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A systematic and comparative binding study between serum-albumins (SA) and a series of monomeric nickel(II)-Schiff-base-complexes (NSCs), which might be imperative to investigate the function of SA behind nickel allergy, has been carried out through docking and different spectroscopic techniques. The initial docking studies indicate structure-dependent selective hydrophobic and hydrophilic interactions. The pyridine and phenyl containing NSCs, which are more aromatic, show better π–π staking compared to pyrrole one. Again all the NSCs bind with BSA though amino acid residues of IB domain affecting local environment of the Trp-134 surrounded by both hydrophobic and hydrophilic residues instead of the hydrophobically buried Trp-212. In HSA the hydophobically buried Trp-214 is influenced by NSCs. The experimental results nicely support the docking outcomes. The changes in Gibbs free energy, binding affinity and the nature of hydrophilic/hydrophobic interactions of NSC–SA systems indicate greater accessibility of N2O2 donor set complex compared to N4 one towards SA. Quantum chemical structure optimizations support the better planarity of NSC with N2O2 which provides better binding. Therefore the structural variation of N2O2 donor set complexes becomes much more useful compared to N4 one to search out the most compatible NSC towards SAs.

The structural effects of different copper(II) and nickel(II) Schiff base complexes on hen egg white lysozyme (HEWL) have been investigated through steady state and time resolved absorption and fluorescence, and circular dichroism spectroscopy. The Schiff base ligands with N4 donor atoms show both hydrophobic and hydrophilic interactions, however hydrophilic interaction prevails with ligands having N2O2 donor atoms. Variation of metal ions from Cu2+ to Ni2+ with each type of Schiff base ligand increases the probability of hydrophilic over hydrophobic interactions, which supports their significance in regulating the binding affinity between HEWL and metal complexes. On photo-excitation the complexes comprising of Cu2+ ion instead of Ni2+ ion and ligands with N4 donor system rather than N2O2 donor system, increases the probability of intersystem crossing to populate the corresponding triplet state as observed from laser flash photolysis study. The better binding affinity of nickel complexes with different selectivities compared to copper complexes towards HEWL emphasizes the potentiality of less explored nickel complexes in drug–protein interactions.

International audience; Three new complexes of cobalt, manganese, and zinc have been synthesized using a hydrazone Schiff base ligand {(E)-N′-[1-(2-hydroxyphenyl)ethylidene]acetohydrazide} (LH2) produced by the 1:1 condensation of acetic hydrazide and 2-hydroxyacetophenone. The ligand has shown three different coordination modes in the three complexes: a monoanionic tridentate coordination mode with the CoII complex ([Co(LH)2]·CH3OH, 1), a dianionic tridentate coordination mode with the MnIV complex ([Mn(L)2], 2), and monoanionic μ2-phenoxo-bridged tridentate coordination mode with the ZnII complex ([Zn(LH)(OOCCF3)]2, 3). All three complexes show interesting supramolecular architectures, especially for 3 a nanoporous supramolecular (4, 4) grid 2D framework is formed. The ligand and the complexes are well characterized by elemental analysis, IR and UV–vis spectroscopy. The spin states of the CoII and MnIV metal ions and hence the coordination modes of the ligand in these complexes are in good agreement with the EPR spectroscopic data. The fluorescence emission spectra of LH2 and the zinc complex 3 are measured in acetonitrile solution as well as in solid state.

A dicyanoamide-bridged 2D polynuclear zinc(II) complex having formula [Zn2(L)(μ-dca-κN1κN5)2]n, 1 has been synthesized using the Schiff base ligand N,N′-bis(salicylidene)-1,3-diaminopentane, (H2L) ...

