Derived Schiff Base Ligands Research Articles

Syntheses, characterization, X-ray crystal structures and emission properties of copper(II), zinc(II) and cadmium(II) complexes of pyridyl–pyrazole derived Schiff base ligand – Metal selective ligand binding modes

The varying coordination modes of the title ligand, L [5-methyl-1-(pyridin-2-yl)- N′-[pyridin-2-ylmethylidene]pyrazole-3-carbohydrazide] towards the different metal centers is reported by preparation and characterization of Cu(II), Zn(II) and Cd(II) complexes, [Cu(L)NO 3.H 2O](NO 3) ( 1) [Zn(L) 2](ClO 4) 2·2DMF ( 2) and [Cd(L)(I) 2] ( 3) respectively. In 1, the neutral ligand serves as tetradentate 4 N donor where both pyridine and pyrazole nitrogen atoms of pyridyl–pyrazole part are coordinatively active, leaving the carbonyl oxygen of the carbohydrazide part inactive. The same pyridine and pyrazole N atoms remain abstained from the coordination process towards the Zn(II) and Cd(II) metal centers. For 2 and 3 the ligand behaves as a tridentate NNO donor where the two nitrogen atoms come from azomethine, pyridine of pyridine-2-carbaldehyde parts and O from carbonyl oxygen atoms (carbohydrazide part). The complex 1 and 2 are distorted octahedral while complex 3 adopts distorted square pyramidal geometry. All the complexes are X-ray crystallographically characterized.

Synthesis, characterization and spectrochemical studies on a few binuclear µ-oxo molybdenum(V) complexes of pyrimidine derived Schiff base ligands

Ten new binuclear singly oxo-bridged molybdenum complexes (complexes 1–10) were prepared using five pyrimidine derived Schiff base ligands and two Mo(V) precursors (NH4)2MoOCl5 and (NH4)2MoOBr5. The ligands are prepared by the condensation of 4,6-dimethyl 2-hydrazino pyrimidine with salicylaldehyde (for HL1), o-hydroxy acetophenone (for HL2) and substituted salicylaldehydes (for HL3, HL4 and HL5) respectively. These ligands are already reported as good donors for Mo(VI) state. The µ-oxo Mo(V) complexes reported here bears a distorted octahedral geometry around each Mo atom with either N2O2Cl or N2O2Br chromophores. Fine variations in the spectroscopic behaviour of the complexes are observed in accordance with the varying electron donating properties of the ligands. All the complexes are unstable in solution and X-ray quality crystal of complex 1 could be isolated. All the complexes are characterized by IR and UV-Vis spectra.

Quinolin-2(1H)-one-triazole derived Schiff bases and their Cu(II) and Zn(II) complexes: Possible new therapeutic agents

Abstract The condensation of 4-amino-1,2,4-triazole with N-substituted-3-formyl-4-hydroxyquinolin-2-(1H)-one derivatives has lead to the synthesis of a new series of quinolin-2(1H)-one-triazole derived Schiff base ligands (1–3). Cu(II) and Zn(II) complexes (1a–3a and 1b–3b, respectively) of these ligands were also prepared. The complexes were characterised by standard techniques and for two of the complexes X-ray crystallography confirmed that the geometry at the metal centre was octahedral in both cases and that the Schiff base acted as a bidentate ligand coordinating to the metal(II) ion through the deprotonated oxygen and azomethine nitrogen atoms. All of the compounds were investigated for their antimicrobial activities against a fungal strain, Candida albicans, and against Gram-positive and Gram-negative bacteria. The compounds were found to be active against C. albicans but inactive against Staphylococcus aureus and Escherichia coli.

