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Four new symmetrical Schiff bases derived from 2,2’-diamino-4,4’-dimethyl-1,1’-biphenyl-salicylaldehyde have been synthesized and characterized by elemental analysis and different spectroscopic techniques. The reaction of 2,2’-diamino-4,4’-dimethyl-1,1’-biphenyl with two equivalents of 5-tert-butyl-, 3,5-dinitro-, 3,5-dibromo- and 3-tert-butyl-salicylaldehyde yielded 2,2’-bis(5-tert-butyl-salicylideneamino)-4,4’-dimethyl-1,1’-biphenyl (A1) as well as the 3,5-dinitro- (A2), 3,5-dibromo- (A3) and 3-tert-butyl- (A4) substituted derivatives. The tetradentate ligands were then reacted with copper-, manganese- and zinc-acetate producing the tetra-coordinate metal complexes which were characterized by FTIR, UV-Visible spectroscopy, magnetic susceptibility and elemental analysis. Zinc complexes were characterized by 1H-NMR spectroscopy. Density functional theory (DFT) calculations at the B3LYP/6-31G(d) level of theory were carried out to fully optimize and examine the molecular geometries of complexes. Subsequently, IR vibrational and UV-Vis absorption spectra were computed and correlated with the observed values and the results are in good agreement with the experimental data. The anticancerous and antiproliferative activity of the A3 ligand and its metal complexes were determined.

The reaction of M(OAc)2 with 2,2′-bis(2-hydroxybenzylideneamino)-4,4′-dimethyl-1,1′-biphenyl (H2L1) allows the synthesis of 2,2′-bis(2-oxidobenzylideneamino)-4,4′-dimethyl-1,1′-biphenyl complexes of Cu(II) (CuL1), Co(II) (CoL1) and Ni(II) (NiL1) that were characterized by elemental analysis, FTIR spectroscopy and for CuL1 also by X-ray crystallography verifying a tetradentate binding mode of L1 via an (ONNO) motif of the two phenolic oxygen atoms and two azomethine nitrogen atoms. Recrystallization from a solvent mixture of dichloromethane and methanol promotes the formation of methanol adducts. Different binding modes of the methanol–complex were investigated using density functional theory calculations and binding energies, and thermodynamic data of the interaction are reported. The results show that the favored interaction occurs when the methanol molecule acts as a Lewis acid weakly binding via an O–H···O hydrogen bridge to a phenoxide moiety leading to an elongation of the respective M–O bond.

Fe(III) complexes, [Fe(CH3CN)6][X]3 and [Fe(CH3CH2CN)6][X]3 (where X: counter anion = B{C6H3(m-CF3)2}4)− and B(C6F5)4−) have been synthesized by the reaction of FeCl3 with Ag[B(X)4]. Full characterization for the complexes has been done in solution and in the solid state. The complexes are obtained in good yields and are moderately sensitive to air. All complexes have been used as catalysts for aniline oxidation with yields up to 62%, in which azobenzene is the only product. Furthermore, they exhibit good antimicrobial properties. The Fe(III) complexes molecular geometries have been studied using DFT calculations at the B3LYP/6-31G(d) and B3LYP/6-31+G(d, p) levels of theory and obtained results are in agreement with the experimental data.

A series of new imine-linked polymers reveal variations of aliphatic and aromatic linkers were synthesized via Schiff base co-condensation polymerization and fully characterized. The polymers are classified as 1,4- and 1,6-based polymers according to their preparation methodology, which depicted by the polymerization of thiophene-based aryl aldehydes with1,4-butanediamine and 1,6-hexanediamine, respectively. The interpretation of their thermal stability from the thermal gravimetric analysis and the first derivative (TGA-DTG) curves have indicated that the variation in the contents of the aryl-aldehydes and the length of the linker are significantly affect the thermal stability behavior. For example, the polymer prepared via the connection of ter-thiophene-aldehyde with 1,4-butanediamine (1,4-TIP) has shown higher thermal stability, higher char residue content, higher limited oxygen index (LOI = 32) than the polymer prepared by bi-thiophene-phenyl-aldehyde (1,4-F2IP) in the same manner. Furthermore, 1,4-TIP has shown the highest LOI value over all polymers and thus, can be considered as a flame-retardant polymer. However, an inverse relation has been observed upon the inclusion of 1,6-hexanediamine with the same aryl-aldehydes. Further insight into the TGA curves was performed by applying well-known fitting models: Coats-Redfren (CR), Arrhenius, Briodo, and Horowitz-Metzeger for the determination and comparison of the activation energy (Ea) values upon degradation process. The CR-method was further used for the determination of the kinetic triplet parameters (Ea), reaction order (n) and pre-exponential factor (A) and thermodynamic parameters include entropy, the heat of enthalpy, and Gibbs free energy of the polymers. All these methods support the fact that the degradation mechanism follows first-order kinetics, thermodynamically favored and the higher thermal stability polymer requires higher (Ea) for thermal degradation.

