Synthesis, crystal structure, hydrogen bonding and spectroscopy of Co, Mn and Ni oxalate complexes with the ligand (N,N′-bis(2-pyridylmethyl)-1,3-propanediamine)

Three new compounds are reported with the tetradentate ligand (N,N′-bis(2-Pyridylmethyl)-1,3-propanediamine) (abbreviated as pypn), two mononuclear compounds i.e. [Co(pypn)(C₂O₄)](ClO₄) (1), [Mn(pypn)(C₂O₄)](ClO₄) (2) and one dinuclear compound [Ni₂(pypn)₂(C₂O₄)](ClO₄)₂(C₂H₆O)_1/4(H₂O) (3). In the Co(III) and Mn(II) complexes the oxalate behaves as bidentate ligand, chelating the metal in the O,O′ mode, whereas in the Ni(II) compound the oxalate behaves as tetradentate ligand binding each Ni(II) ion by two oxygen atoms and bridging the two metallic centers.The synthesis, X-ray crystal structure of all three compounds and their spectroscopic properties are presented in detail. The geometry around the Co³⁺, Mn³⁺, Ni²⁺ ions is essentially octahedrally based, while the stabilization of the crystal lattice in all cases is maintained by interesting hydrogen bond systems.     

Synthesis, structures and properties of alkaline earth metal benzene-1,4-dioxylacetates with three-dimensional hybrid networks

Three novel alkaline earth metal benzene-1,4-dioxylacetates M(L)H₂O (M = Ca, Sr or Ba, L = benzene-1,4-dioxylacetate) with three-dimensional (3D) hybrid frameworks were reported. Both Ca(L)H₂O (1) and Sr(L)H₂O (2) crystallize in the monoclinic space group P2₁/c while Ba(L)H₂O (3) in the monoclinic space group P2₁. As determined by X-ray single-crystal analysis, in these compounds each metal ion is coordinated by eight O atoms: four from different carboxylate groups, two from one carboxylate group, one from the ether oxygen and one from one water molecule. Each L²⁻ ligand coordinates to five alkaline earth metal centers through one of its ether oxygen atoms and two carboxylate groups adopting novel μ₃-η²:η²-bridging and μ₂-η¹:η¹-bridging coordination modes to give rise to a 3D network. The luminescence analysis shows that complexes 1 and 2 exhibit fluorescence in the solid state at room temperature.     

Synthesis, crystal structure and properties of novel isostructural two-dimensional lanthanide-based coordination polymers with 2,3,5,6-tetrafluoro-1,4-benzenedicarboxylic acid

Five new isostructural two-dimensional lanthanide-based coordination polymers with the formula Ln₂(F₄BDC)₃(DEF)₂(EtOH)₂-2(DEF) (Ln = Tb, 1; Gd, 2; Eu, 3; La, 4; Nd, 5; F₄BDC²⁻ = 2,3,5,6-tetrafluoro-1,4-benzenedicarboxylate ligands; DEF = N,N′-diethylformamide), have been synthesized by reaction of Ln(NO₃)₃ and F₄BDC in a DEF/EtOH solvent mixture. The compounds were characterized by single-crystal and powder X-ray diffraction. In all cases, the metal ion is coordinated by nine oxygen atoms from two bidentate μ₂-F₄BDC²⁻ ligands, two bridging μ₂-F₄BDC²⁻ ligands, one μ₃-F₄BDC²⁻ ligand, one DEF molecule and one EtOH molecule forming a tri-capped trigonal prism. The Ln(1) metal ion is linked to an adjacent Ln(1) metal ion through the oxygen atoms of two bridging μ₂-F₄BDC²⁻ ligands and two μ₃-F₄BDC²⁻ bridging ligands to form a Ln₂O₁₈ dimer. The Ln₂O₁₈ polyhedra building units are linked to each other through four F₄BDC²⁻ ligands to form 2D sheets that are held together by hydrogen bonding to form a 3D framework. Compounds 1-5 were further characterized using thermogravimetric analysis and infrared spectroscopy. Studies of the photoluminescence properties of compounds 1 and 3, as well as the catalytic activity of compounds 3-5 in the Biginelli reaction, are presented.     

