M. M. A. Hamed

Molecular Complexes of some N-Aryldithiocarbamates with π-Electron Acceptors

Summary. Solid 1:1 CT complexes formed between some S-alkyl-N-aryldithiocarbamates and π-electron acceptors (2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), tetracyanoethylene (TCNE), chloranil (CHL)) are synthesized and characterized. Spectral characteristics and stability of the complexes are investigated and discussed in terms of donor molecular structure, π-acceptor electron affinity, and solvent polarity. It is deduced that the complexes are mainly of the n-π type where the ground state wave function can be described primarily by the non-bonding structure. Ionization potentials of the donors are estimated from the CT transition energies of their complexes.Zusammenfassung. Charge-transfer-Komplexe aus S-Alkyl-N-aryldithiocarbamaten und π-Elektronenakzeptoren (2,3-Dichlor-5,6-dicyano-1,4-benzochinon (DDQ), Tetracyanoethylen (TCNE) und Chloranil (CHL); stöchiometrisches Verhältnis: 1:1) wurden hergestellt und charakterisiert. Die spektroskopischen Eigenschaften und die Stabilitäten der Verbindungen wurden untersucht und werden im Zusammenhang mit Parametern wie Struktur, π-Elektronenakzeptoraffinität und Lösungsmittelpolarität diskutiert. Es zeigt sich, daß die Komplexe hauptsächlich dem n-π-Typ angehören, in dem die Wellenfunktion des Grundzustands vorwiegend durch eine nichtbindende Struktur beschrieben werden kann. Die Ionisationspotentiale der Donatoren werden aus den charge-transfer-Übergangsenergien ihrer Komplexe abgeschätzt.

Kinetics of hydrolysis of some new heterocyclic azomethines

Kinetics of base hydrolysis of new heterocyclic azomethines derived from active methyl quaternary salts and aromatic nitroso compounds were investigated in the presence of 70% (wt/wt) water-methanol. The base hydrolysis of these compounds is strictly first-order with respect to OH− and azomethine. The rate determining step is suggested to be the attack of the hydroxide ion on the free base. Effects of water content and nature of organic hydroxylic solvent have been studied. It is concluded that specific solute-solvent interactions through dispersion forces play a major role in the base hydrolysis rate of the azomethines investigated. The effect of pH (2.98 – 12.24) on hydrolysis rates of compounds having a diethylamino substituent in the presence of 30% methanol has been studied. In acidic media, the rate determining step is probably the water attack on the protonated substrate.

Solvent characteristics in the spectral behaviour of eriochrome black T

Abstract The visible electronic spectral behaviour of Eriochrome Black T, in a number of organic solvents of different characteristics has been examined. It was concluded that the dye exists in solution in basic solvents (based on their autoprotolysis constant, pK s ) in an azo ⇌ hydrazone tautomeric equilibrium, while in acetone, acetonitrile and DMSO it exists mainly in the azo form. In DMF and other basic solvent solutions, the dye exhibits an acid-base equilibrium of the type H 2 In ⇌ HIn 2− + H + . The proportional concentration of the base form (HIn 2− ), as well as the relative tautomerisation, are largely dependent upon the concentration of Erio T, the basicity of the solvent and the tendency of the base and/or the hydrazone form to be stabilized by H-bonding interaction with the solvent molecules. The compound was found to aggregate in water and hydroxylic solvents. The bands displayed by the differents forms of the compound have been assigned to an electronic transition involving the whole molecule with an appreciable charge transfer character.

