Aqueous solution study of Cu(II) and Ni(II) complexes of macrocyclic oxa- and thia-containing trans-dioxo-tetraamines

Four macrocyclic trans-dioxo-tetraamines containing sulphur or oxygen as additional donors have been prepared: 1-oxa-3,14-dioxo-4,7,10,13-tetraazacyclopentadecane, 1-thia-3,14-dioxo-4,7,10,13-tetraazacyclopentadecane, 1-oxa-3,16-dioxo-4,8,11,15-tetraazacycloheptadecane and 1-thia-3,16-dioxo-4,8,11,15-tetraazacycloheptadecane. Their protonation as well as their metal binding properties with Cu²⁺ and Ni²⁺ have been determined at 25°C in 0.10 mol dm⁻³ KNO₃. The complexation process was investigated by potentiometric, calorimetric and UV/VIS-spectroscopic titrations. IR-spectroscopy was used to establish the involvement of the amido groups in the coordination. Oxidation of the complexes to the trivalent state of the metal ion was also investigated by cyclic voltammetry. Metal ion complexation promotes the deprotonation of the amide nitrogens, resulting in a neutral complex with four nitrogen donors and a MLH_-2 stoichiometry at pH 8. Additional complexes with stoichiometry ML and MLH_-1 were needed to describe the complexation in the pH range 2–11. Their stability constants were calculated. The presence of oxygen or sulphur donors as well as ring enlargement influence the complexation properties. The electronic spectra indicate rather distorted tetragonal coordination geometries for the Cu(II)-complexes. The Ni(II)-complexes are all square–planar with the exception of an equilibrium between a square–planar and an octahedral form for NiL¹H₋₂. All complexes are easily but irreversibly oxidized to the trivalent state of the metal ion.     

Thermochemical study of the stepwise protonation of 1,10-diaza-4,7-dithiadecane,and its complex formation with copper(II) and nickel(II) ions in aqueous solution

The behaviour of 1,10-diaza-4,7-dithiadecane (2,2,2-NSSN) in aqueous solution in equilibria with protons, Cu²⁺ or Ni²⁺ ions has been investigated potentiometrically and calorimetrically. The protonation constants for the ligand, and the stability constants for its complexes at 25°C in 0.5 mole dm^?3 (K)NO₃ are reported, together with the corresponding thermodynamic parameters ΔG, ΔH and ΔS. The results are compared with those for 1-aza-4-thiapentane and 1,7-diaza-4-thiaheptane. The ligand 2,2,2-NSSN forms complexes of formula ML²⁺ and MHL³⁺ with both Cu²⁺ and Ni²⁺. It is found that in the non-protonated 1:1 complexes the ligand acts as a tetradentate. In the CuHL³⁺ complex, the ligand is bound through one nitrogen and two sulphur donors, whereas in the NiHL³⁺ complex the ligand is probably bound through only one nitrogen and one sulphur donor. Explanations are suggested.     

The thermodynamic characteristics of complex formation between Ni<Superscript>2+</Superscript> ions and D,L-threonine in aqueous solution

The heat effects of interaction between solutions of D,L-threonine and Ni(NO₃)₂ were measured by direct calorimetry at 298.15 K and ionic strength values of from 0.5 to 1.5 (KNO₃). The heat effects of formation of the NiL⁺, NiL₂, and NiL ₃ ^? complexes were calculated. The influence of background electrolyte concentration on the heats of complex formation in the Ni²⁺-D,L-threonine system was studied. The standard heat effects of formation of Ni²⁺ complexes with D,L-threonine were obtained by extrapolation to zero ionic strength. The standard enthalpies of formation of NiL⁺, NiL₂, and NiL ₃ ^? in aqueous solution were calculated.     

