Thermochemistry of molecular complexes. 4. Molecular complexes of I2 with chloromethylbenzenes

The enthalpy of formation for twelve molecular complexes of I₂ with chloromethylbenzene molecules in CCl₄ have been determined. The wavelength of maximum absorption for each complex is also reported. The formation enthalpy for the complexes appears to depend strongly on the number and type of substituent groups attached to the benzene ring, but only weakly on the location of the substituent group on the ring. This suggests that it should be possible to predict formation enthalpies for a wide variety of complexes of this type based on a limited number of experimental measurements.     

Etude thermodynamique des complexes de transfert de charge du type n-σ* en solution Complexes de la quinoléine et de quinoléines substituées avec I2, ICI et IBr

Thermodynamic study of charge transfert complexes (n-σ*) in solution Charge transfer complexes of quinoline and substituted quinolines (donors) with iodine, iodine chloride, and iodine bromide (acceptors) have been studied spectrophotometrically in CCl₄. The 1:1 stoechiometry of these complexes was verified by means of the continous variations method and the appearance of isosbestic points. Simultaneous determination of the equilibrium constant and enthalpy of adduct formation was carried out by calorimetry. It was observed for every donor that the equilibrium constants of the complexes studied increase with the strength of the acceptors. A linear correlation between enthalpy of adduct formation and donor strength was obtained only for the complexes Donor ICI.     

The formation of bifurcated charge transfer complexes with molecular iodine

I₂ complexes with triptycene and several di- and triaryl derivatives of methane and ethane were studied. For these complexes the values of λ_CT are virtually identical to those reported for the complexes with the analogous monoaryl donors, while the values of λ for their blue shifted I₂ peaks are significantly lower than those for the monoaryl complexes. Both the equilibrium constants and - ΔH⁰ values for the formation of complexes from the components lead to the conclusion that the complexes with the di- and triaryl compounds are more stable than those with the monoaryl donors. For the diaryl donors, the ΔS⁰₂₉₈ values for complex formation are less favorable than those of the monoaryl donors. The dipole moment for I₂ in diphenylmethane is larger than the moment of I₂ in toluene. All of these observations can be explained by taking into account the transannular effect of one aromatic ring on another and viewing the complexes as bifurcated ones in which the I atom at one end of an I₂ molecule simultaneously interacts with two rings in the donor molecules.     

Polymerization of coordinated monomers. VI. Molecular complex formation of methyl methacrylate coordinated to stannic chloride with styrene or toluene

The equilibrium constants for the complex formation between stannic chloride and methyl methacrylate were determined in n-hexane–toluene solution at 0, ?20, and ?30°C by using the absorption band at 350 nm. Continuous variation plots at ?20°C in n-hexane based on the ¹H-chemical shifts definitely show a 1:1 interaction between the coordinated methyl methacrylate and styrene or toluene. The magnitudes of the shifts for the four groups of protons in methyl methacrylate are found to be in a specific ratio in common with the 1:2 complex–styrene or -toluene system. The equilibrium constants for the ternary molecular complex formation between the 1:2 complex and styrene or toluene were determined in n-hexane in the temperature range ?50 to +20°C by use of the chemical shifts. The concentrations of the complex species in the alternating copolymerization solutions were estimated by use of the equilibrium constants. There is a linear relationship between the enthalpy and the entropy changes for the ternary molecular complex formation, which is governed by the enthalpy factor. The specificity of the interactions indicates a specific time-averaged orientation of benzene ring to the coordinated methyl methacrylate. The effects of the coordination of methyl methacrylate to stannic chloride were discussed on the basis of results of ¹³C-NMR spectroscopy.     

Tetraphenylene molecular inclusion complexes. Crystal structures of 2(tetraphenylene)·X,with X=benzene cyclohexane

The crystal structures of two compounds belonging to the isomorphous series of clathrate inclusion complexes of tetraphenylene, 2C₂₄H₁₆·X (with X=benzene (I) and X-cyclohexane (II), were solved. For (I),a=10.0691(1),c=18.431(5) Å, space groupP4₂/n,Z=2; (II) has a very similar cell.Crystal structure analyses (Nicolet R3m four-circle diffractometer, graphite-monochromated MoK; (I) 926 reflections,R _F =12.8%; (II) 1180 reflections,R _F =10%) showed that the tetraphenylene molecules use crystallographicC ₂ symmetry in the construction of a nearly spherical cavity of point symmetry 4 located about 1/4 1/4 1/4. The geometry of the tetraphenylene molecule agrees well with that reported earlier for the crystals of neat tetraphenylene. The enclosed benzene and cyclohexane guests are necessarily disordered. Thedisorder found for the cyclohexane guest is consistent with its expectedchair conformation. Analysis of the cell dimensions of a number of complexes shows that the tetraphenylene framework adjusts itself according to the steric requirements of the guests. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82003. To obtain copies, see page ii of this issue.Also known as N. Z. Huang.     

