G. Cros

The non-template synthesis of novel non-symmetrical, tetradentate Schiff bases. Their nickel(II) and cobalt(III) complexes

Abstract Novel non-symmetrical, tetradentate Schiff bases have been obtained in a two-step process. In the first step, one mole of ethylene diamine is reacted with one mole of acetylacetone to afford a 1:1 condensation product, which is then reacted with one mole of either salicylaldehyde or 2-hydroxy-acetophenone to yield non-symmetrical diimines. The nickel(II) and and cobalt(III) complexes derived from these ligands have been prepared and characterized.

The syntheses, properties and crystal and molecular structures of the copper(II) and nickel(II) complexes of the non-symmetric schiff bases, derived from 1,2-diaminoethane, pentane-2,4-dione and 2-pyrollecarboxaldehyde

Abstract The synthesis of a non-symmetric Schiff base derived from 1,2-diaminoethane, pentane-2,4-dione and 2-pyrollecarboxaldehyde is described and the copper(II) and nickel(II) complexes are reported. The crystal structure of the nickel(II) complex is monoclinic, R = 0.0368, 1451 reflections: the crystal structure of the copper(II) complex is isomorphous, ( R = 0.0387, 1239 reflections). In both structures, the metals adopt square-planar coordination geometries and long intermolecular contacts lead to weak oligomerisation. The EPR spectra of the copper(II) complex is discussed and related to the structure.

Electrochemical study of some cobalt schiff base complexes and their methyl derivatives. Relation to the behaviour of the cobalt-carbon bond

SummaryTwo series of methyl and nonmethyl cobalt complexes involving closely related quadridentate Schiff bases have been investigated. The use of nonsymmetrical or substituted ligands allows the reduction potential of the cobalt centre to be gradually modified. The data thus obtained are considered in connection with the ability of the cobalt complexes to alkylate tin (IV).

Non-symmetrical Schiff base complexes. Experimental support to an intramolecular, non-symmetrical activation process and synthesis of a new type of tetraaza macrocyclic complexes

Abstract The ‘half-unit’ (AEH) obtained by reacting equimolar quantities of pentane-2,4-dione and diaminoethane may be used to produce non-symmetrical tetradentate Schiff base. The species under examination results from the condensation of an (AEH) unit with 3-(ethoxymethylene)-2,4-pentanedione. This ligand and its copper(II) and nickel(II) complexes display two carbonyl groups which, according to various physical probes, are very different; one is strongly affected by a COCH 3 substituent while the other (which is far remote from this substituent) is almost unaffected. However, both groups are amenable to condensation with ethylenediamine to yield a new type of macrocyclic complex. The properties of the related 13-acetyl-5,7-14-trimethyl-1,4,8,11-tetraazacyclotetradeca-4,6,12,14-tetraenato-(2−) copper(II) and nickel(II) are reported. It is well known that in a series of metal complexes involving macrocyclic ligands, the chemical behaviour and the physical properties depend strongly on the nature of the peripheral substituents on the chelate ring [1–3]. For instance, condensation of Schiff base complexes (M.A) (Fig. 1) with ethylenediamine only occurs if R 2 is an electron-withdrawing group such as -COOR or -COR, the resulting products being N 4 -macrocyclic complexes (M.A′ Ac [4]. Moreover, it has been demonstrated that these electron-withdrawing groups favour the reduction on the metal in agreement with a decrease of its electron density [5]. The influence of the substituents on electron distribution within the chelate ring has been studied by 13 C NMR and electronic spectroscopy [6]. A relationship between the chemical shifts of the C-2 and, to a lesser extent, C-3 nuclei and the ability of the Cue5fbO groups to react with ethylenediamine has also been reported [6]. All these studies are devoted to symmetrical molecules and the two Cue5fbO groups involved in the condensation process are identical. In this paper we present data obtained for non-symmetrical nickel(II) and copper(II) complexes belonging to the Fig. 1. Complexes with their abbreviations. (M.B) and (M.B′) types. The (M.B) complexes are expected to show two significantly different Cue5fbO groups and the attention has been focused on a comparative study of substituent effects in symmetrical and nonsymmetrical species. Various spectroscopies (IR, 1 H and 13 C NMR, mass, electronic and EPR) as well as electrochemical measurements have been used to characterize the complexes and to give materials for the comparison. The complexes of interest are illustrated in Fig. 1.

