- Electropolymerization and electrochemical behavior of nickel Schiff base complexes with different groups between imine linkages
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Nickel Schiff base complexes Ni(salen), Ni(salphen) and Ni(saldmp) are synthesized and electropolymerized on multiwalled carbon nanotube electrodes. The structures of the three monomers are similar except for the groups between the imine linkages, so the difference in electrochemical behavior can be related to the influence of the groups. Polymerization parameters such as the consumed charge, the apparent surface coverage and the doping level are investigated to elucidate the effects of groups between imine linkages. The results show that poly[Ni(salen)] has higher consumed charge and apparent surface coverage than others, which means that poly[Ni(salen)] can be deposited more easily on the electrodes. While poly[Ni(salphen)] has the highest doping level, there are more electrons transferred per monomer unit, indicating a better capacitance for energy storage. The electrochemical characteristics are also evaluated and the peak potential in cyclic voltammetry plots is about 0.9 V for Ni(salen) and Ni(salphen), and about 0.7 V for Ni(saldmp). The different peak potentials indicate the redox potential will be related to the various groups. Meanwhile the galvanostatic charge/discharge curves display a specific capacitance of about 200 F g-1 for poly[Ni(salphen)], and about 150 F g-1 for poly[Ni(salen)] and poly[Ni(saldmp)]. The variation in electrochemical behavior is mainly caused by the different molecular structure and the groups between imine linkages are the unique differences in structure. So we propose a new electronic transmission mechanism that the electrons will transmit via the Ph-CN-Y-NC-Ph path (Y represents groups between imine linkages), and these groups can provide an electronic transmission path as imine bridges and then influence the electrochemical behavior.
- Chen, Cheng,Li, Xinping,Deng, Fuhai,Li, Jianling
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- Homogeneous photochemical water oxidation with metal salophen complexes in neutral media
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The development of water oxidation catalysts based on Earth-abundant metals that can function at neutral pH remains a basic chemical challenge. Here, we report that salophen complexes with Ni(ii), Cu(ii), and Mn(ii) can catalyse photochemical water oxidat
- Asraf, Md. Ali,Ezugwu, Chizoba I.,Zakaria,Verpoort, Francis
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- Synthesis, characterization, antimicrobial, BSA binding, DFT calculation, molecular docking and cytotoxicity of Ni(II) complexes with Schiff base ligands
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A series of a tetradentate N2O2 Schiff base ligands (1a-e), [N,N′-(X)bis(salicylidene)1,2-phenylenediamine], salphens {where X = H (1a), Cl (1b), Br (1c), CH3 (1d), OCH3(1e)} were synthesized from condensation of substituted salicylaldehydes with 1,2-phenylenediamine and nickel(II) complexes(2a-e) from corresponding Schiff base ligands(1a-e). The stoichiometric ratios of the prepared ligands (1a-e) and their Ni(II)-salphen complexes (2a-e) were structurally characterized by various analytical and spectroscopic techniques such as 1H NMR, FT-IR, mass, UV‐–visible, PXRD, magnetic moments and molar conductivity measurements. These results suggest that Ni(II)-salphen complexes (2a-e) have square planar geometry. The molar conductivity measurements indicate that all complexes (2a-e) are non-electrolytes. Density Functional Theory (DFT) calculations have been used to investigate the optimized structure and chemical reactivity of these Ni(II) complexes(2a-e) from their Frontier Molecular Orbitals (FMO). The binding capabilities of the Ni(II) Schiff base complexes (2a-e) with Bovine Serum Albumin (BSA) have been studied through electronic absorption, fluorescence and cyclic voltammetric methods. Further the nature of interaction of Ni(II) complexes (2a-e) towards BSA were confirmed using molecular docking analyses. All these results demonstrated that the Ni(II) complexes 2d and 2e have better binding affinity towards BSA among all the Ni(II) complexes. The antimicrobial studies reveal that the Ni(II)-salphen complexes (2a-e) have higher inhibitory effect than ligands (1a-e) against the selected pathogenic microorganisms. Furthermore, in vitro cytotoxicity of ligands (1a-e) and Ni(II) complexes(2a-e) were evaluated by MTT assay against MCF-7. The observed IC50 values against MCF-7 cell lines suggest that Ni(II) complexes(2a-e) show more significant anticancer activity than their corresponding ligands(1a-e). It is explored that complexes 2d and 2e bearing electron donating groups have greater anticancer potency. Comparison of our results with cisplatin, Zn(II)-salphen and V(IV)-salphen complexes indicated that Ni(II)-salphen complexes can be considered as the potential candidates for use as effective anticancer agent in future.
