Synthesis, characterization and cytotoxic activity of gallium(III) complexes anchored by tridentate pyrazole-based ligands

Reactions of GaCl₃ with pyrazole-containing ligands of the pyrazole-imine-phenol (HL¹-HL³) or pyrazole-amine-phenol (HL⁴-HL⁶) types led to the synthesis of well-defined [GaL₂]⁺ homoleptic complexes (1-6). Complexes 1-6 were characterized by elemental analysis, ESI-MS (electrospray ionization-mass spectrometry), IR and NMR spectroscopies, and in the case of Complex 1 also by X-ray diffraction analysis. In complexes 1-3, the pyrazole-imine-phenolate ligands act as monoanionic chelators that coordinate to the metal in a meridional fashion, while 4-6 contain monoanionic and facially coordinated pyrazole-amine-phenolate ligands. Complexes 1-3 have a greater stability in solution compared to 4-6, which have shown a more pronounced tendency to release the respective ancillary ligands. The cytotoxicity of 1-6 and of the respective ligands (HL¹-HL⁶) was evaluated against human prostate cancer cells PC-3 and human breast cancer cells MCF-7. The substituents of the phenolate rings strongly influenced the cytotoxicity of the compounds. Complexes 3 and 6 that contain chloride substituents at the phenolate rings have shown the highest cytotoxicity, including in the cisplatin-resistant PC-3 cell line. The cytotoxic profile of 3 and 6 is very similar to the one displayed by the respective anchor ligands, respectively HL¹ and HL⁶. The cytotoxic activity of 3 and 6 is slightly increased by the presence of transferrin, and both complexes provoke cell death mainly by induction of apoptotic pathways.     

Copper(II) complexes with tridentate pyrazole-based ligands: synthesis, characterization, DNA cleavage activity and cytotoxicity

Tridentate pyrazole-containing ligands of the Schiff base type, SalPz — HL¹, Cl₂SalPz — HL² and I₂SalPz — HL³, were used to prepare a series of new Cu(II) complexes (CuSalPz — 1, CuCl₂SalPz — 2 and CuI₂SalPz — 3). These new complexes have been studied by different analytical techniques (electrospray ionization mass spectrometry (ESI-MS), elemental analysis, FT-IR and EPR). The spectroscopic properties of 1-3 are consistent with the formation of Cu(II) complexes coordinated by monoanionic and tridentate (N,N,O)-chelators, behaving as monomeric species in aqueous solution, as shown by EPR studies. Crystals of 2 and 3, obtained by slow concentration of methanolic solutions of the compounds, were also analyzed by X-ray diffraction analysis. The X-ray structural study has shown that 2 crystallized as a dinuclear compound, [Cu₂(μ-Cl)₂(Cl₂SalPz)₂], while the solid state structure determined for 3 is best described by monomeric units of [CuCl(I₂SalPz)] displaying short Cu···Cl intermolecular contacts. The in vitro evaluation of 1-3 comprised the study of their DNA-cleaving ability using plasmid DNA and the assessment of their cytotoxic activity against several human cancer cell lines (PC-3 prostate, MCF-7 breast and A2780 and A2780cisR-ovary). The studies with plasmid DNA have shown that 2 and 3 induce extensive DNA cleavage in the presence of different additives. The cytotoxic activity of 2 and 3 is comparable to the one presented by cisplatin, with the exception of the A2780 cell line where cisplatin is more active. It has been found that the introduction of halogen substituents in the phenolate rings of the chelators enhanced the cytotoxicity of the respective Cu(II) complexes.     

