Importance of Transition Metal Complexes with Salen-Based Ligands: A Review

Salen-based Schiff base ligands and their transition metal complexes have a wide range of applications in various fields like catalysis, sensors, materials science and even medicine. A transition metal is an element with a partially-filled d subshell or the capacity to produce cations with an incomplete d subshell. Salen-type salicylaldimine Schiff bases are very common to the synthetic inorganic chemists as very useful ligands for the synthesis of various transition and non-transition metal complexes. It makes an important contribution to iron absorption and maintains health blood vessels, bones, nerves, and an effective immune system. These metal complexes were screened for their biological activities such as in vitro antibacterial and anti-oxidant activity. The Salenbased complexes are also crucial components or architectural motifs in recent detectors, nonlinear absorptional devices, solar cells and the development of bio-inorganic chemistry catalysis, electromagnetism and diagnostic imaging. The Salen- type ligands thus closely resemble metallo-proteins. A good quality of work has been reported on synthesis and structural investigation of different types of Schiff bases and their complexes. These compounds also find catalytic applications ranging from asymmetric epoxidation, solid phase extraction of metal ions, polymerization and for the preparation of ion selective electrodes. The modified electrodes were screened as electrocatalysts for the determination of some biological compounds, such as dopamine, catechol, cysteine and uric acid.