Studies on lanthanide(III) complexes with-(3-coumarinyl)imidazo[1,2-a] pyridine

New lanthanide(III) complexes with 2-(3-coumarinyl) imidazol[1, 2-a]pyridine (CIP) having the general formula [Ln(CIP)2X2]X.nH2O, (Ln La, Ce, Nd, Sm, Gd, Dy and Y; X = NO3-1,Cl-1 and n = 3,6) have been prepared and characterized by elemental analyses, conductance measurements, magnetic susceptibilities, spectroscopic (electronic, IR, and 1H NMR) studies and thermal methods. Molar conductance studies indicate 1:1 electrolytic behaviour for these complexes. IR spectra indicate that CIP acts as a neutral bidentate ligand. TG and DTA studies of Nd(III) and Y(III) complexes indicate that they are stable up to 70 degC and contain lattice held water molecules. The activation energy (Ea), pre-exponential factor (A) and entropy of activation (ΔS) for the thermal decomposition of the Nd(III) complex have been computed by the Coats-Redfern equations using the least-square method for each step of decomposition. The activation energy of the thermal degradation process of Nd(III) is in the range of 4-53 kJ mol-1, which indicates that the metal-ligand bond is very weak. This indicates that the ligands are loosely bound to the metal ion through electrostatic forces, because 4∫ electrons shielded by the 5S2-P6 octet are not available for covalent bonding. The negative values of the entropy of activation indicate that the activated complex has a more ordered structure than the reactants which might be possible through chemisorption of oxygen and other decomposition products. (author)