Pyrimidotetrathiafulvalenes. 3.* synthesis and properties of cation-radical salts,cation-radical betaines,and complexes of dimethyl[2,4-dioxo(1H,3H)pyrimido]tetrathiafulvalene and its N-alkyl substituted derivatives with iodine

The reaction of dimethyl[2,4-dioxo(1H,3H) pynmido]tetrathiafulvalene and its N-alkyl derivatives with iodine leads to the formation of complexes with various numbers of iodine atoms. Depending on the conditions, the betaine of the cation-radical of dimethyl[2, 4-dioxo(1 H, 3H)pyrimidojtetrathiafulvalene or a complex of the latter with dimethy1[2,4-dioxo(1H,3H)pyrimidoltetrathiafulvalene is formed by the oxidation of the pyrimidotetrathiafulvalene. The cation-radical perchlorates are formed on carrying out the oxidation of dimethyl[2,4-dioxo(1H,3H)pyrimidojtetrathiafulvalene and its N-methyl derivatives in the presence of perchloric acid. The preparation of the cation-radical salts is usually linked with the reaction of the cation-radical betaine with acids.For part 2 see [1].     

Oxidimetric determination of triphenylphosphine

A method for the determination of triphenylphosphine based on its oxidation to phosphine oxide by iodine or chloramine-T in acid medium in presence of benzene or carbon tetrachloride is described. The oxidation is completed within 2 min and the analytical values are accurate to within 0.5%. The method is applicable to determination of triphenylphosphine in its metal complexes.     

Evidence for complexes of different stoichiometries between organic solvents and cyclodextrins

The influence of the organic solvent on the acid and basic hydrolysis of N-methyl-N-nitroso-p-toluenesulfonamide (MNTS) in the presence of alpha- and beta-cyclodextrins has been studied. The observed rate constant was found to decrease through the formation of an unreactive complex between MNTS and the cyclodextrins. In the presence of dioxane, acetonitrile or DMSO, the inhibitory effect of beta-CD decreased on increasing the proportion of organic cosolvent as a result of a competitive reaction involving the formation of an inclusion complex between beta-CD and the cosolvent. The disparate size of the organic solvent molecules resulted in stoichiometric differences between the complexes; the beta-CD-dioxane and beta-CD-DMSO complexes were 1 : 1 whereas the beta-CD-acetonitrile complex was 1 : 2. The basic and acid hydrolysis of MNTS in the presence of alpha-CD showed a different behavior; thus, the reaction gave both 1 : 1 and 2 : 1 alpha-CD-MNTS complexes, of which only the former was reactive. This result was due to the smaller cavity size of alpha-CD and the consequent decreased penetration of MNTS into the cavity in comparison to beta-CD. The acid hydrolysis of MNTS in the presence of alpha-CD also revealed decreased penetration of MNTS into the cyclodextrin cavity, as evidenced by the bound substrate undergoing acid hydrolysis. In addition, the acid hydrolysis of MNTS in the presence of acetonitrile containing alpha-CD gave 1 : 1 alpha-CD-acetonitrile inclusion complexes, which is consistent with a both a reduced cavity size and previously reported data.     

Spectrophotometric study of the reaction of iodine and bromine with two new macrocycle diamides and di-ortho methoxybenzoyl thiourea in chloroform solution

The complex formation reactions of iodine and bromine with two new macrocycle diamides (1 and 2) and di-ortho methoxybenzoyl thiourea (DOMBT) (3) have been studied spectrophotometrically at various temperatures in chloroform solution. In all cases the resulting 1:2 (macrocycle to halogen) or (DOMBT to halogen) molecular complexes were formulated as (macrocycle...X(+))X(3)(-) or (DOMBT.... X(+))X(3)(-). The formation constants of the resulting molecular complexes were evaluated from computer fitting of the absorbance-mole ratio data. For iodine complexes we found that the values of K(f) vary in the order of 1 approximately 2>3. In the case of bromine complexes the values of K(f) are larger (>10(8)) and vary in the order of 1>2>3. The enthalpy and entropy of complexation reactions of iodine with 1, 2 and 3 were determined from the temperature dependence of the formation constants. In all cases it was found that the complexation reactions are enthalpy stabilized, but entropy destabilized.     

