Thermodynamic study of the interaction of Co(II)-Schiff base complexes with phosphines

The equilibrium constants and the thermodynamic parameters for the interaction of CoL^x (L¹ = 5-OMe-salabza, L² = salabza, L³ = 5-Br-salabza and L⁴ = 5-NO₂-salabza) as acceptors, with phosphines (PBu₃, PPh₂Me) as donors in dichloromethane were studied. This was performed by using UV-Vis spectrophotometry titration for 1:1 adduct formation of the selected complexes at various temperatures (T = 283–298 K). The trend of the adduct formation of the Co(II) complexes with a given phosphine donor decreases as CoL¹ > CoL² > CoL³ > CoL⁴. The stability of the resulting adducts with different Co(II)-schiff base complexes found to decrease in the order PBu₃ > PPh₂Me.     

Formation of heterometallic compounds in mixed solutions of nickel(II)-Schiff base complexes and lanthanide nitrates: Electrospray ionization mass spectrometry data

Atmospheric-pressure electrospray ionization mass spectrometric data are reported for methanolic Ni(SB) + Ln(NO₃)₃ · nH₂O solutions (H₂SB = N,N′-ethylene-bis(salicylaldiimine), N,N′-ethylene-bis(3-methoxysalicylaldiimine), N,N′-ethylene-bis(acetylacetonediimine); Ln = La, Eu, Lu). Dinuclear and trinuclear heterometallic complexes of composition [(Ni(SB)) _x Ln(NO₃)₃] (x = 1, 2) form in these solutions. The dinuclear-totrinuclear ion intensity ratio depends on the natures of the lanthanide and the Schiff base.     

Three heterotrinuclear Schiff base complexes of nickel(II) with cobalt(II), copper(II) and manganese(II)

The title compounds, bis­(di­methyl­form­amide)‐1κO,3κO‐bis{μ‐2,2′‐[2,2′‐di­methyl­propane‐1,3‐diyl­bis­(nitrilo­methylidyne)]­diphenolato}‐1κ⁴N,N′,O,O′:2κ²O,O′;2κ²O,O′:3κ⁴N,N′,O,O′‐di‐μ‐nitrito‐1:2κ²N:O;2:3κ²O:N‐dinickel(II)­cobalt(II), [CoNi₂(NO₂)₂(C₁₉H₂₂N₂O₂)₂(C₃H₇NO)₂], (I), ‐copper(II), [CuNi₂(NO₂)₂(C₁₉H₂₂N₂O₂)₂(C₃H₇NO)₂], (II), and ‐manganese(II), [MnNi₂(NO₂)₂(C₁₉H₂₂N₂O₂)₂(C₃H₇NO)₂], (III), consist of centrosymmetric linear heterotrinuclear metal complexes. The three complexes are isostructural. There are three bridges across the Ni–M atom pairs (M is Co²⁺, Cu²⁺ or Mn²⁺) in each complex, involving two O atoms of a μ‐N,N′‐bis­(salicyl­idene)‐2,2′di­methyl‐1,3‐propane­diaminate ligand and an N—O moiety of a μ‐nitrito group. The coordination sphere around each metal atom, whether Co²⁺, Cu²⁺, Mn²⁺ or Ni²⁺, can be described as distorted octahedral. The Ni?M distances are 2.9988 (5) Å in (I), 2.9872 (5) Å in (II) and 3.0624 (8) Å in (III).     

Facile strategies for the synthesis and crystallization of linear trinuclear nickel(II)-Schiff base complexes with carboxylate bridges: Tuning of coordination geometry and magnetic properties

