Imine Nitrogen Atoms Research Articles

Investigation of Raman, FT-IR, EPR spectra and antimicrobial activity of 2-(5-H/Me/Cl-1H-benzimidazol-2-yl)-phenol ligands and their Fe(NO3)3 complexes

2-(5-H/Me/Cl-1H-benzimidazol-2-yl)-phenol ligands form 1:1 electrolytes, 5-coordinate monometallic complexes with iron(III) nitrate. The geometry of the [Fe(L)(OH)(H2O)2](NO3) complexes was derived from theoretical calculation in DGauss/DFT level (DZVP basis set) on CACHE. In all of the complexes the ligands are bidentate, via one imine nitrogen atom and phenolate oxygen atom. The coordination is completed with a hydroxide ion, and two water molecules, adopting a distorted square pyramidal geometry. The structures of the compounds were confirmed on the basis of elemental analysis, molar conductivity, magnetic moment, FT-Raman, FT-IR (mid-IR, far-IR), EPR and u.v.–vis. The antimicrobial activities of the free ligands, their hydrochloride salts, and the complexes were evaluated using the disk diffusion method in dimethyl sulfoxide (DMSO) as well as the minimal inhibitory concentration (MIC) dilution method, against nine bacteria and the results are compared with several known antibiotic agents. Antifungal activities were reported for Candida albicans, Kluyveromyces fragilis, Rhodotorula rubra, Debaryomyces hansenii, Hanseniaspora guilliermondii, and the results were referenced against nystatin, ketaconazole, and clotrimazole antifungal agents. In most cases, the compounds tested showed broad-spectrum (Gram+ & Gram− bacteria) activities that were either more active or as potent as the references.

Dual Orbital Effects in N-Philic Cyclizations of Silyl Radicals onto Imines

Abstract Density functional studies revealed that nucleophilic silyl radicals are able to mask as electrophiles by cyclizing with high preference onto the more electron-rich nitrogen atom of imine C=N double bonds. This remarkable behavior is a result of a combination of SOMO–π* and lone pair (LP)–σ* interactions during the reaction. If the LP is not available due to steric reasons, attack of the Si-radical occurs with slight preference at the carbon atom. This indicates that “dual orbital” interactions are directing the regioselectivity of silyl radical cyclizations.

Novel Schiff Bases with Oxime Groups and Their Homo- and Heteronuclear Copper(II) Complexes

Two novel tetradentate Schiff bases containing oxime groups and their homodinuclear, homotrinuclear Cu(II) and heterodinuclear Cu(II)-Mn(II) and Cu(II)-Co(II) complexes were synthesized. The Schiff base ligands (H2L1 and H2L2) were prepared by condensing of diethylenetriamine with 2-(biphenyl-4-yl)-N-(4-chlorophenyl)-N'-hydroxy-2-oxoacetimidamide (HL1) and 2-(biphenyl-4-yl)-N'-hydroxy-N-(4-methylphenyl)-2-oxoacetimidamide (HL2). Structure assignments are supported by a combination of FT-IR, elemental analyses, inductively coupled plasma optical emission spectroscopy (ICP-OES), magnetic susceptibility, molar conductivity and thermal analyses studies. The free ligands were also characterized by 1H and 13C NMR spectra. Elemental analyses, stoichiometric and spectroscopic data indicated that the metal:ligand ratio is 2:1 for the dinuclear copper(II) complexes and 3:2 for the trinuclear copper(II) complexes. The copper(II) ions are coordinated to the oxime and imine nitrogen atoms. Pyrolytic decomposition occurred in melting the metal complexes and metal oxides were the ultimate products.

Complexes of Pd(II) and Pt(II) with 9-Aminoacridine: Reactions with DNA and Study of Their Antiproliferative Activity

