Macrocyclic Schiff Base Complexes Research Articles

Template Synthesis and Physicochemical Studies of 14-Membered Functionalized Pendant Arm Schiff-Base Macrocyclic Complexes of Co(II), Ni(II), Cu(II), and Zn(II): DNA Binding Studies on a Cu(II) Complex

A series of functional pendant armed 14-membered Schiff-base macrocyclic complexes [ML(NO3)2], where M = Co(II), Ni(II), Cu(II), and Zn(II), has been synthesized by template condensation of 3,3′-diaminobenzidene and acetylacetone. The complexes have been characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, and electrospray ionization (ESI) mass, 1H-nuclear magnetic resonance (NMR), infrared (IR), electronic, and electron paramagnetic resonance (EPR) spectral studies. The results of elemental analyses, ESI mass spectroscopy, and conductivity measurements confirmed the stoichiometry of the complexes, while the characteristic absorption bands and resonance peaks in IR and NMR spectra confirmed the formation of frameworks of complexes. The molar conductance measurements of the complexes in dimethyl sulfoxide (DMSO) correspond to being non-electrolyte in nature. However, the overall geometry of the complexes has been assigned on the positions of bands in electronic spectra and magnetic moment data. The distortion in Cu(II) complexes has been deduced on the basis of EPR data. Absorption and fluorescence studies on the Cu(II) complex show a significant binding to CT DNA.

Electro- and photocatalytic hydrogen generation in acetonitrile and aqueous solutions by a cobalt macrocyclic Schiff-base complex

The cobalt(III) macrocyclic Schiff-base complex, [Co III(CR)Cl]ClO 4 (CR = 2,12-dimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]-heptadeca-1(17),2,11,13,15-pentaene), is an active catalyst for the electrocatalytic proton reduction to generate dihydrogen in both acetonitrile and 100% aqueous solution (at −0.57 and −0.85 V vs SCE, respectively), using p-cyanoanilinium tetrafluoroborate and acetic acid as proton sources, respectively. Bulk electrolysis confirmed that dihydrogen is produced with >90% Faradaic yields and >50 TON in both solvents. [Co III(CR)Cl 2]ClO 4 also catalyzes photo-driven ( λ > 390 nm) hydrogen production in aqueous acetonitrile at TON of 180 (not optimized), using [Ir III(ppy) 2(bpy)]PF 6 as the photosensitizer, triethanolamine (TEOA) as the sacrificial donor and acetic acid as the proton source.

A theoretical study on the formation of “1 + 1” versus “2 + 2” macrocyclic Schiff base complexes in the absence of coordinated anions

This work reports a theoretical study on “1 + 1” against “2 + 2” cyclocondensation reactions between 2,6-diacetylpyridine and 3,6-dioxaoctane-l,8-diamine in the presence of Mg(II) and Pb(II) metal ions. The results of calculations at DFT(B3LYP) level of theory using LanL2DZ, SDD and CEP-121G basis sets indicate that in the absence of a coordinated anion the “1 + 1” macrocyclic Schiff base complexes are the preferred products for both Mg(II) and Pb(II) metal ions. However, with considering the coordinated anions the “2 + 2” macrocyclic Schiff base complex is preferred product for Pb(II) metal ion. Thus the results present the first theoretical evidence that the coordinated anions have an important role in the metal template synthesis of “2 + 2” against “1 + 1” macrocyclic Schiff base complexes. A theoretical study on “1 + 1” against “2 + 2” cyclocondensation reactions between 2,6-diacetylpyridine and three different amines in the presence of Pb(II) metal ion is also reported. The results confirm that in some cases the kinetic effects prevent formation of the thermodynamically preferred product.

