Ligating properties of tridentate Schiff base ligands, 2-[[(2-pyridinylmethyl)imino]methyl] phenol (HSALIMP) and 2-[[[2-(2-pyridinyl)ethyl]imino]methyl]phenol (HSALIEP) with zinc(II), cadmium(II), nickel(II) and manganese(III) ions. X-ray crystal structur (2023)

Using (E)-N-(pyridin-2-ylmethylene)adamantan-1-amine (L), four zinc(II) complexes, namely, [ZnL(AcO)₂] (1), ZnL(NO₃)₂] (2), [ZnL(N₃)₂] (3), and [ZnL₂(AcO)][ClO₄] (4), have been synthesized. Ligand L and compounds 1–4 were characterized by elemental analyses, IR, ¹H and ¹³C NMR spectroscopic studies. In addition, the molecular and crystal structures of L and 1–4 were established by single crystal X-ray diffraction studies. Aside from Van der Waals contacts in 1–3, the molecular arrangements in the 2D structures are controlled by C-H⋅⋅⋅O, C-H⋅⋅⋅N, C-H⋅⋅⋅π and π⋅⋅⋅π interactions depending on the anion attached to the zinc(II) ions. The 3D Hirshfeld surfaces and fingerprint plots were mapped and used to examine the intermolecular interactions in comparative manner.

A new pyrazole based ‘NNO’ tridentate ligand, 5-methylpyrazole-3yl-N-(2́-hydroxyphenylamine)methyleneimine, (MP_zOAP) was synthesized and characterized by elemental analyses, mass, IR, ¹H NMR spectral parameters. The versatile coordination mode of the ligand was established by the synthesis of Co(III), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) metal ion complexes. These complexes were characterized by elemental analyses, conductance and magnetic susceptibility measurements, UV–Vis, IR, ¹H NMR spectroscopy, PXRD and thermal analysis. The structures of the ligand and complexes were also investigated using the DFT method. The ligand structure contains the coordination function of the tertiary nitrogen atom of pyrazole ring, the azomethine nitrogen and the phenolic oxygen atom, suitably spaced for chelation with a metal ion and acting as a ‘NNO’ tridentate donor ligand. Invitro antimicrobial activity of the reported ligand and the metal ion complexes were screened and the mode of action was also studied by scanning electron microscopy (SEM) against some pathogenic bacteria.

Three Mn(III) complexes [Mn(L¹)₂] (ClO₄) 1, [Mn(L²)₂] (ClO₄) 2, [Mn(L³)₂] (ClO₄) 3, and one Mn(II) complex [Mn(L⁴)₂] 4 were studied for their efficiency as catalysts for epoxidation of olefins with H₂O₂ at room temperature and 0 °C in the presence of ammonium acetate-acetic acid or triethylamine-perchloric acid system as co-catalyst/buffer. The complexes were obtained from the reaction of Mn(ClO₄)₂.6H₂0 with NNO tridentate Schiff base ligands HL¹-HL⁴ synthesized from the condensation reaction of 2-(2-aminoethyl)pyridine and 2-hydroxybenzaldehyde (HL¹), 5-chloro-2-hydroxybenzaldehyde (HL²), 5-methoxy-2-hydroxybenzaldehyde (HL³), or 5-nitro-2-hydroxybenzaldehyde (HL⁴) respectively. The complexes were characterized by spectroscopic techniques as well as by single crystal X-ray diffraction analysis. Electronic effect of the substituents on epoxide yield was also investigated. The crystal structures of complexes confirm coordination of the manganese ion to the ligands through the NNO atoms of the ligands. The spectral changes observed as a function of time for the reaction of the complexes with aqueous (30%) hydrogen peroxide indicates possible formation of an intermediate product; hydroperoxo-complex implicated in the epoxidation reaction. The complexes catalyzed epoxidation of cyclohexene with low yield at room temperature but higher yield at 0 °C in the order complex 3 lower than 1, 1 lower than 2, with the Mn(II) complex 4 recording highest epoxide yield of 9% with turnover of 2.25 at room temperature and yield of 58% with turnover of 14.5 at 0 °C in the presence of ammonium acetate-acetic acid system/ buffer. With the triethylamine-perchloric acid system/buffer, epoxide yield of 46% and turnover of 11.5 was recorded at room temperature while 44% with turnover of 11.0 was obtained at 0 °C for complex 4.