Four new metal complexes {M = Pd(II) or Pt(II)} containing the ligand 9-aminoacridine (9AA) were prepared. The compounds were characterized by FT-IR and 1H, 13C, and 195Pt NMR spectroscopies. Crystal structure of the palladium complex of formulae [Pd(9AA)(μ-Cl)]2 · 2DMF was determined by X-ray diffraction. Two 9-acridine molecules in the imine form bind symmetrically to the metal ions in a bidentate fashion through the imine nitrogen atom and the C(1) atom of the aminoacridine closing a new five-membered ring. By reaction with phosphine or pyridine, the Cl bridges broke and compounds with general formulae [Pd(9AA)Cl(L)] (where L = PPh3 or py) were formed. A mononuclear complex of platinum of formulae [Pt(9AA)Cl(DMSO)] was also obtained by direct reaction of 9-aminoacridine and the complex [PtCl2(DMSO2]. The capacity of the compounds to modify the secondary and tertiary structures of DNA was evaluated by means of circular dichroism and electrophoretic mobility. Both palladium and platinum compounds proved active in the modification of both the secondary and tertiary DNA structures. AFM images showed noticeable modifications of the morphology of the plasmid pBR322 DNA by the compounds probably due to the intercalation of the complexes between base pairs of the DNA molecule. Finally, the palladium complex was tested for antiproliferative activity against three different human tumor cell lines. The results suggest that the palladium complex of formula [Pd(9AA)(μ-Cl)]2 has significant antiproliferative activity, although it is less active than cisplatin.

Synthesis and Crystal Structure of (N,N,N',N'-Tetrakis((2-benzimidazolyl)-methyl)-1,2-cyclohexanediamine)copper(II) Picrate

The reaction between Cu(Pic)2·6H2O (Pic=picrate anions) and N,N,N′,N′-tetrakis((2-benzimidazolyl)methyl)-1,2-cyclohexanediamine (CDTB) in DMF has resulted in a mononuclear copper(II) complex, [Cu(CDTB)](Pic)2·1.5DMF. Crystallographic studies show that the Cu(II) ion is directly coordinated to four benzimidazole imine nitrogen atoms and two amine nitrogen atoms from CDTB, forming a highly distorted octahedron geometry.

Titanium and Zirconium Complexes with Non‐Salicylaldimine‐Type Imine–Phenoxy Chelate Ligands: Syntheses, Structures, and Ethylene‐Polymerization Behavior

New Ti and Zr complexes that bear imine-phenoxy chelate ligands, [{2,4-di-tBu-6-(RCH=N)-C6H4O}2MCl2] (1: M = Ti, R = Ph; 2: M = Ti, R = C6F5; 3: M = Zr, R = Ph; 4: M = Zr, R = C6F5), were synthesized and investigated as precatalysts for ethylene polymerization. 1H NMR spectroscopy suggests that these complexes exist as mixtures of structural isomers. X-ray crystallographic analysis of the adduct 1HCl reveals that it exists as a zwitterionic complex in which H and Cl are situated in close proximity to one of the imine nitrogen atoms and the central metal, respectively. The X-ray molecular structure also indicates that one imine phenoxy group with the syn C=N configuration functions as a bidentate ligand, whereas the other, of the anti C=N form, acts as a monodentate phenoxy ligand. Although Zr complexes 3 and 4 with methylaluminoxane (MAO) or [Ph3C]+ [B(C6F5)4]-/AliBu3 displayed moderate activity, the Ti congeners 1 and 2, in association with an appropriate activator, catalyzed ethylene polymerization with high efficiency. Upon activation with MAO at 25 degrees C, 2 displayed a very high activity of 19900 (kg PE) (mol Ti)(-1) h(-1), which is comparable to that for [Cp2TiCl2] and [Cp2ZrCl2], although increasing the polymerization temperature did result in a marked decrease in activity. Complex 2 contains a C6F5 group on the imine nitrogen atom and mediated nonliving-type polymerization, unlike the corresponding salicylaldimine-type complex. Conversely, with [Ph3C]+ [B(C6F5)4]-/AliBu3 activation, 1 exhibited enhanced activity as the temperature was increased (25-75 degrees C) and maintained very high activity for 60 min at 75 degrees C (18740 (kg PE) (mol Ti)(-1) h(-1)). 1H NMR spectroscopic studies of the reaction suggest that this thermally robust catalyst system generates an amine-phenoxy complex as the catalytically active species. The combinations 1/[Ph3C]+ [B(C6F5)4]-/AliBu3 and 2/MAO also worked as high-activity catalysts for the copolymerization of ethylene and propylene.

