New macrocyclic Schiff-base complexes incorporating a phenanthroline unit. Part 2: Template synthesis of some manganese(II) complexes and crystal structure studies

A series of Mn(II) macrocyclic Schiff-base complexes [MnLⁿ]²⁺ have been prepared via the Mn(II) templated [1+1] cyclocondensation of 2,9-dicarboxaldehyde-1,10-phenanthroline with appropriate linear and branched amines. In this way ligands the pentaaza macrocycle L¹ which is 15-membered and L² which is 16-membered possessing no pendant arm, L⁶ is 15-membered with one 2-aminoethyl pendant arm and L⁸ which is 18-membered hexaaza macrocycle with two 2-aminoethyl pendant arms are formed. All the complexes have been characterized using spectroscopic methods. The crystal structures of [MnL⁸](ClO₄)₂ · EtOH were determined and indicate that in the solid state the complex adopts a slightly distorted hexagonal bipyramid geometry with the Mn(II) ion located within a hexaaza macrocycle with the two pendant amines coordinating in the axial positions.     

Synthesis, crystal structures and ab initio studies of some heptaaza manganese(II) macrocyclic Schiff-base complexes with two 2-aminoethyl pendant arms

Two new heptaaza Mn(II) macrocyclic bis(pendant donor) Schiff-base complexes, [MnL⁶]²⁺ and [MnL⁷]²⁺, have been prepared via Mn(II) templated [1 + 1] cyclocondensation of 2,6-diacetylpyridine with an appropriate branched hexaamine, and characterized by X-ray crystallography and spectroscopic methods. The ligands are 16- and 17-membered pentaaza macrocycles with two 2-aminoethyl pendant arms [L⁶ = 2,14-dimethyl-6,10-bis(2-aminoethyl)-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19),2,13,15,17-pentaene and L⁷ = 2,15-dimethyl-6,11-bis(2-aminoethyl)-3,6,11,14,20-pentaazabicyclo[14.3.1]eicosa-1(20),2,14,16,18-pentaene]. The crystal structures of [MnL⁷]²⁺ and another related complex, [MnL⁵]²⁺ [L⁵ = 2,13-dimethyl-6,9-bis(2-aminoethyl)-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene] were determined from X-ray diffraction data and the structure of each complex indicates that the geometry of the coordination sphere is that of a slightly distorted pentagonal bipyramid with the Mn(II) ion located within a pentaaza macrocycle and two pendant amines coordinating on opposite sides. The increased macrocycle ring size in [MnL⁷]²⁺ introduces an unusual seven-membered chelate ring and leads to long Mn-N bond lengths within the macrocycle, but to shorter pendant amine-Mn(II) bond lengths. Ab initio HF-MO calculations produce structures for the two complexes which are in close agreement with experimental findings and predict a similar structure for [MnL⁶]²⁺, but with the longest pendant amine-Mn(II) bond lengths of the three structures.     

Synthesis, crystal structure, NMR and ab initio molecular-orbital studies of some magnesium(II) macrocyclic Schiff-base complexes, with two 2-aminoethyl pendant arms

Three new Mg(II) bis(pendant arm) macrocyclic Schiff-base complexes, [MgLⁿ]²⁺(n=5, 6, 7), have been prepared via cyclocondensation of 2,6-diacetylpyridine with branched hexaamines and characterised spectroscopically. In addition, for [MgL⁵](ClO₄)₂ the crystal structure is reported. This is the first X-ray structural determination of an Mg(II) complex coordinated by seven nitrogen atoms. The ligands, L, are 15-, 16- and 17-membered pentaaza macrocycles having two 2-aminoethyl pendant arms [L⁵; 2,13-dimethyl-6,9-bis(aminoethyl)-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18), 2, 12, 14, 16-pentaene, L⁶; 2,14-dimethyl-6,10-bis(aminoethyl)-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19), 2, 13, 15, 17-pentaene and L⁷; 2,15-dimethyl-6,11-bis(aminoethyl)-3,6,11,14,20-pentaazabicyclo[14.3.1]eicosa-1(20),2,14,16,18-pentaene]. The crystal structure of [MgL⁵](ClO₄)₂, was determined by X-ray diffraction and showed that the complex cation that had formed consisted of a pentagonal bipyramidally coordinated Mg(II) ion. All complexes were characterised by IR, ¹H NMR,¹³C NMR, COSY(H,H) and HETCOR(H,C) spectroscopy, and the data indicate that the structure is approximately pentagonal bipyramidal in each case. This structural assignment is also supported by ab initio HF-MO calculations made using the standard 3-21G* basis set.     