International audience; By slightly changing the synthetic conditions, we have prepared two closely related linear tetranuclear CuII complexes with the symmetrical ONNO donor tetradentate Schiff-base ligand [H2L = (OH)C6H4(CH3)Cdouble bond; length as m-dashN(CH2)3Ndouble bond; length as m-dashC(CH3)C6H4(OH)] and with azide ions. These two distinctly coloured crystalline products were characterized by elemental analysis, IR and UV–Vis spectroscopy, CV, EPR spectra and variable temperature magnetic measurements. Single crystal X-ray diffraction studies of the green [Cu4(μ-L)2(μ1,1-N3)2(N3)2] (1) and the red [Cu4(μ-L)2(μ1,1-N3)2(N3)2(H2O)2] (2) crystals show that the coordination environment of the two μ-phenoxo and μ1,1-azido bridged isomorphous tetranuclear CuII complexes are slightly different. Thus, both complexes are formed by very similar building units, although with a significant variation in the bridging Cu–O(phenoxo)–Cu and Cu–N(azido)–Cu bond angles. The consequences of these structural variations on the magnetic properties have been investigated from both the experimental and theoretical points of view by variable temperature magnetic measurements and DFT calculations.

Two terdentate NNO donor Schiff base ligands CH 3 C(OH) CHC(CH 3 ) NCH 2 C 5 H 4 N [ HL 1 ] and C 6 H 5 C(OH) CHC(CH 3 ) NCH 2 C 5 H 4 N [ HL 2 ] were used to synthesize two mononuclear square planar copper(II) complexes, [Cu L 1 (CF 3 COO)] ( 1 ) and [Cu L 2 (CF 3 COO)] ( 2 ). The complexes were characterized by elemental analyses, FT-IR, UV–vis spectral methods and their structures were established by single crystal X-ray diffraction study. The biochemical activity of the complexes towards DNA binding were performed using absorbance and fluorescence titration methods and their mode of binding with calf thymus DNA has been established by viscosity measurement technique.

A new tetradentate N 2 O 2 donor Schiff base ligand [OHC 6 H 4 CH NCH 2 CH 2 CH(CH 2 CH 3 )N CHC 6 H 4 OH = H 2 L ] was obtained by 1:2 condensation of 1,3-diaminopentane with salicylaldehyde and has been used to synthesise an unusual copper(II) complex whose asymmetric unit presents two structurally different almost linear trinuclear units [Cu 3 (μ- L ) 2 (ClO 4 ) 2 ] [Cu 3 (μ- L ) 2 (H 2 O)(ClO 4 ) 2 ] ( 1 ). The ligand and the complex were characterised by elemental analysis, FT-IR, 1 H NMR and UV–Vis spectroscopy in addition electrochemical and single crystal X-ray diffraction studies were performed for the complex. The magnetic properties of 1 reveal the presence of strong intra-trimer ( J 1 = −202(3) cm −1 and J 2 = −233(3) cm −1 ) as well as very weak inter-trimer ( zJ ′ = −0.11(1) cm −1 ) antiferromagnetic interactions.

Three new mono–di–trinuclear cobalt complexes of three different Schiff bases have been synthesised. In all the three complexes psuedohalides (NCO− and N3−) have been incorporated to generate structural variation. Of the three Schiff bases, HL1 and HL2 were obtained by selective condensation of two different 1,3-diamines with 2-hydroxyacetophenone and H2L3 resulted from non-selective condensation of 1,3-diamine with 2-hydroxyacetophenone. Only one –NH2 functionality of 1,3-diaminopropane and 1,3-diaminopentane was selectively condensed with 2-hydroxyacetophenone to generate Schiff bases HL1 and HL2, respectively. H2L3 was obtained by condensing both the amine functionality of 1,3-diaminopropane with 2-hydroxyacetophenone. Therefore HL1 and HL2 behave as a N2O donors, whereas H2L3 provides a N2O2 donor coordination environment for the cobalt ions in the respective complexes. In [Co(L1)2]2 [Co(NCO)4] (1) the asymmetric unit comprises of five mononuclear cobalt centers, [Co2(μ–N3)2(L2)2(N3)2] (2) is a dinuclear and [(H2O)2Co(μ–N3)2(μ–L3)2Co2(N3)1.25(CH3O)0.75] · H2O (3) is a trinuclear cobalt species. The three complexes have been characterised using IR, UV–Vis spectroscopy and cyclic voltammetry. Structural aspects of 1, 2 and 3 have been described by performing single crystal X-ray analysis. EPR analyses of 1 and 3, and DNA binding abilities of all three cobalt complexes have been studied in detail.

