Coordination behaviour of Schiff base 2-acetyl-2-thiazoline hydrazone (ATH) towards cobalt(II), nickel(II) and copper(II)

The synthesis and characterization of Co(II), Ni(II) and Cu(II) complexes of 2-acetyl-2-thiazoline hydrazone (ATH) are reported. Elemental analysis, IR spectroscopy, UV–Vis–NIR diffuse reflectance and magnetic susceptibility measurement, as well as, in the case of copper complex EPR spectroscopy, have been used to characterize the complexes. In addition, the structure of [NiCl₂(ATH)₂] (2) and [{CuCl(ATH)}₂(μ-Cl)₂] (3) have been determined by single crystal X-ray diffraction. In all complexes, the ligand ATH bonds to the metal ion through the imine and thiazoline nitrogen atoms. X-ray data indicates that the environment around the nickel atom in 2 may be described as a distorted octahedral geometry with the metallic atom coordinated to two chlorine atoms, two thiazoline nitrogen atoms and two imino nitrogen atoms. With regard to 3, it can be said that its structure consists of dimeric molecules in which copper ions are bridge by two chlorine ligands. The geometry about each copper ion approximates to a distorted square pyramid with each copper atom coordinated to one thiazoline nitrogen atom, one imine nitrogen atom, one terminal chlorine ligand and two bridge chlorine ligands. In compound 3, magnetic susceptibility measurements in the temperature range 2–300 K show an intradimer antiferromagnetic interaction (J = −7.5 cm⁻¹).     

Structural characterization of five-coordinate copper(II), nickel(II), and cobalt(II) thiocyanato complexes derived from bis(2-(3,5-dimethyl-1-pyrazolyl)ethyl)amine

The reaction of M(ClO₄)₂·6H₂O with NH₄NCS in presence of the organic sterically hindered bis(2-(di-3,5-dimethyl-1-pyrazolyl)ethyl)amine (bedmpza) afforded the five-coordinate mononuclear dithiocyanato-M(II) complexes [M(bedmpza)(NCS)₂]·xMeOH (1: M = Cu²⁺, x = 0; 2: M = Ni²⁺, x = 0; 3: M = Co²⁺, x = 0.84). The compounds which proved to be non-electrolytes were characterized by IR and UV-Vis spectroscopy and their molecular structures were determined by single-crystal X-ray crystallography. In these complexes, the five-coordinate geometry was achieved by the three N-donors of the ligand bedmpza and two N atoms of the terminal thiocyanato ligands. The Cu(II) complex exists in two polymorphs 1-I and 1-II: an intermediate five-coordinate geometry with the two thiocyanato ligands are arranged as cisoid in 1-I and distorted square pyramidal geometry with the thiocyanato ligands are in transoid orientation in 1-II. Although the later geometry was also observed in the nickel complex 2, distorted trigonal bipyramidal geometry was found in 3. Each complex forms hydrogen bonds of type N-H?S from the secondary amine N(3) donor atoms to the adjacent terminal S(1) acceptor atoms of the thiocyanate group. The thermal behavior of the two polymorphs 1-I and 1-II were similar and no significant differences were observed between the two complexes.     

Syntheses and crystal structures of 3-tert-butyl-4-cyano pyrazole and its complexes with cobalt(II), manganese(II), and copper(II)

A new pyrazole ligand, 3-tert-butyl-4-cyano pyrazole (Hpz^t-Bu,4CN), has been synthesized. The crystal structure of this pyrazole, along with the syntheses and crystal structures of Co, Cu, and Mn complexes of this ligand, are reported. The uncoordinated pyrazole shows the formation of a cyclic hydrogen-bound dimer. The Co complex is octahedral, with four coordinated pyrazoles and two coordinated waters. The Mn complex is octahedral, with two coordinated pyrazoles, two coordinated triflates and two coordinated waters. A hydrogen bonding network involving the triflates and waters results in a linear double chain of Mn complexes. The Cu complex has two coordinated pyrazoles and two coordinated chlorides in a slightly distorted square-planar geometry, with a long bond to the cyano N atom of a neighboring Cu complex, forming a pseudodimer.     

