Hexadentate Schiff Base Ligand Research Articles

Structural insights into the counterion effects on the manganese(III) spin crossover system with hexadentate Schiff-base ligands.

A series of new salts [Mn(5-MeO-sal-N-1,5,8,12)]Y (Y = ClO4 for 1, Y = BF4 for 2, Y = NO3 for 3 and Y = CF3SO3 for 4) based on the six-coordinated mononuclear manganese(iii) Schiff-base complex cation [Mn(5-MeO-sal-N-1,5,8,12)](+), has been investigated to determine the impact of counter anion effects, intramolecular ligand distortion and intermolecular supramolecular structures on the spin crossover (SCO) behavior. The SCO in salt 1 has resulted in a crystallographic observation of the coexistence of high-spin (HS, S = 2) and low-spin (LS, S = 1) manganese(iii) complex cations in equal proportions around 100 K. At room temperature, the two crystallographically distinct manganese centers are both close to the complete HS state. Only one of the two slightly different units undergoes SCO in the temperature range 300-180 K, whereas the other remains in the HS state down to 20 K. For salts 2 and 3, crystal structural analysis indicates change in the anion from ClO4(-) to BF4(-) and NO3(-) was led to the close arrangement of the cations and the stacking between phenyl groups from the ligands. With CF3SO3(-) as the counterion, although the cations and the anions separate clearly in one direction, the close arrangement of cations in other directions precludes the spin transformation of the Mn(iii) cations. Magnetic measurements on 2-4 indicate that the manganese(iii) complex cations remain in the HS state in the temperature range 2-300 K.

Synthesis, structural and biochemical activity studies of a new hexadentate Schiff base ligand and its Cu(II), Ni(II), and Co(II) complexes

A new Schiff base ligand (H2L) and its metal complexes have been prepared and characterized by elemental analysis, magnetic moment and spectral studies. The comparative in-vitro antimicrobial activities against various pathogens with reference to known antibiotics activity under the standard control of different concentrations revealed that the metal complexes (6–8) showed enhanced antimicrobial activities in general as compared to free ligand. As an exception, the free ligand showed better activity against Trichoderma. The antifungal activity experiments were performed in triplicate. The order of biochemical activity for metal complexes were observed as in the following. CuL > CoL > NiL, which is exactly same as the order of stability constants of these complexes. Additionally, we performed DFT and TD-DFT calculation for free ligand and Cu(II) complex to support the experimental data. The geometries of the Cu(II) complex have been optimized using the B3LYP level of theory. The theoretical calculations confirm that the copper (II) center exhibits a distorted square pyramidal geometry which is favored by experimental results.

Synthesis and spectroscopic investigation of a new hexadentate Schiff base ligand with N2O4 donor atoms and related metal complexes

Five new complexes [CdH 2 L(NO 3 )]ClO 4 (1), [ZnH 2 L](ClO 4 ) 2 (2), [NiH 2 L](ClO 4 ) 2 (3), [CuH 2 L](ClO 4 ) 2 (4) and [CoH 2 L](ClO 4 ) 2 (5) were prepared by reaction of a new Schiff base ligand and different metal ions in 1:1 ratios. The new Schiff base ligand H 2 L was synthesized by reaction of 2-(4-(2-formylphenoxy)butoxy) benzaldehyde and ethanol amine and characterized with IR, 1 H and 13 C NMR and elemental analysis. The synthesized complexes were also characterized by IR and elemental analysis in all cases and 1 H, 13 C NMR and COSY in the case of [CdH 2 L(NO 3 )]ClO 4 and [ZnH 2 L](ClO 4 ) 2 complexes.