Three new linear trinuclear nickel(II) complexes, [Ni₃(salpen)₂(OAc)₂(H₂O)₂]·4H₂O (1) (OAc = acetate, CH₃COO⁻), [Ni₃(salpen)₂(OBz)₂] (2) (OBz = benzoate, PhCOO⁻) and [Ni₃(salpen)₂(OCn)₂(CH₃CN)₂] (4) (OCn = cinnamate, PhCHCHCOO⁻), H₂salpen = tetradentate ligand, N,N′-bis(salicylidene)-1,3-pentanediamine have been synthesized and characterized structurally and magnetically. The choice of solvent for growing single crystal was made by inspecting the morphology of the initially obtained solids with the help of SEM study. The magnetic properties of a closely related complex, [Ni₃(salpen)₂(OPh)₂(EtOH)] (3) (OPh = phenyl acetate, PhCH₂COO⁻) whose structure and solution properties have been reported recently, has also been studied here. The structural analyses reveal that both phenoxo and carboxylate bridging are present in all the complexes and the three Ni(II) atoms remain in linear disposition. Although the Schiff base ligand and the syn–syn bridging bidentate mode of the carboxylate group remain the same in complexes 1–4, the change of alkyl/aryl group of the carboxylates brings about systematic variations between six- and five-coordination in the geometry of the terminal Ni(II) centres of the trinuclear units. The steric demand as well as hydrophobic nature of the alkyl/aryl group of the carboxylate is found to play a crucial role in the tuning of the geometry. Variable-temperature (2–300 K) magnetic susceptibility measurements show that complexes 1–4 are antiferromagnetically coupled (J = −3.2(1), −4.6(1), −3.2(1) and −2.8(1) cm⁻¹ in 1–4, respectively). Calculations of the zero-field splitting parameter indicate that the values of D for complexes 1–4 are in the high range (D = +9.1(2), +14.2(2), +9.8(2) and +8.6(1) cm⁻¹ for 1–4, respectively). The highest D value of +14.2(2) and +9.8(2) cm⁻¹ for complexes 2 and 3, respectively, are consistent with the pentacoordinated geometry of the two terminal nickel(II) ions in 2 and one terminal nickel(II) ion in 3.     

Nickel(II) and copper(II) complexes of unsymmetrical tetradentate reduced Schiff base ligands

Two new reduced Schiff base ligands, [HL¹ = 4-{2-[(pyridin-2-ylmethyl)-amino]-ethylimino}-pentan-2-one and HL² = 4-[2-(1-pyridin-2-yl-ethylamino)-ethylimino]-pentan-2-one] have been prepared by reduction of the corresponding tetradentate unsymmetrical Schiff bases derived from 1:1: 1 condensation of 1,2-ethanediamine, acetylacetone and pyridine-2-carboxaldehyde/2-acetyl pyridine. Four complexes, [Ni(L¹)]ClO₄ (1), [Cu(L¹)]ClO₄ (2), [Ni(L²)]ClO₄ (3), and [Cu(L²)]ClO₄ (4) with these two reduced Schiff base ligands have been synthesized and structurally characterized by X-ray crystallography. The mono-negative ligands L¹ and L² are chelated in all four complexes through the four donor atoms to form square planar nickel(II) and copper(II) complexes. Structures of 3 and 4 reveal that enantiomeric pairs are crystallized together with opposite chirality in the nitrogen and carbon atoms. The two Cu^II complexes (2 and 4) exhibit both irreversible reductive (Cu^II/Cu^I; E_pc, −1.00 and −1.04 V) and oxidative (Cu^II/Cu^III; E_pa, +1.22 and +1.17 V, respectively) responses in cyclic voltammetry. The electrochemically generated Cu^I species for both the complexes are unstable and undergo disproportionation.     

Equilibrium studies on Schiff base complexes of copper(II) and nickel(II): Ligand substitution and formation of mixed ligand complexes

Summary Vis spectrophotometry has been used to study various ligand substitution equilibria (1) and (2) involving four-coordinate copper(II) and nickel(II) his chelate complexes in methanol, propan-2-ol and toluene. MA₂ + HB MAB+HA, K₁ (1) MAB + HB MB₂ + HA, K₂ (2) The Schiff base ligands, HA and HB, which are monobasic and bidentate, represent salicylaldimine type N,O-ligands ( HSA=NR) (1) or pyrrole-2-aldimine type N,N-ligands ( HPA=NR) (2) with different branching at the - or (3-carbon of the organic group R. For both types of ligand the relative thermodynamic stability of their copper and nickel complexes is governed mainly by the steric demands of R, which determine the degree of tetrahedral distortion. The order of stability as given by = K₁ K₂ is: t-Bu < neo-Pent < i-Pr < i-Bu < Et < n-Pr. The K₁/K₂ ratio is strongly solvent dependent in the sense that the mixed ligand species MAB is stabilised in toluene relative to methanol. Such a solvent effect is not observed for . The MAB complexes could not be isolated. The vis spectrum of the mixed ligand species Ni(SA=NiPr, SA=NEt) was calculated by computer fitting of the experimental data.     