The synthesis, porosity and the capability for carbon dioxide gas-capture of functionalized thiophene- pyridine microporous imine-linked polymer synthesized via the Schiff base condensation reaction between (1,3,5-triformyl thienyl benzene) and 2,6-diaminopyridine is described. The structural formation of the polymer was successfully confirmed via 13C NMR (CP-MAS) and IR spectroscopy, and elemental analysis. The polymer has the good thermal stability up to 380°C, a non-defined aggregated particles morphology and amorphous nature. From the argon sorption isotherm at 87 K, the polymer revealed a moderate Brunauer–Emmett–Teller surface area (372 m2/g) and micro-size pores (~5 A). The CO2 uptake was studied at 273 and 298 K to evaluate the polymer tendency for capturing CO2 from the surrounding atmosphere. At 298 K, the polymer has shown a reversible adsorption-desorption isotherm with significant uptake (11.4 wt %) at 1.0 atm. The binding energy of CO2 at zero gas coverage is 24 kJ/mol and decreased upon loading.

[Ln (phen)2(NO3)3] complexes were synthesized by interaction of lanthanide nitrate {Ln (NO3)3.xH2O where Ln = Tb, Eu, Sm, Dy, and La} with 1,10-phenanthroline {phen} in ethylacetate. The complexes were characterized by several analytical and spectroscopic techniques. Density functional theory (DFT) calculations were carried out to optimize the geometries of all prepared complexes at the B3LYP/6-31G(d) level of theory. Vibrational frequencies of the complexes theoretically calculated were in good agreement with experimentally determined values. Most of the complexes exhibited high to moderate antibacterial and antifungal activities in vitro against seven different clinical isolates. The complexes were tested for their antioxidant activity toward 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical. Dy(III) complex showed the highest activity. Thermal degradation of complexes at different heating rates was investigated by thermogravimetric analysis (TGA). The complexes had high thermal stability. The activation energies (E a ) of the degradation were calculated by Kissinger and Flynn-Wall-Ozawa methods.

Water soluble mono-cationic copper(II) complex of the general formula [Cu(NO2-phen)2Br]Br, (NO2-phen=5-nitro-1.10-phenantholine) was prepared in good yield under ultrasonic irradiation. The desired complex was isolated as a bromide salt and identified by MS, EA, UV-Vis., TG/DTA, FT-IR and XRD. The single-crystal X-ray diffraction and Hirschfield analysis revealed a square pyramidal distorted geometry around the Cu(II) center. The geometry of the [Cu(NO2-phen)2Br]+ complex was fully optimized with ab-initio methods and (DFT/B3LYP) density functional theory, then structural parameters were compared to the XRD data. The solvatochromism of [Cu(NO2-phen)2Br]Br complex was investigated in several polar solvents. Absorption and viscosity titration studies concluded that the [Cu(NO2-phen)2Br]Br complex is a very good CT-DNA binder.

New lanthanide complexes [Ln(LH2)2(NO3)2]NO3 have been synthesized by reaction of Ln(NO3)3·xH2O {Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Er} with N-(2-carboxyphenyl)salicylideneimine Schiff base ligand (LH2). A ten-coordinated lanthanide structure has been proposed based on elemental analysis, spectroscopic analysis (UV–Visible, FT-IR, 1H and 13C NMR), molar conductance and thermal analysis. The molecular geometry of the cationic complex [Sm(LH2)(NO3)2]+ has been examined using DFT calculations at the B3LYP/6-31 G(d) level of theory and the obtained results are in good agreement with the experimental data. The absorption, excitation and emission spectral characteristic of LH2 and Ln-LH2 complexes in DMF and methanol have been investigated. The Eu-LH2, Sm-LH2 and Tb-LH2 complexes display characteristic lanthanide-centered luminescence. The antioxidant activity of LH2 ligand and its Ln(III) complexes has been estimated in terms of the DPPH free radical scavenging activity (DPPH-RSA). The photoconductivity of the LH2 ligand and Ln-LH2 (Pr, Gd, Nd, Sm, and Tb) complexes has also been studied. The results show that Pr-LH2, Nd-LH2 and Gd-LH2 complexes exhibit a remarkable photoconductivity.