Synthesis,structures, and urease inhibition of nickel(II), zinc(II), and cobalt(II) complexes with similar hydroxy-rich Schiff bases

Four new nickel(II), zinc(II), and cobalt(II) complexes, [Zn(L¹)₂]?·?H₂O (1), [Ni(L¹)₂]?·?H₂O (2), [Ni(L²)₂] (3), and [Co(L³)₂]?·?H₂O (4), derived from hydroxy-rich Schiff bases 2-{[1-(5-chloro-2-hydroxyphenyl)methylidene]amino}-2-methylpropane-1,3-diol (HL¹), 2-{[1-(2-hydroxy-3-methoxyphenyl)methylidene]amino}-2-ethylpropane-1,3-diol (HL²), and 2-{[1-(5-bromo-2-hydroxyphenyl)methylidene]amino}-2-methylpropane-1,3-diol (HL³) have been synthesized and characterized by elemental analyses, infrared spectroscopy, and single-crystal X-ray determination. Each metal in the complexes is six-coordinate in a distorted octahedral coordination. The Schiff bases coordinate to the metal atoms through the imino N, phenolate O, and one hydroxyl O. In the crystal structures of HL¹ and the complexes, molecules are linked through intermolecular O–H···O hydrogen bonds, forming 1-D chains. The urease inhibitory activities of the compounds were evaluated and molecular docking study of the compounds with the Helicobacter pylori urease was performed.     

Synthesis,structures, and characterization of copper(II), nickel(II), and cobalt(III) metal complexes derived from an asymmetric bidentate Schiff-base ligand

An asymmetric bidentate Schiff-base ligand (2-hydroxybenzyl-2-furylmethyl)imine (L–OH) was prepared. Three complexes derived from L–OH were synthesized by treating an ethanolic solution of the appropriate ligand with an equimolar amount of metallic salt. Three complexes, Cu₂(L–O^?)₂Cl₂ (1), Ni(L–O^?)₂ (2) and Co(L–O^?)₃ (3), have been structurally characterized through elemental analysis, IR, UV spectra and thermogravimetric analysis. Single crystal X-ray diffraction shows metal ions and ligands reacted with different proportions 1?:?1, 1?:?2 and 1?:?3, respectively, so copper(II), nickel(II), and cobalt(III) have different geometries.     

Syntheses and crystal structures of cobalt and nickel complexes of 2,6-bis(hydroxymethyl)pyridine

2?:?1 (L?:?M) Complexes of 2,6-bis(hydroxymethyl)pyridine (dhmp) with different Co(II) salts [CoCl₂·6H₂O, Co(SCN)₂, Co(NO₃)₂·6H₂O, CoSO₄·7H₂O and Co(OTos)₂·6H₂O] and Ni(II) salts [NiCl₂·6H₂O, Ni(NO₃)₂·6H₂O, NiSO₄·7H₂O and Ni(OTos)₂·6H₂O] have been prepared (1–9) and studied by infrared spectroscopy and X-ray crystallography. Influences on the distortion of the coordination polyhedron, the arrangement of the donor atoms and the packing structure of the complexes were investigated in terms of the different kinds of anions and cations. In the metal chloride Complexes 1 and 2, water of hydration was found, while in Complex 3 the counterion (SCN^–) acts as a ligand. The crystal structures of all complexes, except 3, show N₂O₄ hexacoordinated metal ions; in 3 the coordination environment is N₄O₂. Complex 1 is another exception in containing cobalt(III) instead of cobalt(II) as for the other complexes with cobalt salts. Logically, in Complex 1, one of the dhmp ligands is mono-deprotonated. In the neutral Complexes 2 and 4–9, the basal planes of the octahedra are made up of O donors and N atoms occupy the axial positions. In 1 as well as in 3, two N and two O atoms form the base, but in 1 O, and in 3 N atoms are on the axis of the coordination sphere. Moreover, the nickel Complexes 2, 5, 7 and 9 are more symmetrical in structure than the cobalt Complexes 1, 4, 6 and 8, in accordance with the Jahn–Teller effect. Packing structures of the complexes show specific interactions based on strong and weak H-bonds that involve the counterions, hydroxy groups and aromatic units, leading to extended network structures.     