Green synthesis approach for Fe (III), Cu (II), Zn (II) and Ni (II)-Schiff base complexes,spectral, conformational,MOE-docking and biological studies

Green synthesis of Fe (III), Cu (II), Zn (II) and Ni (II)-Schiff's-base complexes from 2-oxo-N-(pyridine-2-yl)-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)acetamide(H₂L)ligand. All new complexes were characterized via several spectroscopic and analytical techniques, to establish their molecular and structural formulae. All complexes appeared have 1:1 molar ratio (M:L). The ligand contributed as a neutral poly-dentate towards the metal ions. Moreover, material-studio program was used to predict the most fitted atomic-skeletons for investigated compounds by applying DFT method. MOE docking module (vs. 2015) was used to examine the degree of inhibition for new compounds versus three infected-cell proteins (1bqb, 2gt1 and 4esw). Also, antimicrobial and colorimetric assess for compounds that bind DNA were performed     

Heterotrinuclear manganese(II) and vanadium(IV) Schiff base complexes as epoxidation catalysts

The catalytic epoxidation of styrene using urea-hydrogen peroxide and heterotrinuclear Cu(II) complexes with general formula (ML ⁿ )₂Cu(acac)₂, where n = 1–3 and M = VO²⁺ or Mn²⁺ is reported. Schiff base complexes ML ⁿ involving a 3,4-diaminopyridine bridge with free coordination site were used as the ligand, where (Lⁿ)²⁻ is [(5-x-Sal)₂Py]² and x = H, Br or NO₂. The complexes were characterized by physico-chemical and spectroscopic methods. The electrochemical properties of M were modified upon trinuclear complex formation. The trinuclear complexes show high catalytic activity, with up to 86% conversion and 93% selectivity, while no catalytic properties were observed for the monomeric complexes. The catalyst could be reused with some loss of activity.     

Spectroscopic,thermal, non-isothermal decomposition kinetics and quantum chemical computational studies of Ni(II)- and Cu(II)-Schiff base complexes

Research on Chemical Intermediates - Herein we report spectroscopic, thermal, non-isothermal decomposition kinetics and theoretical studies of two mononuclear Ni(II)- and Cu(II)-complex of general...     

Copper(II) and ruthenium(II)/(III) Schiff base complexes

Metal complexes of general formula [Cu(L)](ClO4)2, [Ru(L)(PPh3)2]Cl2 and [Ru(L)(PPh3)Cl]Cl2[L = 1,4-di- (o-benzylidiminophenoxy/benzylidiminophenylthio)butane] containing N2O2 or N2S2 donor atoms have been prepared and characterised by spectral, magnetic and cyclic voltammetric studies. The rhombic nature of the e.s.r. spectra of the RuIII complexes indicates an asymmetry in the electronic environment around the Ru atom. e.s.r. spectra of the CuII complexes show a typical four-line spectrum with approximate tetrahedral distortion. The observed low A values in the CuII complexes, of the order of 132–160 × 10–4cm–1, indicates a tetrahedrally distorted square planar structure.The influence of modified ligands is reflected in the metal-centered redox potentials. CuII complexes having the N2S2 chromophore, in MeCN on a glassy carbon electrode, undergo quasi-reversible reduction in the 540–680 mV range. A depression in E1/2 values for the open chain N2S2 chromophoric macrocyclic CuII complexes, compared to electronically similar cyclic tetradentate CuII analogues, is due to the increased stabilization of the CuI state by added flexibility provided through the open chain donor sites.     