The [3 + 2] cycloaddition reaction of C₆₀ with pyridine‐derived hydrazones (acting as dipolar reagents) was successfully conducted resulting in fullerene derivatives 5a, 5b. The compounds were characterized by means of NMR, UV–Vis spectroscopy, and X‐ray crystallography. The electrochemical behavior was also investigated. The fulleropyrazoline 5a exhibits anodically shifted reduction potentials of about 100 mV when compared with those for C₆₀, whereas 5b exhibits cathodic shifts relative to pristine C₆₀. The complexation reaction of 5b with metallic ions (Zn²⁺, Cd²⁺, and Fe²⁺) was achieved. Job and Benesi–Hildebrand analysis confirmed the formation of complexes with a molar ratio of 1:1 and binding constants between 2.26 × 10⁵ and 1.59 × 10⁵ M⁻¹. Electrochemistry of these complexes showed a marked influence of the metal ion on the reduction potentials. Copyright © 2016 John Wiley & Sons, Ltd.

Nanoparticles of a novel Zn(II) Schiff base complex, [Zn(HL)NO₃]₂ (1), (H₂L=2-[(2-hydroxy-propylimino) methyl] phenol), was synthesized by using solvothermal method. Shape, morphology and chemical structure of the synthesized nanoparticles were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier Transform Infrared Spectoscopy (FT-IR) and UV–vis spectroscopy. Structural determination of compound 1 was determined by single-crystal X-ray diffraction. The results were revealed that the zinc complex is a centrosymmetric dimer in which deprotonated phenolates bridge the two five-coordinate metal atoms and link the two halves of the dimer. The thermal stability of compound 1 was analyzed by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effect of the initial substrates concentration and reaction time on size and morphology of compound 1 nanostructure was investigated as well. Furthermore, the luminescent properties of the complex 1 were examined. ZnO nanoparticles with diameter between 15 and 20nm were simply synthesized by solid-state transformation of compound 1 at 700°C.

A potentially tetradentate Schiff base ligand containing carboxylic acid group, HL, (E)-2-((pyridin-2-yl)methyleneamino)-5-chlorobenzoic acid is synthesized and characterized. Reaction of HL with hydrated zinc(II) trichloroacetate and zinc(II) trifluoroacetate under similar reaction condition yields two discrete dinuclear complexes, [Zn(L)(Cl)]₂ (1) and [Zn(L)(CF₃COO)]₂ (2) and characterized by different physicochemical methods. Single crystal X-ray structural characterization reveals different ligating properties of the coordinated anionic ligand (L⁻) in its zinc(II) complexes. The side arm carboxylate of L⁻ shows μ_1,3-carboxylato-bridging mode in 1 and connects zinc(II) atoms in syn-anti fashion while it exhibits a μ_1,1-carboxylato-bridging mode in 2. The metal ions display distorted square pyramidal geometries in both the structures and associated with different degrees of distortions. The fluorescence spectra of HL and its zinc(II) complexes recorded in methanol at room temperature which reveal the enhancement of emission intensity for the complexes compared to that of the free ligand. Thermogravimetric analyses (TGA) reveal high thermal stabilities of the complexes.

International Journal of Hydrogen Energy, Volume 39, Issue 17, 2014, pp. 9321-9329

We investigated the destabilization of 4mol of hydrazine borane N₂H₄BH₃ in the presence of 1mol of an alkaline borohydride (LiBH₄ or NaBH₄) and, in a second step, of 1mol of NH₃BH₃ in addition. The destabilization was followed by TGA, DSC and μGC. The solid residues were analyzed by solid-state ¹¹B NMR, IR and XRD. The presence of the borohydride effectively destabilizes N₂H₄BH₃ which is thus able to liberate H₂ from 50°C. Seeing the results from the other side, one could consider that the alkaline borohydrides are destabilized by N₂H₄BH₃. Such destabilization approach is attractive as it involves boron-based materials only. The best decomposition results were obtained with the sample containing 4mol of N₂H₄BH₃ and 1mol of LiBH₄ (containing 16equiv. H₂). Upon heating up to 300°C at 5°Cmin⁻¹, this sample releases 12.1mol of H₂ (dehydrogenation extent of 76%) and 1.1mol of N₂H₄. A solid residue of empirical formulae LiB₅N_5.8H_3.4 is formed. It is composed of polyborazylene- and/or boron nitride-like materials. This is an attractive feature as it implies recyclability of the polymer and elaboration of inorganic ceramics at relatively low temperatures. Our main results are reported herein.

Optical Materials, Volume 39, 2015, pp. 199-206

We present a series of novel poly(amideimide)s containing two covalently bonded azobenzene chromophores in the polymer repeating unit. The chromophores possess different substituent in para position such as fluorine, hydroxyl, methyl or do not contain any of them. The synthesized polymers were characterized by ¹H NMR, FTIR spectroscopies and elemental analysis. The polymers showed high glass transition temperatures (250–280°C), which were significantly separated from the temperatures of thermal decomposition (345–590°C). The photoinduced birefringence measurements were performed for continuous wave irradiation at 405nm. A very large, as for polyimides, birefringence of 0.06 was observed with the growth dynamics dependent on the chromophore substituent. The generated birefringence exhibited an exceptionally low relaxation. Apart from the poly(amideimide) with the methyl substituent it decreased by only 1.5% just after switching off the excitation light, and maintained its level during the next 500s.