Complexes of acridine and 9-chloroacridine with I2: formation of unusual I6 chains through charge-transfer interactions involving amphoteric I2

Acridine and 9-chloroacridine form charge-transfer complexes with iodine in which the nitrogen-bound I2 molecule is amphoteric; one end serves as a Lewis acid to the heterocyclic donor, while the other end acts as a Lewis base to a second I2 molecule that bridges two acridine.I2 units. In the acridine derivative [(acridine.I2)2.I2, 1], the dimer has a "zigzag" conformation, while in the 9-chloroacridine derivative [(9-Cl-acridine.I2)2.I2, 2], the dimer is "C-shaped". The thermal decomposition of the two complexes is very different. Compound 1 loses one molecule of I2 to form an acridine.I2 intermediate, which has not been isolated. Further decomposition gives acridine as the form II polymorph, exclusively. Decomposition of 2 involves the loss of two molecules of I2 to form a relatively stable intermediate [(9-Cl-acridine)2.I2, 3]. Compound 3 consists of two 9-Cl-acridine molecules bridged through N...I charge-transfer interactions by a single I2 molecule. This compound represents the first known example, in which both ends of an I2 molecule form interactions in a complex that is not stabilized by the extended interactions of an infinite chain structure. The ability of the terminal iodine of an N-bound I2 to act either as an electron donor (complexes 1 and 2) or as an electron acceptor (complex 3) can be understood through a quantum mechanical analysis of the systems. Both electrostatic interactions and the overlap of frontier molecular orbitals contribute to the observed behavior.     

Stoichiometric and catalytic oxidations with hypervalent organo-lambda3-iodanes

Isolation, characterization, and reaction of the activated iodosylbenzene monomer, hydroxy(phenyl)iodonium ion, as a complex with 18-crown-6 (18C6) are reported. The reaction of iodosylbenzene with HBF(4) in the presence of 18C6 afforded the hydroxy-lambda(3)-iodane complex PhI(OH)BF(4).18C6 as stable yellow prisms. X-ray structure analysis indicated that the close contacts between the iodine(III) and the three adjacent oxygen atoms of 18C6 will be responsible for the increased stability of the complex compared to the uncomplexed PhI(OH)BF(4). The aqua complex of the activated iodosylbenzene, PhI(OH)OTf.18C6.H(2)O, with a water molecule coordinated to iodine(III) was also prepared. These crown ether complexes are highly reactive and serve as versatile stoichiometric oxidants, especially in water. Thus, the complexes undergo oxidative transformations of a variety of functional groups such as olefins, alkynes, enones, silyl enol ethers, sulfides, and phenols under mild conditions. The latter part reports on the iodobenzene-catalyzed alpha-oxidation of ketones, in which diacyloxy(phenyl)-lambda(3)-iodanes generated in situ act as real oxidants of ketones and m-chloroperbenzoic acid (m-CPBA) serves as a terminal oxidant. The oxidation of a ketone with m-CPBA in acetic acid in the presence of a catalytic amount of iodobenzene, BF(3)-Et(2)O, and water at room temperature affords an alpha-acetoxy ketone in good yield. It is noted that the use of water and BF(3)-Et(2)O is crucial to the success of this alpha-acetoxylation.     

Determination of thermodynamic formation values for some solid charge-transfer complexes of iodine

The standard Gibbs free energy, enthalpy, and entropy of complex formation of five solid molecular complexes of iodine have been determined by comparing the e.m.f.'s of galvanic cells having either solid iodine or the iodine complex as cathode. All of the complexes were found to have a negative enthalpy of formation, which was in the range ?5 to ?14 kJ mol^?1, except for one very weak complex. The relative stability of the complexes was largely determined by the standard entropy of formation which varied from +18 J K^?1 mol^?1, for the most stable of the complexes studied, to ?21 J K^?1 mol^?1.     