Synthesis, structures and magnetic properties of nickel(II), manganic(II) and zinc(II) complexes containing pyridyl-substituted nitronyl nitroxide and tris(2-benzimidazolymethyl)amine

Three new magnetic compounds were synthesized by using 2-(2′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NIT2Py) and tris(2-benzimidazolymethyl)amine (NTB) as ligands. The structures and magnetic properties of the complexes with formula [Ni(NIT2Py)(NTB)](ClO₄)₂(CH₃OH) 1, [Mn(NIT2Py)(NTB)](ClO₄)₂2 and {[Zn(NIT2Py)₂(CH₃OH)₂](ClO₄)₂}{[Zn(NTB)(H₂O)](ClO₄)₂} 3 were characterized. Compounds 1 and 2 both have [M(NIT2Py)(NTB)] structural units, where the metal ion is in an octahedral environment bound to one NIT2Py through one pyridyl nitrogen atom and one nitroxide oxygen atom. However, compound 3, the chelating zinc ion has two crystallographically independent molecules in the asymmetric unit: one is six coordinated octahedral structure [Zn(NIT2Py)₂(CH₃OH)₂](ClO₄)₂, and the other one is five coordinated pyramidal structure [Zn(NTB)(H₂O)](ClO₄)₂. The magnetic behaviors of these compounds indicate that both the nickel ion and the manganese ion are antiferromagnetically coupled with the NIT2Py ligand with a coupling constant of −19.44 and −0.37 cm⁻¹, respectively, whereas two NIT2Py ligands in compound 3 are ferromagnetically coupled with a coupling constant of 19.1 cm⁻¹.     

Complexes of dibenzylsulfoxide with the first series transition metal nitrates

Under carefully controlled experimental conditions, a series of metal nitrate complexes of dibenzylsulfoxide (DBSO) have been synthesized and isolated (for the dipositive Co, Ni, Cu and Zn elements). The compounds were characterized by use of infrared-, ultraviolet-, and visible spectra. Their stoichiometric compositions appeared to be [M- (DBSO)₃(NO₃)₂], where MCo, Ni and Cu; and [M(DBSO)_3.5(NO₃)₂], where MZn. The additional information concerning the nature of bonding and structural geometry was derived from X-ray diffraction analysis, molecular conductivities, molecular weight and magnetic susceptibility measurements. The infrared spectra indicated that, in all cases, coordination occurred through the oxygen atom of the DBSO ligand. Both analyses and spectral studies suggest that the transition metal ions manifest a coordination number of six. The slight decrease in metal ion radius across the first transition metal series does not affect the number of DBSO molecules bonded to the M²⁺ ion, but the only variation in total coordination of cation might be attributed to the DBSO competition with nitrato groups for the coordination site due to the ability of the anion to enter the coordination sphere.     

Five novel palladium(II) complexes of 8-hydroxyquinoline and amino acids with hydrophobic side chains: synthesis,characterization, cytotoxicity,DNA- and BSA-interaction studies

Abstract

The side effects and resistance of metal-based anticancer drugs prompted us to synthesis a novel series of five Pd(II) complexes of the type [Pd(8-QO)(AA)]; where 8-QO?=?anion of 8-hydroxyquinoline and AA?=?anions of amino acids having nonpolar aliphatic side chain such as glycine (–H), alanine (–CH₃), valine (–CH(CH₃)₂), leucine (–CH₂–CH(CH₃)₂) and isoleucine (–CH(CH₃)CH₂–CH₃). The complexes have been characterized with the help of FT-IR, UV–Vis, one and two-dimensional ¹H-NMR, elemental analysis and conductivity measurements. On the basis of these characterization data, a four coordinated square planar geometry for all of these complexes have been proposed. The compounds were screened for their in vitro activities against human cancer cell line, MOLT-4 and their 50% inhibition concentration were ascertained by means of MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Since four out of the five newly synthesized compounds were found to be more active than the standard anticancer drug, cisplatin, their detailed interaction with calf thymus DNA (as a target) and bovine serum albumin (BSA) (as a carrier) were also carried out by utilizing absorption spectra, fluorescence spectra and ethidium bromide displacement studies. In these experiments, several binding and thermodynamic parameters were also calculated. These results suggested that hydrogen binding and van der Waals forces play a major role in the interaction between metal complexes with CT-DNA and BSA.