Inorganica Chimica Acta, Volume 408, 2013, pp. 204-208

Nickel dipicolinate complexes (HQ)₂[NiL₂]·5H₂O (1) and (H5AQ)₂[NiL₂]·4H₂O (2) (where L=pyridine-2,6-dicarboxylate anion, Q=quinoline, 5AQ=5-aminoquinoline) are synthesized in solution and also through solvent free cation exchange reactions of H₂[NiL₂]·3H₂O. The crystal structures of the complexes 1 and 2 are determined. The strong π–π interactions between the quinolinium cations disrupt the conventional π-stacking interactions of the nickel–dipicolinate anions. The quinolinium cations of these complexes exchanges with alkali metal cations in basic medium and only at an extreme acidic condition the pyridine-2,6-dicarboxylate can be replaced from these complexes by halide ions.

Polyhedron, Volume 91, 2015, pp. 35-41

The reaction between equimolar amounts of hydrogen tetrachloridoaurate(III) trihydrate (H[AuCl₄]·3H₂O) and 2-(aminomethyl)pyridine (AMP) has been investigated under different reaction conditions. When these reactants were mixed in ethanol with an equimolar amount of HCl and at room temperature, the reaction yielded a gold(III) complex having bidentate coordinated AMP ligand, [Au(AMP)Cl₂]Cl·H₂O (1). However, in the aqueous solution of HCl (pH⩽1.00) at 50°C no coordination of AMP ligand to Au(III) ion was observed and only H₂AMP²⁺Cl⁻[AuCl₄]⁻·0.5H₂O (2) was obtained as the final product. While chelation by AMP ligand in ethanol has stabilized the Au(III) oxidation state, dominant reaction process occurring in water solvent at pH range 1.00–5.00 was reduction of Au(III) to the elemental gold, Au(0), which was rapidly accelerated by increasing pH. Both products 1 and 2 have been characterized by NMR spectroscopic and X-ray diffraction techniques. In crystals, the square-planar coordination around the Au(III) centers is supplemented to elongated square pyramidal (1) or octahedral (2) by means of Au⋯Cl interactions. This is achieved by either arranging the neighboring Au–Cl dipoles in antiparallel (1) or herring-bone (2) mode and additionally engaging in these interactions of the uncoordinated chloride ion (2).

Polyhedron, Volume 83, 2014, pp. 116-121

A family of Ag(I) complexes constructed from the unsymmetrical bent-shaped ligand 2-(pyridine-4-ylthio)pyrazine (abbreviated as 2-PTP), namely [Ag(2-PTP)₂]·ClO₄ (1), {[Ag₂(2-PTP)₂(CF₃CO₂)₂]·(H₂O)}_∞ (2), {[Ag(2-PTP)(NO₂)]}_∞ (3), {[Ag₃(2-PTP)₂(CF₃SO₃)₂]·(CF₃SO₃)·(H₂O)}_∞ (4) and {[Ag₂(2-PTP)₂(SO₄)]·9H₂O}_∞ (5), has been synthesized by varying the silver(I) salts. These complexes have been characterized by single crystal X-ray diffraction, FT-IR spectra and elemental analyses. In 1–5, the 2-PTP ligand adopts versatile coordination modes with various silver(I) salts to generate a series of supramolecular architectures. Weak interactions, such as hydrogen bonding and π⋯π interactions, have been described in detail. The anion influence on the structural diversities of 1–5 has also been discussed.

Polyhedron, Volume 102, 2015, pp. 344-352

The reactions of SnR₂Cl₂ {R=Me, Bu and Ph} and sodium valproate, NaO₂CCH(CH₂CH₂CH₃)₂, NaOVp yielded three diorganotin valproates [{(Me₂SnOVp)₂O}₂] (1), [{(Bu₂SnOVp)₂O}₂] (2) and [{PhSn(O)OVp}₆] (3). These stannoxanes have been authenticated in terms of infrared, ¹H and ¹³C NMR, and solution- and solid-state ¹¹⁹Sn NMR and ¹¹⁹Sn Mössbauer spectroscopy. In addition the crystallographic structures of complexes (1)–(3) have been determined by X-ray diffraction. Complexes (1) and (2) displayed two major signals in the ¹¹⁹Sn NMR spectra in solution corresponding to the exo and endocyclic SnR₂ moiety of the stannoxanes. Other minor resonances have been also observed due to dynamic processes in solution. However in the ¹¹⁹Sn MAS-NMR experiments only two down field signals were detected for complex (1), according to the presence of the exo and endocyclic organotin fragments, but with different resonance in comparison with the chemical shift obtained in solution. On the other hand little difference was observed in the ¹¹⁹Sn chemical shift of complex (3) since only one resonance was detected in solution- or in the solid-state experiments, and the signals are very close to each other.