Self-assembled biomimetic catalysts: studies of the catalase and peroxidase activities of Mn(III)-Schiff base complexes

Five Mn(III) nitrate complexes have been synthesized from dianionic hexadentate Schiff bases obtained by the condensation of 3-ethoxy-2-hydroxybenzaldehyde with different diamines. The complexes have been characterized by elemental analysis, ESI mass spectrometry, IR and ¹H NMR spectroscopy, r. t. magnetic, and molar conductivity measurements. Parallel-mode EPR spectroscopy of 1 is also reported. Ligand H₂L³ and complexes [MnL¹(H₂O)₂](NO₃)(CH₃OH) (1), [MnL³(H₂O)₂]₂(NO₃)₂(CH₃OH)(H₂O) (3), and [MnL⁴(H₂O)₂](NO₃)(H₂O)₂ (4) were crystallographically characterized. The X-ray structures show the self-assembly of the Mn(III)–Schiff base complexes through µ-aquo bridges between neighboring axial water molecules and also by π–π stacking interactions, establishing dimeric and polymeric structures. The peroxidase and catalase activities of the complexes have been studied. Complexes with the shorter spacer between the imine groups (1–2) behave as better peroxidase and catalase mimics, probably due to their ability to coordinate the hydrogen peroxide substrate to manganese.     

Electrochemical synthesis of manganese(II)-Schiff base complexes and their behaviour towards H2O,H2O2 and SO2

Manganese(II) complexes with ONNO tetradentate Schiff bases have been prepared by electrochemical synthesis and characterised by analytical and spectroscopic techniques, magnetism and by studying their redox reversibility character by cyclic and normal pulse voltammetry. The ability of these systems to catalyse the decomposition of water, to yield dioxygen, and their catalase-like activity was checked. Reaction of the complexes with sulfur dioxide was studied in the solid state and in toluene slurries at room temperature. The adducts formed underwent thermogravimetric desorption analyses that highlights the SO₂-irreversible linkage present in all complexes.     

Red-light photosensitized cleavage of DNA by (l-lysine)(phenanthroline base)copper(II) complexes

Ternary copper(II) complexes [Cu(l-lys)B(ClO4)](ClO4)(1-4), where B is a heterocyclic base, viz. 2,2'-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 3) and dipyrido[3,2-a:2',3'-c]phenazene (dppz, 4), are prepared and their DNA binding and photo-induced DNA cleavage activity studied (l-lys =l-lysine). Complex 2, structurally characterized by X-ray crystallography, shows a square-pyramidal (4 + 1) coordination geometry in which the N,O-donor l-lysine and N,N-donor heterocyclic base bind at the basal plane and the perchlorate ligand is bonded at the elongated axial site. The crystal structure shows the presence of a pendant cationic amine moiety -(CH2)4NH3+ of l-lysine. The one-electron paramagnetic complexes display a d-d band in the range of 598-762 nm in DMF and exhibit cyclic voltammetric response due to Cu(II)/Cu(I) couple in the range of 0.07 to -0.20 V vs. SCE in DMF-Tris-HCl buffer. The complexes having phenanthroline bases display good binding propensity to the calf thymus DNA giving an order: 4 (dppz) > 3 (dpq) > 2 (phen)> 1 (bpy). Control cleavage experiments using pUC19 supercoiled DNA and distamycin suggest major groove binding for the dppz and minor groove binding for the other complexes. Complexes 2-4 show efficient DNA cleavage activity on UV (365 nm) or visible light (694 nm ruby laser) irradiation via a mechanistic pathway involving formation of singlet oxygen as the reactive species. The amino acid l-lysine bound to the metal shows photosensitizing effect at red light, while the heterocyclic bases are primarily DNA groove binders. The dpq and dppz ligands display red light-induced photosensitizing effects in copper-bound form.     