Synthesis and characterization of Mg(II), Mn(II), Zn(II) and Cd(II) complexes with a new heptaaza Schiff base pendant-armed macrocycle: X-ray crystal structure, NMR and computational study

New 2-aminoethyl pendant-armed Schiff base macrocyclic complexes, [ML⁷]²⁺ (M = Mn(II), Mg(II), Zn(II) and Cd(II)), have been prepared via M(II) templated [1 + 1] cyclocondensation of 2,6-diacetylpyridine with a new branched hexamine, N,N,N′,N′-tetrakis(2-aminoethyl)-2,2-dimethylpropane-1,3-diamine. The ligand is a 16-membered pentaaza macrocycle having two 2-aminoethyl pendant arms [L⁷ is 2,14-dimethyl-6,10-bis(2-aminoethyl)-3,6,10,13,19-pentaazabicyclo[13.3.1]8,8-dimethylnonadeca-1(19),2,13,15,17-pentaene]. The crystal structures of [MnL⁷]²⁺ and [MgL⁷]²⁺ were determined from X-ray diffraction data. The geometry of the coordination sphere of complexes is a slightly distorted pentagonal bipyramid with the metal ion located within a pentaaza macrocycle and two pendant amines coordinating on opposite sides. All complexes were characterized by IR, microanalysis and except of [MnL⁷]²⁺ by ¹H NMR, ¹³C NMR, DEPT135, COSY(H, H) and HMQC spectroscopy. The data indicate that the structure is pentagonal bipyramidal in each case. The structure of all complexes has also been theoretically studied by ab initio Hartree-Fock and density functional theory methods.     

Synthesis and characterization of nickel(II) and copper(II) complexes with tetradentate Schiff base ligands

The 1:1 condensation of 1,2-diaminopropane and 1-phenylbutane-1,3-dione at high dilution gives a mixture of two positional isomers of terdentate mono-condensed Schiff bases 6-amino-3-methyl-1-phenyl-4-aza-2-hepten-1-one (HAMPAH) and 6-amino-3,5-dimethyl-1-phenyl-4-aza-2-hexen-1-one (HADPAH). The mixture of the terdentate ligands has been used for further condensation with pyridine-2-carboxaldehyde or 2-acetylpyridine to obtain the unsymmetrical tetradentate Schiff base ligands. The tetradentate Schiff bases are then allowed to react with the methanol solution of copper(II) and nickel(II) perchlorate separately. The X-ray diffraction confirms the structures of two of the complexes and shows that the condensation site of the diamine with 1-phenylbutane-1,3-dione is the same.     

Photocytotoxicity and near-IR light DNA cleavage activity of oxovanadium(IV) Schiff base complexes having phenanthroline bases

Oxovanadium(IV) complexes [VO(L)(B)] (1-3), where H₂L is a Schiff base ligand 2-(2-hydroxybenzylideneamino)phenol and B is 1,10-phenanthroline (phen for 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq for 2) or dipyrido[3,2-a:2′,3′-c]phenazine (dppz for 3), have been prepared, characterized and their DNA binding property and photo-induced DNA cleavage activity studied. Complex 3 which is structurally characterized by X-ray crystallography shows the presence of an oxovanadium(IV) moiety in a six coordinate VO₃N₃ coordination geometry. The complexes show a d-d band within 800-850 nm in DMF. The complexes display an oxidative response near 0.7 V versus SCE for V(V)-V(IV) and a reductive response within −1.1 to −1.3 V due to V(IV)-V(III) couple in DMF-0.1 M TBAP. The complexes are avid binders to calf thymus DNA giving binding constant values of 4.2 × 10⁴ to 1.2 × 10⁵ M⁻¹. The complexes do not show any “chemical nuclease” activity in dark. The dpq and dppz complexes are photocleavers of plasmid DNA in UV-A light of 365 nm via ¹O₂ pathway and in near-IR light (752.5 to 799.3 nm IR optics) by HO^• pathway. Complex 3 exhibits significant photocytotoxicity in visible light in HeLa cells giving IC₅₀ value of 13 μM, while it is less toxic in dark (IC₅₀ = 97 μM).     