Synthesis and electrochemical studies of charge-transfer complexes of thiazolidine-2,4-dione with σ and π acceptors

In the present work, we report the synthesis and characterization of novel charge-transfer complexes of thiazolidine-2,4-dione (TZD) with sigma acceptor (iodine) and pi acceptors (chloranil, dichlorodicyanoquinone, picric acid and duraquinone). We also evaluated their thermal and electrochemical properties and we conclude that these complexes are frequency dependent. Charge-transfer complex between thiazolidine-2,4-dione and iodine give best conductivity. In conclusion, complex with sigma acceptors are more conducting than with pi acceptors.     

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.     

A spectroscopic study of the iodine complexes of donors—pyridines,phenanthrolines, bipyridines and diazines

Ultraviolet—visible spectral data of iodine complexes of n- and π-donors have been interpreted by considering that the repulsion energy responsible for the blue shift of the iodine band is also experienced by the donor partner which causes the blue shift of the original band of the donor. This reasoning explains the spectral data of iodine complexes of benzene, pyridine-N-oxide and stilbazoles. Ultraviolet—vis. spectra of the iodine complexes of pyridine, aminopyridines and diazines have been reinvestigated and discussed in the light of the above reasoning. The above reasoning is extended to the CT spectra of iodine complexes of twin-site donors such as 1,10-phenanthroline, its methyl and chloro derivatives, 1,7 and 4,7-phenanthrolines, 2,2′-bipyridine and 4,4′-bipyridine. Arguments are presented which indicate that the donors used in this study form only 1:1 complexes with iodine. The thermodynamic parameters were evaluated for iodine complexes of the above twin-site donors. The kinetics of transformation of outer CT complexes between the donors and iodine to inner complexes is presented and discussed. Two CT bands are observed for the iodine complexes of 1,10-phenanthroline and its substituents. These bands are explained by assuming a structure for the 1,10-phenanthroline complex in which iodine is in dynamic equilibrium between the two nitrogens.     

Polarographic studies of iron complexes as potential contrast as agents in magnetic resonance imaging

Iron(III) complexes of polyaminocarboxylic acids of potential use as contrast agents in magnetic resonance imaging wre investigated by differential pulse polarography. The complexes with diethylenetrinitrilopentaacetic acid, trans-1,2-cyclohexylenedinitrilotetraacetic acid and triethylenetetranitrilohexaacetic acid (TTHA) wre found to decompose slowly at pH 7.2. With TTHA, a mixture of 1:1 and 2:1 complexes was obtained, and the transformation between the two complexes was slow. Ethylenediimonobis[(2-hydroxyphenyl)acetic acid] (EHPG) was found to be the most suitable ligand. The complex formation is kinetically slow, and a special procedure for the preparation of the complex is required; the complex is then stable for one week at pH 7.2. The polarographic measuremeents are preferably made at pH 9.2, where a well-defined reduction peak is obtained. The complex is stable for 2 days at pH 9.2. At pH values below 9, a double peak is obtained, except for low concentrations of the complex. Both Fe(III)EHPG and Fe(II)EHPG adsorb at the mercury electrode. The polarographic determination can be done in the presence of 10% of urine or serum without interference. The detection limit is in the low μM range.     

Spectrophotometric study of the charge-transfer complexes of iodine with antipyrine in organic solvents

The charge-transfer complex formation of iodine with antipyrine has been studied spectrophotometrically in chloroform, dichloromethane (DCM) and 1,2-dichloroethane (DCE) solutions at 25 degrees C. The results indicate the formation of 1:1 charge-transfer complexes. 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 antipyrine: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 values of the equilibrium constant, K, are calculated for each complex and the influence of the solvent properties on the formation of EDA complexes and the rates of subsequent reaction is evaluated.     

