Understanding More on the Coordination Nature of a Series of Lanthanum Complexes from Schiff Bases of Salicylaldehyde Origin by ¹H NMR Investigations

Lanthanum is one among in the longest lanthanide series of the periodic table and it has been grouped as a light rare earth element. Among the series, La³⁺ and Lu³⁺ are diamagnetic due to their non and full occupancy of 4f orbital in addition to the empty of 5d and 6s orbital. The NMR investigation to understand the coordination nature on lanthanum complex can be a prototype for the rest complexes in the series, as the others will have paramagnetically shifted broadened NMR spectra.

All the Schiff base ligands in the present study were synthesised by the condensation reactions of different primary amines and aldehydes of salicylaldehyde origin. A common protocol has been applied for the preparation of all complexes 1–4.

In addition to the ¹HNMR analysis, various physico-chemical methods were used to confirm the coordination nature of the Schiff base ligands to La³⁺ such as elemental analysis, conductance measurement, IR, UV-Vis spectra. The complexes studied are of the formulae, [La(L1)₂Cl₃] (1), [La(L2)₂Cl] (2), [La(L3)₂Cl](3) and [La(L4)₂Cl] (4).

Four novel lanthanum chloride complexes derived from Schiff bases of salicyladehyde derivatives have been synthesised and characterised. In addition to various physico-chemical studies, the coordination of the Schiff base ligands to La³⁺ is further confirmed by comparing ¹H NMR spectra of both the ligands and the lanthanum complexes. This study is very significant and relevant and serve as prototype for other complexes in the lanthanide series, as those result paramagnetically shifted broadened NMR spectra. In nutshell the present study shed light in understanding the coordination nature of lanthanides by NMR spectra, which is useful for the researchers working in the chemistry of lanthanides.