Hydrogen-bonded supramolecular complexes formed between isophthalic acid and pyridine-based derivatives

Two types of supramolecular liquid crystals were prepared through the formation of double hydrogen-bonded complexes between isophthalic acid (A) and two different groups of pyridine-based derivatives ( I n and I _a-e ). The first group of the base, I n (molecular formula 4-C_nH_2n+1OC₆H₄COOC₆H₄-N=N-C₅H₄N) homologues differ from each other by the number of carbon atoms (n) in the alkoxy chain, which varies between 8, 10, 12 and 14 carbons. The second group of the pyridine-based derivatives, I _a-e (molecular formula 4-X-C₆H₄COOC₆H₄-N=N-C₅H₄N) analogues differ from each other by the terminal polar substituent, X, that changes between OCH₃, CH₃, H, NO₂ and Br groups. In this manner two different groups of complexes are formed, one of them is A : 2I n, (Group A ), and the other is A : 2I _a-e , (Group B ). All complexes were investigated for their mesophase behaviour by differential scanning calorimetry and polarised light microscopy. The formation of 1:2 hydrogen-bonded complexes was confirmed by FTIR spectroscopy and binary phase diagrams. Most complexes A and B show nematic and/or SmA phases. X-ray diffraction of the SmA phase of a representative complex of type A indicates a layer distance corresponding to only half of the length of the H-bonded complexes which is interpreted by a phase structure where these complexes adopt a U-shape which intercalate and form non-polar SmA phases.     

Studies on intermolecular interactions of metal chelate complexes. V. copper(ii) dithiophosphate complexes: an example of an inner self-redox reaction

Summary Studies of copper dithiophosphate (dtp) complexes by various physical methods, in the solid and the molten state as well as in solution, are reported. In the solid state all the complexes of dithiophosphate (RO)₂PS ₂ ^– [R = C_nH_2n+1 (n=1–4), Ph, orcyclo-C₆H₁₁] are diamagnetic but in the molten state and in solution they are paramagnetic. Interconversions were found to be reversible, and the effect was ascribed to an inner self-redox reaction. Only the bulkyo-tolyl derivative is paramagnetic in the solid and molten states and in solution. It is proposed that the self-redox reaction involves association between two molecules of Cu^II(dtp)2 during crystallization, followed by formation of [Cu^I(dtp)]₂, and (RO)₂P(S)S-S(S)P(OR)₂, and then [Cu^I(dtp)]₄. The molecular structures of complexes with R = isopropyl ando-tolyl confirm these inferences.Part IV of this series: N. D. Yordanov, V. Iliev, and D. Shopov,Inorg. Chim. Acta, 60, 21 (1982).     

Isothermal titration calorimetry (ITC) study of natural cyclodextrins inclusion complexes with drugs

Isothermal titration calorimetry (ITC) was used to characterize inclusion complex formation of natural cyclodextrins (α- and β-cyclodextrin) with three drugs ((+)brompheniramine, (±)brompheniramine, cyclopentolate) in aqueous solutions. ITC measurements were carried out at 298.15 K on a Microcal OMEGA ultrasensitive titration calorimeter (MicroCal Inc.). The experimental data were analyzed on the basis of the model of a single set of identical sites (ITC tutorial guide). β-CD forms inclusion complexes of stoichiometry 1:1 with the all investigated drugs. In turn, smaller molecule of α-CD forms inclusion complexes of two different stoichiometry: with bigger molecules ((+)brompheniramine and (±)brompheniramine) of a stoichiometry 2:1 and with smaller molecules (cyclopentolate) of a stoichiometry 1:2. Based on the experimental values of equilibrium constant (K) and enthalpy of complex formation (ΔH), the Gibbs energy of complex formation (ΔG), and the entropy of complex formation (ΔS), have been calculated, for all the investigated systems. Obtained results showed that complex formation of β-CD (bigger molecule with wider cavity compared to β-CD) with both (+)brompheniramine, (±)brompheniramine, and cyclopentolate is enthalpy driven while complexes of α-CD with the all investigated drugs are enthalpy-entropy stabilized. This indicated that the difference in the cavity dimensions is reflecting in different driving forces of complex formation and binding modes what resulted in different stoichiometry of the obtained inclusion complexes.     

