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Sadhukhan D.,Jadavpur University | Ray A.,Jadavpur University | Pilet G.,Laboratoire des Multimateriaux et Interfaces | Rizzoli C.,University of Parma | And 5 more authors.
Inorganic Chemistry | Year: 2011

Three different ONO donor acetyl hydrazone Schiff bases have been synthesized from the condensation of acetic hydrazide with three different carbonyl compounds: salicylaldehyde (HL 1), 2-hydroxyacetophenone (HL 2), and 2, 3-dihydroxybenzaldehyde (HL 3). These tridentate ligands are reacted with Ni(OOCCF 3) 2· xH 2O to yield three new Ni(II) complexes having distorted octahedral geometry at each Ni center: [Ni(L 1)(OOCCF 3)(CH 3OH)] 2 (1), [Ni(L 2)(OOCCF 3)(H 2O)] 2 (2), and [Ni(L 3)(L 3H)] (OOCCF 3)(H 2O) 1.65(CH 3OH) 0.35 (3). The ligands and the complexes have been characterized by elemental analysis and IR and UV-vis spectroscopy, and the structures of the complexes have been established by single crystal X-ray diffraction (XRD) study. 1 and 2 are centrosymmetric dinuclear complexes and are structural isomers whereas 3 is a bis chelated cationic monomer coordinated by one neutral and one monoanionic ligand. O-H⋯O hydrogen bonds in 3 lead to the formation of a dimer. Slight steric and electronic modifications in the ligand backbone provoke differences in the supramolecular architectures of the complexes, leading to a variety of one, two, and three-dimensional hydrogen bonded networks in complexes 1-3 respectively. Variable temperature magnetic susceptibility measurements reveal that moderate antiferromagnetic interactions operate between phenoxo bridged Ni(II) dimers in 1 and 2 whereas very weak antiferromagnetic exchange occurs through hydrogen bonding and π-π stacking interactions in 3. All complexes are proved to be efficient catalysts for the epoxidation of alkenes by NaOCl under phase transfer condition. The efficiency of alkene epoxidation is dramatically enhanced by lowering the pH, and the reactions are supposed to involve high valent Ni III-OCl or Ni III-O· intermediates. 3 is the best epoxidation catalyst among the three complexes with 99% conversion and very high turnover number (TON, 396). © 2011 American Chemical Society. Source

Maiti M.,Jadavpur University | Sadhukhan D.,Jadavpur University | Thakurta S.,Jadavpur University | Roy S.,Jadavpur University | And 5 more authors.
Inorganic Chemistry | Year: 2012

Four new dicyanamide (dca) bridged multinuclear ZnII-Schiff-base complexes, {[Zn2L1(μ1,5-dca)dca] ·CH3OH}2 (1), [Zn2L2(μ 1,5-dca)dca]n (2), [Zn3L3 2(μ1,5-dca)2]n (3), and [(ZnL4)2Zn(μ1,5-dca)dca]n (4), have been synthesized using four different Schiff bases L1H 2 = N,N/-bis(3-methoxysalicylidenimino)-1,3- diaminopentane, L2H2 = N,N'-bis(5-bromo-3- methoxysalicylidenimino)-1,3-diaminopropane, L3H2 = N,N'-bis(5-bromosalicylidenimino)-1,3-diaminopropane, and L4H 2 = N,N'-bis(5-chlorosalicylidenimino)-1,3-diaminopropane and NaN(CN)2 in order to extend the metal-ligand assembly. The directional properties of linear end-to-end bridging dca ligands have resulted in different metal ion connectivities leading to unique variety of templates in each of the complexes. All the ligands and complexes have been characterized by microanalytical and spectroscopic techniques. The structures of the complexes have been conclusively determined by single crystal X-ray diffraction studies. Thermogravimetric analyses have been performed to investigate the thermal stability of the metal-organic frameworks. Finally, the photoluminescence properties of the complexes as well as their respective ligands have been investigated with a comparative approach. © 2012 American Chemical Society. Source

Kochem A.,CNRS Molecular Chemistry Department | Kanso H.,CNRS Molecular Chemistry Department | Baptiste B.,CNRS Molecular Chemistry Department | Arora H.,CNRS Molecular Chemistry Department | And 6 more authors.
Inorganic Chemistry | Year: 2012

Square planar cobalt(II) complexes of salen ligands N,N-bis(3-tert-butyl- 5R-salicylidene)-1,2-cyclohexanediamine), where R = OMe (1) and tert-butyl (2), were prepared. 1 and 2 were electrochemically reversibly oxidized into cations [1-H2O]+ and [2-H2O]+ in CH 2Cl2. The chemically generated [1-H2O](SbF 6)·0.68 H2O·0.82CH2Cl2 and [2-H2O](SbF6)·0.3H2O·0. 85CH2Cl2 were characterized by X-ray diffraction and NIR spectroscopy. Both complexes are paramagnetic species containing a square pyramidal cobalt ion coordinated at the apical position by an exogenous water molecule. They exhibit remarkable NIR bands at 1220 (7370 M-1 cm -1) and 1060 nm (5560 M-1 cm-1), respectively, assigned to a CT transition. DFT calculations and magnetic measurements confirm the paramagnetic (S = 1) ground spin state of the cations. They show that more than 70% of the total spin density in [1-H2O]+ and [2-H2O]+ is localized on the metal, the remaining spin density being distributed over the aromatic rings (30% phenoxyl character). In the presence of N-methylimidazole 1 and 2 are irreversibly oxidized by air into the genuine octahedral cobalt(III) bis(phenolate) complexes [1-im 2]+ and [2-im2]+, the former being structurally characterized. Neither [1-im2]+ nor [2-im2]+ exhibits a NIR feature in its electronic spectrum. 1 and 2 were electrochemically two-electron oxidized into [1] 2+ and [2]2+. The cations were identified as Co(III)-phenoxyl species by their characteristic absorption band at ca. 400 nm in the UV-vis spectrum. Coordination of the phenoxyl radical to the cobalt(III) metal ion is evidenced by the EPR signal centered at g = 2.00. © 2012 American Chemical Society. Source