- Rani, J. Jeevitha,Jayaseeli, A. Mary Imelda,Rajagopal,Seenithurai,Chai, Jeng-Da,Raja, J. Dhaveethu,Rajasekaran
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- Mechanistic study of the formation of multiblock π-conjugated metallopolymer
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Electropolymerization of a π-conjugated polymer from [N,N′-bis(salicylidene)-o-phenylenediamine]nickel(II) complex ([Ni(salophen)]) on the surface of indium-tin-oxide (ITO) was studied. Two structures of the polymer have been proposed based on the theorem
- Peverari, Camila R.,David-Parra, Diego N.,Barsan, Madalina M.,Teixeira, Marcos F.S.
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- Surface-enhanced resonance-Raman scattering: An informative probe of surfaces
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Surface-enhanced resonance-Raman scattering (SERRS) experiments using a citrate-coated silver colloid have been performed. Transmission electron microscopy showed that the colloid consists of nearly mondisperse hexagonal particles with a maximum dimension of 36 nm. For maximum sensitivity, SERRS requires the controlled aggregation of the colloid. The nature of the aggregate formed is dependent on the method of aggregation. The effect of poly-L-lysine on the aggregation procedure was characterised using transmission and scanning electron microscopy. With SERRS, sensitivities down to 6.87 × 10-18 mol dm-3 were obtained using rhodamine dye. This corresponds to less than 200 molecules in the beam at any one time and suggests a sensitivity equal to or greater than that of fluorescence. A comparison of the use of SERRS with surface-enhanced Raman scattering (SERS) to follow adsorbate reactivity on a surface at less than monolayer coverage was obtained by studying metal complex formation using a preresonant Schiff base (SERRS) and 2-hydroxy-1-naphthaldehyde excited off resonance (SERS). In the former case, complex formation on the surface at well below monolayer coverage was observed and differences between the surface and the bulk complex characterised. In the latter complex formation was again observed but the bands were broad and problems of contamination, photodecomposition and selectivity evident. Copyright 1996 by the Royal Society of Chemistry.
- Rodger, Caroline,Smith, W. Ewan,Dent, Geoffrey,Edmondson, Michael
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- Elastic Crystalline Fibers Composed of a Nickel(II) Complex
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The generation of elastic crystalline fibers from a nonfibrous crystal of metal complex is demonstrated. Applying mechanical stimuli to a platelike crystal of NiII(salophen) [1; H2salophen = N,N′-bis(salicylidene)-o-phenylenediamine] resulted in this complex being transformed into crystal fibers, which could be bent into a loop and demonstrated its high elasticity. Single-crystal X-ray diffraction analyses revealed that the transformation reflects the presence of molecular strands that are composed of a one-dimensional assembly of the slip-stacked arrangement by nearly planar Ni(salophen) molecules. The fiber flexibility was demonstrated to be lost upon the introduction of chloroform solvent molecules into the crystal lattice by recrystallization.
- Kusumoto, Sotaro,Sugimoto, Akira,Zhang, Yingjie,Kim, Yang,Nakamura, Masaaki,Hayami, Shinya
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- Synthesis and spectroscopic characterization of some tetradentate Schiff bases and their nickel, copper and zinc complexes
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Three ligands have been formed by the 1:2 molar condensation of o-phenylenediamine with salicylaldehyde, 2-hydroxy-1-naphthaldehyde or o-hydroxyacetophenone. The potentially tetradentate ligands are N,N-bis(salicylaldehyde)-o-phenylenediamine (SalophHsub
- Abd-Elzaher, Mokhles M.