Electrochemical synthesis and crystal structure of iron(II), cobalt(II), nickel(II) and copper(II) complexes of dianionic tetradentate N4 Schiff base ligand

The electrochemical oxidation of anodic metal (iron, cobalt, nickel and copper) in an acetonitrile solution of the potentially chelating Schiff base N,N(dithiodiethylenebis-(aminylydenemethylydene)-bis(1,2-phenylene)ditosylamide (H₂L) afforded stable complexes of empirical formula [ML]. The compounds obtained have been characterized by microanalysis, IR spectroscopy and ES-MS mass spectrometry. The crystal and molecular structures of [FeL]·CH₃CN (1) [CoL]·CH₃CN (2), [NiL]·CH₃CN (3) and [CuL]·CH₃CN (4) have been determined by X-ray diffraction in all complexes, the metal atom is in a distorted tetrahedral environment with the Schiff base acting as a tetradentate N4 donor.     

Novel palladium(II) and Zinc(II) Schiff base complexes: Synthesis,biophysical studies,and anticancer activity investigation

BackgroundSchiff base metal complexes are considered promising chemotherapeutic agents due to their potential application in cancer therapy.MethodsThe current work sought to synthesize a brand-new Schiff base ligand obtained from 2-hydroxybenzohydrazide and (E)− 1-(2-(p-tolyl)hydrazono)propan-2-one with metal ions which included Pd(II) and Zn(II) ions. Elemental analyses, FT-IR, mass spectra, 1H NMR, UV-Vis spectrometer, and computational analysis characterized the compound's structure. In vitro, the breast cancer cell line (MCF-7) was tested for its sensitivity to Schiff base (HL) and its Pd(II) and Zn(II) complexes. The half-maximal inhibitory concentration IC₅₀ of the compounds was determined and used to perform the comet assay, which was carried out to reveal the photo-induced DNA damaging ability of the compounds of individual cells. Moreover, the compounds' effects on antioxidant defense systems of enzymes in cells: superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities and oxidant Malondialdehyde (MDA) were examined in MCF-7 cells.ResultsThe Pd(II) complex displayed approximately the same IC₅₀ as Cisplatin, while Zn(II) complex had better activity than Cisplatin with very low IC₅₀, 1.40 μg/ml. Significant alterations in SOD, CAT, GPx, and MDA production were discovered, inducing oxidative stress, enlarging ROS production, and reducing the antioxidant amount. This change was approximately similar in most compounds. Consequently, it promoted apoptosis, particularly the Zn(II) complex, which demonstrated an improved impact because of its ability to influence the antioxidant defense systems of enzymes, mostly SOD and GPx, besides increasing MDA levels.ConclusionIt can be concluded that Zn(II) complex is the most effective anticancer drug since it induced a very similar genotoxic effect as Cisplatin and has a very low IC₅₀ value.     

Hydrogen-bonded copper(II) and nickel(II) complexes and coordination polymeric structures containing reduced Schiff base ligands

Complexes [Cu(HSas)(H₂O)] · 2H₂O (H₃Sas = N-(2-hydroxybenzyl)-l-aspartic acid) (1), [Cu(HMeSglu)(H₂O)] · 2H₂O (H₃MeSglu = (N-(2-hydroxy-5-methylbenzyl)-l-glutamic acid) (2), [Cu₂(Smet)₂] (H₂Smet = (N-(2-hydroxybenzyl)-l-methionine) (3), [Ni(HSas)(H₂O)] (4), [Ni₂(Smet)₂(H₂O)₂] (5), and [Ni(HSapg)₂] (H₂Sapg = (N-(2-hydroxybenzyl)-l-aspargine) (6) have been synthesized and characterized by chemical and spectroscopic methods. Structural determination by single crystal X-ray diffraction studies revealed 1D coordination polymeric structures in 2 and 4, and hydrogen-bonded network structure in 5 and 6. In contrast to previously reported coordination compounds with similar ligands, the phenol remains protonated and bonded to the metal ions in 2 and 4, and also probably in 1. However, the phenolic group is non-bonded in 6.     