International audience; A new tridentate N2O donor Schiff base ligand [(C6H5C(OH)CHC(CH3)NCH2C5H4N)LH] was obtained by 1:1 condensation of benzoylacetone with 2-picolylamine and has been used to synthesise a mononuclear [CuLCl] (1) and an end-to-end dicyanamide bridged polynuclear {[Cu2(μ-L)2(μ2-1,5-(CN)2N)]ClO4}n (2) copper(II) complexes. The ligand, 1 and 2 were clearly characterised by elemental analysis, FT-IR, 1H NMR, UV–Vis spectral studies, electrochemical studies and in addition single crystal X-ray diffraction studies were performed for 1 and 2. The Schiff base ligand [LH] shows a significant variation in its coordination behaviour with copper(II) ion in absence and in presence of dicyanamide ion in 1 and 2 respectively. In absence of dicyanamide the deprotonated enolato oxygen of the tridentate Schiff base ligand [L]− coordinates the copper(II) ion in a monodentate fashion generating a mononuclear species (1) whereas in presence of the dicyanamide ion, the deprotonated enolato oxygen of [L]− bridges two adjacent [CuL(CN)2N] units through μ-OL bridges, forming dimers. The dimeric units are further linked to adjacent dimeric units through μ2-1,5-dicyanamide bridges to produce 1D polymeric chains in 2. Variable temperature magnetic susceptibility measurements for 2 in the temperature range 2-300 K reveal the presence of weak antiferromagnetic exchange interactions in the polymeric chain.

A novel hydroxo-bridged cyclic tetranuclear copper(II) complex with the guanazole ligand (3,5-diamino-1,2,4-triazole = Hdatrz), [Cu4(datrz)4(μ2-OH)2(NO3) (H2O)6] · (NO3) · 5(H2O) (1) has been synthesised and characterised by X-ray crystallography. In 1, the four copper(II) centres are linked by hydroxo bridges and the N1,N2-coordination of the deprotonated guanazole ligands. The core has considerably short Cu⋯Cu distances in the range of 3.3550(4)–3.3611(4) A. Thermal analysis of 1 reveals that the cyclic framework constructed with hydroxo and guanazole ligands is stable up to 285 °C.

International audience; Metal complexes of Schiff bases derived from an aromatic hydrazide are well characterised and have been reported several times. Single crystal structures of metal hydrazone complexes derived from an aliphatic hydrazide are very rare and still remain unexplored. In this paper we report two new end-on azido bridged dinuclear copper(II) and cobalt(III) hydrazone complexes derived from an aliphatic hydrazide. The Schiff base [LH = CH3C(O)NHNCHC5H4N] has resulted from the condensation of acetic hydrazide and pyridine-2-carboxaldehyde. The ligand and the complexes [Cu2(L)2(μ1,1-N3)2] (1) and [Co2(L)2(μ1,1-N3)2(N3)2] (2) are characterised by elemental analysis, IR and UV–Vis spectral studies and in addition mass spectroscopy has been also carried out for LH. The structures of 1 and 2 have been established by X-ray crystallography. Variable temperature magnetic susceptibility measurement studies of 1 indicate the χMT values remain constant in the whole range of temperature 10 to 300 K at a value close of 0.75 cm3 K mol−1, which is in good agreement with the one expected for two uncoupled copper(II) centers.

A nickel(II) and a cobalt(III) complex of two different potentially tetradentate Schiff bases with different binding modes have been synthesised. The nickel(II) complex [NiL1] · CH3OH (1) was formed, on reacting the metal salt with a perfectly symmetrical N2O2 tetradentate Schiff base ligand H 2 L 1 , which is the 1:2 condensation product of 1,3-diamino propane and 2-hydroxyacetophenone. The cobalt(III) complex [Co(HL2)3] · (ClO4)3 · H2O (2) was synthesised using an asymmetric N2O2 tetradentate Schiff base ligand HL 2 on condensing N,N-dimethyl-1,3-diamino propane with o-vanillin in 1:1 mmol ratio. Although both Schiff bases are N2O2 functionalised, they showed variation in their coordinative property with nickel(II) and cobalt(III) ions. Both the complexes were characterised by IR spectroscopy and cyclic voltammetry and their single crystal structures clearly indicate that 1 is a mononuclear species whereas 2 is a hydrogen-bonded dimer.