Carbonato-bridged heteronuclear NiII2LnIII2 (Ln = Tb, Dy, Ho, Er, Tm, Yb, Lu) complexes synthesized by fixation of atmospheric CO2 – Structural and magnetic studies

A series of carbonato-bridged heteronuclear NiII2LnIII2 complexes 2[(μ4-CO3)2{NiLn(L)(MeOH)(CH3COO)}2]·9H2O·8MeOH (Ln=Tb (1), Dy (2), Ho (3), Er, (4)), [(μ4-CO3)2{NiLn(L)(MeOH)(CH3COO)}2]·2H2O·4MeOH (Ln=Tm (5)) and [(μ4-CO3)2{NiLn(L)(MeOH)(CH3COO)}2]·4MeOH (Ln=Yb (6), Lu(7)) with N,N′-bis(5-bromo-3-methoxysalicylidene)propylene-1,3-diamine (L) are reported. The complexes were obtained by a one-pot reaction with spontaneous fixation of atmospheric CO2 into the coordination species during crystallization process. In each complex the NiII2LnIII2 metal core has a similar topology. The hexadentate Schiff base ligands chelate the Ni(II) and Ln(III) ions forming two binuclear units, that are linked by two CO32− ions giving a carbonato bridged (μ4-CO3)2{NiIILnIII}2 structures. Ferromagnetic interactions between 3d–4f metal centers have been observed for compounds 1 and 2. In complexes 3–6 both the isotropic exchange as well as of thermal depopulation of mJ sublevels and magnetic anisotropy are observed. In compound 7, due to the nonmagnetic nature of the ground state of Lu(III) ions, only a weak antiferromagnetic interaction between Ni(II) ions occurs.

Cd(II) and Zn(II) complexes of two new hexadentate Schiff base ligands derived from different aldehydes and ethanol amine; X-ray crystal structure, IR and NMR spectroscopy studies

Four new [Cd(H2L1)(NO3)]ClO4 (1), [Zn(H2L1)](ClO4)2 (2), [Cd(H2L2)(NO3)]ClO4 (3), and [Zn(H2L2)](ClO4)2 (4), complexes were prepared by the reaction of two new Schiff base ligands and Cd(II) and Zn(II) metal ions in equimolar ratios. The ligands H2L1 and H2L2 were synthesized by reaction of 2-[2-(2-formyl phenoxy)ethoxy]benzaldehyde and/or 2-[2-(3-formyl phenoxy)propoxy]benzaldehyde and ethanol amine and characterized by IR, 1H and 13C NMR spectroscopy. All complexes were characterized by IR, 1H and 13C NMR, COSY, and elemental analysis. Also, the complex 1 was characterized by X-ray in addition to the above methods. The X-ray crystal structure of compound 1 showed that all nitrogen and oxygen atoms of ligand (N2O4) and a molecule of nitrate with two donor oxygen atom have been coordinated to the metal ion and the Cd(II) ion is in an eight-coordinate environment that is best described as a distorted dodecahedron geometry.

Substituent effects on spin state in a series of mononuclear manganese(III) complexes with hexadentate Schiff-Base ligands.

Eleven new mononuclear manganese(III) complexes prepared from two hexadentate ligands, L1 and L2, with different degrees of steric bulk in the substituents are reported. L1 and L2 are Schiff bases resulting from condensation of N,N'-bis(3-aminopropyl)ethylenediamine with 3-methoxy-2-hydroxybenzaldehyde and 3-ethoxy-2-hydroxybenzaldehyde respectively, and are members of a ligand series we have abbreviated as R-Sal2323 to indicate the 323 alkyl connectivity in the starting tetraamine and the substitution (R) on the phenolate ring. L1 hosts a methoxy substituent on both phenolate rings, while L2 bears a larger ethoxy group in the same position. Structural and magnetic properties are reported in comparison with those of a previously reported analogue with L1, namely, [MnL1]NO3, (1e). The BPh4(-) and PF6(-) complexes [MnL1]BPh4, (1a), [MnL2]BPh4, (2a), [MnL1]PF6, (1b'), and [MnL2]PF6, (2b), with both ligands L1 and L2, remain high-spin (HS) over the measured temperature range. However, the monohydrate of (1b') [MnL1]PF6·H2O, (1b), shows gradual spin-crossover (SCO), as do the ClO4(-), BF4(-), and NO3(-) complexes [MnL1]ClO4·H2O, (1c), [MnL2]ClO4, (2c), [MnL1]BF4·H2O, (1d), [MnL2]BF4·0.4H2O, (2d), [MnL1]NO3, (1e), and [MnL2]NO3·EtOH, (2e). The three complexes formed with ethoxy-substituted ligand L2 all show a higher T1/2 than the analogous complexes with methoxy-substituted ligand L1. Analysis of distortion parameters shows that complexes formed with the bulkier ligand L2 exhibit more deformation from perfect octahedral geometry, leading to a higher T1/2 in the SCO examples, where T1/2 is the temperature where the spin state is 50% high spin and 50% low spin. Spin state assignment in the solid state is shown to be solvate-dependent for complexes (1b) and (2e), and room temperature UV-visible and NMR spectra indicate a solution-state spin assignment intermediate between fully HS and fully low spin in 10 complexes, (1a)-(1e) and (2a)-(2e).