Self-Organized Monolayer ofmeso-Tetradodecylporphyrin Coordinated to Au(111)

The structure of molecular monolayers formed at the interface between atomically flat surfaces and a solution of free-base meso-tetradodecylporphyrins (H2Ps) was examined by scanning tunneling microscopy (STM) at the liquid/solid interface. On the surface of graphite (HOPG), H2Ps form a well-ordered monolayer characterized by an oblique unit cell. On Au(111), H2Ps form a self-organized monolayer comprised of two distinct domain types. In both types of domains, the density of the porphyrin cores is increased in comparison to the arrangement observed on HOPG. Also, high-resolution STM images reveal that, in contrast to what is observed on HOPG, physisorption on Au(111) induces a distortion of the porphyrin macrocycle out of planarity. By using X-ray photoelectron spectroscopy, we demonstrate that this is likely to be due to the coordination of the lone pairs of the iminic (-C=N-) nitrogen atoms of the porphyrin macrocycle to Au(111).

Synthesis and structural studies of (2E,3E)-3-[(6-{[(1E,2E)-2-(hydroxyimino)-1-methylpropylidene]amino}pyridin-2-yl)imino]butan-2-one oxime, ligand and its mono-, di- and trinuclear copper(II) complexes

A new dioxime ligand, (2E,3E)-3-[(6-{[(1E,2E)-2-(hydroxyimino)-1-methylpropylidene]amino}-pyridin-2-yl)imino]butan-2-one oxime, (H2Pymdo) (3) has been synthesized in H2O by reacting 2,3-butenedione monoxime (2) with 2,6-diaminopyridine. Mono-, di- and tri-nuclear copper(II) complexes of the dioxime ligand (H2Pymdo) and/or 1,10-phenanthroline have been prepared. The dioxime ligand (H2Pymdo) and its copper(II) complexes were characterized by 1H-n.m.r., 13C-n.m.r. and elemental analyses, magnetic moments, i.r. and mass spectral studies. The mononuclear copper(II) complex of H2Pymdo was found to have a 1:1 metal:ligand ratio. Elemental analyses, stoichiometric and spectroscopic data of the metal complexes indicated that the metal ions are coordinated to the oxime and imine nitrogen atoms (C=N). In the dinuclear complexes, in which the first Cu(II) ion was complexed with nitrogen atoms of the oxime and imine groups, the second Cu(II) ion is ligated with dianionic oxygen atoms of the oxime groups and are linked to the 1,10-phenanthroline nitrogen atoms. The trinuclear copper(II) complex (6) was formed by coordination of the third Cu(II) ion with dianionic oxygen atoms of each of two molecules of the mononuclear copper(II) complexes. The data support the proposed structure of H2Pymdo and its Cu(II) complexes.

Crystal structures of nitrato-{4-bromo-2-[(2-hydroxyethylimion)methyl]phenolo}-(3,5-Dibromopyridine)copper and nitrato-{2,4-dibromo-6-[(2-hydroxyethylimino)methyl]phenolo}-(3,5-dibromopyridine)copper

The crystal structures of nitrato-{4-bromo-2-[2-hydroxyethylimino)methyl]phenolo}-(3,5-dibromopyridine)copper (I) and nitrato-{2,4-dibromo-6-[(2-hydroxyethylimino)methyl]phenolo}-(3,5-dibromopyridine)copper (II) are determined. The crystals of compound I are orthorhombic: a = 14.157(3) A, b = 15.420(3) A, c = 17.494(4) A, space group Pbca, Z = 8, R = 0.067. The crystals of compound II are monoclinic: a = 10.675 A, b = 13.973 A, c = 14.007 A, β = 111.92°, space group P21/n, Z = 4, R = 0.0464. In the structures of compounds I and II, the copper atom coordinates, correspondingly, singly deprotonated 4-bromo-2-[(2-hydroxyethylimino)methyl]phenol and 2,4-dibromo-6-[(2-hydroxyethylimino)methyl]phenol molecules, and 3,5-dibromopyridine, and the nitrate ion. The coordination polyhedron of the copper ion in complexes I and II is a slightly distorted tetragonal pyramid. The bases of the pyramids are formed by the imine and pyridine nitrogen atoms and the phenolic and alcoholic oxygen atoms, and the axial vertices are occupied by the oxygen atoms of the monodentate nitrato groups. In the complexes under study, the six-membered metallocycles have asymmetric gauche conformation. In crystal, complexes I are united, due to the slip plane a, through bifurcate hydrogen bonds into infinite chains along the direction [100]. Complexes II in crystal form two-dimensional networks by means of hydrogen bonds.