Synthesis, characterisation and crystal structures of a few coordination complexes of nickel(II), cobalt(III) and zinc(II) with N′-[(2-pyridyl)methylene]salicyloylhydrazone Schiff base

Four new coordination complexes, Ni^II(L)₂ (1), [Co^III(L)₂]ClO₄ (2), [Zn(HL)(L)]ClO₄ · H₂O (3) and [Zn(L)₂][Zn(L)(HL)]ClO₄ · 7H₂O (4) (where L is a monoanion of a Schiff base ligand, N′-[(2-pyridyl)methylene]salicyloylhydrazone (HL) with NNO tridentate donor set), have been synthesised and systematically characterised by elemental analysis, spectroscopic studies and room temperature magnetic susceptibility measurements. Single crystal X-ray diffraction analysis reveals that 1 is a neutral complex, while 2-4 are cationic complexes. Among them, 4 is a rare type of cationic complex with two molecules in the asymmetric unit. The ligand chelates the metal centre with two nitrogen atoms from the pyridine and imino moieties and one oxygen atom coming from its enolic counterpart. All the reported complexes show distorted octahedral geometry around the metal centres, with the two metal-N (imino) bonds being significantly shorter than the two metal-N (Py) bonds.     

Chlorido-bridged polymeric and dinuclear copper(II) complexes with tridentate Schiff base: Synthesis, crystal structure and magnetic properties

Two copper(II) complexes, [Cu(qsal)Cl](DMF) (1) and [Cu₂(qsalBr)₂Cl₂](DMF) (2), with tridentate Schiff base ligands, 8-(salicylideneamino)quinoline (Hqsal) and 8-(5-bromo-salicylideneamino)quinoline (HqsalBr), respectively, were synthesised and structurally characterized. Each copper(II) ion in the two complexes is in a distorted square pyramidal N₂OCl₂ environment. Complex 1 exists as a polymeric species via equatorial-apical chloride bridges, whereas 2 is a di-chlorido-bridged dinuclear complex, where each bridging chloride simultaneously occupies an in-plane coordination site on one copper(II) ion and an apical site on the other copper(II) ion. Variable-temperature magnetical susceptibility measurements on the two complexes in the temperature range 2-300 K indicate the occurrence of intrachain ferromagnetic (J = +6.58 cm⁻¹) and intramolecular antiferromagnetical (J = −6.91 cm⁻¹) interactions.     

Template synthesis, characterization and crystal structure of heptaazadentate Schiff base lanthanide aminopodates

The Schiff base condensation reactions between 2,6-diacetylpyridine and diethylenetriamine in the presence of lanthanum(III) and praseodymium(III) ions as template agents yield, exclusively, heptaazadentate complexes of a podate type with two terminal amine groups, irrespective of the molar ratio of the starting materials used in the synthesis. These complexes, which might be regarded as possible intermediates in the template synthesis of macrocyclic compounds, appear to be the final products. The ring-closure of the partial Schiff base condensation products does not occur either by the transamination mechanism or by the 2,6-diacetylpyridine addition. The rare heptaazadentate behavior of the Schiff base aminopodand in lanthanide complexes is proved by single-crystal X-ray diffraction analysis correlated with spectroscopic characterization. All the seven potential nitrogen donor atoms are available for coordination to the metal ions. The high coordination number of eleven is achieved by the incorporation of two bidentate nitrate anions in the lanthanide coordination sphere.     