Synthesis, spectroscopic and structural characterization, and antimicrobial studies of metal complexes of a new hexadentate Schiff base ligand. Spectrophotometric determination of Fe(III) in water samples using a recovery test

New Schiff base complexes were prepared using the bioactive antimicrobial bis-Schiff base ligand synthesized by condensation of 2-aminobenzoic acid and 2,2′-(ethylenedioxy)bis(benzaldehyde). The pK A value of the bis-Schiff base was determined through visible spectrophotometric experiments and the stability constants of its complexes were also studied. The structural features of the complexes were determined from their elemental analyses, magnetic susceptibility, molar conductance, and spectral (IR and 1H NMR) studies. Powder XRD indicates that all the complexes are amorphous except the Cr(III) and Cu(II) chelates which are crystalline. The data revealed that the stoichiometries of all prepared complexes are of 1:1 M/L type. The UV–vis absorption spectral data for the complexes suggest an octahedral geometry around the central metal ion. Thermogravimetric data (TG and DTG) were also studied. The kinetic and thermodynamic parameters for thermal decomposition of the complexes were calculated by graphical methods using the Coats–Redfern approach. The antimicrobial activity of the bis-Schiff base and its complexes was tested against a number of bacteria and fungi to assess their inhibiting potential. Most of the complexes exhibit antibacterial activity more than the parent bis-Schiff base. Also Cr(III), Co(II), and Ni(II) complexes have antifungal activity against Candida albicans whereas the parent bis-Schiff base is inactive. A recovery test was also applied for the spectrophotometric determination of Fe(III) in different natural water samples.

Heterometallic trinuclear 3d–4f–3d compounds based on a hexadentate Schiff base ligand

The new heterometallic trinuclear complexes [Ni2Ln(L)2(CH3COO)2(MeOH)2]NO3·4H2O (where Ln=Ce(III) 1, Pr(III) 2 and H2L=the Schiff base resulting from the condensation of 5-bromo-3-methoxysalicylaldehyde and 1,3-diaminopropane) were synthesized and characterized by elemental analysis, FTIR, TG/DSC, TG-FTIR, single crystal X-ray diffraction, magnetic, UV–Vis and luminescence studies. In the isostructural crystals of 1 and 2 the nickel(II) and lanthanide(III) ions are bridged by two Schiff base’s phenolato oxygens and additionally by the acetate ions. The clathrate type of crystal architecture in reported complexes, results in their quite high stability in air and nitrogen atmospheres at room temperature despite the relatively large amount of non-coordinated water. The temperature dependence (1.8–300K) of the magnetic susceptibility investigations and the field-dependent magnetization indicate crystal field effect, as well as, the presence of an antiferromagnetic interaction between spin carriers of NiII and LnIII pairs in the NiII–CeIII–NiII (1) and NiII–PrIII–NiII (2) compounds operating via oxygen atoms (JNiCe=−1.1(4)cm−1 (1) and JNiPr=−1.3(8)cm−1 (2)).