Synthesis, characterization and equilibrium study of the dinuclear adducts formation between nickel(II) Salen-type complexes with diorganotin(IV) dichlorides in chloroform

Adduct formation between R₂SnCl₂ (R = methyl and n-butyl) as acceptors, and nickel(II) complexes of tetradentate Schiff base ligands ([NiL]) where L = [3-methoxysalen, N,N′-bis(3-methoxysalicylidene)ethylenediamine], [4-methoxysalen, N,N′-bis(4-methoxysalicylidene)ethylenediamine], [5-methoxysalen, N,N′-bis(5-methoxysalicylidene)ethylenediamine], [salen, N,N′-bis(salicylaldehydo)ethylenediamine], [5-chlorosalen, N,N′-bis(5-chlorosalicylidene)ethylenediamine] and [5-bromosalen, N,N′-bis(5-bromosalicylidene)ethylenediamine] as donors have been investigated in chloroform as a solvent by means of UV-Vis spectrophotometeric analysis. Adducts have been characterized by ¹H NMR, IR and electronic spectroscopy. The formation constants and the thermodynamic free energies were measured using UV-Vis spectrophotometry titration for 1:1 adduct formation at various temperatures (T = 278-308 K). The trend of the adduct formation of the nickel Schiff base complexes with a given tin acceptor decreases as follow:

Ni(3-MeOSalen)>Ni(5-MeOSalen)>Ni(4-MeOSalen)     

Synthesis, structural characterization, formation constants and in vitro cytotoxicity of phenanthroline and imidazolidine-2-thione copper(II) complexes

The synthesis, crystal structures, physicochemical properties and complex formation constants of [Cu(phen)₂(L)](ClO₄)₂ complexes, where phen is 1,10-ortho-phenanthroline and L is a series of substituted imidazolidine-2-thione, have been studied. Single crystal X-ray diffraction revealed a distorted trigonal-bipyramidal geometry for all the molecules. The complex formation constants were determined in nonaqueous media by spectrophotometric measurements. Testing copper(II) complexes in mouse neuroblastoma N2a cells persistently infected with the 22L strain of the scrapie prion protein (22L-N2a) resulted in high cytotoxicity but no antiprion activity at nontoxic doses.     

Synthesis, characterization and thermodynamic study of copper(II) complexes with unsymmetric tetradentate Schiff base ligands and X-ray structure of {methyl-2-[N-[2-(5-chloro-2-phenolate)methylidynenitrilo]ethyl}aminato(-1)-1-cyclopentenedithiocarboxylatecopper(II)

A set of two Cu(II) complexes, [Cu(cdXsalen)] and [Cu(cdXsalMeen)] derived from Schiff base ligands (H₂cdXsalen: methyl-2-{[2-(2-X-phenyl)methylidynenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate and H₂cdXsalMeen: methyl-2-{[1-methyl-2-(2-X-phenyl)methylidynenitrilo]ethyl}amino-1-cyclopenteneithiocarb-oxylate where X = hydroxyl, methoxy, nitro, sodiumsulfite, chloro, bromo and H₂cdMesalen: methyl-2-{[2-(2-hydroxyphenyl)ethylidynenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate; H₂cdPhsalen: methyl-2-{[2-(2-hydroxyphenyl)phenylidynenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate; H₂cdMesalMeen: methyl-2-{[1-methyl-2-(2-hydroxyphenyl)ethylidynenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate; H₂cdPhsalMeen: methyl-2-{[1-methyl-2-(2-hydroxyphenyl)phenylidynenitrilo]ethyl}amino-1-cyclopentenedi-thiocarboxylate) with an unsymmetric NNOS coordination sphere have been synthesized and characterized by elemental analysis, IR, UV-Vis and mass spectrometry. The thermodynamic formation constants of the complexes were measured spectrophotometrically, at constant ionic strength 0.1 M (NaClO₄), at 25 °C in DMF solvent. The trend of the complex formation for copper is as follow:

[Cu(cdMesalen)]>[Cu(cdsalen)]>[Cu(cdPhsalen)][Cu(cdMesalMeen)]>[Cu(cdsalMeen)]>[Cu(cdPhsalMeen)]     

Synthesis characterization and cytotoxicity studies of platinum(II) complexes with reduced amino pyridine schiff base and its derivatives as ligands

A series of reduced amino pyridine Schiff base platinum(II) complexes were prepared as potential anticancer drugs, and characterized by NMR, IR spectroscopy, elemental analysis, and molar conductivity. UV and CD results showed the binding mode between these compounds and salmon sperm DNA may be intercalation. The cytotoxicity of these complexes was validated against A549, Hela, and MCF-7 cell lines by MTT assay. Some complexes exhibited better cytotoxic activity than cisplatin against Hela and MCF-7 cell lines.     

