, which is fixed to the benzene nucleus and which is unable for coordination for steric reasons. Using an anisothermal calorimeter ΔH values for the formation of the complexes MA- and MB^2? in aqueous solution have been measured at an ionic strength 0.1 m KNO₃. From these data, and from the stability constants of the complexes, entropy changes ΔS have been calculated. In all cases investigated (M^m+ = H⁺, Mg²⁺, Ca²⁺, Sr²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺) the ΔH values are more negative for the complexes MA^m-3 than for complexes MB^m-4, whereas the ΔS values are greater for complexes MB^m-4. Using a simple model for the molecules of the complexes MB^m-4 and empirically determined dielectric constants of the medium between the central ions and the noncoordinated ionized carboxylic group, the electrostatic attraction between these charges was calculated. Basing on these results the influence of the noncoordinated carboxylic group on the central atom by the mesomeric and inductive effect is discussed.     

Thermodynamics of mixed-ligand complex formation of samarium(III) and cerium(III) ethylenediaminetetraacetates with various ligands in aqueous solution

The thermodynamic parameters of reaction (logK, Δ_r G ⁰, Δ_r H, Δ_r S) are determined for the mixed-ligand complex formation of SmEdta^? and CeEdta^? with glycinate, iminodiacetate, aspartate, and nitrilotriacetate ions in aqueous solution at 298.15 K and ionic strength of I = 0.5 (KNO₃). Based on these thermodynamic data, the most likely coordination modes are suggested for the complexone and the ancillary ligand in the mixed-ligand complexes.     

Energies of the gas-phase deprotonation of nitro-substituted benzenesulfonic and benzoic acids: The role of the conformation isomerism of sulfonic acids

The Gibbs energies of deprotonation Δ_r G ₂₉₈ ^○ of gaseous benzoic acid (BA), benzenesulfonic acid (BSA) and their six mono-, di-, and trinitro-substituted derivatives are calculated by means of B3LYP/cc-pVTZ and MP2/6-311++G**. The dependences of Δ_r G ₂₉₈ ^○ on the number and the position of nitro groups in an aromatic ring are revealed, as is the possibility of intramolecular hydrogen bond (IHB) formation in ortho-substituted acids. It is found that the deprotonation of conformers of ortho-nitro-substituted BSA without IHBs requires less energy (by 4–5 kcal/mol) than for conformers with IHBs. It is shown that the Δ_r G ₂₉₈ ^○ values for substituted BA are ～22 kcal/mol higher than the corresponding values for substituted BSA. A trend of diminishing Δ_r G ₂₉₈ ^○ for nitro-substituted acids is observed when the number of nitro groups is increased, and di- and trinitro-substituted BSA may therefore be considered superstrong acids.     

Calorimetric investigations of association equilibria: the pyridine-iodine complex in cyclohexane and in carbon tetrachloride

The results of two independent calorimetric investigations of the pyridine- iodine complex are reported. “Best” values are reported as K_m = 128 1/mol and ΔH° = -8.4 kcal mol^?1 for the formation of the complex in cyclohexane at 25°C, and K_m = 104 and ΔH° = -7.9 kcal mol^?1 in carbon tetrachloride. Evidence is presented to support the contention that association constants for weak complexes determined by calorimetric methods can be as reliable as those determined by spectrometric methods, and that values of ΔH° determined by the calorimetric method are much more reliable than those derived from the temperature dependence of equilibrium constants.     

Simplified formula for the1 A 1⇄5 T 2 spin transition temperature in Fe(II) complexes

A formula relating the¹A₁?⁵T₂ spin transition temperature (T_c) in Fe(II) complexes to characteristics of the compounds is derived. With certain assumptions, T_c is determined by the splitting parameter Δ_LS of e_g- and t_2g-orbitals for the low-spin complexes and by the frequency ratio of normal vibrations of the low- and high-spin phases. For the group of compounds possessing spin transitions, the values of Δ_LS are found and analyzed. Correlations between T_c and Δ_LS are established; the values of the change in the probability of the Mössbauer effect are correlated with those of entropy of spin transition. The correlations are substantiated. It is concluded that for mononuclear Fe(II) complexes possessing sharp spin transitions, T_c may not be significantly higher than for Fe(Phy)₂(BF₄)₂ (T_c=282 K).     