Communicated by Ramaswamy H. Sarma     

Anti-hemolytic and Peroxyl Radical Scavenging Activity of Organoselenium Compounds: An In Vitro Study

Selenium-containing amino acids, selenocystine (CysSeSeCys), methylselenocysteine (MeSeCys), and selenomethionine (SeMet) have been examined for anti-hemolytic and peroxyl radical scavenging ability. Effect of these compounds on membrane lipid peroxidation, release of hemoglobin, and loss of intracellular K⁺ ion as a consequence of peroxyl radicals-induced oxidation of human red blood cells were used to evaluate their anti-hemolytic ability. The peroxyl radicals were generated from thermal degradation of 2,2′-azobis(2-methylpropionamidine) dihydrochloride. Significant delay (t _eff) was observed in oxidative damage in the presence of the selenium compounds. From the IC₅₀ values for the inhibition of hemolysis, lipid peroxidation, and K⁺ ion leakage, the relative anti-hemolytic ability of the compounds were found to be in the order of CysSeSeCys > MeSeCys > SeMet. The anti-hemolytic abilities of the compounds, when compared with sodium selenite (Na₂SeO₃) under identical experimental conditions, were found to be better than Na₂SeO₃. Relative rate constants estimated for the reaction of MeSeCys and SeMet with peroxyl radicals by competition kinetics using ABTS²⁻ as a reference confirmed that all the compounds are efficient peroxyl radical scavengers. Comparison of the GPx-like activity of these compounds, by NADPH–GSH reductase coupled assay, indicated that CysSeSeCys exhibits the highest activity. Based on these results, it is concluded that among the compounds examined, CysSeSeCys, possessing the ability to reduce peroxyl radicals and hydroperoxides showed efficient anti-hemolytic activity.     

Syntheses, structures and magnetic properties of Mn(II), Co(II) and Ni(II) metal-organic frameworks constructed from 1,3,5-benzenetricarboxylate and formate ligands

Three compounds, [(CH₃)₂NH₂][M₃(BTC)(HCOO)₄(H₂O)]·H₂O (M = Mn (1), Co (2), Ni (3), H₃BTC = 1,3,5-benzenetricarboxylic acid), were synthesized under hydrothermal conditions and were characterized by single crystal and powder X-ray diffraction, IR spectra, elemental analysis, coupled TG-MS and magnetic measurements. Compounds 1-3 are isostructural analogues and crystallize in monoclinic space group P2₁/c. Each metal ion in these compounds connects to six oxygen atoms to form a MO₆ octahedron. Six MO₆ octahedra link to each other to form a corner-shared hexameric M₆ cluster, which is linked by BTC ligands to form two-dimensional layers. The two-dimensional layers are further connected by formic ions to form a three-dimensional network with channels, where (CH₃)₂NH₂⁺ ions and water molecular are located. Magnetic measurements indicate that anti-ferromagnetic ordering occurs at low temperature for these compounds.     

Metal complexes of modified cyclen as catalysts for hydrolytic restriction of plasmid DNA

Simple and novel nuclease models have been synthesized. These involve metal-binding ligand 1,4,7,10-tetraazlcyclododecane (cyclen) tethered to an acridine ring (a DNA-binding group) by amide linkers of various lengths. Binding of these probes to DNA was studied by monitoring changes in their UV-visible spectra affected by the presence of DNA. Titration of these compounds with increasing amounts of pBR322 DNA caused hypochromic effects and shifted the acridine absorption at 360 nm to a longer wavelength. Under biologically relevant conditions (37 °C and pH 7.4), specific transition metal complexes of these compounds are found to be highly effective catalysts toward the hydrolysis of plasmid DNA. This is demonstrated by their ability to convert the super-coiled DNA (form I) to open-circular DNA (form II). Structure-activity correlation studies show that hydrolytic activity depends on both the structure of ligand (L₁ > L₂ > L₃) and the nature of metal ion cofactor (Co³⁺ > Zn²⁺ > Cr²⁺ > Ni²⁺ > Cu²⁺ > Fe³⁺).     

Metal complexes with two tri-aza,tri-oxa pendant-armed macrocyclic ligands: Synthesis,characterization, crystal structures and fluorescence studies