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.     

Pulsradiolyse organischer Halogenverbindungen I. Nachweis kurzlebiger Charge-Transfer Komplexe mit Chloratomen

In a solution of benzene in carbon tetrachloride a transient absorption in the visible part of the spectrum could be detected. It appears within less than 0.3 μs after the irradiation by a high-energy electron pulse, and it can be shown to be due to the charge-transfer complex between the chlorine atoms as electron acceptors and benzene molecules as electron donors. A variety of aromatic hydrocarbons also yield similar absorption bands in the visible. They show a linear correlation between the absorption energy and the ionisation potential of the aromatic molecules, which is typical for charge-transfer complexes. A minimum value for the equilibrium constant of complex formation is given. The equilibrium is almost fully shifted to the complex side. An estimated G value for the charge-transfer complex indicates that the complex is actually part of a main reaction in the radiation-induced mechanism. The decay of the charge-transfer complex is mostly pseudo-first order with a half life of a few microseconds.     

Semiconducting polymers based on charge-transfer complexes. III. Complexing and chemical stability of charge-transfer complexes in solution

10-Methylphenothiazine and p-(methylthio)anisole were compared to polymers which contained these donor molecules on the side chains of N-acyl-substituted polyethylenimines. Charge-transfer absorption spectra were compared for these donors with the acceptors: dichlorodicyanobenzoquinone, tetracyanoquinodimethane, tetracyanoethylene, and 2,4,5,7-tetranitrofluorenone. Benesi-Hildebrand plots show that the formation of the polymer complexes have 3 to 50 times higher equilibrium constants than those of the corresponding model complexes. This can be explained by complexing parallel to the polymer backbone. The polymer has the proper geometry for complexing (6.4 Å, repeat distance in the polymer backbone), and an acceptor molecule can therefore be inserted between two adjacent donor molecules for increased stability. Shifts of the absorption maxima to longer wavelength for some of the polymer complexes can be rationalized by the probability that in the polymer, an acceptor is sandwiched between two donors and thus forms 2:1 complexes; the extra resonance energy may shift the absorption maximum to longer wavelength. A second possible explanation is based on solvation of the complex which reduces the energy of the excited state. Polymers absorb mainly in the complex form. Model compounds absorb mainly by contact charge transfer, which is nonsolvated and thus occurs at higher energy or shorter wavelength. Extinction coefficients are higher for the model complexes than for the polymer complexes. Contact charge transfer, which can contribute in greater proportion to the model than to the polymer complexes, explains this. The amount of contact charge transfer can be calculated simply from the probability of a donor being in the solvent shell of an acceptor. Complex decomposition rates were determined based on measuring changes in the intensities of the charge-transfer absorption spectra. Dichlorodicyanoquinone complexes were unstable, while the other complexes were stable.     

Hydration of the carboxylate group: Anab initio molecular orbital study of acetate-water complexes

The hydration of the carboxylate group in the acetate anion has been investigated by performingab initio molecular orbital calculations on selected conformers of complexes with the form CH₃CO₂ ^– ·nH₂O·mH₂O, wheren andm denote the number of water molecules in the first and second hydration spheres around the carboxylate group, andn + m 7. The results of RHF/6–31G^* optimizations for all the complexes and MP2/6–31+G^** optimizations for several one-water complexes are reported. The primary consequence of hydration on the structure of the acetate anion is a decrease in the length of the C-C bond. Enthalpy and free energy changes calculated at the MP2/6–31+G^** and MP2/6–311+ +G^** levels are reported for the reactions CH₃CO₂ ^– + [H₂O] _P CH₃CO₂ ^– ·nH₂O ·mH₂O where [H₂O] _P is a water cluster containingp water molecules andp=n+m 7. The calculations show that conformers with the lowest enthalpy change on complex formation are often not those with the lowest free energy change, due to a greater entropic loss in complexes with tighter and more favorable enthalpic interactions. Hydrogen bonding of six water molecules directly to the carboxylate group in CH₃CO₂ ^– is found to account for approximately 40% of the enthalpy change and 37% of the free energy change associated with bulk solvation.     