Synthesis, structures, photoluminescent and electroluminescent properties of boron complexes with anilido-imine ligands

Syntheses of three new N-arylanilido-arylimine bidentate Schiff base type ligand precursors, ortho-C₆H₄[NH(2,6-ⁱPr₂C₆H₃)](CHNAr¹) [Ar¹ = p-FC₆H₄ (2a); C₆H₅ (2b); p-OMeC₆H₄ (2c)], and their four-coordinated boron complexes, ortho-C₆H₄[N(2,6-ⁱPr₂C₆H₃)](CHNAr¹)BF₂ [Ar¹ = p-FC₆H₄ (3a); C₆H₅ (3b); p-OMeC₆H₄ (3c)] are described. The boron complexes 3a-3c were synthesized from the reaction of BF₃(OEt₂) with the lithium salt of their corresponding ligand. All complexes were characterized by ¹H and ¹³C NMR spectroscopy and molecular structures of complexes 3a and 3c were determined by X-ray crystallography. The photophysical properties of complexes 3a-3c were briefly examined. All three complexes display bright green fluorescence in solution and in the solid state. Electroluminescent devices with complex 3c as the emitter were fabricated. These devices were found to give green emission with maximum current efficiency of 2.92 cd/A and maximum luminance of 670 cd/m².     

Synthesis, characterization and crystal structures of nickel complexes with dissymmetric tetradentate ligands containing a mixed-donor sphere

Four new nickel(II) complexes of dissymmetric tetradentate ligands, containing mixed-ligand donor sets of NSNS or NSNO, have been synthesized. These complexes were prepared by facile template reactions of the appropriate aldehyde and amine in the presence of [Ni(H₂O)₆](BF₄)₂, resulting directly in the desired nickel compounds. The nickel compounds were characterized by analytical, spectroscopic and electrochemical methods. The structures of [Ni(pyzs)]BF₄, [Ni(pyrs)]BF₄ and [Ni(pyzo)]BF₄ (see Scheme 1) have been determined by single-crystal X-ray crystallography, showing the geometry of the nickel ion to be square-planar. Vis–NIR spectra show that the phenolate-containing complexes [Ni(pyzo)]BF₄ and [Ni(pyro)]BF₄ (see Scheme 1) are essentially square-planar in nitromethane, but tetragonal octahedral in methanol, whereas the thiophenolate-containing compounds [Ni(pyzs)]BF₄ and [Ni(pyrs)]BF₄ remain square-planar in both solvents. Titration of the thiophenolate-containing complexes with 1-methylimidazole results in diamagnetic five-coordinated complexes. Electrochemistry shows quasi-reversible reductions to Ni(I) to occur for [Ni(pyzo)]BF₄, [Ni(pyrs)]BF₄ and [Ni(pyro)]BF₄.     

Synthesis, characterization and antioxidant activity of water soluble Mn complexes of sulphonato-substituted Schiff base ligands

