Determination of the stability constants of some lanthanon complexes with 1-nitroso-2-naphthol, 2-nitroso-1-naphthol, and 3-nitroso-4-hydroxycoumarin

Potentiometric, spectrophotometric, conductimetric and thermodynamic studies on some transition metal complexes derived from 3-methyl-1-phenyl- and 1, 3-diphenyl-4-arylazo-5-pyrazolones

“…It is also interest to study the logβ 1 and logβ 2 values of the transition metal complexes with the investigated ligands (L1-L6) as a function of atomic number 1/r (the inverse of ionic radius) as well as EN (electronegativity) [28] of metal ions. In this investigation, it was found that the stability constants of the first raw transition metal complexes with the investigated ligands (L1-L6) (logβ values) are generally increase with decreasing ionic radius r (or increasing 1/r) and increase with increasing atomic number [29], also logβ increases with increasing electonegativity, this is because upon increasing electronegativity of the metal ions, the electronegativity difference between the metal atom and the donor atom of the ligand would expectedly associate with increase of covalent character of the metal-ligand bond. These relations are not linear and there are some exceptions from the mentioned observations because of the presence of steric effects and ionic bonds.…”

“…The semi linear correlation observed in this study demonstrates that factors which increase or decrease pK a of the ligand also affect the logK ML values for the metal ions in a parallel fashion. This means that substituent groups that tend to increase electron density on donor atom and hence tend to increase the coordination ability of the ligand increase logK ML , and also increase the value of pK a of the ionizable hydrogen [29]. The assumption here is that ligand basicity is directly related to ligand stability i.e., more stable complexes being formed from basic ligands [29].…”

“…This means that substituent groups that tend to increase electron density on donor atom and hence tend to increase the coordination ability of the ligand increase logK ML , and also increase the value of pK a of the ionizable hydrogen [29]. The assumption here is that ligand basicity is directly related to ligand stability i.e., more stable complexes being formed from basic ligands [29]. Such correlation cannot be generalized because of the presence of some exceptions from linearity and because this result was observed form the ligands and the metal ions used in this study only.…”