Thermochemical and spectrophotometric study of the complex formation of nickel(II) ions with sulfur containing α,ω-aminopyridines

The complexation in aqueous solution of ligands of the type o-Py? (CH₂)_(n-1) S(CH₂)_mNH₂ (n and m: 2 or 3) with Ni^II ions has been investigated. The thermodynamic functions ΔG, ΔH, and ΔS of the complex formation have been determined at 25°C in 0.5 M KNO₃ solution by means of potentiometric and of direct calorimetric titrations. They revealed that all ligands, except o-Py? (CH₂)₂S(CH₂)₃NH₂ for which no appreciable complexation with Ni^II could be stated, act as tridentates towards Ni^II. Information on the stereochemistry of the Ni^II complexes was obtained from the electronic spectra. The NiL²⁺ and NiL₂²⁺ complexes both have distorted octahedral structures. The NiL₂²⁺ species were also compared to the corresponding NiL₂(NO₃)₂ compounds in the solid state.     

Synthesis and characterization of Co(II), Ni(II), Zn(II) and Cu(II) complexes with a new tetraazamacrocyclic Schiff base ligand containing a piperazine moiety: X-ray crystal structure determination of the Co(II) complex

Two macrocyclic Schiff base ligands, L¹ [1+1] and L² [2+2], have been obtained in a one-pot cyclocondensation of 1,4-bis(2-formylphenyl)piperazine and 1,3-diaminopropane. Unfortunately, because of the low solubility of both ligands, their separation was unsuccessful. In the direct reaction of these mixed ligands (L¹ and L²) and the appropriate metal ions only [CoL¹(NO₃)]ClO₄, [NiL¹](ClO₄)₂, [CuL¹](ClO₄)₂ and [ZnL¹(NO₃)]ClO₄ complexes have been isolated. All the complexes were characterized by elemental analyses, IR, FAB-MS, conductivity measurements and in the case of the [ZnL¹(NO₃)]ClO₄ complex with NMR spectroscopy.     

Nickel(II) complexes of a thiosemicarbazone prepared from 2-Acetylpyridine

Summary The ligand 3-azabicyclo[3.2.2]nonane-3-thiocarboxylic acid 2-[1-(2-pyridinyl)ethylidene]hydrazide (HL), which is observed in an unusual tautomeric form in the solid state, and its selenium analogue (HLSe) have been used to prepare a series of nickel(II) complexes. Compounds of the general formula [NiLX] (X=Cl, Br, NCS, N₃, NO₂ or NCSe) as well as [Ni(LSe)Cl] have been found to be diamagnetic, planar complexes. A single crystal study of [NiL(NCS)] shows the deprotonated ligand bound in a tridentate mannervia its pyridyl nitrogen, imine nitrogen and the thione sulphur atom with the nitrogen atom of the thiocyanato-ligand occupying the fourth coordination position. The solids prepared from the nickel(II) salts having tetrafluoroborate, nitrate and iodide ions approximate to octahedral symmetry and have neutral HL ligands coordinated in a bidentate fashionvia the pyridine and imine nitrogens with the remaining coordination sites being occupied by the anions or water molecules. The [NiL₂] solid is also octahedral with the two deprotonated ligands bonding as tridentate groupsvia the same atoms as in the [NiLX] complexes.     

Spectral and structural studies of nickel(II) complexes of salicylaldehyde 3-azacyclothiosemicarbazones

Mononuclear nickel(II) complexes with two ONS donor thiosemicarbazone ligands {salicylaldehyde 3-hexamethyleneiminyl thiosemicarbazone [H₂L¹] and salicylaldehyde 3-tetramethyleneiminyl thiosemicarbazone [H₂L²]} have been prepared and physico-chemically characterized. IR and electronic spectra of the complexes have been obtained. The thiosemicarbazones bind to the metal as dianionic ONS donor ligands in all the complexes except in [Ni(HL¹)₂] (1). In compound 1, the ligand is coordinated as a monoanionic (HL⁻) one. The magnetic susceptibility measurements indicate that all the complexes are mononuclear and are diamagnetic. The complexes were given the formulae [Ni(HL¹)₂] (1), [NiL¹py] (2), [NiL¹α-pic] (3), [NiL¹γ-pic] · H₂O (4), [NiL²py] (5) and [NiL²γ-pic] (6). The structures of compounds 2 and 3 have been solved by single crystal X-ray crystallography and were found to be distorted square planar in geometry with coordination of azomethine nitrogen, thiolato sulfur, phenolato oxygen and pyridyl nitrogen atoms.     