Synthesis, crystal structure and photo-induced DNA cleavage activity of ternary copper(II) complexes of NSO-donor Schiff bases and NN-donor heterocyclic ligands

New ternary copper(II) complexes [CuLⁿB](ClO₄) (1-3), where HLⁿ is the NSO donor Schiff base derived from the condensation of 2-mercaptoethylamine hydrochloride with salicylaldehyde (HL¹) or 2-hydroxy-3-methoxybenzaldehyde (HL²) and B is NN-donor heterocyclic base like 2,2′-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2) or 2,9-dimethyl-1,10-phenanthroline (dmp, 3), are prepared, structurally characterized by X-ray crystallography and their DNA cleavage activity studied. The complexes show distorted square-pyramidal (4 + 1) CuN₃OS coordination geometry in which the NSO-donor Schiff base is bonded at the basal plane and the NN-donor heterocyclic base displays axial-equatorial mode of bonding [Cu-S distance: ∼2.4 Å]. The one-electron paramagnetic (μ_eff = ∼1.9 μ_B) complexes display axial EPR spectra in DMF glass at 77 K giving g_∥ = ∼2.2 (A_∥ = 162 G) and g_⊥ = ∼2.0, indicating {d_x²-y²}¹ ground state. The complexes exhibit visible spectral d-d band in MeCN near 650 nm and two charge transfer bands near 400 nm. Complexes 1 and 2 display quasireversible cyclic voltammetric response in DMF-Tris buffer (1:4 v/v, pH 7.2) for the Cu(II)/Cu(I) couple at ca. −0.1 V vs. SCE. Complex 3 exhibits an irreversible reduction process forming [Cu^I(dmp)₂]⁺. Binding of 1-3 to calf thymus DNA shows the relative order: 2 (phen) ? 3 (dmp) > 1 (bpy). Complex 2 efficiently cleaves supercoiled pUC19 DNA in the presence of mercaptopropionic acid (MPA) forming hydroxyl radical or on irradiation with light of 312, 532 and 632.8 nm wavelength in a type-II process. Complexes 1 and 3 are cleavage inactive.     

Synthesis, characterization and X-ray crystal structures of copper(II) and nickel(II) complexes with potentially hexadentate Schiff base ligands

Copper(II) and nickel(II) complexes of potentially N₂O₄ Schiff base ligands 2-({[2-(2-{2-[(1-{2-hydroxy-5-[2-phenyl-1-diazenyl]phenyl}methylidene)amino] phenoxy}ethoxy) phenyl]imino}methyl)4-[2-phenyl-1-diazenyl]phenol (H₂L¹) and 2-({[2-(4-{2-[(1-{2-hydroxy-5-[2-phenyl-1-diazenyl]phenyl}methylidene)amino] phenoxy}butoxy) phenyl]imino}methyl)4-[2-phenyl-1-diazenyl]phenol (H₂L²) prepared of 5-phenylazo salicylaldehyde (1) and two various diamines 2-[2-(2-aminophenoxy)ethoxy]aniline (2) and 2-[4-(2-aminophenoxy)butoxy]aniline (3) were synthesized and characterized by a variety of physico-chemical techniques. The single-crystal X-ray diffractions are reported for CuL¹ and NiL². The CuL¹ complex contains copper(II) in a near square-planar environment of N₂O₂ donors. The NiL² complex contains nickel(II) in a distorted octahedral geometry coordination of N₂O₄ donors. In all complexes, H₂L¹ behaves as a tetradentate and H₂L² acts as a hexadentate ligand. Cyclic voltammetry of copper(II) complexes indicate a quasi-reversible redox wave in the negative potential range.     

Synthesis, crystal structure and magnetic characterization of a series of four phenoxo-bridged binuclear manganese(III) Schiff base complexes

A family of four new phenoxo-bridged binuclear manganese(III) complexes of the general formula, [Mn(L)(X)]₂ where L = [N,N′-bis(salicylidene)]propane-1,2-diamine and X = salicylaldehyde anion (sal⁻) (1); NCS⁻ (2); NCO⁻ (3) and [Mn(L′)(N₃)]₂·2C₂H₅OH (4) where L′ = [N,N′-bis(2-hydroxyacetophenylidene)]propane-1,2-diamine has been prepared. The syntheses have been achieved by reacting manganese perchlorate with 1,2-diaminopropane and salicylaldehyde (or 2-hydroxyacetophenone for 4) or along with the respective pseudohalides so that the tetradentate Schiff base H₂L or H₂L′ is obtained in situ to bind the Mn(III) ion. The complexes have been characterized by IR spectroscopy, elemental analysis, crystal structure analysis and variable-temperature magnetic susceptibility measurements. The single crystal X-ray diffraction studies show that the compounds are isostructural containing dimeric Mn(III) units with bridging phenolate oxygen atoms. Low temperature magnetic studies indicate that the complexes 1-3 exhibit intradimer ferromagnetic exchange as well as single-molecule magnet (SMM) behavior while complex 4 is found to undergo an intradimer antiferromagnetic coupling.     