Two new Mn^III complexes Na[Mn(5-SO₃-salpnOH)(H₂O)] ⋅ 5H₂O (1) and Na[Mn(5-SO₃-salpn)(MeOH)] ⋅ 4H₂O (2) (5-SO₃-salpnOH = 1,3-bis(5-sulphonatosalicylidenamino)propan-2-ol, 5-SO₃-salpn = 1,3-bis(5-sulphonatosalicylidenamino)propane) have been prepared and characterized. Electrospray ionization-mass spectrometry, UV-visible and ¹H NMR spectroscopic studies showed that the two complexes exist in solution as monoanions [Mn(5-SO₃-salpn(OH))(solvent)₂]⁻, with the ligand bound to Mn^III through the two phenolato-O and two imino-N atoms located in the equatorial plane. The E_1/2 of the Mn^III/Mn^II couple (−47.11 (1) and −77.80 mV (2) vs. Ag/AgCl) allows these complexes to efficiently catalyze the dismutation of , with catalytic rate constants 2.4 × 10⁶ (1) and 3.6 × 10⁶ (2) M⁻¹ s⁻¹, and IC₅₀ values of 1.14 (1) and 0.77 (2) μM, obtained through the nitro blue tetrazolium photoreduction inhibition superoxide dismutase assay, in aqueous solution of pH 7.8. The two complexes are also able to disproportionate up to 250 equivalents of H₂O₂ in aqueous solution of pH 8.0, with initial turnover rates of 178 (1) and 25.2 (2) mM H₂O₂ min⁻¹ mM⁻¹ catalyst⁻¹. Their dual superoxide dismutase/catalase activity renders these compounds particularly attractive as catalytic antioxidants.     

Oxo-bridged bis oxo-vanadium(V) complexes with tridentate Schiff base ligands (VOL)2O (L = SAE, SAMP, SAP): Synthesis, structure and epoxidation catalysis under solvent-free conditions

The dinuclear V(V) complexes (VOL)₂O (L = SAE (1), SAMP (2), SAP (3)) have been synthesized from VO(acac)₂ and the corresponding tridentate ligands LH₂ in methanol under reflux conditions and subsequent air oxidation in organic solvent. They have been characterized by IR and NMR spectroscopy, by thermogravimetric analysis, and by single crystal X-ray diffraction for 1 and 2. DFT calculations were carried out for a better understanding of the vibrational pattern, principally the V-O related vibrations. Complex [VO(SAP)]₂O (3) catalyzes the epoxidation of cyclooctene by TBHP in water in the absence of any added solvent with good selectivity.     

Synthesis, characterization and the thermodynamic study of intermediate sitting-atop (i-SAT) complexes of free base meso-tetraarylporphyrins with InCl3

The reaction of free base para-substituted meso-tetraarylporphyrins (H₂T(p-X)PP, X = H, OMe, Me, and Cl) with indium(III) chloride in CHCl₃ and mild conditions produced intermediate sitting-atop (i-SAT) complexes, [InCl₂(H₂T(p-X)PP)]InCl₄, as sole products. In the proposed structures of these complexes, four pyrrole rings are tilted alternatively up and down the porphyrin plane. This distortion makes suitable orientation of lone pairs of two pyrrolenine nitrogens for electron donation to an indium center of cation. The 1:2 (porphyrin:indium) formation constant of resulting i-SAT complexes were calculated by the computer fitting of the complexes absorbance versus mole ratio data based on appropriate equations. Thermodynamic parameters, ΔG⁰, ΔH⁰, and ΔS⁰, have been determined and the influence of electron donation of the para-substituted aryl groups in the free base porphyrins on the stability of the complexes is discussed.     

Synthesis, crystal structure and DNA cleavage activities of copper(II) complexes with asymmetric tridentate ligands

Two asymmetric tridentate copper(II) complexes, [Cu(dppt)Cl(2)].0.25H(2)O (1) (dppt=3-(1,10-phenanthrolin-2-yl)-5,6-diphenyl-as-triazine) and [Cu(pta)Cl(2)] (2) (pta=3-(1,10-phenanthrolin-2-yl)-as-triazino[5,6-f]acenaphthylene), have been prepared and characterized by elemental analysis, IR and Fast atomic bombardment mass spectra. Complex 1 has also been structurally characterized. The complexes exist as distorted square pyramid with five co-ordination sites occupied by the tridentate ligand and the two chlorine anions. DNA interaction studies suggest that the ligand planarity of the complex has a significant effect on DNA binding affinity increasing in the order [Cu(dppt)Cl(2)]< [Cu(pta)Cl(2)]. In the presence of ascorbate or glutathione, the two complexes are found to cause significant cleavage of double-strand pBR 322 DNA and [Cu(pta)Cl(2)] exhibited the higher cleaving efficiency.     