Synthesis and characterization of three heptaaza manganese(II) macrocyclic Schiff base complexes containing two 2-pyridylmethyl pendant arms

Three new Mn(II) bis(pendant arm)-macrocyclic Schiff base complexes, [MnLn]2+(n = 1, 2, 3), have been prepared via cyclocondensation of 2,6-diacetylpyridine with three different branched hexadentate amines (3,6-bis(2-pyridylmethyl)-3,6-diazaoctane-1,8-diamine (1), 3,7-bis(2-pyridylmethyl)-3,7-diazanonane-1,9-diamine (2) and 3,8-bis(2-pyridylmethyl)-3,8-diazadecane-1,10-diamine (3)) in the presence of MnCl2 in methanol. The ligands, L, are 15-, 16- and 17-membered pentaaza macrocycles having two 2-pyridylmethyl pendant arms [L1; 2,13-dimethyl-6,9-bis(2-pyridylmethyl)-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18), 2, 12, 14, 16-pentaene, L2; 2,14-dimethyl-6,10- bis(2-pyridylmethyl)-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19), 2, 13, 15, 17-pentaene and L3; 2,15-dimethyl-6,11-bis(2-pyridylmethyl)-3,6,11,14,20-pentaazabicyclo[14.3.1]eicosa-1(20),2,14,16,18-pentaene]. All the complexes have been characterized by physicochemical and spectroscopic methods. The crystal structure of [MnL1](ClO4)2·CH3CN has been determined and indicates that in the solid state, the complex adopts a slightly distorted pentagonal bipyramidal geometry with the Mn(II) centre located within a pentaaza macrocycle with two 2-pyridylmethyl pendants coordinating in the axial positions.

Computational evidence of preferred energy and preferred binding energy in the formation of “1 + 1” versus “2 + 2” macrocyclic Schiff base complexes

This work reports a theoretical study on “1 + 1” versus “2 + 2” cyclocondensation reactions between 2,6-diacetylpyridine and 3,6-dioxaoctane-l,8-diamine in the presence of Mg(II) and Pb(II) metal ions. The results of calculations at DFT(B3LYP) level of theory using LanL2DZ, SDD and CEP-121G basis sets were consistent with the experimental observations and all showed that “1 + 1” and “2 + 2” macrocyclic Schiff base complexes are preferred products for Mg(II) and Pb(II) metal ions, respectively. It was shown that the prediction of the type of cyclocondensation reaction is possible if we calculate a “preferential energy” and/or a “preferential binding energy” for one of the corresponding products.

Synthesis, characterization and crystal structures of di-three-coordinated copper(I) macrocyclic Schiff base complexes

The air-stable di-copper(I) complexes Cu 2L(SCN) 2 ( 1) and Cu 2L(SCN) 1.86I 0.14 ( 2) of the N 4 macrocyclic Schiff base ligand L have been synthesized and characterized by IR, elemental analysis, UV–Vis and crystal structure determination. X-ray analysis of the complexes shows an approximate distorted trigonal planar geometry around each copper(I) ion that is constructed from one N-bonded thiocyanate (or iodide in 2) group and two imine nitrogen atoms. DFT calculations were used to determine the structural features of the Cu 2L(SCN) 2 complex, and these were consistent with the experimental data for the complex.

Synthesis, Spectral Characterization and Antimicrobial Evaluation of Schiff Base Cu(II), Ni(II) and Co(II) Novel Macrocyclic Complexes

A series of Schiff base macrocyclic complexes of the type [HLMX2] where M = Cu(II), Ni(II), Co(II) and X = Cl, OAc have been synthesized by condensation of acetylacetone and thiocarbohydrazide (2:2) in the presence of divalent metal salt in methanolic medium. The complexes have been characterized with the help of elemental analysis, conductance measurements, magnetic measurements and their structural configuration have been determined by various spectroscopic (Electronic, IR,1H NMR,13C NMR, GCMS) techniques. Electronic and magnetic moments of the complexes indicate that the geometries of the metal centers are octahedral. These metal complexes were also tested for their antimicrobial activities to assess their inhibiting potential.