Metal complexes of two new tri-aza, tri-oxa macrocycles containing ethyl acetate (L¹) or carboxymethyl (H₂L²) pendant arms with hydrated nitrate or perchlorate salts of alkaline earth, post-transition and lanthanide metal ions have been synthesized and characterized by microanalysis FAB MS, conductivity measurements, IR, UV–Vis spectroscopy and fluorescence emission studies. The synthesis and characterization of the Pb(II) complexes with the armless macrocyclic precursors L (Schiff base macrocycle) and L′ (diaminic reduced macrocycle) are also reported. The crystal structures of complexes [PbL(ClO₄)(H₂O)](ClO₄), [PbL′(ClO₄)](ClO₄) and ([Zn₂L²(Cl)(H₂O)](ClO₄))_∞ have been determined. In both lead(II) complexes, the metal ion is located inside the macrocyclic cavity and is coordinated by all N₃O₃ donor atoms in the complex with L′ but only by the nitrogen atoms present in the ligand in the complex with L. In both cases, the coordination sphere of the metal atom is completed with a perchlorate anion or a water molecule in the iminic complex of L. X-ray studies on the Zn(II) complex show the presence of a supramolecular structure that is consistent with a linear polymer formed alternately by an endomacrocyclic metal atom coordinated to a macrocyclic ligand and an exomacrocyclic metal ion in distorted octahedral and tetrahedral environments, respectively. UV–Vis and fluorescent emission studies were carried out on the ligands L¹ and H₂L² and their metal complexes, but only the luminescence spectra of the Eu(III) and Tb(III) complexes with L¹ in aqueous solution at ca. pH 7 show the characteristic visible emission of the metal. The value of the quantum yield determined for the Eu(III) complex is similar to that reported in the literature for other Eu(III) complexes.     

Silver(I) carboxylates. I. Mass spectra and low frequency infrared spectra

The mass spectra six silver(I) carboxylates, AgO₂CR, (R = Me, Et, Prⁿ, Ph, CF₃ and (CF₂)₂CF₃) show these compounds to be dimeric in the vapour phase, the base peak being the ion Ag₂(O₂CR)⁺ in each case. Two fragmentation pathways are observed. The alkyl carboxylates initially lose mainly RCO₂· from the radical ion Ag₂O₂CR)₂⁺, whereas the benzoate and the perfluorocarboxylates also easily lose carbon dioxide from the radical ion leading to the formation of abundant organosilver ions. The low frequency (500−40 cm⁻¹) infrared spectra of these silver(I) carboxylates are compared with the spectra of the copper(I) analogues and bands selected which may be assigned to predominantly skeletal modes.     

New homoleptic tris(diphosphanylamido) complexes of the lanthanides - synthesis and structure

New homoleptic diphosphanylamido compounds of the lanthanides, [Ln{N(PPh₂)₂}₃] (Ln = Sm, Gd, Dy), were synthesized and characterized by single crystal X-ray diffraction in the solid state and partly by NMR in solution. In the solid state the complexes solely show a η²-coordination of the {(Ph₂P)₂N}⁻ ligand. The dependence of the Ln-N and the Ln-P bond distance on the ion radius of the center metal was investigated.     

Electrokinetic Phenomena Enhanced Lithium‐Ion Transport in Leaky Film for Stable Lithium Metal Anodes

The application of lithium (Li) metal anodes in Li metal batteries has been hindered by growth of Li dendrites, which lead to short cycling life. Here a Li‐ion‐affinity leaky film as a protection layer is reported to promote a dendrite‐free Li metal anode. The leaky film induces electrokinetic phenomena to enhance Li‐ion transport, leading to a reduced Li‐ion concentration polarization and homogeneous Li‐ion distribution. As a result, the dendrite‐free Li metal anode during Li plating/stripping is demonstrated even at an extremely high deposition capacity (6 mAh cm^?2) and current density (40 mA cm^?2) with improved Coulombic efficiencies. A full cell battery with the leaky‐film protected Li metal as the anode and high‐areal‐capacity LiNi_0.8Co_0.1Mn_0.1O₂ (NCM‐811) (≈4.2 mAh cm^?2) or LiFePO₄ (≈3.8 mAh cm^?2) as the cathode shows improved cycling stability and capacity retention, even at lean electrolyte conditions.     

Outersphere and innersphere coordinated metal ions in an aminoacyl-tRNA synthetase ribozyme

Metal ions are essential cofactors for various ribozymes. Here we dissect the roles of metal ions in an aminoacyl-tRNA synthetase-like ribozyme (ARS ribozyme), which was evolved in vitro. This ribozyme can charge phenylalanine on tRNA in cis, where it is covalently attached to the 5′-end of tRNA (i.e. a form of precursor tRNA), as well as in trans, where it can act as a catalyst. The presence of magnesium ion is essential for this ribozyme to exhibit full catalytic activity. Metal-dependent kinetics, as well as structural mappings using Tb³⁺ in competition with Mg²⁺ or Co(NH₃)₆³⁺, identified two potential metal-binding sites which are embedded near the tRNA-binding site. The high affinity metal-binding site can be filled with either Mg²⁺ or Co(NH₃)₆³⁺ and thus the activity relies on a metal ion that is fully coordinated with water or ammonium ions. This site also overlaps with the amino acid-binding site, suggesting that the metal ion plays a role in constituting the catalytic core. The weak metal-binding site is occupied only by a metal ion(s) that can form innersphere contacts with ligands in the ribozyme and, hence, Mg²⁺ can enhance ribozyme activity, but Co(NH₃)₆³⁺ cannot. The experiments described in this work establish the roles of metal ions that have distinct coordination properties in the ARS ribozyme.     