Trinuclear metal complexes with hexadentate Schiff base ligand derived from diacetylbis p-phenylendiamine and salicylaldehyde

A number of trinuclear complexes with hexadentate Schiff base ligand H2L= (a condensation product of diacetylbis p-phenylendiamine and salicylaldehyde ) have been prepared . The synthesized complexes having formula [ M2M- (H2L)2 Cl4]Cl2 and [M2M- (L)2]Cl2 ; where M = Co(II) , Ni(II) , Cu(II) and M- = Zn(II) , Cd(II) , Hg(II) . H2L and L the neutral and dibasic forms of Schiff base . The complexes were prepared by the reaction of metal chloride with the ligand in both neutral and basic media . The ligand and its complexes were studies by means of chemical physical and spectral methods. These studies were revealed that the Schiff base act as neutral hexadentate and dibasic hexadentate ligand coordinated through the azomethine nitrogen and phenolic oxygen atoms in neutral and basic media .These studies suggested an octahedral geometry or square planar for two side metal ions in neutral and basic media respectively; The central metal atom is tetra – coordination in all complexes .

Fe(nsal2trien)]SCN, a New Two-Step Iron(III) Spin Crossover Compound, with Symmetry Breaking Spin-State Transition and an Intermediate Ordered State

We report the synthesis of the iron(III) complex of the hexadentate Schiff base ligand nsal2trien obtained from the condensation of triethylenetetramine and 2 equiv. of 2-hydroxy-1-naphthaldehyde. The study of the salt [Fe(nsal2trien)]SCN (1) by magnetic susceptibility measurements and Mössbauer spectroscopy reveals a rather unique behavior that displays thermally induced spin crossover (SCO) with two well-separated steps at 250 (gradual transition) and 142 K (steep transition). Single crystal X-ray structures were obtained at 294, 150, and 50 K, for the high spin (HS), intermediate (Int), and low spin (LS) phases. The HS and LS phases are isostructural, and based on a single Fe(III) site (either HS or LS) an unusual symmetry break occurs in the transition to the Int ordered phase, where the unit cell includes two distinct Fe(III) sites and is based on a repetition of the [HS-LS] motif. The two-step SCO behavior of 1 must result from the existence of structural constraints preventing the full conversion HS ↔ LS in a single step.

Structural effects of potentially hexadentate Schiff base ligands involving pyrrolic, etheric or thioetheric donors towards zinc(II) cation: Synthesis, characterization and crystal structures

The three new zinc (II) complexes (ZnLm, m=1–3) of potentially hexadentate Schiff base ligands containing N4O2 and N4S2 donors with pyrrole terminal binding groups H2L1:[(1Z)-1H-pyrrole-2-ylmethylene]{2-[2-(2-{[(1Z)-1H-pyrrole-2-ylmethylene]amino}phenoxy)ethoxy]phenyl}amine, H2L2:[(1Z)-1H-pyrrole-2-ylmethylene]{2-[4-(2-{[(1Z)-1H-pyrrole-2-ylmethylene]amino}phenoxy)butoxy]phenyl}amine and H2L3:[1H-pyrrole-2-ylmethylene][2-({2-[(2-{[1H-pyrrole-2-ylmethylene] amino}phenyl)thio]ethyl}thio)phenyl]amine, were synthesized and physicochemically characterized. Cyclic voltammetry data indicate that the complexes are electrochemically inactive. The molecular structures of the complexes were determined by single crystal X-ray diffraction. The Zn(II) is five coordinated by N4O donor set of the ligands in the ZnL1 and ZnL2 and six coordinated by N4S2 donor set in the ZnL3.

Biomimetic Catalysts for Oxidation of Veratryl Alcohol, a Lignin Model Compound

Kraft pulp has to be bleached to eliminate the chromophoric structures, which cause a darkening of the pulp. In Nature, an equivalent role is assumed by ligninolytic enzymes such as lignin peroxidases, manganese peroxidases and laccases. The development of low molecular weight manganese peroxidase mimics may achieve environmentally-safe bleaching catalysts for the industry. Herein we report the synthesis and characterization of six manganese(III) complexes 1–6, incorporating dianionic hexadentate Schiff base ligands (H2L1-H2L4) and different anions. Complex 4, Mn2L22(H2O)2(DCA)2 was crystallographically characterized. Complexes 1–4 behave as more efficient mimics of peroxidase in contrast to 5–6. We have studied the use of these complexes as catalysts for the degradation of the lignin model compound veratryl alcohol. The biomimetic catalysts were used in conjunction with chlorine-free inexpensive co-oxidants as dioxygen or hydrogen peroxide. Yields up to 30% of veratryl alcohol conversion to veratraldehyde have been achieved at room temperature in presence of air flow using 0.5% of catalyst.