Ultrasonic method of determination of stability constants of charge transfer complexes of certain carbonyl compounds and diethylamine in n -hexane

The ultrasonic velocities (U), densities (ρ) and viscosities (η) were measured for solutions containing equimolar concentrations of diethylamine (donor), nine aldehydes and nine ketones (acceptors) in n-hexane at 303 K. Acoustical parameters such as adiabatic compressibility (β), free length (L _f), viscous relaxation time (τ), and molecular interaction parameter (χ_U) have been computed. These values indicate the formation of charge transfer complexes between carbonyl compounds and amine. Formation constant (K) values of the complexes have been evaluated using the equation proposed by Kannappan. The constant values of free energy of activation (ΔG ) and relaxation time indicate the formation of similar charge transfer complexes in these systems. However, the variation in free energy of formation (ΔG°_F) values suggests that their thermodynamic stability depends on the structure of donor and acceptor.     

Solvent effect on the equilibrium constant of the chain reversible reaction of <Emphasis Type="Italic">N,N</Emphasis>′-diphenyl-1,4-benzoquinonediimine with 2,5-dichlorohydroquinone

The temperature dependences of the equilibrium constant K of the reversible chain reaction of N,N′-diphenyl-1,4-benzoquinonediimine with 2,5-dichlorohydroquinone in benzene, chlorobenzene, anisole, benzonitrile, and CCl₄ were studied. The enthalpies and entropies of the reaction in these solvents were determined, and a linear dependence between them in aromatic solvents was found. The equilibrium constant depends on the solvent nature: the replacement of CCl₄ by benzene at T = 298 K increases K from 13.6 to 140. The solvation effects are caused by several types of intermolecular interactions of participants of equilibrium with the medium. The decrease in K in the benzene-anisole-benzonitrile series is related, to a great extent, to complex formation with hydrogen bonding between 2,5-dichlorohydroquinone and the solvents. In anisole a charge-transfer complex is formed between the solvent and reaction product (2,5-dichloroquinone). The constant and enthalpy of the complexation were estimated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2296–2302, December, 2007.     

Synthesis and characterization of some potential antitumor palladium(II) complexes of 2-aminomethylbenzimidazole and amino acids

The stoichiometry and stability constants of complexes formed between [Pd(AMBI)(H₂O)₂]²⁺ (AMBI?=?2-(aminomethyl)-benzimidazole) with some selected bio-relevant ligands containing different functional groups were investigated at 25°C and 0.1?mol?L^?1 ionic strength. The ligands used are imidazole, cysteine, glutathione (GSH), threonine, aspartic acid, 1,1-cyclobutane dicarboxylic acid (CBDCA) and lysine. The stoichiometry and stability constants of the formed complexes were reported and the concentration distribution of the various complex species was evaluated as a function of pH. The results show ring opening of CBDCA and monodentate complexation of the DNA constituent with the formation of [Pd(AMBI)(CBDCA–O)DNA], where (CBDCA–O) represents cyclobutane dicarboxylate coordinated by one carboxylate oxygen. The equilibrium constant of the displacement reaction of coordinated inosine, as a typical DNA constituent, by glutathione, as a typical thiol ligand, was investigated. The effect of dioxane on the formation constant of CBDCA with Pd(AMBI)²⁺ is reported. Five new palladium(II) complexes of the formula [Pd(AMBI)(AA)] ^{n +} (where AMBI?=?2-aminomethyl benzimidazole, AA is an anion of glycine, alanine, cysteine, methionine, and serine) have been synthesized. These palladium(II) complexes have been ascertained by elemental, molar conductance, infrared and ¹H-NMR spectroscopy. The isolated Pd(II) complexes were screened for their antibacterial and cytotoxic activities and the results are discussed.     