Copper(II) and nickel(II) complexes of a neutral pentadentate Schiff base

A new pentadentate Schiff base 2,6,10-triaza-1,11-bis(2′-aminophenyl)-undeca-1,10-diene, abaDPT, and its complexes of general formula M(abaDPT)X₂ where M = Cu(II), Ni(II), X = Cl, Br, I, NO₃ and ClO₄, have been prepared. The complexes have been characterized by electronic and IR spectra, EPR, magnetic moments, molar conductances, and elemental analysis. IR data show an interaction between halide anion of the outer coordination sphere and the complexed amino group. EPR and spectrophotometric data of most of the copper compounds are consistent with a distorted square pyramidal geometry. Single crystal EPR studies of Cu(abaDPT)(NO₃)₂ and Cu(abaDPT)Br₂ revealed that copper atoms in the former compound occupy two magnetically inequivalent places in the lattice while copper atoms in the latter compound take identical sites. Principal g tensor axes of the two compounds have been determined.     

Thermal decomposition kinetics of Schiff base complexes of copper(II) and palladium(II)

Thermogravimetric (TG), derivative thermogravimetric (DTG) and differential thermal analysis (DTA) curves of CuL₂ and Pd(LH)₂Cl₂ (LH=salicylidene-2-aminofluorene and 2-hydroxy-1-naphthalidene-2-aminofluorene) in air are studied. Mass loss considerations at the main decomposition stages indicate conversion of the complex to oxides. Mathematical analysis of TG data shows that first order kinetics are applicable in all cases. Kinetic parameters (energy and entropy of activation and preexponential factor) are reported.     

Imidazolate bridged Cu(II)-Cu(II) and Cu(II)-Zn(II) complexes of a terpyridinophane azamacrocycle: a solution and solid state study

The dinuclear Cu2+ and Zn2+ as well as the mixed Cu2+-Zn2+ complexes of a 5,5'-pentaazaterpyridinophane ligand (L) are able to incorporate imidazolate (Im-) as a bridging ligand. The crystal structure of [Cu(2)L(Im)(Br)(H2O)](CF(3)SO(3))(2).3H2O (1) shows one copper coordinated by the three pyridine nitrogens of the terpyridine unit, one nitrogen of the imidazolate bridge (Im-) and one bromide anion occupying the axial position of a distorted square pyramid. The second copper atom is coordinated by the remaining imidazolate nitrogen, the three secondary nitrogens at the centre of the polyamine bridge and one water molecule that occupies the axial position. Magnetic measurements have been performed in the 2.0-300.0 K temperature range. Experimental data could be satisfactorily reproduced by using an isotropic exchange model H = -JS(1)S(2) with J = -52.3 cm(-1) and g = 2.09. Potentiometric studies have provided details of the speciation and stability constants for the mixed Cu2+-L-HIm, Zn2+-L-HIm (HIm = imidazole) and Cu2+-Zn2+-L-HIm systems. The apparent stability constant obtained at pH = 9 for the addition of imidazole to the dinuclear Cu2+ complexes is one of the highest so far reported (log K = 7.5). UV-Vis spectroscopy and paramagnetic NMR data show that imidazole coordinates to the Cu2+ ions as a bridging imidazolate ligand from pH 5 to 10. Electrochemical reduction of the Cu2+-Zn2+-L complex occurs in two successive one-electron per copper ion quasi-reversible steps. The formal potential of the Cu2+-Zn2+-L/Cu+-Zn2+-L couple is close to that of SOD. The IC50 values measured at pH 7.8 by means of the nitro blue tetrazolium method show significant SOD activity for the dinuclear Cu2+ complexes (IC50 = 2.5 microM) and moderate activity for the Cu2+-Zn2+ mixed systems (IC50 = 30 microM).     

Synthesis, characterization and spectra studies on Zn(II) and Cu(II) complexes with thiocarbamide ligand containing Schiff base group

The ligand of 4-phenyl-1-(1-phenylethylidene)thiosemicarbazide (HL) and its metal complexes of ZnL₂ (1) and CuL₂ (2) have been synthesized. Elemental analysis, IR and X-ray single crystal diffraction characterizations for 1 and 2 have been carried out. In the complexes 1 and 2, the central metallic ions Zn²⁺ and Cu²⁺, coordinate with two deprotonated ligands, L⁻, respectively and adopt distorted tetrahedral geometries. The thermal analyses result shows that the two complexes undergo two similar decomposition processes because of their similar geometric configurations. For the two complexes, UV–Vis spectra have been measured and DFT calculations at B3LYP/LANL2DZ level of theory prove that the electronic spectra of 1 are corresponding with intraligand electronic transitions, and the electronic spectra of 2 are attributed to intraligand electronic transitions as well as d–d electronic transitions. Fluorescence spectra measurements indicate that the complex of 1 emits stronger fluorescence than the ligand of HL, and the complex 2 does not emit fluorescence at all. Electrochemical analyses reveal that both the oxidation peak currents and the reduction peak currents of 1 and 2 are stronger than those of the ligand, respectively.     