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- Air-Stable Cobalt(II) and Nickel(II) Complexes with Schiff Base Ligand for Catalyzing Suzuki–Miyaura Cross-Coupling Reaction
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The Co(II) complex [Co{C6H4–1,2-(N=CH–C6H4O)2}] (I) and Ni(II) complex [Ni{C6H4–1,2-(N=CH–C6H4O)2}] (II) with Schiff base of o-phenylenediamine and salicylaldehyde have been synthesized. The structure of the ligand and its complexes were derived on the basis of various techniques such as elemental analysis, mass, FT-IR, electronic spectra and magnetic susceptibility. From the Singal crystal X-ray diffraction (SCXRD) analysis techniques (CIF file CCDC no. 1498772 (II)), it has been confirmed that the Schiff base ligand (L), coordinates to the metal ion in a tetradentate fashion through the nitrogen and oxygen atom. In addition, the square planar geometry of Ni(II) complex also has been confirmed from SCXRD. Electronic spectra, mass spectra, and magnetic susceptibility measurements reveal square planar geometry for the Co(II) complex. Synthesized complexes were used in cross-coupling of arylhalides with phenylboronic acid. The transformation offers products in good yields using 0.02 mmol catalysts loading, thereby proving the efficiency of the complexes as catalysts for Suzuki–Miyaura reaction.
- Ansari,Kumar,Bhat
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- Oxidation of 4-chloro-3-methylphenol using zeolite Y-encapsulated iron(III)-, nickel(II)-, and copper(II)-N,N'-disalicylidene-1, 2-phenylenediamine complexes
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The degradation of 4-chloro-3-methylphenol (PCMC) using zeolite-encapsulated iron(III), nickel(II), and copper(II) complexes of N,N'-disalicylidene-1,2-phenylenediamine as catalysts, in a heterogeneous Fenton-like advanced oxidation process, was studied.
- Hailu, Solomon Legese,Nair, Balachandran Unni,Redi-Abshiro, Mesfin,Diaz, Isabel,Aravindhan, Rathinam,Tessema, Merid
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- Function of 7,7,8,8-tetracyanoquinodimethane (TCNQ) on electrocatalytic hydrogen generation catalyzed by N,N′-benzene bis(salicylideniminato)nickel(II)
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In the presence of trimethylamine, the reaction of N,N′-benzene bis(salicylidenimine) (H2L) with NiCl2·6H2O affords a nickel(II) complex, [NiL] (1), and the reaction of H2L with NiCl2·6H2O
- Xue, Dan,Lv, Qi-Ying,Lin, Chen-Neng,Zhan, Shu-Zhong
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- Carbon-Carbon Bond Formation and Cleavage resulting from a Long-range Metal-promoted Redox Process in the Reactions of Nickel(II) Complexes of N,N'-o-Phenylenebis(salicylideneamine)
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Alkali metals (Li or Na) promote the dimerization of N,N'-o-phenylenebis(salicylideneaminato)nickel(II) , causing the reductive coupling of two imino functional groups between two units, which are joined by a rather long C-C bond in the dimer 2; the dimer is able to transfer two electrons to various substrates by a process cleaving the C-C bond and restoring the original structure.
- Gambarotta, Sandro,Floriani, Carlo,Chiesi-Villa, Angiola,Guastini, Carlo
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- Zeolite encapsulated Ni(ii) Schiff-base complexes: improved catalysis and site isolation
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Two series of zeolite encapsulated Ni(ii) Schiff-base complexes,i.e., the Ni(ii) sal-1,2-phen and Ni(ii) sal-1,3-phen series, have been synthesized in neat and encapsulated states and characterized by using different characterization techniques such as XRD, SEM-EDS, BET, thermal analysis, XPS, IR spectroscopy, UV-vis spectroscopy and magnetic studies. UV-vis spectroscopy, XPS and magnetic studies all together reveal the structural modification of the guest complex and, thereby, the adaptation of electron density around the metal center upon encapsulation. However, encapsulation causes structural alterations for these two series differently and, hence, introduces a certain level of proficiency to these Ni(ii) complexes as catalysts for phenol oxidation reaction. However, analysis of catalytic data emphasizes site isolation as a major governing factor for the improved reactivity over the modified electron density around the metal center for phenol oxidation reaction where the heterogeneous mode of catalysis is concerned.