Thermodynamics of the formation of Sm3+-ethylenediamine-N,N′-disuccinic acid complexes in aqueous solutions at 298.15 K

The thermodynamic parameters of the formation of the complexes of ethylenediamine-N,N′-disuccinic acid (H₄Y) with Sm³⁺ ion are determined by means of calorimetry and measuring pH at 298.15 K and ionic strengths of 0.5, 1.0, and 1.5 (KNO₃). The values of logK, Δ _r G, Δ _r H, and Δ _r S are calculated for the formation of SmY^? and SmHY complexes at fixed and zero values of ionic strength. The resulting values are interpreted.     

Building up 1‐D, 2‐D,and 3‐D Polyiodide Frameworks by Finely Tuning the Size of Aryls on Ar‐S‐TTF in the Charge‐Transfer (CT) Complexes of Ar‐S‐TTFs and Iodine

The arylthio‐substituted tetrathiafulvalenes (Ar‐S‐TTFs) are electron donors having three reversible states, neutral, cation radical, and dication. The charge‐transfer (CT) between Ar‐S‐TTFs ( TTF1 — TTF3 ) and iodine (I₂) is reported herein. TTF1 — TTF3 show the CT with I₂ in the CH₂Cl₂ solution, but they are not completely converted into cation radical state. In CT complexes of TTF1 — TTF3 with I₂, the charged states of Ar‐S‐TTFs are distinct from those in solution. TTF1 is at cation radical state, and TTF2 — TTF3 are oxidized to dication. The iodine components in complexes show various structures including 1‐D chain of V‐shaped (I₅)^–, and 2‐D and 3‐D iodine networks composed of I₂ and (I₃)^–.     

Thermodynamics of the formation of nickel(II) complexes with L-histidine in aqueous solutions

The heat effects of the formation of Ni(II) complexes with L-histidine in an aqueous solution are determined via direct calorimetry at 298.15 K and ionic strengths of 0.2, 0.5, and 1.0 (KNO₃). The standard thermodynamic characteristics (Δ_r H ^○, Δ_r G ^○, Δ_r S ^○) of complex formation in the investigated system are calculated. It is concluded that the resulting values are consistent with the results from studying the structure of L-histidine complexes with Ni²⁺ ions by various spectral methods.     

Thermodynamics of Mixed-Ligand Complex Formation of Mercury(II) Ethylenediaminetetraacetate with Ethylenediamine and Hexamethylenediamine in an Aqueous Solution

The thermodynamic parameters (logK, Δ _r G ⁰, Δ _r H, Δ _r S) of formation of the HgEdtaL^2?, HgEdtaHL^? and (HgEdta)₂L^4? complexes (L = NH₂(CH₂)₂NH₂, NH₂(CH₂)₆NH₂) have been determined by the calorimetric and pH-metric methods at 298.15 K and the ionic strength I = 0.5 (NaClO₄). The most probable coordination mode for the complexone and an ancillary ligand in the composition of the mixed complexes was discussed.     

Thermochemical study of the stepwise protonation of 1,10-diaza-4,7-dithiadecane,and its complex formation with copper(II) and nickel(II) ions in aqueous solution

The behaviour of 1,10-diaza-4,7-dithiadecane (2,2,2-NSSN) in aqueous solution in equilibria with protons, Cu²⁺ or Ni²⁺ ions has been investigated potentiometrically and calorimetrically. The protonation constants for the ligand, and the stability constants for its complexes at 25°C in 0.5 mole dm^?3 (K)NO₃ are reported, together with the corresponding thermodynamic parameters ΔG, ΔH and ΔS. The results are compared with those for 1-aza-4-thiapentane and 1,7-diaza-4-thiaheptane. The ligand 2,2,2-NSSN forms complexes of formula ML²⁺ and MHL³⁺ with both Cu²⁺ and Ni²⁺. It is found that in the non-protonated 1:1 complexes the ligand acts as a tetradentate. In the CuHL³⁺ complex, the ligand is bound through one nitrogen and two sulphur donors, whereas in the NiHL³⁺ complex the ligand is probably bound through only one nitrogen and one sulphur donor. Explanations are suggested.     

