In this study, three new immobilized Schiff bases and their Co(II), Cu(II) and Ni(II) metal complexes have been prepared.
The ligands silica-Si[N-(3-propyl)2,4-dihydroxybenzaldimine] (1) H2L, silica-Si[N-(3-propyl)4-methylsalicylaldimine-3-methoxy] (2) HL and silica-Si[N-(3-propyl)2-pyridinecarboxyaldimine] (3)
L have bidentate characters. Therefore, the complexes are the mononuclear. Ligands and metal complexes were characterized
by FTIR, AAS and thermoanalytical techniques. On the basis of analytical data and IR studies, a 1:1 metal to ligand stoichiometry
has been suggested. TG and DTA results showed that these ligands and complexes had good thermal stability. The heat capacities
of ligands were reported in the temperature range 273–363 K as no thermal anomaly was found in this temperature range.
Authors:M. Thankamony, B. Sindhu Kumari, G. Rijulal, and K. Mohanan
Condensation of 2-amino-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene with carbonyl compounds such as isatin, o-hydroxyacetophenone or benzoin in 1:1 ratio in ethanol medium yielded three distinctly different heterocyclic Schiff bases
viz. 2-(N-indole-2-one)amino-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene (ISAT), 2-(N-o-hydroxyacetophenone)amino- 3-carboxyethyl-4,5,6,7-tetrahydro-benzo[b]thiophene (HAAT) or 2-(N-benzoin)amino-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene
(HBAT) respectively. These ligands formed well defined complexes with lanthanum(III) chloride under suitable conditions.
The ligands and the complexes have been characterized on the basis of elemental analyses, molar conductance measurements,
UV-visible, IR and proton NMR spectral studies. Kinetics and mechanism of the thermal decomposition of the ligands and the
metal complexes have been studied using non-isothermal thermogravimetry. Kinetic parameters were calculated for each step
of the decomposition reactions using Coats-Redfern equation. The rate controlling process for all the ligands and complexes
is random nucleation with the formation of one nucleus on each particle (Mampel equation). Relative thermal stabilities of
the ligands and the metal complexes have been compared.
In order to evidence the ligand influence on the thermal stability for Co(II) complex combinations, we have synthesized five
complex combinations of this metal with Schiff bases obtained by condensation of ethylenediamine with acetylacetone and benzoylacetone;
phenylenediamine with benzoylacetone and also anthranilic acid with benzaldehyde.
Authors:H. Abdel-Fattah, A. El-Ansary, and N. Abdel-Kader
Several new complexes of Schiff bases ligands H4La and H4Lb with transition metal ions such as Cr(III), Fe(III), Co(II) and Zn(II) are synthesized. Elemental analysis, infrared, UV–Vis
and thermal analysis, as well as conductivity and magnetic susceptibility measurements are used to elucidate the structure
of the newly prepared metal complexes. A square planar geometry is suggested for Zn(II) complexes, while an octahedral geometry
suggested for the Cr(III), Fe(III) and Co(II) complexes. The thermal decomposition of complexes was found to be first order
reaction and the thermodynamic parameters corresponding to the different decomposition steps were reported.
Potentiometric studies on Schiff bases derived from5,7-dihydroxy-6-formyl-2-methylbenzopyran- 4-one were carried out at different
ionic strengths (0.02, 0.04, 0.06, 0.10 and 0.14 M NaCl), at different temperatures (25, 35, 45 and55C) and in ethanol-water
media of varying compositions (60, 70, 80 and 90% v/v). The ionization constants of the Schiff bases were investigated in
the presence of different organic solvents (70% v/v), e.g. methanol, ethanol, n-propanol, isopropanol, acetone, DMSO and DMF-water
media. The thermodynamic parameters (ΔG, ΔH and ΔS) were also calculated.
Authors:Irina Cârlescu, Gabriela Lisa, and D. Scutaru
Taking into account the importance of thermal stability in the liquid crystals field, the study presents the thermal behavior
of some ferrocene containing Schiff bases. Some other kinetic characteristics, such as reaction order (n), activation energy (Ea) and pre-exponential factor (lnA) have been also evaluated. The thermal stability series of Schiff bases was established analysis associated with three parameters
(Td, Tmax, Ea) is: S6<S4<S3<S5<S1<S2.
The thermal decomposition using TG, DTG and DTA, of seven complexes of the types Bu2SnL(I) and Bu2SnL(II) (where H2L(I)=Schiff base derived from acetylacetone and glycine [H2L-1(I)] or L-leucine [H2L-4(I)] or methionine [H2L-5(I)] or phenylglycine [H2L-6(I)]; H2L(II)=Schiff base derived from o-hydroxynaphthaldehyde and β-alanine [H2L-2(II)] or DL-valine [H2L-3(II)] or L-leucine [H2L-4(II)] is shown to fall into one of two categories, viz, (1) Bu2SnL(I) complexes that decompose without melting to give SnO as the final tin containing product, (2) Bu2SnL(II) complexes that melt and then decompose to give SnO. Mathematical analysis of TG data using Coats-Redfern equation,
Horowitz-Metzger equation, and Fuoss method shows that the first order kinetics is applicable in all the complexes except
Bu2SnL-2(II). Kinetic parameters such as the energy and entropy of activation and pre-exponential factor are reported.
New cadmium complexes of the salicylidene-2-amino-thiophenol (I) and 3-methoxysalicylidene-2-amino-thiophenol (II) Schiff bases have been prepared and characterized by elemental analyses, IR, 1H-NMR spectra, conductimetric and thermogravimetric analyses. The results suggested that the Schiff bases are bivalent anions with tridentate ONS donors derived from the phenolic oxygen azomethine nitrogen and thiophenolic sulphur. The formulae are found to be [MLH2O] and [ML2]for the 1:1 and 1:2 non-electrolytic complexes, respectively. The thermal decomposition of the complexes follows first order kinetics and the thermodynamic parameters of the decomposition are reported.
Dianionic tridentate O, N, S Schiff bases derived from salicylaldehyde and 2-mercaptoamines react with Tc/V/ gluconate to form radiochemically pure neutral Tc chelates. The existence of lipophilic Tc complexes could be proved by high voltage electrophoresis, thin layer chromatography and octanol/water partition coefficients.