A pyridine-diacylhydrazone Schiff base ligand, L = 2,6-bis[(3-methoxy benzylidene)hydrazinocarbonyl]pyridine was prepared and characterized by single crystal X-ray diffraction. Lanthanide complexes, Ln–L, {[LnL(NO3)2]NO3.xH2O (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Er)} were prepared and characterized by elemental analysis, molar conductance, thermal analysis (TGA/DTGA), mass spectrometry (MS), Fourier transform infra-red (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. Ln–L complexes are isostructural with four binding sites provided by two nitro groups along with four coordination sites for L. Density functional theory (DFT) calculations on L and its cationic [LnL(NO3)2]+ complexes were carried out at the B3LYP/6–31G(d) level of theory. The FT-IR vibrational wavenumbers were computed and compared with the experimentally values. The luminescence investigations of L and Ln–L indicated that Tb–L and Eu–L complexes showed the characteristic luminescence of Tb(III) and Eu(III) ions. Ln–L complexes show higher antioxidant activity than the parent L ligand.

A new series of extended–conjugated and thermally stable thiophene-containing imine-linked polymers were synthesized via a Schiff-base condensation reaction between aryl aldehydes and 2,6-diaminopyridine building blocks. The backbones of the polymers were functionalized with phenyl, fluorosubstituted phenyl, thienyl, and pyridyl aromatic rings. The successful synthesis was confirmed with spectrochemical characterization techniques, including IR, 1H-NMR, 13C-NMR, and elemental analyses. The electronic properties of the polymers were investigated with ultraviolet–visible (UV–vis) absorption spectroscopy; the properties were collected experimentally and calculated with density functional theory (DFT) in the gas phase. The maximum absorption calculated from DFT was higher than the experimental values by about 60 nm; this was attributed to the absence of the solvent effect in the DFT case. The frontier molecular orbital ((HOMO) highest occupied molecular orbital and (LUMO) lowest unoccupied molecular orbital), optical band gap (Eg), and total energy (ET) values of the optimized structures were calculated. Apparently, there was a significant relation between the number of thiophene rings and the resulting Eg and ET values. As the number of thiophene rings in the polymer chain increased, Eg and ET decreased, and the thermal stability of the polymers increased. Eg and the absorption band edges were determined experimentally from the UV–vis and transmittance spectra, respectively. Poly(terthienyl–azomethine–pyridine–azomethine), with the highest thiophene content, had the lowest experimental and calculated Eg values (2.10 and 2.63 eV, respectively). In contrast, upon fluorination, poly[(2,5-dithienyl–1,4-difluorobenzene)–azomethine–pyridine–azomethine] exhibited the highest Eg (2.81 eV) and absorption band edges (2.94 eV), whereas the thermal stability decreased to 250 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44331.

In this study, geometrical optimizations, infrared spectroscopic analysis and relative stabilities of 1-methylcyclobutene and methylenecyclobutane tautomers were investigated by utilizing high-level ab initio and DFT calculations. The thermodynamic data showed that 1-methylcyclobutene is the more stable isomer with enthalpy [Formula: see text][Formula: see text]kcal/mol and Gibbs energy [Formula: see text][Formula: see text]kcal/mol lower than that for methylenecyclobutane at the M06/aug-cc-PVTZ level of theory. These results are in good agreement with the available experimental data. Additionally, the geometrical parameters and vibrational frequencies agree well with the recorded results in literatures.

Fe(III) complexes of general formulae [FeIII(CH3CN)6][B(Ph)4]3 (1) and [FeIII(C2H5CN)6][B(Ph)4]3 (2) were synthesized by a direct reaction of FeCl3 and Ag(B(Ph)4) in acetonitrile and propionitrile, respectively. The complexes were characterized in the solid state and in solution. The complexes were used as catalysts for the oxidation of aniline and its derivatives. Complex 1 has better activity than complex 2, with product yield reaching 60%. The Fe(III) complexes exhibit good antibacterial and antifungal activities. The molecular geometries of the prepared iron(III) complexes were examined using density functional theory calculations at the B3LYP/6-31G(d) level of theory and the results obtained are in good agreement with experimental data.