Synthesis and aggregation phenomena of multifunctional Schiff bases and Ni(II) complexes: an X-ray investigation

Multifunctional Schiff base ligands Ln, namely the tetradentate N,N′-bis[2-hydroxy-5-(azopyridine)benzylidene]propylendiamine and the bidentate N-dodecyl-5-(azopyridine)salicylaldimine, both containing a flexible azo spacer, a metallation site and a terminal pyridine group, were synthetised and fully characterised. Mesogenic structures, analysed by polarised optical microscopy, DSC and powder X-ray diffraction, were obtained from self-assembly of the mono or bifunctional hydrogen-bond acceptors Ln with carboxylic acid donors. Ni(II) mono and bis-chelate, four- and six-coordinated, Ln derivatives were synthetised. The octahedral structure of the [Ni(py)2(L2)2] complex was confirmed by single crystal X-ray analysis. H-bonded self-assembly of Ni(II) complexes and carboxylic acids results in the formation of supramolecular networks whose structure and thermal stability were studied by DSC and powder X-ray diffraction analysis at variable temperatures.