Syntheses and crystal structures of nickel(II), copper(II), and zinc(II) complexes with a biphenyl-bridged bis(pyrrole-2-yl-methyleneamine) ligand

The reactions of nickel(II), copper(II), and zinc(II) acetate salts with a potentially tetradentate biphenyl-bridged bis(pyrrole-2-yl-methyleneamine) ligand yielded three complexes with different coordination geometries. X-ray crystal structural analysis reveals that in the nickel(II) complex each nickel is five-coordinate, distorted trigonal bipyramid. In the copper(II) complex, each copper is four-coordinate, between square planar and tetrahedral. In the zinc(II) complex, each zinc is four-coordinate with a distorted tetrahedral geometry and the molar ratio of the zinc and ligand is 1 : 2.     

Copper(II), nickel(II) and cobalt(II) complexes of 4-cyanobenzonic acid: syntheses, crystal structures and spectral properties

Three new metal complexes, Cu(4-Hcba)₂(4-cba)₂(Py)₂ (4-Hcba=4-cyanobenzoic acid) 1 and M[H(4-cba)₂]₂(Py)₂ (M=Ni 2, Co 3), have been prepared by the treatment of 4-Hcba with the respective metal nitrate M(NO₃)₂ (M=Cu, Ni, Co) in the presence of pyridine (Py). Single-crystal X-ray diffraction analyses (3 is isostructural to 2) show that the obtained complexes are of isolated mononuclear and the metal atoms have distorted octahedral coordination environment. Two different types of intramolecular hydrogen bonds exist: asymmetrical O–HO for 1 and symmetrical OHO for 2 and 3. The crystal packing between the molecular complexes is controlled mainly by T-shaped C–Hπ interactions between pyridine and phenyl rings. Preliminary discussions on IR, UV–VIS and fluorescent spectra have also been carried out.     

Mononuclear and homobinuclear cobalt(II), nickel(II) and copper(II) complexes with mono and bis-azocompounds derived from 2,7-dihydroxynaphthalene and anthranilic acid or o-aminophenol

Two new series of mononuclear and homobinuclear Co(II), Ni(II) and Cu(II) complexes with mono- and bis-azo compounds derived from 2,7-dihydroxynaphthalene and anthranilic acid or o-aminophenol are prepared and characterized by elemental and thermal analyses, conductance, IR, electronic, ESR spectra and magnetic moment measurements. The ligand field splitting parameters and Racah constant are calculated. The spectral and magnetic results obtained are utilized to determine the geometries around the metal(II) ion. The geometry of the complex formed depends on the structure of the ligand and the type of metal(II) ion. The mode of bonding of the ligand with the metal ions is deduced from IR spectra.     

Syntheses and crystal structures of two Schiff-base copper(II) complexes with antibacterial activities

Two structurally similar trinuclear complexes, [Cu(Cu(μ-Cl)₂L1)₂] (1) and [Cu(Cu(μ-Cl)₂L2)₂] (2) (HL1 = 4-chloro-2-[(2-morpholin-4-ylethylimino)methyl]phenol, HL2 = 1-[(2-piperidin-1ylethylimino)methyl]naphthalen-2-ol), have been synthesized and structurally characterized. Both complexes are bridged trinuclear compounds. The central Cu in each complex is in an octahedral environment with two phenolate and four bridging chlorides. The symmetry-related terminal Cu in each complex is square pyramidal with one phenolate oxygen, one imine nitrogen and one amine nitrogen of the Schiff-base ligand, one Cl^? in the basal plane, and one bridging Cl^? in the apical position. The complexes and Schiff bases were tested in vitro for their antibacterial activities.     

Syntheses,crystal structures,and antibacterial activities of manganese(III), nickel(II), and copper(II) complexes containing a tetradentate Schiff base

Three new mononuclear Schiff-base complexes, namely [Mn(L)Cl] (1), [Ni(L)] (2), and [Cu(L)] (3), where L?=?anion of [N,N′-bis(2-hydroxybenzophenylidene)]propane-1,2-diamine, have been synthesized by reacting equimolar amounts of the respective metal chloride and the tetradentate Schiff base, H₂L, in methanol. The complexes have been characterized by microanalytical, spectroscopic, single-crystal X-ray diffraction, and other physicochemical studies. Structural studies reveal that 1 adopts a distorted square-pyramidal geometry whereas 2 and 3 are isotypic with distorted square-planar geometries. The antibacterial activities of 1–3 along with their Schiff base have been tested against some Gram(+) and Gram(?) bacteria.     