Modulation of fluorescence emission of 1-(2-pyridyl) pyrazole derived Schiff base ligands by exploiting their metal ion sensitive binding modes

Dioxomolybdenum(VI) complexes [MoO 2(B 1)H 2O] ( 1), [MoO 2(B 2)EtOH] ( 2), [MoO 2(B 3)EtOH] ( 3) and [MoO 2(B 4)EtOH] ( 4) were synthesized using the Schiff base ligands H 2B 1(previously reported), H 2B 2, H 2B 3 and H 2B 4, respectively. These ligands were prepared by condensation of 1-(2-pyridyl) 5-methyl 3-pyrazole carbohydrazide with salicylaldehyde, o-hydroxy acetophenone, 5-bromo salicylaldehyde and 5-nitro salicylaldehyde respectively. Due to the presence of a substituted 1-(2-pyridyl) pyrazole unit, ligands H 2B 1, H 2B 2 and H 2B 3 exhibit fluorescent emissions, and the most intense emission was obtained for H 2B 3. H 2B 4 is incapable of showing fluorescence emission. As the ligands are capable of using different binding modes, according to the demands of the guest metal ions, their emission properties also change accordingly. The dioxomolybdenum(VI) complex of the ligand H 2B 1, i.e. complex 1, shows quenched emission compared to H 2B 1. Again when Cu 2+, Co 2+ or Ni 2+ ions are added to a solution of 1, in each case a new complex of Cu 2+ Co 2+ or Ni 2+ is formed in solution and further quenching was observed. However, with Zn 2+ input to a solution of 1, fluorescence recovery was observed up to the level of the free ligand. The copper(II) complex of H 2B 1 (complex 5), produced by adding equivalent amount of Cu 2+ salt to a solution of 1, was isolated and characterized. One of the dioxomolybdenum(VI) complexes, 3, when subjected to an oxo-transfer reaction with PPh 3 produces complex [MoO(B 3)CH 3CN] ( 6). Complex 6 shows reduced fluorescence emissions compared to 3 in the solid phase. These observations open up the possibilities for these ligands to work as fluorescent signaling system with different metal ion inputs. All the complexes are characterized by elemental analyses, electronic spectra, IR, 1H NMR, magnetic measurements, EPR and by cyclic voltammetry. Complexes 1 and 5, as well as the ligands H 2B 2 and H 2B 3, have been crystallographically characterized.

Synthesis and structural characterization of copper(II) and vanadium(V) complexes of pyridyl/pyrimidyl–pyrazole derived Schiff base ligands – Metal specific adjustment of ligand binding mode

Two mononuclear copper(II) complexes [Cu(L 1)ClO 4] ( 1), [Cu(L 2)ClO 4] ( 3) and two mononuclear vanadium(V) complexes [{VO(L 1)(OCH 3)(CH 3OH)}{VO(L 1)(OCH 3)}] ( 2) and [VO(L 2) (OCH 3)(CH 3OH)] ( 4) have been synthesized using two Schiff base ligands HL 1 [ N′-(2-hydroxybenzylidene)-5-methyl-1-(pyridin-2-yl)-1 H-pyrazole-3-carbohydrazide] and HL 2 [1-(4,6-dimethylpyrimidin-2-yl)- N′-(2-hydroxybenzylidene)-5-methyl-1 H-pyrazole-3-carbohydrazide]. These two similar ligands HL 1 and HL 2 in their ‘ketoimine’ form function as mononegative NNNO tetradentate ones towards the Cu(II) centre forming square planar part of the square pyramidal geometry. Where as the same ligands in their ‘imineol’ form behave as binegative ONO tridentate ones to form their V(V) analogues. In the asymmetric unit of 2, there are two independent V(V) complex molecules differing in their conformations as well as in coordination environment – octahedral V(V) in ‘unit A’ is hexa-coordinated while that in ‘unit B’ being penta-coordinated is square pyramidal. Vanadium atom in 4 is in octahedral geometry with NO 5 chromophore. The ligands HL 1 and HL 2 have been synthesized for the first time in our laboratory and characterized by X-ray crystallography and spectroscopy. The complexes ( 1, 2 and 4) are also characterized by X-ray crystallography, spectroscopic and electrochemical studies.