Thermal Studies of N-phenylethane-1,2-diamine Complexes of Nickel(II) in the Solid State

[NiL₃]X₂ (where L=N-phenylethane-1,2-diamine and X=I⁻ and ClO₄ ⁻), [NiL₂X₂] (X is Cl⁻, Br⁻, NCS⁻, 0.5SO₄ ²⁻ or 0.5SeO₄ ²⁻) and [NiL₂(H₂O)₂](NO₃)₂ have been synthesized from solution and their thermal study has been carried out in the solid phase. [NiL₂Cl₂] upon heating undergoes irreversible endothermic phase transition (142–152°C, ΔH=0.35 kJ mol⁻¹) without showing any visual colour change. This phase transition is assumed to be due to conformation changes of the diamine chelate rings. NiLCl₂ and NiL_2.5I₂ have been prepared pyrolytically from [NiL₂Cl₂] and [NiL₃]I₂ respectively in the solid state. [NiL₂(H₂O)₂](NO₃)₂ upon heating undergoes deaquation-anation reaction without showing any visual colour change. [NiL₂X₂] (X is Cl⁻, Br⁻, NCS⁻), [NiL₂(H₂O)₂](NO₃)₂ and [NiL₂(NO₃)₂] possess trans-octahedral configuration, whereas, [NiL₂X₂] (X is 0.5SO₄ ²⁻ or 0.5SeO₄ ²⁻) are having cis-octahedral configuration. Amongst the complexes, only NiLCl₂ shows unusually high (5.1 BM at 27°C) magnetic susceptibility value. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ni(II) complexes with 8-aminoquinoline derivatives

Some Ni(II) complexes with 5,7-dicloro-8-aminoquinoline (dcaq), 5,7-dibromo-8-aminoquinoline(dbaq) and 5,7-diiodo-8-aminoquinoline(diaq) are described. The compounds are of stoichiometry NiL₂X₂(L= dcaq, dbaq, diaq; X= NO^?₃ and L= dbaq; X= Cl^?, Br^?, I^?, NCS^?) and NiLX₂·H₂O(L= dcaq, diaq; X= Cl^?). The electronic spectra and magnetic susceptibility data at room temperature, are consistent with octahedral geometry for the Ni(II) in each compound. I.r. spectra show the presence of ionic and bridging nitrate groups in the compounds NiL₂(NO₃)₂(L= dcaq, dbaq, diaq) and we assign them polymeric structures. Polymeric structures with bridging chloride are proposed for the compounds NiLCl₂·H₂O(L= dcaq, diaq) and monomeric octahedral structures for NiL₂X₂(L= dbaq; X= Cl, Br, I, NCS).     

Diamine complexes of nickel(II) nitrate: X-ray single crystal structural analysis of trans-[NiL2(NO3)2] [L = 1-(2-aminoethyl)piperidine]

Trans-[NiL₂(H₂O)₂](NO₃)₂ (pale blue) (1), trans-[NiL₂(NO₃)₂] (dark blue) (2), [L = 1-(2-aminoethyl)piperidine] and trans-[NiL₂ (H₂O)₂](NO₃)₂ (blue) (3) [L = 1-(2-aminoethyl)pyrrolidine] have been prepared. Complexes (1) and (3) upon heating undergo deaquation-anation yielding trans-[NiL₂(NO₃)₂] (dark blue) (2) and cis-[NiL₂(NO₃)](NO₃) (blue) (3a), respectively. The X-ray single crystal structure of complex (2) has been determined.     

