Push-Pull Metal Complexes with Unsymmetrically Substituted Salen-Type Ligands for NLO Applications

In the last few decades, the research in the nonlinear optical (NLO) field has received a strong push toward the synthesis and the study of new materials, especially inorganic and organometallic derivatives, due to the great possibility to modulate their electronic behaviour. Our research group has started a systematic study of metal complexes with tetradentate Schiff base ligands (‘salen’ analogues), that has led to the complete study and comprehension of the electronic and nonlinear optical features of unsymmetrical salen-type copper(II) complexes 1, substituted along the x-axis with electron-donor D and acceptor A groups.1 With the same template synthetic procedure, compounds 2 with chiral diamines (1,2-diaminocyclohexane and 1,2-diphenyl ethylendiamine) have been obtained and studied. The understanding of the role of the metal centre in such systems is quite important, due to its central position in the metallorganic framework. A template path for the synthesis of nickel(II) unsymmetrically substituted derivatives with 1,3-diaminopropane (tn) has been detected2 and used to synthesise compounds 3, and the results obtained will be presented. The monocondensation product of o-phen and 5-NO2-salicylaldehyde has allowed the synthesis of a new series of unsymmetrically substituted tetradentate Schiff base ligands. The results obtained on their metal complexes 4 will be outlined.