Homobivalent Quinazolinimines as Novel Nanomolar Inhibitors of Cholinesterases with Dirigible Selectivity toward Butyrylcholinesterase

Homobivalent dimers of quinazolinimines, which bridge the imine nitrogen atoms via a hepta- and an octamethylene spacer, with different ring sizes of the alicycles were synthesized from the corresponding quinazolinethiones. The resulting compounds show >100-fold increase of inhibitory activities compared to related monomeric compounds yielding low-nanomolar inhibitors. For heptamethylene dimers, mixed inhibition profiles were obtained, whereas for the octamethylene compounds selectivity toward butyrylcholinesterase (>180) can be achieved with an eight-membered alicycle.

A Ruthenium(II) Complex with a Tripodal Ligand Containing Three Imidazole Groups

AbstractThe orange [RuII(H3L)](ClO4)2·3H2O (1) complex was synthesized from cis‐[RuCl2(dmso)4] and H3L, where H3L (tris{[2‐{(imidazol‐4‐yl)methylidene}amino]ethyl}amine) is a tripodal ligand obtained by condensation of tris(2‐aminoethyl)amine and 4‐formylimidazole in a 1:3 mol ratio. The X‐ray crystal structure analysis revealed that the complex has an octahedral structure coordinated by three imidazole nitrogen atoms and three Schiff base (imine) nitrogen atoms. The uncoordinated NH groups of the imidazole moieties of 1 are easily deprotonated by the action of a base. The effect of deprotonation on the RuIII/RuII redox potential was studied by cyclic voltammetry in methanol containing 0.1 M LiClO4. Complete deprotonation shifts the RuIII/RuII potential to a much more negative value from –0.18 to –0.72 V vs. Ag/Ag+, making it easier to oxidize. The bluish‐purple RuIII complex, [RuIII(H3L)]3+, was formed by controlled‐potential electrolysis of 1, and the electronic spectrum is reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis and characterization of novel unsymmetrical macrobicyclic tricompartmental mono and binuclear nickel(II) complexes: Electrochemical and kinetic studies of phosphate hydrolysis

A series of macrobicyclic mono and binuclear nickel(II) complexes of type [NiL](ClO 4) and [Ni 2L](ClO 4) 2, where L is macroyclic ligand derived from the precursor compound 3,4:10,11-dibenzo-1,13[ N, N′-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}diaza]-5,9-dioxocyclopentadecane, have been synthesized in order to examine electrochemical and catalytic studies on the basis of macrocyclic ring size. The macrocycle consists of three dissimilar compartments arising from ether oxygen, tertiary nitrogen and imine nitrogen atoms. Electrochemical studies have shown that the mononuclear nickel(II) complexes undergo quasireversible single step one electron reduction and oxidation and binuclear nickel(II) complexes undergo two quasireversible one electron reduction and oxidation. The EPR silent nature is ascribed to Ni(II) state and all the nickel(II) complexes have square planar geometry and are diamagnetic in nature. The complexes were subjected to hydrolysis of 4-nitrophenyl phosphate and the catalytic activities of the complexes are found to increase with macrocyclic ring size of the complexes. As the macrocyclic ring size of the complexes increases, the spectral, electrochemical and catalytic studies of the complexes show remarkable variation due to distortion in the geometry around the nickel(II) centre.

Synthesis and Structural Studies of 2-(hydroxyimino)-1-methylpropylideneamino-phenyliminobutan-2-one Oxime, Ligand and its Complexes with Cu(II) and Ni(II)

A new ligand incorporating a dioxime moiety, (2E,3E)-3-[(2-{[(1E,2E)-2-(hydroxyimino)-1-methylpropylidene]amino}phenyl)imino]butan-2-one oxime, (H2Phmdo) (3) has been prepared by reacting 2,3-butanedionemono-{O-[4-(1-methyl-2-oxo-propylideneaminooxy)-2,3-bis-(1-methyl-2-oxo-propylideneaminooxy-methyl)-but-2-enyl]-oxime} (2) with 1,2-phenylenediamine. Mono-, di- and trinuclear copper(II) and/or nickel(II) complexes of H2Phmdo were characterized by elemental analyses, magnetic moments, 1H-n.m.r. and 13C-n.m.r., i.r. and mass spectral studies. The mononuclear copper(II) and nickel(II) complexes of H2Phmdo were found to have a 1:1 metal:ligand ratio. Elemental analyses, stoichiometric and spectroscopic data of the metal complexes indicated that the metal ions are coordinated to the oxime and imine nitrogen atoms (C=N). In the dinuclear complexes, in which the first Cu(II) or Ni(II) ion was complexed with nitrogen atoms of the oxime and imine groups, the second Cu(II) ion is ligated with dianionic oxygen atoms of the oxime groups and are linked to the 1,10-phenanthroline nitrogen atoms. The data support the proposed structure of H2Phmdo and its complexes.