Syntheses and structures of two NiIICoIINiII complexes of macrocyclic ligands

Two new linear trinuclear complexes, [Co(NiL¹)₂(SCN)₂] (1) and [Co(NiL²)₂(H₂O)₂](ClO₄)₂?·?2C₂H₅OH (2), have been prepared by using Co(ClO₄)₂?·?6H₂O and two macrocyclic complex ligands NiL¹ and NiL². L¹ and L² are the doubly deprotonated forms of dimethyl 5,6,7,8,15,16-hexahydro-6,7-dioxodibenzo[1,4,8,11]tetraazabicyclo[12.4.0^15,16]13,18-dicarboxylate and dimethyl 5,6,7,8,15,16-hexahydro-15-methyl-6,7-dioxodibenzo[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate, respectively. X-ray single crystal analyses reveal the coordination geometries around Ni(II) in both 1 and 2 are identical and slightly distorted square planar with N₄ donors; all Ni–N bonds in the two complexes are very short. The Co(II) ions are at the centers of the trinuclear complexes and have distorted octahedral coordination geometries of O₄N₂ donors in 1 and an O₆ in 2. π?···?π interactions involving aromatic and non-aromatic π-systems join the trinuclear entities to form 2-D layers in the crystals of 1 and 2.     

Pyridine-type complexes of transition metal halides

Formation of nitrogen ligated complexes of types NiL₆X₂, NiL₄X₂, NiL₂X₂ and NiL₁X₂ (whereL=pyridine, 2-, 3- and 4-methyl-pyridine andX=F, Cl, Br, I) have been studied by traditional preparative methods, i.e. from solutions and by solid-gas phase chemisorption. Quaternary mixed complexes were obtained by chemisorption from heated intermediates. The complexes thus formed were further analysed by simultaneous TG-DTG-DTA. Effects of the ligands on stoichiometry and thermal properties of the complexes are discussed.     

Synthesis,characterization and structural assessment of nitrato,chloro, bromo,perchlorato, thiocyanato and sulphato mono-(benzoin thiosemicarbazonato) copper(II) complexes

Summary Some copper(II) complexes of the type Cu(HL)X·nH₂O (where H₂L = benzoin thiosemicarbazone; X=NO₃; Cl, Br, SCN, ClO₄ or 1/2SO₄; n=O–2) have been prepared and characterized. All complexes have tetragonally distorted octahedral stereochemistry except the sulphatocomplex which is square pyramidal. The i.r. spectra reveal that HL acts as a monobasic tridentate ligand coordinating through the azine group nitrogen atom, thiocarbonyl sulphur atom and hydroxylic oxygen atom while NO₃, Cl, Br and ClO₄ act as terminal monodentate ligands and SCN and SO₄ act as bidentate bridging ligands. The polycrystalline e.s.r. spectra suggest tetragonal symmetry for the copper(II) ion, involving a dx ²–y² ground state.     

Influence of complexing species on the extraction of trivalent actinides from lanthanides with CyMe<Subscript>4</Subscript>–BTBP: a theoretical study

We studied geometric and electronic structures as well as thermodynamic properties of complexes [M(CyMe₄–BTBP)₂(NO₃)]²⁺ and [M(CyMe₄–BTBP)₂]³⁺ with M?=?Am(III), Cm(III) and Ln(III) (La–Lu) theoretically. The actinide–nitrogen bonding is principally ionic with higher covalency in An–N bonds than in the Ln–N analogues. The selectivity towards An(III) over Ln(III) (La, Ce, Pr, Pm, Sm, Eu and Yb) is influenced by formed complexes to different extents by comparison of changes of Gibbs free energy of reaction, ΔΔG_Am/Ln, for formation of [AmL₂]³⁺/[LnL₂]³⁺, [AmL₂(NO₃)]²⁺/[LnL₂(NO₃)]²⁺, and [AmL₂(NO₃)]²⁺/[LnL₂]³⁺. The Am(III) selectivity is enhanced for [AmL₂(NO₃)]²⁺/[LnL₂]³⁺ over [AmL₂]³⁺/[LnL₂]³⁺.     