One-dimensional zigzag chain of Cu–Gd coordination polymers derived from chiral hexadentate Schiff base ligands: Synthesis, structure and magnetic properties

One couple of enantiomerically pure chiral CuIIGdIII coordination polymers [Cu((S, S)-Salcy)Gd(NO3)3·CH3OH]n (1) and [Cu((R, R)-Salcy)Gd(NO3)3·CH3OH]n (2) [(S, S)-Salcy or (R, R)-Salcy=(S, S)- or (R, R)-N, N′-(1,2-cyclohexanediylethylene) bis(3-ethoxysalicylideneiminato)dianion], were synthesized and structurally characterized. The self-assembly by intermolecular semicoordination of nitrate to copper(II) formed a one-dimensional zigzag chain structure. Magnetic property studies indicated that 1 and 2 exhibited very strong ferromagnetic interaction (J=6.285 and 7.408cm−1, respectively) between copper(II) and gadolinium(III) metal centers among the related complexes, although the dihedral angles (8.1° and 8.6°, respectively) of CuO2 and GdO2 are a little large.

Synthesis and characterization of a series of transition metal complexes with a new symmetrical polyoxaaza macroacyclic Schiff base ligand: X-ray crystal structure of cobalt(II) and nickel(II) complexes and their antibacterial properties

A new symmetrical [N4O2] hexadentate Schiff base ligand, (E)-N-(pyridin-2-ylmethylene)-2-(3-(2-((E)-pyridin-2-lmethyleneamino)phenoxy)naphthalen-2-yloxy)benzenamine, abbreviated to L, and its complexes of Ni(II), Cu(II), Zn(II), Co(II), Cd(II) and Mn(II) have been synthesized in the presence of metal ions. The complexes were structurally characterized by elemental analyses, IR, UV–Vis, NMR and molar conductivity. The crystal structures of two complexes, [NiL(ONO2)2]·2H2O and [CoLCl2]CH3OH·0.5H2O, have been determined by a single crystal X-ray diffraction study. In these complexes, the ligand is coordinated in a neutral form via pyridine and azomethine nitrogen atoms. The metal ions complete their six coordination with two coordinated nitrate or chloride ions, forming a distorted octahedral geometry. The synthesized compounds have antibacterial activity against the three Gram-positive bacteria: Enterococcus faecalis, Bacillus cereus and Staphylococcus epid and also against the three Gram-negative bacteria: Citrobacter freundii, Enterobacter aerogenes and Salmonella typhi. The activity data show that the complexes are more potent antibacterials than the parent Schiff base.

Lattice Effects on the Spin‐Crossover Profile of a Mononuclear Manganese(III) Cation

Six solvated salts of a mononuclear manganese(III) complex with a chelating hexadentate Schiff base ligand are reported. One member of the series, [MnL]PF(6)⋅0.5 CH(3)OH (1), shows a rare low-spin (LS) electronic configuration between 10-300 K. The remaining five salts, [MnL]NO(3)⋅C(2)H(5)OH(2), [MnL]BF(4)⋅C(2)H(5)OH(3), [MnL]CF(3)SO(3)⋅C(2)H(5)OH (4), [MnL]ClO(4)⋅C(2)H(5)OH (5) and [MnL]ClO(4)⋅0.5 CH(3)CN (6), all show gradual incomplete spin-crossover (SCO) behaviour. The structures of all were determined at 100 K, and also at 293 K in the case of 3-6. The LS salt [MnL]PF(6)⋅0.5 CH(3)OH is the only member of the series that does not exhibit strong hydrogen bonding. At 100 K two of the four SCO complexes (2 and 4) assemble into 1D hydrogen-bonded chains, which weaken or rupture on warming. The remaining SCO complexes 3, 5 and 6 do not form 1D hydrogen-bonded chains, but instead exhibit discrete hydrogen bonding between cation/counterion, cation/solvent or counterion/solvent and show no significant change on warming.