- Kumari, Susheela,Ray, Saumi
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supporting information
p. 14953 - 14963
(2020/09/23)
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- A simple and efficient mechanochemical route for the synthesis of salophen ligands and of the corresponding Zn, Ni, and Pd complexes
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A number of salophen ligands and their Zn, Ni, and Pd complexes were synthesized by an efficient one-pot mechanosynthesis protocol. The reaction products were characterized by means of complementary solid-state techniques, i.e., powder X-ray diffraction,
- Leoni, Luca,Carletta, Andrea,Fusaro, Luca,Dubois, Jean,Tumanov, Nikolay A.,Aprile, Carmela,Wouters, Johan,Cort, Antonella Dalla
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supporting information
(2019/07/04)
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- Design, synthesis and biological evaluation of cobalt(II)-Schiff base complexes as ATP-noncompetitive MEK1 inhibitors
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In this report, we designed and synthesized a series of cobalt(II)-Schiff base complexes (CoSBC) with competent MEK1 (mitogen-activated protein kinase kinase?1) inhibitory activity. Based on our previous report, the CoSBC exhibited high binding affinity with MEK1 protein. To further explore metal complexes as MEK1 inhibitors, a series of transition metals and ligands were employed to build a library of various metal Schiff base complexes. The MEK inhibition assays revealed that only CoSBC exhibited obvious inhibitory activity, complex 2b showed the best inhibition both in BRaf (B-rapidly accelerated fibrosarcoma)/MEK1 and MEK1/ERK2 (extracellular signal-regulated kinases-2) cascading (IC50 is 1.988 ± 0.14 μM and 1.589 ± 0.054 μM respectively). In addition, homogeneous time-resolved fluorescence test method was used to prove that CoSBC as ATP-noncompetitive MEK1 inhibitor. MEK kinase selectivity assay indicated that CoSBC can selectively inhibit MEK1/2 kinases rather than other MAPKs (mitogen-activated protein kinases) family kinases. Moreover, the interaction mode of 2b with MEK1 protein has been demonstrated by computer aided drug design.
- Li, Hongyue,Xi, Dandan,Niu, Yan,Wang, Chao,Xu, Fengrong,Liang, Lei,Xu, Ping
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p. 174 - 181
(2019/04/08)
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- A Straightforward Electrochemical Approach to Imine- and Amine-bisphenolate Metal Complexes with Facile Control Over Metal Oxidation State
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Synthetic methods to prepare organometallic and coordination compounds such as Schiff-base complexes are diverse, with the route chosen being dependent upon many factors such as metal–ligand combination and metal oxidation state. In this work we have shown that electrochemical methodology can be employed to synthesize a variety of metal–salen/salan complexes which comprise diverse metal–ligand combinations and oxidation states. Broad application has been demonstrated through the preparation of 34 complexes under mild and ambient conditions. Unprecedented control over metal oxidation state (MII/III/IVwhere M=Fe, Mn) is presented by simple modification of reaction conditions. Along this route, a general protocol-switch is described which allows access to analytically pure FeII/III–salen complexes. Tuning electrochemical potential, selective metalation of a Mn/Ni alloy is also presented which exclusively delivers MnII/IV–salen complexes in high yield.
- Chapman, Michael R.,Henkelis, Susan E.,Kapur, Nikil,Nguyen, Bao N.,Willans, Charlotte E.