Nickel versus copper: enhanced antibacterial activity in a series of new nickel(II) Schiff base complexes

Five new Ni(II) Schiff base complexes [NiL^x(Solv)₂] denoted by NiL^x, x = 1–5, were synthesized and characterized. The Schiff base ligands were synthesized from the condensation of 5-bromo-2-hydroxy-3-nitrobenzaldehyde with different aliphatic and aromatic diamines. The X-ray crystal structure of NiL³ was determined. The ligands and complexes were tested as antibacterial agents against two gram(+) and two gram(?) human pathogenic bacteria. The complexes showed moderate antibacterial activity against both gram type bacteria. The new Ni(II) complexes showed enhanced antibacterial activity compared to the previously reported Cu(II) complexes of the same ligands.     

Synthesis, characterization and X-ray crystal structures of seven-coordinate pentagonal-bipyramidal zinc(II), cadmium(II) and tin(IV) complexes of a pentadentate N3S2 thiosemicarbazone

New complexes of the general formula, [M(H₂dap⁴NMetsc)(H₂O)₂](NO₃)₂·H₂O (M = Zn²⁺, Cd²⁺; H₂dap⁴NMetsc = 2,6-diacetylpyridinebis(⁴N-methylthiosemicarbazone) and [Sn((dap⁴NMetsc)X₂] (X = Ph, Cl and I) (dap⁴NMetsc = the doubly deprotonated form of 2,6-diacetylpyridine bis(⁴N-methylthiosemicarbazone) have been synthesized and structurally characterized by a variety of physico-chemical techniques. X-ray crystallographic structure determination shows that in the zinc and cadmium complexes, the bis(thiosemicarbazone) ligand coordinates as a neutral N₃S₂ pentadentate chelating agent through the two azomethine nitrogen atoms, the pyridine nitrogen atom and the two thione sulfur atoms. The N₃S₂ donors of the ligand occupy the equatorial plane and the two aqua ligands occupy the sixth and seventh axial positions of the seven-coordinated cadmium(II) and zinc(II) ions. In the tin(IV) complexes, however, the thiosemicarbazone is coordinated to the tin(IV) ion as a dinegatively charged pentadentate chelating agent via the pyridine nitrogen atom, the two azomethine nitrogen atoms and the two thiolate sulfur atoms. The two apical positions of the seven-coordinate tin(IV) ion are occupied by either phenyl, chlorido or iodido ligands. In each of the complexes, the overall geometry adopted by the metal ion may be considered as a distorted pentagonal-bipyramid.     

Complexation of Ni(II) with Benzoic,p-Methoxybenzoic,and Isonicotinic Acids Hydrazides in Aqueous Acetonitrile

Solvation and complexation of Ni(II) with benzoic (L¹), p-methoxybenzoic (L³), and isonicotinic (L) acids hydrazides in water and aqueous acetonitrile were studied. The coordination of acetonitrile with Ni(II) was qualitatively estimated, and the formation constant were determined for the complexes Ni(L¹)^{2 +}, Ni(L¹)2^{2 +}, Ni(L³)^{2 +}, Ni(L³)2^{2 +}, Ni(HL)^{3 +}, NiL^{2 +}, NiL(HL)^{3 +}, and NiL₂ ^{2 +}. The effects of dilution, ligand basicity, and ligand solvation on the stability of Ni(II) compounds with hydrazides of benzoic acid and its derivatives were demonstrated. The stability of the Ni(II) complexes with isonicotinic acid hydrazide is governed by dehydration of the metal ion, decrease in the donor power of the coordinating hydrazide fragment on protonation of the pyridine substituent L, formation of the intracomplex hydrogen bond between the protonated and deprotonated pyridine nitrogen atoms in NiL(HL)^{3 +}, and stacking interaction between the heterocycles in NiL₂ ^{2 +}.     