Metal complexes of 2-benzoylpyridine semicarbazone: Spectral, electrochemical and structural studies

2-Benzoylpyridine semicarbazone (H2BzPS) and its complexes [Cu(H2BzPS)Cl 2] ( 1) and [Zn(H2BzPS)Cl 2] ( 2) have been synthesized and their spectral properties have been studied. The electrochemical behaviour of [Cu(H2BzPS)Cl 2] ( 1) has been investigated. [Cu(H2BzPS)Cl 2] ( 1) crystallizes in the triclinic P-1 space group, a=9.278(1), b=12.848(1), c=13.923(1) Å, α=84.54(1), β=71.91(1), γ=85.14(1)°, with two complexes per asymmetric unit ( Z=4) and a disordered methanol solvent molecule (occupancy=1/4). [Zn(H2BzPS)Cl 2] ( 2) crystallizes in the orthorhombic P2 12 12 1 space group with a=11.983(1), b=14.067(1), c=18.706(1) Å, and two independent molecules per asymmetric unit ( Z=8). In both cases, the neutral semicarbazone acts as a tridentate ligand which coordinates the metal through the pyridine and imine nitrogen atoms and the carbonyl oxygen. Two chloride ions occupy the fourth and fifth coordination positions.

Structural Characterization and Antimicrobial Activity of 2-(5-H/methyl-1H-benzimidazol-2-yl)-4-bromo/nitro-phenol Ligands and their Fe(NO3)3 Complexes

2-(5-H/methyl-1H-benzimidazol-2-yl)-4-bromo/nitro-phenol (HL x :X=1–4) ligands and their iron(III) nitrate complexes have been synthesized and characterized. In all of the complexes, the ligands are bidentate, via one imine nitrogen atom and a phenolate oxygen atom. The coordination is completed with a bidentate nitrate anion, and a water molecule. Elemental analysis, molar conductivity, magnetic susceptibility, FT-Raman, FT-IR (mid i.r., far i.r.), UV–visible and as well as quantum chemical calculations performed with CACHE are in agreement with a 1:1 electrolyte structures that are mononuclear, and distorted 5-coordinate square pyramidal. The antimicrobial activities of free ligands, their hydrochloride salts and the complexes were evaluated using the disk diffusion method in dimethyl sulfoxide (DMSO) toward nine bacteria, each with multiple, fresh clinical isolates, and the results are compared with those for penicillin-g, ampicillin, cefotaxime, vancomycine, oflaxacin and tetracycline. Antifungal activities were reported for Kluyveromyces fragilis, Rhodotorula rubra, Candida albicans, Hanseniaspora Guilliermondii and Debaryomyces hansenii yeasts, each with multiple isolates, and the results were referenced against nystatin, ketaconazole and clotrimazole antifungal agents. In most cases, the compounds tested showed broad-spectrum (Gram+ and Gram−) activities that were either more active or as potent as the references particularly as antifungal agents.

Synthesis and Characterization of 1,8-bis(ferrocenylmethyl)-5,5,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, a Macrocyclic Ligand and its Complexes

A new diferrocenyl-substituted macrocyclic ligand (H2L) and its complexes ML(M = CuII, NiII, ZnII, CdII) were prepared and characterized by IR, elemental analysis, absorption spectra and FAB mass spectra. The ferrocenyl-substituted macrocyclic ligand was characterized by single crystal X-ray diffraction analysis. The superconjugative effect of the cyclopentadienyl (CP) rings increase the activity of the hydrogen atoms in the tetra-azacyclotetradecane macrocyclic ligand. The imine nitrogen atoms lose two protons and coordinate to the metal. The electrochemical properties of these compounds are discussed.