Cooperative self-assembly of a macrocyclic Schiff base complex

A metal template approach affords in high yield a tetra-Zn(salphen) macrocycle (3) which shows strong and cooperative self-assembly mediated by the formation of Zn(salphen) dimer units held together via μ(2)-phenoxo interactions. A cooperative binding mode for the tetranuclear Zn(4) macrocycle 3 is supported by comparison of UV-vis and fluorescence titration data recorded for 3 when compared with respective mononuclear and dinuclear Zn(salphen) model compounds. UV-vis dilution experiments carried out for Zn(4) macrocycle 3 and its Pd(4) analogue 4, as well as comparative TEM studies involving the same tetranuclear macrocycles further support the strong assembly behavior of 3. This self-assembly seems to be primarily dictated by its ability to form multiple, self-assembled dimeric [Zn(salphen)](2) units.

Coordination chemistry of two new tetraaza Ni(II) and Cu(II) macrocyclic and two new Co(II) and Zn(II) macroacyclic Schiff base complexes containing piperazine moiety: X-ray crystal structures of Ni(II) and Zn(II) complexes

A new potentially tetradentate (N4) Schiff base ligand (L), 1,9,12,20-tetraazatetracyclo[18.2.2.02,7.014,19]tetracosa-2(7),3,5,8,12,14(19),15,17-octaene containing a piperazine moiety is described. Macrocyclic Schiff base complexes, [NiL](ClO4)2 (1) and [CuL](ClO4)2 (2) have been obtained from equimolar amounts of ligand (L) with nickel(II) and copper(II) metal ions. While the equilibrium reaction in the presence of cobalt(II) and zinc(II) metal ions with ligand L in a 1:1 molar ratio yielded the open-chain Schiff base complexes, [CoL′](ClO4)2 (3) and [ZnL′](ClO4)2 (4) containing two terminal primary amino groups. The ligand L′ is 1,4-bis(2-(2-aminoethyliminomethyl)phenyl)piperazine. The crystal structures of (1) and (4) have been also determined by X-ray diffraction. It was shown that the Ni(II) is coordinated to the ligand L by two nitrogen atoms of piperazine group and two nitrogen atoms of the imine groups, in a slightly distorted square-planar geometry. Also single crystal X-ray analysis of (4) confirmed a distorted octahedral arrangement in the vicinity of Zn atom with N6 donor set. The spectroscopic characterization of all complexes is consistent with their crystal structures.

Synthesis and characterization of Cd(II) macrocyclic schiff base complex with two 2-Aminoethyl pendant arms

A new pendant armed Schiff base macrocyclic complex of [CdL]2+, was prepared via cyclocondensation of 2,6-bis(2- formylphenoxymethyl)pyridine with branched hexaamine in the presence of Cd(II) ion. The ligand was 23-membered oxaazamacrocycle having two 2-aminoethyl pendant arms [L: 3,28-dioxa-14,17-bis(aminoethyl)-11,14,17,20,34- pentaazatetracyclo[34.3.1] tetratriacontane-1(34), 4, 6, 8, 10, 20, 22, 24, 26, 30, 32-undecaene]. The complex was investigated by IR, 1H NMR, microanalysis and MALDI mass spectroscopy. The structure of the complex was verified by ab initio HF-MO calculations using a standard 3-21G* basis set. This article introduces an unusual seven-membered chelate ring and shows that by its using, the Cd-N bonds lengths within the macrocycle would be longer and also Cd(II)-pendant amine bonds lengths would be shorter.

Synthesis and characterization of Ni(II), Cu(II) and Zn(II) complexes with new macrocyclic Schiff base ligands containing piperazine moiety

Two new macrocyclic Schiff base ligands L 1 and L 2 from [1 + 1] and [2 + 2] condensation reaction, respectively, have been obtained in a one-pot synthesis starting from 1,4-bis(2-formylphenyl)piperazine and 2,2-dimethyl-propylendiamine. Unfortunately, because of the low solubility of two products, we were unable to separate them effectively. Macrocyclic Schiff base complexes [NiL 1](ClO 4) 2, [CuL 1](ClO 4) 2 and [ZnL 1](ClO 4) 2 were prepared from the reaction of a mixture of L 1 and L 2 in the presence of nickel(II), copper(II) and zinc(II) metal ions, respectively. In all cases, only [1 + 1] condensation products were obtained and no metal complexes were isolated with the L 2 macrocycle. All of complexes have been characterized by elemental analysis, IR spectra, FAB-MS, conductivity measurements and in the case of Zn(II) complex by 1H and 13C NMR spectroscopy. Crystal structures of [NiL 1](ClO 4) 2 and [NiL 1′](ClO 4) 2 complexes have been also determined. The Ni(II) is coordinated to the ligand L 1 and L 1′ by two nitrogen atoms of piperazine group and two nitrogen atoms of the imine groups, in a slightly distorted square-planar geometry.