Spectroscopic studies and determination of the formation constants and thermodynamic parameters for a new water-soluble Co(II) Schiff-base complex and some imidazole derivatives

A new water-soluble Co(II) Schiff-base complex, sodium[{N,N′-bis(5-sulfosalicylidene)-1,8-diamino-3,6-dioxaoctan}cobalt] dihydrate, abbreviated as Na₂[Co(II)L], was synthesized and characterized. The formation constants and thermodynamic parameters for the interaction of this complex with imidazole (Im) and 1-methylimidazole (MeIm) were determined spectroscopically in aqueous solution, ethanol/water (10/90), and methanol/water (10/90) under physiological conditions (pH?=?7), constant ionic strength (I?=?0.1?mol?dm^?3 KNO₃), and various temperatures ranging from 294 to 310?K. Our spectroscopic and thermodynamic results show that this adduct formation is endothermic and the positive values of ΔS _f° make ΔG _f° negative. The trend in variation of ΔH _f° and ΔS _f° for Im is in the order water?>?methanol?>?ethanol, but for MeIm it is in the opposite order which is related to the hydrogen bonding between solvents and these donors. Formation constants between MeIm and Na₂[Co(II)L] in these three solvents are larger than for Im which depends on the electron donation of methyl on MeIm.     

Further studies on polyhalide formation in polar solvents using the positron annihilation lifetime spectroscopy

The rate constants for the reactions of positronium with I ₃ ⁻ , Br⁻, and I⁻ in dimethylsulphoxide (DMSO) and for I ₃ ⁻ in water have been determined, and the orthopositronium lifetime variations have been used for studying polyhalide formation in the (I₂+Br⁻)/DMSO system. It is found that the formation of more than one polyhalide is needed to account for the data. On basis of this new evidence, previous results in methanol and in DMSO are re-examined. Besides the primary I₂X⁻ (X⁻: halide), I₂X ₂ ²⁻ complexes have to be invoked. Trial absorption measurements confirm the presence of solvolysis equilibria for I₂ in DMSO. Taking these facts into account, much higher, albeit poorly defined, values than previously reported are found for the I₂X⁻ formation constants. The reliable K_c values deduced are 28M⁻¹, 0.57M⁻¹ and 2.5M⁻¹ respectively for I₂Cl⁻, I₂Cl ₂ ² and I₂Br ₂ ²⁻ in methanol, and 1.4M⁻¹ and 0.8M⁻¹, respectively for I₂Cl ₂ ²⁻ and I₂Br ₂ ²⁻ in DMSO.     

4,7,10,13-Tetrakis(carboxymethyl)-1-oxa-4,7,10,13-tetraazacyclopentadecane and properties of its metal complexes

A new N-carboxymethyl derivative of the oxa-tetraaza macrocyle, 4,7,10,13-tetrakis-(carboxymethyl)-1-oxa-4,7,10,13-tetraazacyclopentadecane, has been synthesised. The protonation constants of this compound and the stability constants of its complexes with several di- and trivalent metal ions were determined by potentiometric or spectrophotometric methods, at 25°C and ionic strength 0.10 M in tetramethyl ammonium nitrate. The ligand exhibits two high or fairly high values of protonation constants and two low ones, and its overall basicity is about 27 in log units. Mono- and dinuclear complexes were found. The stability constant values of the 1:1 complexes with most of the metal ions studied are lower than expected, but not those of the dinuclear complexes. This was interpreted, in the case of mononuclear complexes, as the non-involvement in the co-ordination to these metal ions of two nitrogen atoms of the macrocycle backbone and, probably also, of one or two carboxylate groups. The Cu²⁺ ion has an exceptional behaviour, its 1:1 complex exhibits a high stability constant value. Spectroscopic data have indicated, for the last complex, the presence of two octahedral isomers in solution, one of them having only two nitrogens in the co-ordination sphere, while in the other three nitrogen donor atoms of the macrocyclic framework are co-ordinated in the equatorial plane. A third species appears at pH values higher than 7. These features suggest that the presence of four carboxymethyl arms and the relatively large size of the macrocycle severely constrains the geometric arrangement of the nitrogen donor atoms of the macrocyclic backbone around the metal centre decreasing the co-ordination number or leading to a preferred co-ordination with oxygen atoms. Another consequence of these structural features, is their easy ability to form dinuclear complexes, as found in the equilibria studies in solution and also by EPR spectroscopy of the Cu²⁺ complexes where the presence of two types of signals in the ΔM_s=1 and ΔM_s=2 regions, clearly reveals the presence of the dinuclear complex.     