International audience; A tridentate NNO donor Schiff base ligand [(1Z,3E)-3-((pyridin-2-yl)methylimino)-1-phenylbut-1-en-1-ol = LH] in presence of azide ions coordinates with cobalt(II) and copper(II) ions giving rise to three new coordination complexes [Co2(L)2(μ1,1-N3)2(N3)2] (1), [Cu2(L)2(μ1,3-N3)]·ClO4 (2) and [(μ1,1-N3)2Cu5(μ-OL)2(μ1,1-N3)4(μ1,1,1-N3)2]n (3). The complexes have been characterized by elemental analysis, FT-IR, UV–Vis spectral studies, and single crystal X-ray diffraction studies. These complexes demonstrate that under different synthetic conditions the azide ions and the Schiff base ligand (LH) show different coordination modes with cobalt(II) and copper(II) ions, giving rise to unusual dinuclear and polynuclear species (1, 2 and 3) whose structural variations are discussed. Magneto-structural correlation for the very rare singly μ1,3-N3 bridged CuII–Schiff base dinuclear species (2) has been studied. In addition, the catalytic properties of 1 for alkene oxidation and the general catalase-like activity behavior of 2 have been discussed.

International audience; Two new coordination complexes {[(L)Cu2('-L)(NO3)(CH3OH)0.3(H2O)0.7]·NO3}[Cu(L)(NO3)(CH3OH)] (1) and [Mn2(-L)2(H2O)(1-N3)2(CH3OH)] (2) derived from (E)-N-(2-hydroxy-3-methoxybenzylidene)acetohydrazide [LH] have been synthesized. The new potentially tetradentate ONOO donor hydrazone ligand [LH] has shown considerable metal ion selective phenoxo bridging in 1 and 2. It has coordinated copper(II) ions in its tridentate as well as in tetradentate fashion whereas for manganese(II) ions it solely showed its tetradentate character. In 1 the two adjacent pentacoordinate copper(II) centers are connected by a rare single phenoxo linkage of the hydrazone ligand whereas 2 is a doubly phenoxo-bridged heptacoordinated manganese(II) dinuclear species. The 3D supramolecular networks of 1 and 2 have resulted from extensive H-bonding interactions in the respective complexes. Structural variations observed for 1 and 2 have been described by performing single-crystal X-ray analysis. The ligand and the complexes are characterized by elemental analyses, IR, UV/Vis and 1H NMR spectroscopy. Cryomagnetic investigations, DFT studies and EPR analysis, of 1 and 2 have also been studied in detail.

A new Na(I)/Cu(I-II) heterometallic coordination complex [Cu(2)L(2)Na(NCO)(2)Cu](n) (1) with an unusual architecture has been synthesised. In 1 cyclic Na-O-Cu-O-Cu cages constructed by the tetradentate N(2)O(2) donor Schiff base ligand (H(2)L = N, N'-bis(2-hydroxyacetophenone) propylenediimine) are interconnected to each other by a rare singly end-to-end bridged OCN-Cu(I)-NCO link generating 1D chain. The complex has been characterised by elemental, spectral and structural analysis. The cyclic voltammogram of 1 has been compared with the analogous complexes. Cryomagnetic susceptibility studies indicate the copper(II) centers in the cyclic Na-O-Cu-O-Cu cages are antiferromagnetically coupled with J = -13.8 cm(-1). Complex 1 is a new addition to a class of rare singly end-to-end cyanato bridged copper(I) species and interestingly the copper ions involved in OCN-Cu(I)-NCO links possess a linear 2-coordinate geometry. Density functional theory calculations have been carried out to gain additional insights into the metal and ligand orbitals participating in this unusual structure.