Preparation, characterization and biological relevance of calcium(II)/diethylmalonate(-1,-2) complexes

Reactions of Ca(NO₃)₂·4H₂O and diethylmalonic acid (Et₂malH₂, its anions represent functional side-chain analogs of γ-carboxyglutamic acid residues which are implicated as essential Ca²⁺-binding ligands in a variety of proteins) in aqueous media have afforded compounds [Ca(Et₂malH)₂(H₂O)₃]_n (1) and [Ca(Et₂mal)(H₂O)]_n (2) at pH 4 and 8, respectively. The structure of 1 was determined by single-crystal, X-ray crystallography, which revealed an 1D coordination polymer. The diethylmalonate ligands exist in their monoanionic form and present two different coordination modes. The Ca^II ion is 7-coordinate with a pentagonal bipyramidal geometry. IR data are discussed in terms of the known (1) and proposed (2) structures of the complexes. The role of the carboxylate binding modes in determining the affinity of Ca²⁺ for the various metal binding sites in proteins containing the γ-carboxyglutamate residue is discussed in the light of our and previous results.     

Biochemical effects of binding [(H2O)(NH3)5RuII]2+ to DNA and oxidation to[(NH3)5RuIII]n—DNA.

The reaction of [(H₂O)(NH₃)₅Ru^II]²⁺ with calf thymus and salmon sperm DNA has been studied over a wide fange of transition metal ion concentrations. Kinetic studies revealcd a biphasic reaction with an initial fairly rapid coordination of the metal ion being followed by slower reactions. Binding studies were done under pseudo-equilibrium conditions following completion of the initial rapid reaction. Spectra and HPLC of acid-hydrolyzed samples of [(NH3)₅Ru^II]n-DNA prepared by incubation of [(H₂O)(NH₃)₅Ru^II]²⁺ with DNA (where [P_DNA] = 1.5 mM and reactant [Ru^II]/[P_DNA] ratios were in the fange 0.1 to 0.3) followed by air oxidation showed the predominant binding site on helical DNA to be in the major groove at the N-7 of guanine. The equilibrium constant for [(H₂O)(NH₃)₅Ru^II]²⁺ binding to the G⁷ site in helical CT DNA is 5.1 x 103. Differential pulse voltammetry exhibited a single peak at 48 mV, which is attributed to the reduction of Rum on the G⁷ sites.At [Run]/[P_DNA] <0.5, Tm values for the DNA decreased linearly with increasing ruthenium concentration and an increase in the intensity of the 565 nm dG→ Ru(III) charge transfer band was noted upon melting. The UV and CD spectra of these samples indicated no extensive destacking or alteration in geometry (B family) compared to unsubstituted DNA. At [Run]/[P_DNA]〉 0.5 or when single-stranded DNA was used, increased absorbance at 530 nm and 480 nm suggested additional binding to the exocyclic amine sites of adenine and cytosine residues. HPLC and individual spectrophotometric identification of the products derived from hydrolysis of these spec~es yielded both [(Gua)(NH₃)₅Ru^III] and [(Ade)(NH₃)₅Ru^III]. Earlier studies have established the cytidine and adenosine binding sites of [(NH₃)₅Ru^III] to be at their exocyclic amines (C4 and A6). Coordination to these positions indicates disruption of the double helix since these amines are involved in hydrogen bonding on the interior of B-DNA.Agrose gel electrophoresis of superhelical pBR322 plasmid DNA after exposure to various complexes of [(nh₃)₅Ruⁱⁱⁱ] in the presence of a reductant and air generally revealed moderately efficient cleavage of the DNA, presumably due to the generation of hydroxyl radical via Fenton's chemistry. However, similar studies involving [(NH₃)₅Ru^III] directly coordinated to the DNA showed no strand cutting above background. Polyacrylamide gel electrophoresis of a 381 bp, 3′-³²P-labeled fragment of pBR322 plasmid DNA containing low levels of bound [(NH₃)₅ Ru^III] further indicated negligible DNA cutting by the coordinated metal ion.     