Ni(II) complexes of stereo-isomeric hexazamacrocyclic ligands derived from 2,6-diacetylpyridine

The nitrate and perchlorate Ni(II) complexes of the stereo-isomeric hexazamacrocyclic ligands L¹ (3,6,14,17,23,24-hexaazatricyclo[17.3.1.18,12]tetracosa-1(23),8,10,12(24),19,21-hexaene,2,7,13,18-tetramethyl) and L² (3,7,15,19,25,26-hexaazatricyclo[19.3.1.19,13]hexacosa-1(25),9,11,13(26),21,23-hexaene,2,8,14,20-tetramethyl) derived from 2,6-diacetylpyridine have been synthesized and characterized by microanalysis, LSI-MS, conductivity measurements, IR, UV–Vis spectroscopy and magnetic studies. Crystal structures of L¹·2H₂O as well as of the complexes [NiL¹](ClO₄₎₂$[{\text{NiL}}^1]({\text{ClO}}_4{)}_2$ and [NiL²](NO₃₎₂$[{\text{NiL}}^2]({\text{NO}}_3{)}_2$ have been determined. The X-ray studies show the presence of mononuclear endomacrocyclic complexes with the metal ion coordinated to all the nitrogen donor atoms from the macrocyclic framework in a N6 core. The geometry around the metal ions can be described as distorted octahedral. The nitrate and perchlorate anions do not coordinate to the metal ions, but they are involved in intermolecular interactions through hydrogen bonds to the amine groups of the macrocyclic ligands.     

Synthesis,crystal structure and biological activity of the nickel(II) complex of 2,6-diacetylpyridinedihydrazone

A complex of Ni^II with 2,6-diacetylpyridinedihydrazone (L) towards nickel(II) has been prepared and characterized by means of elemental analyses, IR, electronic spectra and single crystal X-ray analyses. [NiL₂](NO₃) was crystallized in the tetragonal space group P-4 21 c. The complex exhibits the expected coordination sphere with six nitrogen atoms coordinated to the central Ni^II with a deformation from pseudo-octahedral geometry. Antimicrobial activities of the ligand and its complex were investigated.     

Thermoanalytical study of selected transition bivalent metal complexes with 5-carbaldehyde-4-methylimidazole

To compare thermal stability of Co(II), Zn(II), and Cd(II) complexes with 4-CHO-5-MeIm, the two compounds of formula [MnL₂(NO₃)₂] and [NiL₃](NO₃)₂ have been prepared and structurally characterized. Elemental analysis and spectroscopic studies have confirmed a bidentate fashion of coordination of the ligand to Mn(II) and Ni(II) ions. IR and Raman spectra indicate that there are different coordination modes of the NO₃ ^? in compounds: non-coordinated and coordinated. The decomposition process of the studied complexes in nitrogen and argon (Ni(II) complex) atmosphere proceeds in three main stages, except Zn(II) complex, in temperature range 353?C1163?K. The final products of decomposition are CoO, MnO, Cd, ZnN₄, NiN₃. In addition, we have to admit that the different coordination mode of the NO₃ ^? ions in complexes: non-coordinated (in the (1), (4), and (5)) and coordinated (in the (2) and (3)) correlate with its thermal behavior. Thus, temperature ranges of its decompositions are observed: below 533?K and above 533?K, respectively. In Co(II), Mn(II), and Cd(II) complexes the fragments of N-donor atom-containing ligands decompose in the last stages, contrary to Zn(II) and Ni(II) compounds, in which metal ion surrounded by N atoms remains until the end. The course of pyrolysis and molecular structure of the complexes lead to the same conclusion about the strength of metal?Cligand bonds. On the basis of obtained results, it is concluded that the thermal stability of the studied compounds follows the order: (1)?<?(5)?<?(2)?<?(3)?<?(4).