On the structure of carotenoid iodine complexes

Previous work on carotenoid-iodine complexes is briefly reviewed. The formation of iodine complexes of beta,beta-carotene and of (3R,3' R )-beta,beta-carotene-3,3'-diol (zeaxanthin) has been studied by modern methods including UV/VIS/NIR, IR MS, EPR, ENDOR and NMR (1H, 1H-1H COSY, TOCSY, 2D ROESY, 1H-13C HSQC and 1H-13C HMBC) spectroscopy, and chemical reactions monitored by HPLC, TLC and spectral analysis (VIS, MS, 1H NMR). beta,beta-Carotene formed a solid complex C40H56 x 4I with iodine in hexane and a solvent complex with lambdamax 1010 nm in chlorinated solvents. Iodine was not covalently bound to the carotene. Spectroscopic and chemical evidence is consistent with the representation of the beta,beta-carotene-iodine complex containing iodine in a pi complex with cationic/radical cationic properties. Extensive E/Z isomerisation was noted for all quenching products obtained in acetone, with thiosulfate, by dilution, or by reaction with nucleophile (MeOH). Key products obtained from the beta,beta-carotene-iodine complex were 4',5'-didehydro-4,5'-retro-beta,beta-carotene (isocarotene) and 4-methoxy-beta,beta-carotene. The zeaxanthin-iodine complex was not suitable for a practical synthesis of (3S,3'S)-4',5'-didehydro-4,5'-retro-beta,beta-carotene-3,3'-diol (eschscholtzxanthin).     

Spectroscopic analysis of charge transfer complexes between morpholine and iodine.

It has been demonstrated spectroscopically that many nitrogen-containing heterocyclic compounds can form charge transfer complexes with iodine. The complexes of morpholine with iodine were shown to be of the n-sigma type with a 1:1 stoichiometry. A strong donor-acceptor interaction was found (Kc = 1261 +/- 12 mol-1 at 20 degrees C in CCl4), considerably higher than those of complexes of aromatic compounds with iodine. The high value of the formation constant for this complex indicated that morpholine could serve as a starting point for the synthesis of novel anti-thyroid drugs.     

Charge transfer complexes of N-substituted 2-pyrrolidinones

The complex formation of 1-ethyl-2-pyrrolidinone, 1-benzyl-2-pyrrolidinone and 1-phenyl-2-pyrrolidinone with iodine, iodine monobromide and iodine monochloride has been studied by u.v. and visible spectroscopic methods in carbon tetrachloride, dichloromethane, 1,2-dichloroethane, n-heptane and cyclohexane. The results show the equilibrium constants (K), complexation enthalpies (ΔH) and the wavelengths of maximum absorption bands (λ_max) of the complexes to vary markedly with the solvent. The decrease in the K values with increasing acceptor number (AN) of the solvent may be due to the competition of the solvent and the halogen molecule for the amide; for halogenated hydrocarbon solvents can act as weak electron acceptors. The complex formation ability of the electron donors decreases in the order 1-ethyl-2-pyrrolidinone ⪢ 1-benzyl-2-pyrrolidinone ⪢ 1-phenyl-2-pyrrolidinone, and the electron acceptor properties decrease in the order iodine monochloride ⪢ iodine monobromide ⪢ iodine.     

Formation and structure of 1:1 complexes between aryl hydroxamic acids and vanadate at neutral pH

Although aryl hydroxamic acids are well-known to form coordination complexes with vanadate (V(V)), the nature of these complexes at neutral pH and submillimolar concentrations, the conditions under which such complexes inhibit various serine amidohydrolases, is not well established. A series of qualitative and quantitative experiments, involving UV/vis, (1)H NMR, and (51)V NMR spectroscopies, established that both 1:1 and 1:2 vanadate/hydroxamate complexes form at pH 7.5, with the former dominating at submillimolar concentrations. Formation constants for the complexes of several aryl and alkyl hydroxamic acids were determined; for example, for benzohydroxamic acid, the stepwise formation constants of the 1:1 and 1:2 complexes were 3000 and 400 M(-1), respectively. The (51)V chemical shift of the 1:1 4-nitrobenzohydroxamic acid complex was -497 ppm, and that of its unsubstituted analogue was -498 ppm. A (1)H-(15)N HSQC spectrum of the 4-nitrobenzo-(15)N-hydroxamic acid/vanadate complex indicated the presence of an N-H group with (15)N and (1)H chemical shifts of 115 and 5.83 ppm, respectively. A (13)C NMR spectrum of the complex of 4-nitrobenzo-(13)C-hydroxamic acid with vanadate displayed a resonance at 170.1 ppm and thus a coordination-induced shift (CIS) of +3.8 ppm. In contrast, the CIS value of an established 1:2 complex, thought to contain chelated hydroxamic acid ligands, was +11.9 ppm. These spectral data led to the following structural picture of 1:1 complexes of vanadate and aryl hydroxamic acids. They contain penta- or hexa-coordinated vanadium. The ligand is in the hydroxamate rather than hydroximate form. The ligand is presumably bound to vanadium through the hydroxamic hydroxyl oxygen, but the hydroxamic acid carbonyl oxygen interacts weakly with vanadium. These species are the most likely candidates for the inhibitors of serine amidohydrolases found in vanadate/hydroxamic acid mixtures.     