Thermochemistry of molecular complexes. 5. Molecular complexes of I2 with ethylbenzenes andn-alkylbenzenes

The enthalpies of formation and equilibrium constants are reported for molecular complexes of I₂ with five ethylbenzene and ninen-alkylbenzene donor molecules in CCl₄. The wavelength of maximum absorbance for each complex is also reported. For ethylbenzene donor molecules, the formation enthalpy and equilibrium constant for the complexes depend strongly on the number of ethyl groups attached to the benzene ring, but only weakly on the position of the groups. For then-alkylbenzene donor molecules, both the formation enthalpy and equilibrium constant for complex formation are indenpendent of the length of the alkyl chain. These results are consistent with previous observations on weak complexes of I₂ with substituted benzene donors.     

Charge-transfer complexes of 4-nitrocatechol with some amino alcohols

Charge-transfer (CT) complexes formed from the reactions of 4-nitropyrocatechol (4-nCat) as an electron acceptor with four amino alcohols: 2-aminoethanol, 1-amino-2-propanol, 4-aminobutanol and N-(2-hydroxyethyl)-1,3-diaminopropane (NHEDAP) as electron donors, have been studied spectrophotometrically in H₂O and H₂O/EtOH at 20, 25, 30, 35 and 40 °C. The calculated values of the oscillator strength and transition moment confirm the formation of CT-complexes. The thermodynamic and spectroscopic parameters were also evaluated for the formation of CT-complexes. The equilibrium constants ranged from 9.00 to 2.20 l mol^?1 (M^?1). These interactions are exothermic and have relatively large standard enthalpy and entropy changes (ΔH values ranged from ?15.58 to ?3.10 kJ mol^?1; ΔS ranged from 26.81 to ?3.25 J K^?1 mol^?1). The solid CT-complexes have been synthesized and characterized by IR, NMR, mass spectrometry and thermal analysis. The photometric titration curves and other spectrometric data for the reactions indicated that the data obtained refer to the formation of 1:1 charge-transfer complex of [(4-nCat) (NHEDAP)] and 1:2 charge-transfer complexes of other amino alcohols [(4-nCat) (amino alcohol)₂]. The effect of alkali and alkaline earth metals on increasing the equilibrium constant of the CT-complexation was also investigated.     

Synthesis of Aryl-Manganese(III) Fluoride Complexes via α-Fluorine Elimination from CF3 and Difluorocarbene Generation

We report the synthesis of cyclometalated monoaryl Mn^III fluoro complexes using bis(trifluoromethyl)zinc reagent, Zn(CF₃)₂(DMPU)₂, under mild conditions via a reaction pathway that involves initial transmetalation followed by α-fluorine elimination. The formation of difluorocarbene in these reactions was detected by trapping experiments. Such facile difluorocarbene generation from Mn^III results in moderate enhancement of difluoropropanation and difluoropropenation of alkenes and alkynes using Zn(CF₃)₂(DMPU)₂ at lower temperature (20–60 °C) and short reaction time, suggesting potential application of manganese(III) perfluoroalkyl complexes as reactive species for carbene transfer reactivity.     

Thermodynamique de la complexation des metaux de transition par les acides α-amines. I. Etude potentiometrique des systemes cuivre(II)—phenylalanine et cobalt(II)—phenylalanine

Protonation constants for phenylalanine anion (L) and formation constants for complexes ML⁺ and ML₂ (M = Cu²⁺ or Co²⁺) are reported for I = 1 M (Na)ClO₄ and I = 1 M (Na)Cl at 25°C. The results are compared with those of other workers.