Determination of cadmium(II) ion by atomic absorption spectrometry after cloud point extraction

In this work, cloud point extraction (CPE) technique was developed for the separation and pre-concentration of Cd(II). CPE was used with lipophilic hexadentate (N4O2) Schiff base ligand, L22pysa (1, C24H26N4O2). The methodology is based upon the formation of a Cd(II)/L complex soluble in a micellar phase the non-ionic surfactant Triton X-114. This complex is then extracted into the surfactant-rich phase above its cloud point temperature. Several important variables that affect the CPE were investigated and optimized. Under the optimum experimental conditions, the calibration graph was linear over the range 1–100 ng mL−1 with a correlation coefficient of 0.9997. The detection limit obtained under optimum conditions was 0.44 ng mL−l. The proposed method was successfully applied to the determination of Cd(II) in rice and various water samples.

Anion driven modulation of magnetic intermolecular interactions and spin crossover properties in an isomorphous series of mononuclear iron(iii) complexes with a hexadentate Schiff base ligand

A series of spin crossover iron(III) complexes with the general composition [Fe(4OH-L6)]X (H2-4OH-L6 = 1,8-bis(4-hydroxysalicylaldiminato)-3,6-diazaoctane; X = Cl, 1a; Br, 1b; I, 1c) was prepared. A combination of the results following the single crystal X-ray analysis, infrared and EPR spectroscopy, and temperature dependent magnetic experiments revealed that the Fe(III) atoms occur in the low-spin state below room temperature and the crystal structures of the complexes involve rich networks of non-covalent intermolecular contacts resulting in two-dimensional supramolecular structures. Alterations in the halide anions influence the strength of the non-covalent contacts and affect the magnetic properties of the studied complexes. The antiferromagnetic exchange interaction between the non-covalently bound cations is the most obvious in the case of 1a and it weakens with the growing anionic volume of X. The 1D and 2D spin Hamiltonian models were applied to quantitatively extract the information about the intermolecular magnetic exchange (fit on 1D infinite chain gives J(1a) = −2.86 cm−1, J(1b) = −2.02 cm−1, J(1c) = −1.16 cm−1). Furthermore, gradual spin crossover behaviour for all of the compounds of the series was observed above room temperature in the solid state. Spin crossover accompanied by thermochromism was also demonstrated by EPR experiments in solution.

Dinuclear and polynuclear dioxomolybdenum(VI) Schiff base complexes: Synthesis, structural elucidation, spectroscopic characterization, electrochemistry and catalytic property

Several new binuclear and polynuclear dioxomolybdenum(VI) Schiff base complexes have been synthesized. The reaction of bis(acetylacetonato)dioxomolybdenum with 5-dichlorosalicylaldehyde 4-ethylthiosemicarbazide (L1/L2) in the presence of 4,4′-bipyridine (4,4′-bpy) or 4,4′-bipyridine N,N′-dioxide (4,4′-dpdo) gave a binuclear cis-dioxomolybdenum complex [(MoO2)2L2(D-D)], in which the bidentate ligand, 4,4′-bipyridine or 4,4′-bipyridine N,N′-dioxide (D-D), formed a bridge between the two molybdenum atoms. A second type of dinuclear dioxomolybdenum(VI) Schiff base complex, [(MoO2)2L′D2], was formed by the reaction of bis(acetylacetonato)dioxomolybdenum with 1,4-bis(3-ethoxy-salicylaldehyde carbohydrazonato)butane (L′) in the presence of ethanol or hexamethylphosphoramide (D). In this case, the two molybdenum atoms are not bridged directly by a bidentate ligand, but are coordinated at each end to the O,N,O donor atoms of the symmetrical hexadentate Schiff base ligand. The syntheses of polynuclear dioxomolybdenum(VI) [(MoO2)L′(D-D)]n complexes were achieved by the reaction of the second type of dinuclear dioxomolybdenum(VI) complex, [(MoO2)2L′D2], with the bidentate ligand 4,4′-bipyridine (D-D). These complexes were characterized by elemental analysis, electronic spectra, IR, 1H and 13C NMR spectroscopies, thermogravimetric analysis and cyclic voltammetry. An X-ray study shows that each molybdenum site in the dinuclear and polynuclear complexes adopts an octahedron geometry. The dioxomolybdenum(VI) complexes show catalytic activity for the oxidation of alcohols with H2O2 as an oxidant.