Synthesis, characterization and magnetostructural correlation studies on three binuclear copper complexes of pyrimidine derived Schiff base ligands

Three binuclear Cu(II) complexes of two pyrimidine derived Schiff base ligands, 2- S-methyl-6-methyl-4-formyl pyrimidine- N(4)-ethyl thiosemicarbazone (HL 1) and salicyl hydrazone of 2-hydrazino-4,6-dimethylpyrimidine (HL 2), have been prepared. HL 1 produces a bis(μ-thiolato) Cu(II) complex co-crystallizing with its mononuclear analog, [Cu 2(L 1) 2(NO 3) 2][Cu(L 1)(NO 3)] ( 1). On the other hand HL 2 shows versatility by producing two different classes of binuclear Cu(II) complexes, a bis(μ-phenoxo) complex [Cu 2(L 2) 2(NO 3) 2] ( 2) and another a (μ-4,4′-bipyridyl) complex, [Cu 2(L 2) 2(μ-4,4′-bipyridyl)(NO 3) 2] ( 3) under suitable conditions. All the three complexes show distorted square pyramidal geometry around each Cu atom but to a varied extent. Magnetic behavior of complex 1 shows that it is strongly ferromagnetic in nature whereas compounds 2 and 3 are weakly antiferromagnetic in nature. A magnetostructural correlation study combined with molecular modelling on complexes 1 and 2 has thrown light on the difference on magnetic interaction between the Cu atoms in these two complexes. Various factors that may be responsible for such differences are also explored. A novel and potentially useful pH dependant conversion of 3 to 2 has also been noticed.

Syntheses, characterization and X-ray crystal structures of Co(III) and Mn(II) complexes of pyrimidine derived Schiff base ligands

Two pyrimidine based NNS tridentate Schiff base ligands S-methyl-3-((2- S-methyl-6-methyl-4-pyrimidyl)methyl)dithiocarbazate [HL 1] and S-benzyl-3-((2- S-methyl-6-methyl-4-pyrimidyl)methyl)dithiocarbazate [HL 2] have been synthesised by 1:1 condensation of 2- S-methylmercapto-6-methylpyrimidine-4-carbaldehyde and S-methyl/ S-benzyl dithiocarbazate. One Co(III) and one Mn(II) complex of HL 1 and one Mn(II) complex of HL 2 have been prepared and characterized by elemental analyses, molar conductivities, magnetic susceptibilities and spectroscopic studies. All the bis-chelate complexes have a distorted octahedral arrangement with an N 4S 2 chromophore around the central metal ion. Each ligand molecule binds the metal ion using pyrimidyl nitrogen, azomethine nitrogen and the thiolato sulfur atoms. In the free ligand moieties, the pyrimidine nitrogen atoms, azomethine nitrogen atoms and thione sulfur atoms are in EEE orientation to each other. During chelation, all the donor sites of the ligands are reoriented to ZEZ configuration in order to facilitate the chelation process. In all the complexes, the respective ligand molecule functions as the monoanionic tridentate one. All complexes were analyzed by single crystal X-ray diffraction and significant differences concerning the distortion from octahedral geometry of the coordination environment were observed.

WITHDRAWN: A dinuclear copper(II) complex and a zigzag chain iron(II) polymer based on the 4-antipyrine derived Schiff base ligands: The hydroxylation and redox occurred under the solvothermal conditions

This article has been withdrawn consistent with Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). The Publisher apologizes for any inconvenience this may cause.

A dinuclear copper(II) complex and a zigzag chain iron(II) polymer based on the 4-antipyrine derived Schiff base ligands: The hydroxylation and redox occurred under the solvothermal conditions

A new dinuclear copper(II) compound, [Cu 2(L1-O) 2] ( 1) (L1 = (4E)-4-(2-hydroxybenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one), and zigzag chain polymer, {[FeCl 2(L2)]} n ( 2) (L2 = 1,5-dimethyl-2-phenyl-4-{[(1 E)-pyridine-4-ylmethylene]amino}-1,2-dihydro-3 H-pyrazol-3-one), were synthesized by solvothermal reactions and structurally characterized. The methyl group hydroxylation and the redox have been observed in the preparation of 1 and 2, respectively.

Trinuclear coordinatively labile Cu(ii) complex of 4,6-O-ethylidene-β-d-glucopyranosylamine derived Schiff base ligand and its reactivity towards primary alcohols and amines

A novel neutral trinuclear Cu(II) complex of a Schiff base ligand derived from D-glucose has been synthesised and structurally characterised, which exhibits excellent alcohol binding affinity and activates the C-Cl bond of chloroform in the presence of primary amine.