Synthesis,structures, and property studies on Zn(II), Ni(II), and Cu(II) complexes with a Schiff base ligand containing thiocarbamide group

A Schiff base ligand containing thiocarbamide group of 4-phenyl-1-(4-methoxyl-1-phenylethylidene)thiosemicarbazide (HL) and its three mononuclear metal complexes of ZnL₂ (1), NiL₂ (2), and CuL₂ (3) have been synthesized. Elemental analysis, IR, and X-ray single crystal diffraction characterizations for the ligand and the three complexes have been carried out. In the three complexes, the central metallic ions of Zn²⁺, Ni²⁺, and Cu²⁺ coordinate with two deprotonated ligands of L⁻, respectively. In 1, Zn²⁺ ion adopts a distorted tetrahedral geometry, while in 2 and 3, both the Ni²⁺ and Cu²⁺ ions possess distorted square planar configurations. For the four compounds, UV–Vis spectra have been measured and DFT calculations at B3LYP/LANL2DZ level of theory prove that the electronic spectra of HL and 1 are corresponding with electronic transitions of n → π* and π → π* in the ligand itself and the electronic spectra of 2 and 3 are attributed to intraligand electronic transitions as well as d–d electronic transitions. Electrochemical investigations reveal that the different metal–ligand interactions have changed the peak shapes and peak locations, which are corresponding with the DFT-B3LYP/LANL2DZ calculational results. Fluorescence spectra measurements indicate that the ligand emits purple fluorescence and the complex 1 emits stronger blue fluorescence, while the complexes 2 and 3 quench fluorescence. The thermal analyses result show that the three complexes undergo two similar decomposition processes because of their similar geometric configurations.     

Synthesis and characterization of tetradentate bis -Schiff base complexes of di- and tri-valent transition metals

The bis-Schiff bases of N₂O₂ dibasic ligands, H₂La and H₂Lb are synthesized by the condensation of ethylenediamine (a) and trimethylenediamine (b) with 6-formyl-7-hydroxy-5-methoxy-2-methylbenzo-pyran-4-one. The ligands are characterized using elemental analysis, IR, UV–Vis, ¹H-NMR and mass spectroscopy. The ionization constant pKa values are determined spectrophotometrically. The ¹H-NMR spectra of the ligands show the presence of phenolic coordinating groups. New complexes of H₂La and H₂Lb with metal ions Cr(III), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) are synthesized. Elemental analyses, infrared, ultraviolet-visible, electron spin resonance and thermal analysis, as well as conductivity and magnetic susceptibility measurements, are used to elucidate the structures of the newly prepared metal complexes. Thermal degradation studies for some complexes show that the final product is the metal oxide. A square planar geometry is suggested for the Cu(II), Zn(II) (for H₂La and H₂Lb) and Ni(II) (for H₂La) complexes; an octahedral geometry for the Co(II), Cr(III), Fe(III) (for H₂La and H₂Lb), and Ni(II) (for H₂Lb) complexes. The coordination sites are two azomethine nitrogens and two phenolic oxygens in the tetradentate Schiff bases.     

Diaza-crown-N,N-dialkanoic acids copper(II) and dicopper(II) complexes

Twelve-, fifteen-, and eighteen-membered diaza-crown-N, N-′dialkanoic acids LH₂ and their inner salt copper(II) complexes CuL and dicopper complex [CuL(3). CuCl₂. CH₃OH_n were obtained. The complexes of 15- and 18-membered ligands contain Cu²⁺ ion inside the ring.