Charge Transfer Molecular Complexes of Some Pyrazoles with σ‐ and π‐Electron Acceptors

Charge‐transfer (CT) complexes of some pyrazoles with iodine as a σ‐electron acceptor and with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ), tetracyanoethylene (TCNE), chloranil (CHL) as a π‐electron acceptors were investigated spectroscopically. The spectral characteristics and stability constants of the formed 1: 1 CT complexes were examined and discussed in terms of the donor molecular structure, the nature of the electron acceptor as well as the solvent polarity. It is deduced that the complexes with iodine exist in the ionic structure (pyrazole)2 I+ · I3 − whereas the complex with DDQ is mainly in the dissociated state (radical cation and anion; pyrazole· +, DDQ· −). On the other hand pyrazoles‐TCNE, –CHL complexes are essentially of the nonbonding type (pyrazole‐TCNE, –CHL). Moreover, it is concluded that the solvent polarity plays an important role in determining the stability of these kinds of CT complex. The ionization potentials of the donors were calculated based on the CT transition energies of their complexes.

Charge-transfer molecular complexes of 2-amino-1,3,4-thiadiazoles

Abstract Charge-transfer molecular complexes of 2-amino-5-X-1,3,4-thiadiazole (D) (X = H, I ; = CH 3 , II ; = phenyl, III ) with some π-electron acceptors (A) have been studied in methanol. It is concluded that these complexes are predominantly of the π-π type. Solid 1:1 CT complexes of the donors I – III with π-acceptors DDQ and TCNE have been synthesized and characterized.

Divalent Transition Metal Ion Ternary Complexes of N-(2-Acetamido)iminodiacetic Acid and Some Bi- and Tricarboxylic Aliphatic Acids

Abstract Ternary complexes of Co(II), Ni(II), Cu(II) with N-(2-acetamido)iminodiacetic acid (disodium salt, Na2ADA) and some bi- or tricarboxylic aliphatic acids (succinic, malic, tartaric and citric, H2L or H3L) were prepared. The structure of the complexes was determined by elemental and thermal analyses, IR and electronic spectra as well as conductivity measurements. The general formulas [M(ADA) (L) (H2O)]Na2 (H2O)× and [M(ADA) (L)]Na3 (H2O)× are deduced for the secondary ligand bi- and tricarboxylate aliphatic acid anions, respectively. An octahedral structure is suggested for the Co(II) and Ni(II) complexes, while a tetragonally distorted structure is proposed for the Cu(II) complexes. Stability constant of the different binary and ternary complexes formed in such system were determined at 25°C and μ=0.1 mol dm−3 KNO3 using the pH-titrimetric technique. It is deduced that the mixed complex is more stable than the corresponding binary aliphatic acid anion complex. The order of stability of the binary ...

MEDIUM EFFECTS ON THE ACID DISSOCIATION CONSTANTS OF SOME DIIMINE HETEROCYCLIC BASES

The acid dissociation constants of the protonated form of diimine heterocyclic compounds (imidazole, 2-methylimidazole, 2,2′-bipyridyl, and 1,10-phenanthroline) were determinedpH-meterically in aqueous media containing different amounts of organic solvents, viz. amphiprotic (methanol, ethanol), dipolar aportic (DMSO), and low basic aprotic (acetonitrile) at 25±0.1 °C. It was observed that by increasing the amount of alcohol orDMSO in the aqueous medium thepKa, values of the investigated compounds decreased. On the other hand, thepKa values increased as the amount of acetonitrile in the medium was increased. These results are discussed in terms of various solvent characteristics. It is concluded that solvent effects, viz. differences in stabilization of the free base by dispersion forces and of the proton by its interaction with solvent molecules in amphiprotic or dipolar aprotic solvent-aqueous media relative to that in pure aqueous one, as well as the basicity effect of acetonitrile play a vital role in the ionisation equilibria of the investigated compounds.ZusammenfassungDie Säuredissoziationskonstanten der protonierten Formen der heterocyclischen Dimin-Basen Imidazol, 2-Methylimidazol, 2,2′-Bipyridyl und 1,10-Phenanthrolin wurdenpH-metrisch in wäßrigem Medium mit einem Anteil an organischen Lösungsmitteln bei 25±0.1 °C bestimmt. Dabei wurden als amphiprotische Zusätze Methanol und Ethanol, als dipolar aprotisches organisches LösungsmittelDMSO und als aprotisches niederer Basizität Acetonitril ausgewählt. Es wurde beobachtet, daß bei ansteigenden Konzentrationen an Alkohol oderDMSO diepKa-Werte der untersuchten Verbindungen kleiner werden. Andererseits bewirkt Acetonitril ein Ansteigen derpKa-Werte. Die Ergebnisse werden mittels verschiedener Lösungsmittelparameter diskutiert. Lösungsmitteleffekte wie Stabilisierung der freien Base mittels Dispersionskräften, Protonwechselwirkungen in den verschiedenen Lösungsmittelgemischen und Basizitätseffekte des Acetonitril spielen dabei eine entscheidende Rolle.

