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

Synthesis and characterization of some coordinated metal and charge transfer complexes of isonicotinic acid hydrazide ligand with 2-hydroxyacetophenonylidene

A new series of coordinated metal (Fe(III), Co(II) and Cu(II)) and charge transfer complexes of Schiff base isonicotinic acid (2-hydroxy acetophenonylidene) hydrazide (L) have been synthesized. The ligand (L), its metals and CT complexes were characterized by UV-Vis spectra, FT-IR, 1HNMR and elemental analysis as well as conductance measurements. The pKa of L was determined in universal buffer solutions (20% v/v EtOH-H2O) with varying pH's values. The molar conductivity measurements prove the non-electrolytic nature of all metal complexes. Furthermore, the thermogravimetry (TG) and differential thermal analysis (DTA) of the synthesized complexes were carried out in the range of 30-1000 °C. In addition, interaction of (L) as an electron donor with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as π-type electron acceptor has been studied and characterized. The observed new band at 585 nm might be assigned as charge transfer (CT) absorption band. The electronic absorption spectrum of L-DDQ interaction is found to be dependent on time. The IR spectra of L with the coordinated metals and CT-complexes revealed new main IR bands, which strongly support the formation of complexes. The stoichiometry of the complexes was determined from photometric titration methods which are in accordance with the results of elemental analyses. The ratio were found to be 1:2 (metal:L) and 1:1 (L:DDQ). The spectra of L, its coordinated metals and CT complexes are fully discussed.

Multiple and sequential charge transfer interactions occurring in situ: A redox reaction of thiazolidine-2-thione with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

Interaction of thiazolidine-2-thione (T2T) as an electron donor with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an electron π-acceptor has been studied. Electronic absorption spectra of the system T2T-DDQ in several organic solvents of different polarities have been measured. A charge transfer (CT) complexation has occurred between T2T and DDQ. This CT interaction has led to a redox reaction in which T2T has been oxidized to the corresponding dehydrogenated T2T (T2T-2H), meanwhile DDQ has been fully reduced to the corresponding hydroquinone (DDQH2). However, the two new species, resulting in situ, have been interacted, whereas a CT complex having the formula (T2T-2H·DDQH2) has occurred. IR, 1H NMR and mass spectra were used for ascertaining the structural formula of the synthesized CT complex. Formation constants (KCT), molar absorption coefficients (ɛCT) and thermodynamic properties of this CT interaction in various organic solvents were determined and discussed. The obtained KCT and ɛCT values have indicated that T2T-2H is a weak CT donor, whereas the formed CT complex has a low stability and it is classified as a contact-type CT complex.

Solvent effect on the charge transfer complex of oxatomide with 2,3-dichloro-5,6-dicyanobenzoquinone

The charge transfer complex (CT-complex) between oxatomide drug and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) was studied spectrophotometrically in 10 solvents at different temperatures. The donor oxatomide is found to form stable 1:1 stoichiometric complex with DDQ and the stoichiometry was unaffected by change in polarity of the solvent studied. The DeltaH degrees, DeltaS degrees and DeltaG degrees values are all negative, so the studied complex is reasonably stable and exothermic in nature. The ionization potential of the drug was determined using the CT-absorption bands of the complex in all the solvents. The dissociation energy of the charge transfer excited state for the CT-complex in different solvents was also determined and is found to be constant. The spectroscopic and thermodynamic properties were observed to be sensitive to the nature of the solvent.

Charge Transfer Molecular Complexes of 4-(Dimethylamino)pyridine with Some Conventional and Unconventional Acceptors Involving Fluoroarenes

Charge transfer (CT) complexes of 4-(dimethylamino)pyridine (DMAP) with iodine as a typical σ-type acceptor and with typical π-type acceptor, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), have been synthesized and characterized. Octafluorotoluene (OFT), octafluoronaphthalene (OFN), perfluorophenanthrene (PFP), and 2,3,5,6-tetrafluoropyridine-4-carbonitrile (TFP) were also used as acceptors for interaction with DMAP. Properties of such CT complexes were investigated by UV/VIS and IR spectra, and elemental analyses of the isolated complexes. The systems DMAP-iodine and DMAP-DDQ are characterized by formation of triiodide ions (I3-) and DDQ•- anion radicals, respectively, which is proposed to occur via initial formation of outer-sphere CT complexes. The systems (DMAP-OFT, DMAP-OFN, DMAP-PFP and DMAP-TFP) are characterized by the appearance of new UV/VIS spectral bands assigned as CT bands; they also furnished the corresponding solid complexes with the stoichiometric ratio 1:1. 1H and 19F NMR spectra were used on confirming the formation of the DMAP-PFP CT complexes. The formation constants (KCT) and molar absorption coefficients (εCT) of the latter complex were obtained.

Spectrophotometric and electrical studies of charge transfer complexes of 2-amino-1,3,4-thiadiazole with pi-acceptors

Charge transfer (CT) complexes formed between 2-amino-1,3,4-thiadiazole as donor and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), p-chloranil (p-CHL), o-chloranil (o-CHL), p-bromanil (BRL) and chloranilic acid (CHA) as acceptors, have been studied spectrophotometrically. Benesi-Hildebrand and Job continuous variation methods were applied to the determination of association constant (K), molar extinction coefficients (epsilon), dipole moment and stoichiometric ratio, respectively. The solid CT complexes have been synthesized and characterized by different spectral methods. The spectral changes reveal that the CT interaction depends on the type of the acceptors. The magnetic properties of the various complexes were also investigated. The electrical properties for the solid CT complexes are measured from which the activation energies are calculated.

Spectroscopic study on charge transfer molecular complexes of pyrazole derivatives with some pi-electron acceptors

Charge transfer molecular complexes of some pyrazole donors (pyrazole, 4-methylpyrazole, 3-methylpyrazole and 3,5-dimethylpyrazole) with 2,3-dichloro-5,6-dicyano-1,4-p-benzoquinone and tetracyanoethylene as pi-electron acceptors have been studied in CH2Cl2 at 25 degrees C. Spectral characteristics and stability constants of the formed charge transfer (CT) complexes are discussed in terms of the nature of donor and acceptor molecular structure, as well as in relation to solvent polarity. Thermodynamic parameters (deltaH, deltaG and deltaS) associated with CT complex formation are also examined. It was concluded that the formed CT complexes are of n-pi type with 1:1 (D:A) composition.