Surface treatment of poly(3-pentylthiophene) by ionizing radiation

The influence of radioactive krypton⁸⁵Kr on the surface properties of poly(3-pentylthiophene) has been studied. Irradiation by gaseous⁸⁵Kr leads to structural polymeric chain changes, which induce after iodine doping the formation of charge-transfer complexes with iodine as well as with gaseous sulfur dioxide manifesting itself by the increased electric conductivity. The presence of ammonia brings about reaction with iodine bound in the complex with a conducting polymer.     

Fluorescence of zirconium-naphthalene complexes: effect of ortho-naphthalene substitution

The effect of the position of substituents on the formation of metal-naphthalene complexes has been investigated. Two positional isomers, 1-hydroxy-2-naphthoic acid (1H2NA) and 3-hydroxy-2-naphthoic acid (3H2NA), have been chosen. A comparative study of the luminescence behaviour of the two isomers in the presence of Zr(IV) has been performed. Interesting results were obtained. While 1-hydroxy-2-naphthoic acid is quenched in the presence of Zr(IV), 3-hydroxy-2-naphthoic acid produced high-fluorescence enhancement. Several pH studies were performed between pH 2.5 and 5.0 and the stoichiometries of the complexes were also established at the different pH values tested, by use of the Benesi-Hildebrand method. In addition, the formation constants have been calculated. Finally, quenching and lifetime studies were performed in an attempt to establish the type of quenching (static or dynamic) that is produced when a complex is formed between 1-hydroxy-2-naphthoic acid and zirconium metal ion.     

Spectroscopic investigation of the charge-transfer interactions between 1,4,7-trimethyl-1,4,7-triazacyclononane and the acceptors iodine, TCNE, TCNQ and chloranil

The interaction of the interesting polynitrogen cyclic base 1,4,7-trimethyl-1,4,7-triazacyclononane (TMTACN) with the sigma-acceptor iodine and pi-acceptors tetracyanoethylene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ) and tetrachloro-p-benzoquinone (chloranil) have been studied spectrophotometrically and cyclic voltametrically in chloroform at 20 degrees C. Based on the obtained data, the formed charge-transfer complexes were formulated as [(TMTACN)I](+).I(3)(-), [(TMTACN)(TCNE)(5)], [(TMTACN)(TCNQ)(3)] and [(TMTACN)(chloranil)(3)] where the stoichiometry of the reactions, donor:acceptor molar ratios, were shown to equal 1:2 for iodine complex, 1:3 for chloranil and TCNQ complexes and 1:5 for TCNE complex.     

Synthesis,Characterization and Thermal Decomposition of p-iodo-phenylalanine Complexes of Cobalt or Nickel

New complexes of the non-natural amino acid (p-iodo-phenylalanine) with divalent cobalt and nickel ions have been synthesized. The composition of the complexes is [M(IC₆H₄CH₂CHNH₂COO)₂]×2.5H₂O (M=Co, Ni) and the crystal structure belongs to orthorhombic system. Infrared spectra indicate the nature of bonding in the complex. The first stage in the thermal decomposition process of the complex shows the presence of crystal water. The thermal decomposition process of cobalt complex differs from that of nickel. The intermediate and final residues in the thermal decomposition process have been analyzed to check the pyrolysis reactions. Thermal analysis indicates that the iodine atom of the ligand may coordinate to the metal ion in the lattice. This revised version was published online in August 2006 with corrections to the Cover Date.