New asymmetric heptaaza Schiff base macrocyclic complex of Mn(II): Crystal structure, biological and DFT studies

A new asymmetric heptaaza Schiff base macrocyclic bis(pendant donor) manganese(II) complex, [MnL 1](ClO 4) 2·CH 3CN ( 1), has been prepared and characterized by X-ray diffraction and spectroscopic methods. The antimicrobial activity of 1 and a series of its familiar symmetric heptaaza [15]pydieneN 5, [16]pydieneN 5, and [17]pydieneN 5-based bis-(2-aminoethyl) pendant armed Schiff base macrocyclic complexes of Mn(II) were tested against Escherichia coli, Staphylococcus aureus and Candida albicans. The results showed that the symmetric heptaaza [16]pydieneN 5, and [17]pydieneN 5-based Schiff base macrocyclic complexes of Mn(II) had remarkable inhibition zone on the culture of S. aureus and E. coli as compared with standard drugs. The optimized geometry of the prepared complex has been obtained from density functional method, DFT, using B3LYP/6-31G* basis set.

Mn(II) and Cd(II) macrocyclic Schiff base complexes with a single pendant coordinating 2-pyridylmethyl arm: Synthesis, X-ray crystal structure and NMR studies

Six new macrocyclic Schiff base complexes were prepared by the template condensation of two tripodal ligands and with 2-[2-(2-formyl phenoxy)ethoxy] benzaldehyde and 2-[3-(2-formyl phenoxy)propoxy]benzaldehyde in the presence of Cd(NO 3 )·4H 2 O or MnCl 2 in equimolar ratios. The resulting compounds were characterized by IR spectroscopy, elemental analysis and mass spectrometry in all cases and by X-ray and NMR in the case of all Cd(II) complexes. The cyclocondensation reaction of N-(2-pyridylmethyl)-N-(2-aminoethyl)-1,2-diaminoethane, L 22py , with both 2-[2-(2-formyl phenoxy)ethoxy] benzaldehyde and 2-[3-(2-formyl phenoxy)propoxy]benzaldehyde, and reaction of N-(2-pyridylmethyl)-N-(2-aminoethyl)-1,3-diaminopropane, L 33py , with 2-[2-(2-formyl phenoxy)ethoxy] benzaldehyde in the presence of equimolar amounts of Cd(II) or Mn(II) metal ions is reported. The resulting compounds [CdL 1 Cl](ClO 4 )·1/2CH 3 CN ( 1 ), [MnL 1 Cl](ClO 4 ) ( 2 ), [CdL 2 (NO 3 )](ClO 4 )·CH 3 CN ( 3 ), [MnL 2 Cl]ClO 4 ( 4 ), [CdL 3 Cl](ClO 4 )·H 2 O ( 5 ) and [MnL 3 Cl]ClO 4 ( 6 ) were characterized by IR spectroscopy, elemental analysis and mass spectrometry in all cases and by X-ray and NMR in the case of the Cd(II) complexes. X-ray single crystal structure analysis of a selected single crystal of compound ( 1 ) showed that it contains two cations ( A ) and ( B ), [CdL 1 Cl] + , with similar N 4 OCl donor sets. In contrast, the results of microanalysis, NMR and mass spectra showed that in the bulk sample, there are two different cations [CdL 1 Cl] + and [CdL 1 (NO 3 )] + in the ratio of 4–1, respectively. X-ray crystal structure determination of other cadmium complexes, ( 3 ) and ( 5 ), confirmed that in addition to the expected macrocylic ligand with a N 4 O 2 donor set, the NO 3 - and Cl − anions are coordinated to the central metal ion, respectively.