Mono- and Bi-nuclear metal complexes of arylidene-anthranilic acidSchiff bases

Arylidene-anthranilic acidSchiff base complexes with Th(IV), UO2(II), La(III), Ce(III), and Zr(IV) have been isolated and studied by several techniques, e.g. elemental analysis, electronic and IR spectra and conductance measurements. It is concluded that the salicylideneanthranilic acidL3 is coordinated to the metal ion as bivalent tridentate ONO ligand (L−2) while the other ligands behave as monovalent bidentate ON ligands. Furthermore, the molecular structure effect of these compounds on their tendency towards complex formation was investigated and discussed. The possibility that the Cu(II) complex ofL3 can act as bidentate ligand, coordinating through itscis-oxygen atoms to form binuclear metal complexes was studied.ZusammenfassungEs wurden Aryliden-Anthranilsäure-Schiff-Basen mit Th(IV), UO2(II), La(III), Ce(III) und Zr(IV) isoliert und mittels Elementaranalysen, Elektronen-und IR-Spektroskopie und Leitfähigkeitsmessungen untersucht. Es wird aus den Untersuchungen geschlossen, daß Salicylidenanthranilsäure (L3) als bivalenter dreizähniger ONO-Ligand (L−2) an das Metallion koordiniert, währenddessen die anderen Liganden als monovalente zweizähnige Liganden agieren. Außerdem wurden Struktureffekte dieser Verbindungen in bezug auf ihre Komplexbildungstendenz untersucht. Die Möglichkeit, daß der Cu(II)-Komplex vonL3 über die Koordination mit dencis-Sauerstoff-Atomen und unter Bildung eines zweikernigen Metallkomplexes als zweizähniger Ligand agieren kann, wurde untersucht.

Potentiometric studies on ternary complexes of some heavy metal ions containing N-(2-acetamido)-iminodiacetic and amino acids

Solution equilibria of the ternary systems UO2(II), La(III), Ce(III)-N-(2-acetamido)-iminodiacetic acid and dicarboxylic amino acids are studied potentiometrically. The formation of 1∶1∶1 mixed ligand complexes are inferred from the potentiometric titration curves. The formation constants of the different binary and ternary complexes in such system are evaluated at t=24±0.1°C and μ=0.1 mol dm−3 (KNO3). It is deduced that the ternary complex is more stable than the corresponding binary amino acid anion complex. Moreover, the order of stability of the binary or ternary complexes in termes of nature of amino acid and metal ion is investigated and discussed.

Molecular Complexes of Macrocyclic Polyamines with π-Electron Acceptors

Abstract The charge-transfer interaction of macrocyclic polyamines 1,4,8,11-tetraazacyclotetradecane (TACTD); 1,4,8,12-tetraazacyclopentadecane (TACPD) and 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (TMTACTD) with chloranil (CHL), tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as π-electron acceptors was investigated spectroscopically. Spectral characteristics and stability constants of formed CT complexes are examined and discussed in terms of molecular structure of both electron donor and acceptor as well as solvent polarity. It is deduced that the CT complexes are of strong kind where macrocyclic polyamines-DDQ, TMTACTD-TCNE, -CHL complexes essentially exist in the dissociated state (radical cations and anions D+, A−). On the other hand, the TCNE and CHL complexes with TACTD and TACPD exist in a dative structure (D+-A−). Solid 1:1 CT complexes are synthesized and characterized.