Dinuclear organoiridium(III) mono- and bis-intercalators with rigid bridging ligands: Synthesis, cytotoxicity and DNA binding

The DNA binding and in vitro cytotoxicity of the dinuclear Ir(III) polypyridyl complexes [{(η⁵-C₅Me₅)Ir(dppz)}₂(μ-pyz)](CF₃SO₃)₄1 and [{(η⁵-C₅Me₅)Ir(pp)}₂(μ-4,4′-bpy)](CF₃SO₃)₄2-4 (pp = dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq), dipyrido[2,3-a:2′,3′-c]phenazine (dppz), benzo[i]dipyrido[3,2-a:2′,3′-c]phenazine (dppn)) with the rigid bridging ligands pyrazine (pyz) or 4,4′-bipyridine (4,4′-bpy) have been studied. Stable intercalative binding into CT DNA (calf thymus DNA) is indicated for the dppz complexes 1 and 3 by induced negative CD bands at about 300 nm and large viscosity increases, with the individual measurements being in accordance with intrastrand bis-intercalation for 3 and mono-intercalation for 1. The observed interruption of specific interresidue NOE cross peaks from the relevant nucleobase H6/H8 protons to the sugar H2′/H2″ protons of the preceding nucleotide is in accordance with bis-intercalation of complex 3 between the C3G18 and G4C17 base pairs and the T5A16 and A6T15 base pairs of the decanucleotide d(5′-CGCGTAGGCC-3′). Complexes 1 and 3 exhibit a greatly improved uptake by HT-29 (colon carcinoma) cells and significantly improved in vitro IC₅₀ values of 1.8 ± 0.1 and 3.8 ± 0.1 μM towards this cell line in comparison to the mononuclear complex [(η⁵-C₅Me₅)IrCl(dppz)](CF₃SO₃) (IC₅₀ = 7.4 ± 0.9 μM).     

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

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

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

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

Synthesis, characterization and crystal structures of the organotin(IV) compounds with the Schiff base ligands of pyruvic acid thiophene-2-carboxylic hydrazone and salicylaldehyde thiophene-2-carboxylic hydrazone

A series of organotin (IV) compounds of the type [R₃SnL]₂, R is Me (1), Bu (2), [R₂SnL]₂, R is Ph (3), Me (4), Bu (5), L is pyruvic acid thiophene-2-carboxylic hydrazone, and R₂SnL, R is Me (6), Bu (7), Ph (8), L is salicylaldehyde thiophene-2-carboxylic hydrazone have been synthesized in 1:1 molar ratio. All compounds were characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR and ¹¹⁹Sn NMR spectra. The crystal structure of compounds 1, 3, 4, 8 have been determined by X-ray single crystal diffraction analyses, study found that the compounds 1 and 3 are rendered one-dimensional chain structure and the tin atoms are five-coordinated in a distorted trigonal-bipyramidal geometry. The compound 4 has a dimeric structure and the central tin atom is rendered seven-coordinate in a distorted pentagonal-bipyramid configuration. While the compound 8 is a monomer in which the tin atom adopts five-coordinated in distorted trigonal-bipyramidal geometry.     

Syntheses, characterization, and reactivity of copper complexes with tridentate N-donor ligands

The reaction of dioxygen with the copper(I) complex of the tridentate ligand 1,1,4,7,7-pentamethyldiethylenetriamine (Me₅dien) has been investigated using low-temperature stopped-flow techniques. The formation of a bis(μ-oxo)copper(III) complex as a reactive intermediate could be detected spectroscopically at low temperatures and a quantitative kinetic analysis was performed for this system. Crystal structures of the copper(II) complexes [(Me-bpa)Cu(Cl)₂] (1), [{(Me-bpa)Cu(Cl)(ClO₄)}₂] (2), [{(MeL)Cu(Cl)(ClO₄)}₂] (3), and [(MeL)Cu(NCS)₂] (4) (Me-bpa = N-methyl-[bis(2-pyridyl)methyl]amine; MeL = N-methyl-[(2-pyridyl)ethyl(2-pyridyl)methyl]amine) are reported.     