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p. 351 - 356
(2016/08/19)
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- Activity on Leishmania tropica of metal complexes with NNOO tetradentate Schiff base ligand: Kinetic and thermodynamic studies from TG-DTA analysis
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In the search for antileishmanial drug, tetradentate Schiff base ligand 2-{(E)-[(2-{[(Z)-(2-hydroxyphenyl)methylidene]amino}phenyl)imino]methyl}phenol (H2L) was reacted with transition metal ions to yield the complexes of the composition ML [where M = Co (II), Ni (II), Cu (II), & Zn (II)]. The copper based compound 3 (IC50 = 5.857 μM) showed activities even higher than the standard drug. TG and DTA analyses under static air in the temperature range 30-1000 °C were also observed for all the compounds. The TG-DTA analyses and the subsequent themodynamic and kinetic parameters calculated using the TG-DTA curves, have potential relevance for the biological activities. Horowitz-Metzger method was applied for calculating the activation energies and order of pyrolysis. Thermodynamic parameters like ΔS?, ΔH? and ΔG? were subsequently calculated using the corresponding expressions. The order of decreasing thermal stability and decreasing activation energy follow the orders Ni(II) >Co(II) >Zn(II) >Cu(II) and E?Cu>E?Co>E?Ni>E?Zn, respectively.
- Ikram, Muhammad,Rehman, Sadia,Jamal, Qaisar,Shah, Akram
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p. 869 - 878
(2016/01/12)
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- Sodium thiosulfate-assisted synthesis of NiS2 nanostructure by using nickel(ii)-Salen precursor: Optical and magnetic properties
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A NiS2 nanostructure with a protective layer of Ni2+ and SO42- ions around it has been successfully synthesized using the Ni(ii)-Salen (Salen = N,N′-bis(salicylidene)ethylenediamine) complex via a simple solvoth
- Akbarzadeh, Raziyeh,Dehghani, Hossein,Behnoudnia, Fatemeh
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p. 16745 - 16753
(2015/02/02)
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- A convenient approach to the synthesis of different types of schiff's bases and their metal complexes
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Various metal complexes derived from different Schiff bases are conveniently prepared using solvent-free condensation reactions in one-pot synthesis, resulting in significantly enhanced yields. Initial calorimetric studies, and/or TGA of reaction mixtures, led to better optimization of reaction conditions. The ligands like imines, hydrazones, semicarbazones, and nitrones are also synthesized by this method; thus this process is general and expedient.
- Pradhan, Kiran,Selvaraj, Kaliaperumal,Nanda, Ashis K.
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p. 1078 - 1079
(2011/01/09)
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- Expedient method for the transmetalation of Zn(II)-centered salphen complexes
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Various mono- and bis-ZnII complexes derived from salphen ligands have been conveniently transmetalated with a number of transition metal (TM) acetates (M = Ni, Pd, Mn) in THF to afford their respective TM-salphen counterparts in excellent isolated yields (80-100%). This new transmetalation procedure allows in situ switching between supramolecular and catalytic functions of the metallosalphen complex.
- Escudero-Adan, Eduardo C.,Benet-Buchholz, Jordi,Kleij, Arjan W.
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p. 7265 - 7267
(2008/10/09)
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- Spectral studies of complexes of nickel(II) with tetradentate schiff bases having N2O2 donor groups
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Complexes of nickel(II) of N,N′-disalicylidene-1,2-phenylenediamine (H2dsp), N,N′-disalicylidene-3,4-diaminotoluene (H2dst), 4-nitro-N,N′-disalicylidene-1,2-phenylenediamine (H2ndsp) and N,N′-disalicylidene ethylenediamine
- Garg,Nandan Kumar, Deo
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p. 229 - 234
(2008/10/08)
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- Metal-mediated transfer of electrons between two different C-C single bonds that function as electron-donor and electron-acceptor units
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Concerted cleavage of two C-C single bonds provides the basis for a novel concept for the storage and release of electrons. Electron transfer, mediated by metal ions, occurs between the cyclopropyl ring of a Ni porphyrinogen and the interligand C-C bond of a bis(Ni-salophen) complex (see scheme).