Sarwar M.,University of Bucharest | Madalan A.M.,University of Bucharest | Tiseanu C.,National Institute for Laser, Plasma and Radiation Physics | Novitchi G.,CNRS French National High Magnetic Field Laboratory | And 4 more authors.
New Journal of Chemistry | Year: 2013

Sixteen new 3d-4f binuclear complexes have been obtained using two Schiff-base ligands, Hvalampy and Hvalaepy, derived from the reaction of o-vanillin and 2-aminomethyl-pyridine or 2-(2-aminoethyl)-pyridine, respectively. Hvalaepy ligand: [Zn(valaepy)2Sm(O2NO) 3]·CH3CN 1; [Ni(valaepy)2Eu(O 2NO)3(H2O)]·CH3CN 2; [Ni(valaepy)2Gd(O2NO)3(H2O)] ·CH3CN 3; [Ni(valaepy)2Dy(O2NO) 3(H2O)]·CH3CN 4; [Ni(valaepy) 2Ho(O2NO)3(H2O)]·CH 3CN 5; [Cu(valaepy)2Eu(O2NO) 3]·CH3CN 6; [Cu(valaepy)2Gd(O 2NO)3]·CH3CN 7; Hvalampy ligand: [Zn(valampy)2Pr(O2NO)3]·CH 3CN 8, [Zn(valampy)2Sm(O2NO) 3]·CH3CN 9; [Zn(valampy)2Gd(O 2NO)3]·CH3CN 10; [Zn(valampy) 2Tb(O2NO)3]·CH3CN 11; [Zn(valampy)2Dy(O2NO)3]·CH 3CN 12; [Zn(valampy)2Eu(O2NO) 3]·CH3CN 13; [Ni(valampy)2La(O 2NO)3(H2O)2]·2H2O 14, [Ni(valampy)2Sm(O2NO)3(H2O) 2]·2H2O 15; [Ni(valampy)2Eu(O 2NO)3(H2O)]·2CH3CN 16. The crystal structures of the sixteen compounds can be described as resulting from the coordination of two valaepy- (or valampy-) ligands to the 3d metal ions through two phenoxo oxygen atoms and nitrogen atoms, arising from the pyridyl and azomethynic groups. In all these compounds the 3d and 4f metal ions are bridged by the phenoxo oxygen atoms. The comparative analysis of the crystal structures shows several differences, which arise mainly from the stereochemical preference of the 3d metal ions. These ions arrange the two organic ligands in positions that favour or not the coordination of the methoxy groups to the lanthanide ions. The magnetic properties of compounds 2, 3, 4, 5, 7, 14, 15, and 16 have been investigated. The exchange interactions between NiII and GdIII in 3, and between CuII and GdIII in 7 were found to be ferromagnetic (JNiGd = 1.56 cm-1; JCuGd = 4.94 cm-1; H = -JS GdSM). For the 3d-4f binuclear complexes derived from the Hvalampy ligand (namely 8-13) the photoluminescence (PL) properties were investigated in the Vis spectral region. The results provide evidence for the relatively stronger antenna effect in 9 and 11 compared to 8, 12 and 13. © 2013 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique. Source

Maiti M.,Jadavpur University | Sadhukhan D.,Jadavpur University | Thakurta S.,Jadavpur University | Pilet G.,Laboratoire des Multimateriaux et Interfaces | And 4 more authors.
Polyhedron | Year: 2014

Potentially hexadentate N2O4 donor Schiff base ligands N,N′-bis(3-ethoxysalicylidenimino)-1,2-diaminoethane (L 1H2) and N,N′-bis(3-methoxysalicylidenimino)-1,3- diaminopropane (L2H2) have been used to synthesize two manganese(III) compounds [MnL1(SCN)(H2O)].[MnL 1(H2O)2](ClO4)·CH 3CN (1) and [MnL2(SCN)(H2O)] (2). All the ligands and the complexes have been characterized by microanalytical and spectroscopic techniques. The X-ray structural characterization of all the complexes shows a tetragonally elongated octahedral geometry for the manganese coordination sphere. The octahedron entities are further connected in pairs through intermolecular hydrogen bonding to form μ-aquo dimers, which are further stabilized by π-π interactions occurring between the aryl rings of the Schiff base ligands. These noncovalent interactions have been investigated in terms of energies and geometries using theoretical calculations. The catalytic activity of compounds 1 and 2 on the oxidation of 3,5-di-tert- butylcatechol was determined spectrophotometrically by monitoring the increase of the 3,5-di-tert-butyl-o-benzoquinone characteristic absorption band at about 400 nm over time in methanol saturated with O2. The complexes were able to oxidize 3,5-di-tert-butylcatechol to the corresponding o-quinone with distinct catalytic activity. © 2014 Elsevier Ltd. All rights reserved. Source

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