Assembled Dendritic Titanium Catalysts for Enantioselective Hetero‐Diels—Alder Reaction of Aldehydes with Danishefsky′s Diene.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Assembled dendritic titanium catalysts for enantioselective hetero-Diels-Alder reaction of aldehydes with Danishefsky's diene.

A new type of dendritic 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN)-derived Schiff-base ligands have been synthesized and applied to the titanium-catalyzed hetero-Diels-Alder reaction of Danishefsky's diene with aldehydes. These reactions afforded the corresponding 2-substituted 2,3-dihydro-4H-pyran-4-ones in quantitative yields and with excellent enantioselectivities (up to 97.2 % ee). The disposition of the dendritic wedges and the dendron size in the ligands were found to have significant impact on the enantioselectivity of the reaction. The recovered dendritic catalyst could be reused without further addition of the Ti source or a carboxylic acid additive for at least three cycles, retaining similar activity and enantioselectivity. The high stability of this type of assembled dendritic titanium catalyst may be attributed to the stabilization effect of large-sized dendron units in the catalyst molecule. The other important phenomenon observed with this catalyst system is that a higher degree of asymmetric amplification has been achieved by attachment of the dendron unit to the chiral ligand, which represents a new advantage of dendrimer catalysts for asymmetric reactions using chiral ligands of lower optical purity.

Synthesis of Dendritic Schiff Base Ligands for Titanium Catalyzed Enantioselective HDA Reaction of Danishelfsky's Diene with Aldehydes

AbstractA new type of dendritic NOBIN derived Schiff base ligands has been synthesized and applied to titanium catalyzed hetero‐Diels‐Alder reaction of Danishelfsky's diene and aldehydes, affording the corresponding 2‐substituted 2,3‐dihydro‐4H‐pyran‐4‐one in good yields and moderate enantioselectivities (up to 59.2% ee). It was found that the size of dendron attached to the tri‐dentated ligands has slight impact on the enantioselectivity of the reaction and the second generation of dendritic ligand exhibited the best enantioselectivity.

Synthesis, characterization and antibacterial properties of symmetric 1,1?-ferrocene derived Schiff-base ligands and their Co(II), Cu(II), Ni(II) and Zn(II) chelates

Symmetric 1,1′-dimethylferrocene derived Schiff-base ligands have been prepared by the condensation reaction of 1,1′-diacetylferrocene with 2-aminopyrazine, 2-aminopyridine and 2-aminothiazole respectively. Their transition metal chelates, of the type [M(L)]Cl2 [M = Cu(II)] and [M(L)(Cl2)] [M = Co(II), Ni(II) and Zn(II)] have been prepared. The synthesized Schiff-base ligands and their metal(II) chelates have been characterized by their physical, analytical and spectral data. Copyright © 2000 John Wiley & Sons, Ltd.

Synthesis, Characterisation and Biological Role of Anions (Nitrate, Sulphate, Oxalate and Acetate) in Co(II), Cu(II) and Ni(II) Metal Chelates of Some Schiff Base Derived Amino Acids

Biologically active amino acid (alanine, glycine and tyrosine) derived Schiff base ligands and their Co(II), Cu(II) and Ni(II) metal chelates having the same metal atom but different cations (e.g., nitrate, sulphate, oxalate or acetate) have been synthesised and characterised by their physical, spectral and analytical data. The role of anions in these biologically active metal chelates against the bacterial species Staphylococcus aureus: Escherichia coli, Klehsiella pneumonae, Proteus vulgarus and Pseudomonas aeruginosa has been investigated and reported.

Spectral, Magnetic and Biological Studie on Some Bivalent 3d Metal Complexes of Hydrazine Derived Schiff‐Base Ligands

Metal(II) complexes of hydrazine derived Schiff-base ligands of the type M(L)2Cl2 where M = Co, Cu, Ni and Zn and L = L1 and L2 have been prepared and characterised by molar conductance, magnetic moment, elemental analysis and electronic, IR, H-NMR and 13C spectral data.The different modes of chelation of the ligands and their comparative biological properties against different bacterial species are reported.