Tris(4-oxy-pyridinium)nitrato lanthanide complexes [M(4-O-C6H4NH)3(NO3)2(H2O)2][NO3] {M = La, Ce, Pr, Nd, Eu, Gd} - Synthesis, properties and structural characterization

Preferential formation and X-ray structures of tris(4-hydroxypyridinium) nitrato complexes [M(4-O-C₆H₄NH)₃(NO₃)₂(H₂O)₂][NO₃] {M = La, Ce, Pr, Nd, Eu, Gd} in the simple reaction of 4-hydroxypyridine with the respective nitrates is described. All these compounds are isostructural and crystallize in the space group P2₁2₁2₁. There are, however, minor differences in the hydrogen bonding features. The central metal ion in all these complexes has a coordination number of nine and the geometry may be described as tricapped trigonal prism. The neodinium complex has a chirality opposite to that of the rest of the structures. TGA data are also consistent with the solid state structures of these compounds.     

Computer graphics applications of electron deformation densities and electrostatic potentials in coordination chemistry

Computer programs have been developed in order to display on a raster scan device electron deformation densities and electrostatic potentials, both as 2D colour-filled contour maps and as 3D solid models. Furthermore, as this quantum chemical model has proved to be adequate for transition metal complexes, the combined use of the Xα formalism and computer graphics is expected to be of value in rationalizing the reactivity of coordination and organometallic compounds. The examples of [Cr(O₂)₄]³⁻, [Mo(O₂)₄]²⁻ and [Nb(O₂)₄]³⁻ are discussed in an attempt to understand the differences in catalytic properties exhibited by parent metal dioxygen complexes.     

Complexation of NADH analogs with divalent metal ions: Dependence on the 3-substituent of 1-benzyl-1,4-dihydropyridines

In light of the critical role of divalent metal ions in the chemistry of coenzyme NADH analogs, complexation of 1-benzyl-3-substituted(X)-1,4-dihydropyridines (1, X=CONH₂; 2, X=CSNH₂; 3, X=COOCH₃; 4, X=COCH₃) with divalent metal ions (Mg²⁺, Zn²⁺, and Co²⁺) in dry acetonitrile was studied spectroscopically and kinetically. Presence of the metal ions causes red-shift of absorption band of NADH analogs and the rate retardation for the reaction between NADH analogs and N-methylacridinium ion. Analysis of the spectroscopic and kinetic data indicates that the NADH analogs form 1 : 1 complexes with the metal ions. The decreasing order of the magnitude of the association constants, K, is 1 2 4 3 for a given metal ion, and Mg²⁺ Zn²⁺ > Co²⁺ for a given NADH analog. The results strongly suggest that the primary binding site for the metal ions is the carbonyl oxygen (or thiocarbonyl sulfur) of the 3-substituent and that the amide nitrogen atom of the 3-substituent of 1 and 2 also ligates the metal ions, forming a bidentate structure and providing extra stability to the complexes of 1 and 2. Inhibition of reaction between NADH analogs and N-methylacridinium ion by the metal ions is attributed to inaccessibility of N-methylacridinium ion to the NADH analogs complexed with metal ions due to electrostatic repulsion.     

Synthesis, characterization and bioactivity of two novel trinuclear Cu(II)/Ni(II) complexes with pentadentate ligand N-2-methyl-acryloyl-salicylhydrazide

Two new trinuclear complexes, Cu₃L₂(py)₂ (1) and Ni₃L₂(py)₄ (2), have been synthesized and characterized, where L³⁻ is N-2-methyl-acryloyl-salicylhydrazidate. Central metal ion and two terminal metal ions in the two complexes are combined by two bridging deprotonated L³⁻ ligands, forming a bent trinuclear structure unit with an M-N-N-M-N-N-M core. The bent angles in complexes 1 and 2 are 167.6(1)° and 75.4(1)°, respectively. Three nickel ions in compound 2 exhibit alternating square-planar and octahedral geometries, while three copper ions in compound 1 follow square-planar mode. The studies in solution integrity and stability of compounds 1 and 2 show they are soluble and stable in DMF. UV-Vis titrations demonstrate compound 1 is stable in DMF even in the presence of excess metal ions. Antibacterial screening data indicate the two compounds all have stronger antimicrobial activities against the tested microorganisms than ligand. The trinuclear copper compound 1 is more active than monocopper compounds in the previous study, and the trinuclear nickel compound 2 is less active than tetranuclear nickel compound in the previous study.