Novel Polyfunctional Tautomeric Systems Containing Salicylideneamino and Proton Sponge Moieties

AbstractThe first salicylidenearylamines containing a proton sponge residue with 5′‐bromo (6), 5′‐nitro (7), and 3′,5′‐dinitro (8) substituents have been synthesized. X‐ray diffraction and 1H, 13C, and 15N NMR and infrared spectra revealed that 6 and 7 contain very strong OHN bridges typical of o‐hydroxy Schiff bases. Additional π‐electron coupling with the dimethylaminonaphthyl ring is manifested both in geometrical and infrared parameters. In the case of 7, proton transfer to the imine nitrogen atom occurs in the solid state, accompanied by a remarkable shortening of the OHN bridge (2.553 Å). In dinitro derivative 8, the OH proton jumps to the dimethylamino groups, giving a new tautomeric form with the formation of a homoconjugated [NHN]+ cation. Protonation of 6 and 7, affecting the (dimethylamino)naphthyl moiety, disrupts the π‐coupling and makes these molecules, unlike common aromatic Schiff bases, highly sensitive to hydrolysis, while 8, being already self‐protonated, equilibrates in wet DMSO with the corresponding salicylaldehyde and arylamine in a ca. 1:1 ratio at room temperature.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis, Structure, and Properties of a Tetranuclear Cubane-like Nickel(II) Complex with Tridentate Schiff Base Ligand

A new tetranuclear cubane-like complex, [Ni4(L)4(EtOH)4]·(H2O), has been synthesized from the reaction of simple metal salt with tridentate Schiff base ligand derived from salicylidene-2-aminobenzoic alcohol (H2L), and its crystal structure, spectroscopic and electrochemical properties have been studied. The complex possessed a [Ni4O4] core comprising a distorted cubane arrangement, of which four nickel(II) ions were bridged by μ3-alkoxo group. Each nickel(II) ion was coordinated to three μ3-alkox oxygen atoms, one imine nitrogen atom and one phenolic oxygen atom from Schiff base ligand. The peripheral ligation was completed by four terminal EtOH ligands, which participated in intramolecular hydrogen bonding interactions.

Novel tricyclic quinazolinimines and related tetracyclic nitrogen bridgehead compounds as cholinesterase inhibitors with selectivity towards butyrylcholinesterase

Tetracyclic nitrogen bridgehead compounds, dibenzodiazecines and tricyclic quinazolinimines, in which the size of the alicyclic ring system and the length of the alkyl chain between the quinazolinimine moiety and a phenyl ring connected to the imine nitrogen atom were changed systematically, were synthesized and their ability to inhibit acetyl- and butyrylcholinesterase (AChE/BChE), respectively, was evaluated. Moderate and strong inhibitors of BChE—compared to galanthamine and rivastigmine—were identified, which show mixed affinities or are moderately or highly selective towards BChE, respectively.

Synthesis, characterization and X-ray crystal structures of dinuclear nickel(II) complexes of a novel potentially hexadentate but functionally tetradentate binucleating ligand

A binucleating potentially hexadentate chelating agent containing oxygen, nitrogen and sulfur as potential donor atoms (H 2ONNO) has been synthesized by condensing α,α-xylenebis( N-methyldithiocarbazate) with 2,4-pentanedione. An X-ray crystallographic structure determination shows that the Schiff base remains in its ketoimine tautomeric form with the protons attached to the imine nitrogen atoms. The reaction of the Schiff base with nickel(II) acetate in a 1:1 stoichiometry leads to the formation of a dinuclear nickel(II) complex [Ni(ONNO)] 2 (ONNO 2− = dianionic form of the Schiff base) containing N, O-chelated tetradentate ligands, the sulfur donors remaining uncoordinated. A single crystal X-ray structure determination of this dimer reveals that each ligand binds two low spin nickel(II) ions, bridged by a xylyl group. The nickel(II) atoms adopt a distorted square-planar geometry in a trans-N 2O 2 donor environment. Reaction of the Schiff base with nickel(II) acetate in the presence of excess pyridine leads to the formation of a similar dinuclear complex, [Ni(ONNO)(py)] 2, but in this case comprises five coordinate high-spin Ni(II) ions with pyridine ligands occupying the axial coordination sites as revealed by X-ray crystallographic analysis.