Synthesis and crystal structure of some new cadmium (II) macrocyclic Schiff-base complexes containing piperazine moiety

The metal templated Cd(II) cyclocondensation of 2,6-diacetylpiridine or 2,6-pyridinedicarbaldehyde and two different amines containing piperazine moieties have been investigated. The resulting ligands, L 1 and L 2 are 16- and L 3 and L 4 17-membered pentaaza macrocycles. The complexes have been characterized by a variety of methods including IR, 1H, 13C NMR, DEPT, COSY(H,H), HMQC(H,C), FAB spectrometry and conductivimetry measurements. The crystal structures of [CdL 2Cl](CH 3OH)ClO 4 (2) and [CdL 4(NO 3)(H 2O)]ClO 4 (4) have been also determined, and it was shown that the geometry of the Cd(II) ion in the complexes is slightly distorted pentagonal pyramidal and pentagonal bipyramidal, respectively. The gas-phase structures of ligands, L 2 and L 4 and their Cd(II) complexes have also theoretically studied.

Synthesis and characterization of two zinc(II) macrocyclic Schiff-base complexes containing piperazine moiety, crystal structure of one complex

Two symmetrical and asymmetrical Zn(II) complexes of a pentadentate (N 5) macrocyclic Schiff-base ligands, were prepared via templated [1 + 1] cyclocondensation of 2,6-diacetylpyridine with two different amines containing piperazine moiety. The complexes have been characterized by a variety of methods including, IR, FAB mass spectrometry, elemental analysis and conductivity measurements. The crystal structure of the asymmetric complex, [ZnL 1Br]ClO 4 was determined by X-ray diffraction. It is shown that in the solid state the complex adopts a distorted pentagonal–pyramidal geometry, with the macrocycle in the pentagonal plane and the bromide ion in the axial position.

Synthesis and characterization of three novel manganese(II) octaaza macrocyclic Schiff base complexes containing a phenanthroline and two pyridyl units as pendant arms. X-ray crystal structure determination of one manganese(II) complex

Three new branched hexadentate amines (N 6), 3,6-bis(2-pyridylmethyl)-3,6-diazaoctane-1,8-diamine ( 1), 3,7-bis(2-pyridylmethyl)-3,7-diazanonane-1,9-diamine ( 2) and 3,8-bis(2-pyridylmethyl)-3,8-diazadecane-1,10-diamine ( 3) have been synthesized. Subsequently, three novel Schiff base macrocyclic complexes containing a phenanthroline and two 2-pyridylmethylpendant arms have been prepared by template [1+1] cyclocondensation of 2,9-dicarboxaldehyde-1,10-phenanthroline and the branched hexadentate amines ( 1– 3), in the presence of Mn(II) in methanol. These complexes have ligands with 18-, 19- and 20-membered hexaaza macrocycles and two 2-pyridylmethyl pendant arms (L 1, L 2 and L 3, respectively). All the complexes have been characterized by elemental analysis and IR spectroscopy. The crystal structure of [MnL 1](ClO 4) 2 · 3CH 3CN was determined and indicates that in the solid state the complex adopts a slightly distorted hexagonal bipyramidal geometry with the Mn(II) ion located within a hexaaza macrocycle with the two 2-pyridylmethyl pendant arms coordinating in axial positions.

Synthesis and Characterisation of Macrocyclic Copper(II) Complexes Containing N3O4 Donor Sets

Two new macrocyclic Schiff-base complexes of Cu(II) have been prepared by the template reaction of 2,6-bis (2-formylphenoxymethyl)pyridine with 1,2-bis(2′-aminophenoxy)benzene [L1] or with 1,2-bis(2′-aminophenoxy)-4-tert-butylbenzene [L2] in the presence of Cu(II) perchlorate. The amines used have low flexibility and therefore the formation of complexes was very difficult. The synthesised 23-membered, heptadentate N3O4 complexes were characterised by elemental analysis, IR, and FAB-mass spectroscopy.