Tetra- and hexadentate Schiff base ligands and their Ni(II), Cu(II) and Zn(II) complexes. Synthesis, spectral, magnetic and thermal studies

Tetradentate N 2O 2, N 4 Schiff bases, 1,2-bis(4-oxopent-2-ylideneamino) benzene (BOAB), 1-(4-oxopent-2-ylideneamino-2-[(2-hydroxyphenyl)ethylideneamino] benzene (OAHAB), 7,16-bis(4-chlorobenzylidene)-6,8,15,17-tetra-methyl-7,16-dihydro -5,9,14,18-tetraza-dibenzo[a,h] cyclo tetradecene (BCBDCT), 7,16-bis(2-hydroxy-benzylidene)-6,8,15,17-tetramethyl-7,16-dihydro-5,9,14,18-tetraza-dibenzo [a,h] cyclo tetradecene (BHBDCT) and hexadentate N 4O 2 Schiff bases, 2,4-bis {2-[1-(2-hydroxyphenyl) ethylideneamino] phenylimino}-3-(2-hydroxybenzylidene) pentane (BHAPHP), 2,4-bis {2-[1-(2-hydroxyphenyl) ethylideneamino] phenylimino}-3-(4-chlorobenzylidene) pentane (BHAPCP) were prepared and characterized by elemental analysis, IR, UV–Vis, 1H NMR and mass spectra. The solid complexes of the prepared Schiff base ligands with Ni(II), Cu(II) and Zn(II) ions were isolated and characterized by elemental and thermal analyses, IR, electronic and ESR spectra as well as conductance and magnetic susceptibility measurements. The results showed that most complexes have octahedral geometry but few can attain the tetrahedral arrangement. The TG analyses suggest high stability for most complexes followed by thermal decomposition in different steps. The kinetic and thermodynamic parameters for decomposition steps in Cu(II) complexes thermograms have been calculated.

A series of transition and non-transition metal complexes from a N 4O 2 hexadentate Schiff base ligand: Synthesis, spectroscopic characterization and efficient antimicrobial activities

Some transition and non-transition metal complexes of the hexadentate N 4O 2 donor Schiff base ligand 1,8- N-bis(3-carboxy)disalicylidene-3,6-diazaoctane-1,8-diamine, abbreviated to H 4fsatrien, have been synthesized. All the 14 metal complexes have been fully characterized with the help of elemental analyses, molecular weights, molar conductance values, magnetic moments and spectroscopic (UV–Vis, IR, NMR, ESR) data. The analytical data helped to elucidate the structures of the metal complexes. The Schiff base, H 4fsatrien, is found to act as a dibasic hexadentate ligand using N 2N 2O 2 donor set of atoms (leaving the COOH group uncoordinated) leading to an octahedral geometry for the complexes around all the metal ions except VO 2+ and UO 2 2+. However, surprisingly the same ligand functions as a neutral hexadentate and neutral tetradentate one towards UO 2 2+ and VO 2+, respectively. In case of divalent metal complexes they have the general formula [M(H 2fsatrien)] (where M stands for Cu, Co, Hg and Zn); for trivalent metal complexes it is [M(H 2fsatrien)]X· nH 2O (where M stands for Cr, Mn, Fe, Co and X stands for CH 3COO, Cl, NO 3, ClO 4) and for the complexes of VO 2+ and UO 2 2+, [M(H 4fsatrien)]Y (where M = VO and Y = SO 4; M = UO 2 and Y = 2 NO 3). The Schiff base ligand and most of the complexes have been screened in vitro to judge their antibacterial ( Escherichia coli and Staphylococcus aureus) and antifungal ( Aspergillus niger and Pencillium chrysogenum) activities.