Formation of poly(vinyl alcohol)–iodine complexes in solution

The effect of the dissolved state of poly(vinyl alcohol) (PVA) molecules in water on the color development due to PVA–iodine complexes was investigated at each given PVA and iodine concentration using two kinds of syndiotactic-rich PVA (S-PVA) which are unstable in water because of the formation of intermolecular hydrogen bonds and form the complex easily. In the reaction mixtures prepared by mixing PVA solutions and an iodine solution, the color development was constant and independent of standing time of the PVA solution before the addition of iodine up to a certain time, after which it decreased with the standing time. The color development obtained with use of the PVA solution allowed to stand for a fixed time was higher for S-PVA with a lower s-(diad)%. In the case of the reaction mixture prepared by dissolving PVA in an iodine solution, the color development was higher for S-PVA with a higher s-(diad)%. The initial ratio of the I₅⁻/I₃⁻ and the rate of decrease in the ratio of I₅⁻/I₃⁻ were larger than those in the preceding case. The color development decreased for the PVA with an s-(diad) % of 58, whereas it increased for the PVA an s-(diad) % of 61.3 with increasing propanol content, an inhibitor of gelation. From these results, the aggregates of PVA molecules have been assumed to play an important role in forming the complexes. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1701–1709, 1997     

Stability constants of metal complexes of macrocyclic ligands with pendant donor groups

Abstract

In our studies of the stability constants of metal complexes, we have investigated a number of macrocyclic ligands with pendant donor groups. The ligands are characterized by the fact that they have nitrogen donors in the macrocyclic ring and oxygen or sulfur donors in the pendant arms. These ligands represent seven different macrocycles, and by varying the pendant donor groups, ten different ligands are indicated. The affinities of these ligands for fifteen metal ions will be described. The Fe(III) complex of triazanonane with o-hydroxypyridyl or o-hydroxybenzyl pendant donor groups are the most stable ferric complexes ever reported. The In(III) complex of triazacyclononane with pendant mercaptoethyl donor groups, is exceptionally stable. Also, the Ca(II) complex of DOTA probably has the highest stability of any calcium(II) complex. These, and other comparisons will be made on the basis of the thermodynamic stability constant data for the ligands described.     

Formation of aqua and tetraammine Cu(II) complexes inside the cavities of cucurbit[6,8]urils: A DFT forecast

Results of DFT calculations of the structure and thermodynamics of formation of aqua and tetraammine Cu(II) complexes inside CB[n] (n = 6,8) are presented in this study. Formation thermodynamics of the complexes in the cavitands was evaluated by taking into account the most probable number of water molecules inside CB[n]. In this methodology, the complexation was first considered as a substitution reaction in which the guest complex displaces partially or completely the water molecules that are located inside the cavity. The water molecules present in the cavitand were shown to play an important role in the fixation of the guest complex inside the cavity due to the hydrogen bonds with the oxygen portals. The hydration of Cu(II) ion inside CB[6] leads to the formation of an inclusion compound with the formula {[Cu(H₂O)₄]²⁺·2H₂O}@CB[6] while in CB[8] {[Cu(H₂O)₆]²⁺·4H₂O}@CB[8] is formed. For the binding of tetraammine Cu(II) complex, CB[8] was determined to be a significantly more suitable “container” than CB[6]. Both a direct embedding of this complex into the CB[8] and another mechanism in which ammonia molecules replace the water molecules in the Cu(II) aqua complex, preexisting in CB[8] were determined to be thermodynamically possible. Both these lead to the formation of the resultant inclusion compound described by the formula {[Cu(NH₃)₄(H₂O)₂]²⁺·4H₂O}@CB[8].     

Synthesis,crystal structures,and catalytic property of dioxomolybdenum(VI) complexes with hydrazones

Two new dioxomolybdenum(VI) complexes, [MoO₂(L₁)] _n · 0.5 _n CH₃OH (I) and [MoO₂(L₂)(CH₃OH)] (II), where L1 and L₂ are the dianionic form of N′-[1-(4-diethylamino-2-hydroxyphenyl)methylidene]isonicotinohydrazide and N′-(2-hydroxy-4-methoxybenzylidene)-3-methylbenzohydrazide, respectively, were prepared and structurally characterized by physicochemical and spectroscopic methods and single-crystal X-ray determination. For complex I, a polymeric structure is obtained, which is linked by coordination of the pyridine N atoms to the Mo atoms of other [MoO₂(L₁)] units. Complex II is a mononuclear molybdenum compound. In both complexes, the Mo atoms are in octahedral coordination. The catalytic properties of the complexes indicate that they are efficient catalysts for sulfoxidation.