Synthesis, characterization and cytotoxicity studies of palladium(II)-proflavine complexes

An investigation of the reaction of Pd(II) complexes with proflavine (3,6-diaminoacridine) resulted in the isolation of the compounds [Pd(terpy)(proflavine)](NO₃)(HSO₄)3H₂O, 1, (terpy = 2,2′:6′,2″-terpyridine), [Pd(en)(proflavineH))](NO₃)(SO₄), 2, (en = ethylenediamine), and [Pd(proflavineH)Cl₂](SO₄)_0.5H₂O, 3. They have been isolated and characterized by NMR, IR, and electro-spray ionization mass spectrometry techniques and by elemental analyses. The proflavine was bonded to the Pd(II) through the endocyclic nitrogen in 1, but through the proflavine NH₂ in 2. Compound 3 appeared to be polymeric in the solid state with a 1:1 mole ratio of Pd(II):proflavine. Upon solution of 3 in DMSO, two unique species were formed. In one species the Pd(II) was bonded to two proflavines through the endocyclic nitrogen (1:2 mole ratio) and in the other species, a Pd(II) was bonded to each NH₂ group of a single proflavine (2:1 mole ratio). Molecular modeling of the equilibrium geometry by Spartan 8 produced structures which were consistent with the experimental data on the solutions of the three compounds. In vitro cytotoxicity testing against two breast cancer cell lines and one ovarian cancer cell line showed that compounds 1 and 3 had significant activity.     

Synthesis,characterization, biological and catalytic applications of transition metal complexes derived from Schiff base

A novel series of Cu(II), Ni(II), Zn(II), Co(II), and Cd(II) complexes have been synthesized from the Schiff base. Structural features were determined by analytical and spectral techniques like IR, ¹H NMR, UV–vis, elemental analysis, molar electric conductibility, magnetic susceptibility and thermal studies. The complexes are found to be soluble in dimethylformamide and dimethylsulfoxide. Molar conductance values in dimethylformamide indicate the non-electrolytic nature of the complexes. Binding of synthesized complexes with calf thymus DNA (CT DNA) was studied. There is significant binding of DNA in lanes 2, 3, and 5. Lanes 4 and 6 are showing more florescence when compared to the control indicating that these molecules are strongly bound to the DNA by inserting themselves between the two stacked base pairs and exhibiting their original property of fluorescence. Angiogenesis study has revealed that the compounds B-2, B-4 and B-5 have potent antitumor efficacy and activation of antiangiogenesis could be one of the possible underlying mechanisms of tumor inhibition.     

Syntheses, characterization and X-ray crystal structures of a mono- and a penta-nuclear nickel(II) complex with oximato Schiff base ligands

A mononuclear octahedral nickel(II) complex [Ni(HL¹)₂](SCN)₂ (1) and an unusual penta-nuclear complex [{(NiL²)(μ-SCN)}₄Ni(NCS)₂]·2CH₃CN (2) where HL¹ = 3-(2-aminoethylimino)butan-2-one oxime and HL² = 3-(hydroxyimino)butan-2-ylidene)amino)propylimino)butan-2-one oxime have been prepared and characterized by X-ray crystallography. The mono-condensed ligand, HL¹, was prepared by the 1:1 condensation of the 1,2-diaminoethane with diacetylmonoxime in methanol under high dilution. Complex 1 is found to be a mer isomer and the amine hydrogen atoms are involved in extensive hydrogen bonding with the thiocyanate anions. The dicondensed ligand, HL², was prepared by the 1:2 condensation of the 1,3-diaminopropane with diacetylmonoxime in methanol. The central nickel(II) in 2 is coordinated by six nitrogen atoms of six thiocyanate groups, four of which utilize their sulphur atoms to connect four NiL² moieties to form a penta-nuclear complex and it is unique in the sense that this is the first thiocyanato bridged penta-nuclear nickel(II) compound with Schiff base ligands.