Technetium labeling of bi, tri and tetradentate ligands derived from 2-aminocyclopentene-1-dithiocarboxylic acid: Characterization and biodistribution of their oxo and nitrido 99mtechnetium complexes

We have synthesized and characterized seven ligands derived from 2-aminocyclopentene-1-dithiocarboxylic acid with different donor sets (SN2-, SNO2-, SNN2-, SNNO3- and SNNN3-) and different substituents on the sulfur moieties-SR (with R = H, CH3 or C2H5O(CH3)CH). With five of these ligands technetium nitrido complexes have been obtained with high yields (over 95%) using rather harsh conditions (pH = 1, temperature > or = 80 degrees C), whereas for technetium oxo complexes similar high yields were only obtained with two ligands but with mild conditions (pH = 7-8, temperature approximately equal to 50 degrees C). Changing an OH group for an NH2 has a drastic effect upon labeling yields. The possibility of complexing ligands as either oxo (TcO)3+ or nitrido (TcN)2+ derivatives increases the number of available labeled agents with different overall change and consequently with different biological behavior.

A new example of ligand-to-metal electron-transfer process : one-electron reduction products of nickel(II)-tetradentate schiff base complexes

Abstract The reduction of three nickel(III) complexes involving two symmetrical N,N′-ethylenebis (acetylacetoneiminato) and N,N′-ethylenebis (salicylideneiminato) and one non-symmetrical N,N′-ethylene (acetylacetoneiminatosalicylideneiminato) and Schiff bases has been investigated by electrochemistry and ESR spectroscopy. In all cases, exhaustive reduction results in the formation of nickel(I) complexes. However, ESR data support the formation of a nickel(II)-stabilized ligand radical species at the early stage of the reduction of the non-symmetrical Schiff base complex.

Synthesis and characterization of neutral oxorhenium(V) and nitridotechnetium(V) complexes with a tetradentate N2S2 unsaturated ligand derived from dithiocarboxylic acid

Abstract Neutral complexes of technetium(V) and rhenium(V) of the type TcN(L2) and ReO(L2)CI, where L2 corresponds to the dianionic form of the tetradentate N 2 S 2 ligand N , N ′-ethylene bis(methyl 2-aminocyclopentane-l-dithiocarboxylate), were prepared by substitution reaction on the starting materials 99 TcNCl 2 (PPh 3 ) 2 and ReOCl 3 (PPh 3 ) 2 , respectively. The complexes were characterized by elemental analysis, IR, NMR spectroscopy and conductimetry. The molecular and crystal structure of the nitrido complex TcN(L2) was determined by single-crystal X-ray diffraction technique (monoclinic P 2 1 / c , a = 13.380(6), b = 9.945(2), c = 15.839 A, β = 113.91(3)°). The electrochemical behaviour of the nitrido complex was investigated.

Halogen substituted quadridentate schiff bases, their nickel(II) and cobalt(III) complexes

SummaryElectrophilic substitutions have been performed on the methyne carbon of NiL and [CoL,2py]ClO4 [L=N,N′-bis(acetylacetone) ethylenediiminato-]. The effects of substituents (H, Cl, Br and I) on the electron distribution within the cobalt(III) complexes have been investigated through1H and13C n.m.r., i.r. spectroscopy and half-wave potential measurements

Synthesis, characterization and biodistribution of new 99mTc oxo and nitrido complexes with Bi- and tetradendate unsaturated NS and N2S2 Schiff bases derived from 2-aminocyclopentene-1-dithiocarboxylic acid as potential heart imaging agents

The synthesis, characterization and 99mTc labelling of unsaturated diamino dithiol ligands with methyl dithiocarboxylate functions: 2-aminocyclopentene-1-dithiocarboxylic methyl ester (H2L1), N,N-ethylene bis(methyl 2-aminocyclopentene-1-dithiocarboxylate) (H2L2) and N,N-propylene bis (methyl 2-aminocyclopentene-1-dithiocarboxylate) (H2L3) are described. Cationic oxo (Tc = O) and neutral nitrido (Tc = N) complexes were obtained. Biodistribution studies in rat showed a good heart uptake of 99mTcN-L2 (2% ID at 5 min) with a high heart-to-blood ratio (5.8 at 5 min), but this complex also exhibited high lung and liver uptake.

Unusual dinuclear copper(II) and nickel(II) complexes of a novel Schiff base deriving from 2-aminoethanol

Abstract It is generally accepted that copper(II) complexes involving 2-aminoethanol or a Schiff base deriving from this aminoalcohol display a tetranuclear structure with a Cu4O4 ‘cubane’ core. Using a Schiff base obtained by reacting 2′-aminoacetophenone with 2-aminoethanol, we have prepared copper(II) and nickel(II) complexes whose properties are fully consistent with a dinuclear structure. The copper complex is characterized by a low antiferromagnetic interaction.