Syntheses and crystal structures of two 2D coordination polymers of cobalt(II) and nickel(II) with the Malonate Dianion Ligand

Two 2D complexes, [Co(mal)(phen)(H₂O)₂] (1) and [Ni(mal)(phen)(H₂O)₂] (2) (mal?=?malonate dianion; phen?=?1,10-phenanthroline), have been synthesized by the reaction of Co(ClO₄)₂·6H₂O and Ni(ClO₄)₂·6H₂O with disodium malonate and 1,10-phenanthroline in MeOH/H₂O solution. Their crystal structures have been determined by X-ray diffraction. The structures of Complexes 1 and 2 show that each metal ion is coordinated by one 1,10-phenanthroline, two water molecules and a malonate ligand forming a distorted octahedral environment and each mononuclear fragment forms a 2D supramolecular network through H-bonding interactions.     

Synthesis,structures, and magnetic properties of two pyrazolato-bridged trinuclear copper(II) complexes

One nonlinear and one linear trinuclear copper(II) complex [Cu₃(dien)₂(pdc)₂CH₃OH]₂?·?6CH₃OH (1) and [Cu₃(pdc)₂(CH₃OH)₆(H₂O)₄] (2) were prepared and characterized structurally, where dien is diethylenetriamine and pdc^3? the trianion of 3,5-pyrazoledicarboxylic acid. Both complexes consist of 3,5-pyrazoledicarboxylato-bridged trinuclear copper(II) centers. In 1, copper(II) ions are five-coordinate in distorted square pyramids with bond angles 164.78° for Cu(1)–Cu(2)–Cu(3) and 164.51° for Cu(4)–Cu(5)–Cu(6). In 2, the three copper(II) ions are six-coordinate with elongated octahedral geometry. The trinuclear units of 1 and 2 interact through hydrogen bonds to form 3-D and 2-D supramolecular networks, respectively. Variable temperature magnetic susceptibility measurements show that 1 and 2 are antiferromagnetically coupled with J values of ?11.2 and ?13.3?cm^?1.     

Synthesis,crystal structure,and antibacterial activity of mononuclear nickel(II) and cobalt(III) Schiff-base complexes

Four new mononuclear complexes, [Ni(L¹)(NCS)₂] (1), [Ni(L²)(NCS)₂] (2), [Co(L¹)(N₃)₂]ClO₄ (3), and [Co(L²)(N₃)₂]ClO₄ (4), where L¹ and L² are N,N′-bis[(pyridin-2-yl)methylidene]butane-1,4-diamine and N,N′-bis[(pyridin-2-yl)benzylidene]butane-1,4-diamine, respectively, have been prepared. The syntheses have been achieved by reaction of the respective metal perchlorate with the tetradentate Schiff bases, L¹ and L², in presence of thiocyanate (for 1 and 2) or azide (for 3 and 4). The complexes have been characterized by microanalytical, spectroscopic, single crystal X-ray diffraction and other physicochemical studies. Structural studies reveal that 1–4 are distorted octahedral geometries. The antibacterial activity of all the complexes and their constituent Schiff bases have been tested against Gram-positive and Gram-negative bacteria.     

Two binuclear lanthanide complexes with 4-quinoline carboxylic acid: crystal structures and luminescent properties

Two isomorphic lanthanide complexes [Eu₂(L)₆(H₂O)₄] · 2H₂O (1) and [Tb₂(L)₆(H₂O)₄] · 2H₂O (2), (HL = 4-quinoline carboxylic acid) have been synthesized and structurally characterized by single-crystal X-ray diffraction. Both complexes are binuclear and each metal center adopts nine-coordination with nine oxygens from two H₂O molecules and carboxylates of three ligands; L exhibits three different coordination modes. Luminescent properties of 1 and 2 at room temperature indicate that the triplet-state level of this ligand matches better with the lowest excited state level of Eu(III) than with Tb(III).     