- Franceschi, Federico,Solari, Euro,Scopelliti, Rosario,Floriani, Carlo
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p. 1685 - 1687
(2007/10/03)
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- Spectroscopic characterisation of electrogenerated nickel(III) species. Complexes with N2O2 Schiff-base ligands derived from salicylaldehyde
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Several nickel(II) complexes with tetradentate N2O2 Schiff-base ligands (H2L) have been synthesized and their oxidative chemistry studied in dimethylformamide and in dimethyl sulfoxide. Electrochemical and EPR data for the oxidised solution revealed that in these strong co-ordinated solvents almost all nickel(II) complexes were oxidised to low-spin six-co-ordinate nickel(III) complexes, formulated as [NiIIIL(solv)2]+, where solv stands for a solvent molecule. Upon addition of pyridine to fluid solutions of [NiIIIL(solv)2]+ new species were formed which on the basis of their EPR spectra can be formulated as [NiIIIL(py)2]+. Extensive electronic characterisation of the nickel(III) compounds was made by coupling of EPR and electronic spectroscopic data.
- Freire, Cristina,De Castro, Baltazar
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p. 1491 - 1497
(2007/10/03)
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- Synthesis, characterization, optical spectroscopic, electronic structure, and second-order nonlinear optical (NLO) properties of a novel class of donor-acceptor bis(salicylaldiminato)nickel(II) Schiff base NLO chromophores
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The synthesis, characterization, thermal stability, optical spectroscopic, electronic structure, and second-order nonlinear optical (NLO) response of a series of donor-acceptor bis(salicylaldiminato)nickel(II) Schiff base complexes and the free ligand precursors are reported. The effect of the metal center in such complexes is manifold: it templates the formation of acentric molecular structures, imparts high thermal stability to the chelate ring, and both 'switches on' and enhances NLO response. Metal complexation imparts new linear optical spectroscopic features, having metal-to-ligand charge transfer character, which are responsible for the second-order nonlinearity. Moreover, the present synthetic strategy represents a novel route to inorganic NLO chromophores. Solution-phase hyperpolarizability values, deduced by electric field-induced second-harmonic-generation experiments are as high as -79 x 10-30 cm5 esu-1 (hω = 0.92 eV). Experimental linear and nonlinear optical features are fully consistent with INDO/SCI-SOS theoretical calculations. They provide a rationale for the NLO response of these materials and are attractive for designing new, highly efficient second-order nonlinear optical inorganic chromophores.
- Di Bella, Santo,Fragalà, Ignazio,Ledoux, Isabelle,Diaz-Garcia, Maria A.,Marks, Tobin J.
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p. 9550 - 9557
(2007/10/03)
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- Catalysis of alkene hydrogenation and oxidation by nickel-saloph complex; a novel bifunctional catalyst
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Hydrogenation of cyclohexene to cyclohexane and cyclooctene to cyclooctane with H2 in presence of Ni(saloph), 1, (saloph= bis(salicylaldehyde)-o-phenylenediamine) were carried out at moderately high pressure (60 atm) and temperature (50°C) in ethanol medium. At normal temperature and pressure, the same catalyst (complex 1) catalyses the epoxidation of cyclohexene and cyclooctene with KHSO5 in presence of CTAB (cetyl trimethyl ammonium bromide; a phase-transfer reagent) in CH2Cl2. Cyclohexene oxide and cyclooctene oxide were found to be the major products of the epoxidation reactions.
- Chatterjee,Bajaj,Halligudi,Bhatt
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- Aromatic Diimine Dependent Structural Features of Iron(II), Cobalt(II) and Nickel(II) Complexes with some Tetradentate Schiff Base Ligands
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Complexes of iron(II), cobalt(II) and nickel(II) with four tetradentate (ONNO) Schiff base ligands viz. salicylaldehyde o-phenylenediimine (Salophen) salicylaldehyde metaphenylenediimine (Salmphen), 2-hydroxy-1-naphthaldehyde o-phenylenediimine (Nalophen) and 2-hydroxy-1-naphthaldehyde m-phenylenediimine (Nalmphen) are shown to have aromatic diimine dependent structural features.Although, Salophen complexes are known, complexes of FeII, CoII and NiII with Salmphen, Nalophen and Nalmphen Schiff base ligands are prepared and characterised by various physicochemical and spectral studies.While Salophen and Nalophen give monomeric and low-spin complexes, the ligands prepared using metaphenylenediamine form binuclear complexes presumably due to longer chain length and less steric strain present in the latter ligands.The structural characterisation of a group of complexes are presented.In addition, organocobalt complexes of Salophen and Nalophen are prepared and characterised.