Synthesis, structural characterization, antiradical and antidiabetic activities of copper(II) and zinc(II) Schiff base complexes derived from salicylaldehyde and beta-alanine

A series of copper(II) and zinc(II) complexes involving a tridentate O,N,O'-donor Schiff base derived from salicylaldehyde and beta-alanine {i.e. N-salicylidene-beta-alanine(2-), (L)}, having the composition [Cu(2)(L)(2)(H(2)O)].H(2)O (1), [Cu(L)(H(2)O)](n) (2), and [Zn(L)(H(2)O)](n) (3), have been prepared and characterized by elemental analyses, UV-visible (UV-VIS), FT-IR and ESI-MS spectra, and thermal analyses. Complexes 1 and 2 have been investigated by single crystal X-ray analysis and also by temperature dependent magnetic susceptibility measurements (294-80K). All prepared complexes have been evaluated by the antiperoxynitrite activity assay and alloxan-induced diabetes model. The significant antioxidant and antidiabetic activities have been found in the case of both copper(II) complexes 1 and 2. In spite of first two complexes, the zinc(II) complex 3, as well as the potassium salt of the ligand (KHL) showed only insignificant protective effect against the tyrosine nitration in vitro.     

Study on potential antitumor mechanism of a novel Schiff base copper(II) complex: synthesis, crystal structure, DNA binding, cytotoxicity and apoptosis induction activity

A new cytotoxic copper(II) complex with Schiff base ligand [Cu^II(5-Cl-pap)(OAc)(H₂O)]·2H₂O (1) (5-Cl-pap = N-2-pyridiylmethylidene-2-hydroxy-5-chloro-phenylamine), was synthesized and structurally characterized by X-ray diffraction. Single-crystal analysis revealed that the copper atom shows a 4 + 1 pyramidal coordination, a water oxygen appears in the apical position, and three of the basal positions are occupied by the NNO tridentate ligand and the fourth by an acetate oxygen. The interaction of Schiff base copper(II) complex 1 with DNA was investigated by UV-visible spectra, fluorescence spectra and agarose gel electrophoresis. The apparent binding constant (K_app) value of 6.40 × 10⁵ M^− 1 for 1 with DNA suggests moderate intercalative binding mode. This copper(II) complex displayed efficient oxidative cleavage of supercoiled DNA, which might indicate that the underlying mechanism involve hydroxyl radical, singlet oxygen-like species, and hydrogen peroxide as reactive oxygen species. In addition, our present work showed the antitumor effect of 1 on cell cycle and apoptosis. Flow cytometric analysis revealed that HeLa cells were arrested in the S phase after treatment with 1. Fluorescence microscopic observation indicated that complex 1 can induce apoptosis of HeLa cells, whose process was mediated by intrinsic mitochondrial apoptotic pathway owing to the activation of caspase-9 and caspase-3.     

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, crystal structure, and magnetic properties of a new tetranuclear Cu(II) Schiff base compound

A new tetranuclear Cu(II) compound [Cu₄(HL)₂(L)₂(ClO₄)₂] (1) was synthesized from the reaction of Cu(ClO₄)₂ · 6H₂O with Schiff base ligand (H₂L) condensed from ethanolamine with 2-hydroxyacetophenone. X-ray diffraction studies revealed that 1 is formed from the self-assembly of two dinuclear units [Cu₂(HL)(L)(ClO₄)] through the doubly phenoxo bridging. The variable temperature magnetic susceptibility measurements were performed between 300 K and 2 K and show χ_MT value for 1 at 300 K is 1.395 cm³ mol⁻¹ K and fall to 0.0459 cm³ mol⁻¹ K at 2 K. These values are smaller than that expected for tetranuclear copper (II) units, indicating antiferromagnetic coupling present in the compound. This result is also confirmed from the DFT calculations.