Copper(II), Cobalt(II), and Nickel(II) Complexes of two Novel Pyridine‐derived Macrocyclic Ligands bearing o‐ and pNitrobenzyl Pendant Groups

The pendant‐armed ligands L¹ and L² were synthesized by N‐alkylation of the four secondary amine groups of the macrocyclic precursor L using o‐nitrobenzylbromide (L¹) and p‐nitrobenzylbromide (L²). Nitrates and perchlorates of Cu^II, Ni^II and Co^II were used to synthesize the metal complexes of both ligands and the complexes were characterized by microanalysis, MS‐FAB, conductivity measurements, IR and UV‐Vis spectroscopy and magnetic studies. The crystal structures of L¹, [CuL¹](ClO₄)₂·CH₃CN·H₂O, [CuL²](ClO₄)₂·6CH₃CN, [CuL²][Cu(NO₃)₄]·5CH₃CN·0.5CH₃OH and [NiL²](ClO₄)₂·3CH₃CN·H₂O were determined by single crystal X‐ray crystallography. These structural analysis reveal the free ligand L¹, three mononuclear endomacrocyclic complexes {[CuL¹](ClO₄)₂·CH₃CN·H₂O, [CuL²](ClO₄)₂·6CH₃CN and [NiL²](ClO₄)₂·3CH₃CN·H₂O} and one binuclear complex {[CuL²][Cu(NO₃)₄]·5CH₃CN·0.5CH₃OH} in which one of the metals is in the macrocyclic framework and the other metal is outside the ligand cavity and coordinated to four nitrate ions.     

Syntheses,structures, and spectroscopic properties of copper(II) and cobalt(III) complexes containing 1,4,7-tribenzyl-1,4,7-triazacyclononane ligand

Three new complexes [CuL(N₃)₂] (1), [CuL(SCN)₂] (2), and [CoL(SCN)₃] (3) (L?=?1,4,7-tribenzyl-1,4,7-triazacyclononane) have been synthesized and structurally characterized. Complex 1 crystallizes in monoclinic space group P2(1)/n with unit cell parameters a?=?14.105(7), b?=?8.999(5), c?=?21.603(11)?Å, β?=?100.470(7)°. While 2 crystallizes in triclinic space group P-1 with unit cell parameters a?=?9.6380(16), b?=?10.6993(18), c?=?15.798(3)?Å, α?=?106.636(3), γ?=?116.478(3)°. Complex 3 crystallizes in trigonal space group P–3c1 with unit cell parameters a?=?14.744(3), b?=?14.744(3), c?=?16.098(4)?Å, γ?=?120°. Elemental analysis, IR, UV-vis spectra of complexes 1–3 and ESR spectra of complexes 1–2 were also determined.     

Synthesis,crystal structure,and SOD-like activity of two copper(II) complexes with hydroxymethyl pendants

To mimic the active site of Cu,Zn-SOD, new copper(II) complexes (1, [Cu₂(HL)₂(L)₂](ClO₄)₂; 2, [Cu(HL)₂(phen)](ClO₄)₂; where HL?=?(N-methyl-2-methylol)imidazole, phen?=?1,10-phenanthroline) have been synthesized and characterized by elemental analysis, IR, and single-crystal X-ray diffraction. Copper(II) in 1 is four-coordinate by a N₂O₂ plane with two copper(II) ions bridged with two oxygens from the deprotonated hydroxylmethyl pendants. Each Cu²⁺ in 2 is coordinated by four nitrogens from two HL and one co-ligand of 1,10-phenanthroline. Electrochemistry of the complexes was studied by cyclic voltammetry. The atomic net charges distribution and frontier molecular orbital energies were obtained by Gaussian 98 program with DFT method at B3LYP/lanl2dz level. The SOD-like activity (IC₅₀) of 1 and 2 were measured as 0.10?±?0.01 and 0.19?±?0.01?μM by NBT assay at pH 7.8. The higher SOD activity of 1 could be attributed to the coordination configuration and the labile hydroxymethyl pendants.     

Crystal structures and DNA cleavage activities of two mononuclear nickel(II) complexes

Two new nickel complexes, [Ni(L₁)₂]?·?2(CH₃OH) (1) and [Ni(L₂)₂]?·?2(CH₃OH) (2), where HL₁ is 4-chloro-2-((2-hydroxy-ethylimino)methyl)phenol and HL₂ is 4-fluoro-2-((2-hydroxy-ethylimino)methyl)phenol, have been synthesized and characterized by single-crystal X-ray diffraction and UV-Vis absorption spectra. The coordination polyhedron of nickel(II) in each complex can be described as distorted octahedral. The interactions between the complexes and calf thymus (CT)-DNA/DNA were investigated by UV-Vis spectra and agarose gel electrophoresis. The results show that the complex transforms supercoiled to nicked form and exhibits effective DNA cleavage activity via hydrolytic cleavage mechanism.