- Sreenivasulu, Y.,Reddy, K. Hussain
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- Bimetallic Complexes of Nickel(II)-Tetradentate Schiff Bases with Tin(IV), Selenium(IV) and Tellurium(IV) Chlorides
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A few bimetallic complexes have been obtained by the reaction of nickel(II) complexes of tetradentate schiff bases with tin(IV), selenium(IV), tellurium(IV) and zirconium(IV).The complexes are colored, semicrystalline in nature and are insoluble in common
- Aminabhavi, T. M.,Biradar, N. S.,Divakar, M. C.
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p. 283 - 284
(2007/10/02)
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- Hetero-binuclear Schiff Base Complexes of Copper(II) and Nickel(II) with Zinc(II) or Cadmium(II)
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Hetero-binuclear schiff base complexes of the types and , where LH = schiff base derived from salicylaldehyde and ammonia; M = Zn(II) or Cd(II); X = Cl(-), NO3(-) or ClO4(-); and L'H2 = schiff base derived from salicylaldehyde and o-phenylenediamine have been prepared and characterised by elemental analyses, spectral data (IR and electronic) and magnetic susceptibility measurements.Square-planar configuration around Cu(II) and Ni(II) has been proposed for these complexes.
- Dani, C. M.,Das, A. K.
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p. 1041 - 1043
(2007/10/02)
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- Carbon-carbon bond forming and breaking by a metal-assisted redox process in a nickel(II)-Schiff base complex
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Alkali metals (M = Li, Na) promote the reductive coupling of imino functional groups in [Ni(salophen)] (salophen = N,N′-ophenylenebis(salicylidenaminato) dianion). By such a reaction, two Ni(salophen) units are joined through a C-C bond to form a dimeric structure, [Ni(salophen)MLn]2 (L = THF; M = Li, n = 2; M = Na, n = 3). No change in the oxidation state of the metal and in its coordination geometry was observed as a consequence of the reaction with alkali metals. In the final dimeric complex salophen acts as a bidentate ligand toward the alkali cation. The most relevant structural parameters concern the C-C bridging unit [1.64 (4) ?, M = Li; 1.58 (2) ?, M = Na] and the change occurring on the C=N imino functional unit of salophen [C-Nav = 1.48 (3) ?; C=Nav = 1.30 (3) ?]. An excess of alkali metals reacted with [Ni(salophen)] promoting its polymerization through a C-C bond formation involving all the C=N units present in the ligand. Mild oxidizing agents (Mel, O2, I2) removed two electrons from the dimeric compounds, promoting the C-C bond cleavage and restoring the original imino group. [Ni(salophen)] was recovered from all these reactions. The attack of the oxidizing agent does not occur at the ligand. Crystallographic details for [Ni(salophen)Li(THF)2]2-2THF: space group C2/c (monoclinic); a = 39.619 (5), b = 12.461 (2), c = 24.522 (4) ?; β = 91.28 (2)°; V = 12 103 ?3; Z = 8; final R factor 0.089 for 1509 observed reflections. Crystallographic details for [Ni(salophen)Na(THF)3]2·C4H 8O2: space group P21/c (monoclinic); a = 11.194 (2), b = 17.597 (3), c = 16.639 (3) ?; β = 90.59 (1)°; V = 3277 ?3; Z = 2; final R factor 0.060 for 1447 observed reflections.
- Gambarotta, Sandro,Urso, Fabio,Floriani, Carlo,Chiesi-Villa, Angiola,Guastini, Carlo
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p. 3966 - 3972
(2008/10/08)
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