Synthesis and biological activity of Magnesium(II) complexes of heptaaza Schiff base macrocyclic ligands; 1H and 13C chemical shifts computed by the GIAO-DFT and CSGT-DFT methodologies

Two new pendant armed Schiff base macrocyclic complexes, [MgL1](ClO4)2 (1), and [MgL2](ClO4)2 (2), have been prepared via cyclocondensation of 2,6-diformylpyridine and 2,6-diacetylpyridine with two hexadentate hexaamines, ten and tmen, in the presence of Mg(II) ion. The ligands are 15-membered pentaaza macrocycles having two 2-aminoethyl pendant arms. The newly prepared complexes are investigated by IR, 1H NMR, 13C{1H} NMR, DEPT(135), COSY(H, H) and HMQC spectroscopic methods. The antimicrobial screening of newly prepared complexes, 1 and 2, as well as previously prepared similar complexes, [MgL3](ClO4)2 (3) and [MgL4](ClO4)2 (4), against Escherichia coli, Staphylococcus aureus and candidia albicans showed that the macrocyclic complexes of Mg(II) containing 15-membered pentaaza ring (1, 2 and 3) have no activity. Where as the compound 4, which contain 16-membered pentaaza ring, had remarkable inhibition zone on the culture of S. aureus and E. coli as compared with standard drugs. The 1H and 13C chemical shieldings of gas phase complexes were also studied by the gauge independent atomic orbital (GIAO) and continuous set of gauge transformations (CSGT) methods at the level of density functional theory (DFT). The computed 13C chemical shifts are in reasonably good agreement with the experimental data.

Synthesis and crystal structure of Mn(II) complexes with novel macrocyclic Schiff-base ligands containing piperazine moiety

A series of Mn(II) macrocyclic Schiff-base complexes [MnL n Cl] + ( n = 1–4) have been prepared via the Mn(II) templated [1+1] cyclocondensation of 2,6-diacetylpyridine or 2,6-pyridinedicarbaldehyde with the symmetrical 1,4-bis(3-aminopropyl)piperazine or the novel asymmetrical N, N′(2-aminoethyl)(3-aminopropyl)piperazine linear amines containing piperazine moiety. The complexes have been characterized by elemental analyses, IR, FAB-MS, magnetic studies and conductivity measurements. The crystal structure of [MnL 2(CH 3OH)Cl](ClO 4) and [MnL 4Cl](PF 6) complexes have also been determined showing the metal ion in a N 4OCl pentagonal bipyramidal or N 4Cl highly distorted octahedral geometry, respectively.

Synthesis of two new tripodal ligands and their cyclocondensation with 2-[2-(2-formylphenoxy)ethoxy]benzaldehyde in the presence of manganese(II) and cadmium(II) metal ions

Two new asymmetric tripodal tetraamine ligands, 2-((bis(2-aminoethyl)amino)methyl)benzenamine (L 2) and 2-(((2-aminoethyl)(3-aminopropyl)amino)methyl)benzenamine (L 3) were synthesized and characterized. [1+1] Macrocyclic Schiff-base complexes containing 1,2-diphenoxyethane head units and a 2-aminobenzyl pendant arm, were synthesized as [MnL 4(MeOH)](ClO 4) 2 ( 1), [MnL 5(MeOH)](ClO 4) 2 ( 2), [CdL 4(H 2O)](NO 3) 2 ( 3) and [CdL 5(H 2O)](NO 3) 2 ( 4) from the metal ion templated cyclocondensation reactions of 2-[2-(2-formylphenoxy)ethoxy]benzaldehyde with the (L 2) or (L 3) tripodal tetraamine ligands. The crystal structure determination of ( 1) and ( 4) showed that the complex cations that had formed consisted of pentagonal bipyramidally coordinated Mn(II) and Cd(II) ions, centrally located in a N 3O 2 macrocycle, with one 2-aminobenzyl pendant arm. Supporting ab initio HF-MO calculations have been undertaken using the standard 3-21G ∗ and 6-31G ∗ basis sets.