No abstract

Novel four-coordinate copper(II) complexes of the type [CuL], L = N, N′-di-(4-hexadecyloxysalicylidene)-4-substituted(X)l,2-diamino-benzene (X = H, CH 3 , NO 2 ) were synthesised. The compounds were characterised by elemental analyses, Fourier transform infrared spectroscopy, 1 H, 13 C nuclear magnetic resonance, ultravioletvisible spectroscopy and fast atom bombardment mass spectrometry. The liquid crystalline properties were ascertained using polarised optical microscopy, differential scanning calorimetry and powder X-ray diffraction technique. The ligands are non-mesomorphic, but the complexes with methyl (CH 3 ) or no substituent on the aromatic spacer showed rectangular columnar (Col r ) mesophase and rectangular plastic columnar (Col rp ) phase, respectively. An antiparallel dimeric association of half-disc shaped molecule forming a disc-like arrangement in the mesophase is proposed on the basis of X-ray diffraction study. The complex with nitro (NO 2 ) substituent in the spacer linkage decomposes before melting precluding any mesomorphic study. The density functional theory calculations carried out using Gaussian 09 program at B3LYP level revealed distorted square planar geometry around the metal centre. The natural charges and electronic configuration of the atoms of the complexes and free ligand were evaluated by natural bond orbital analysis.

A series of new mononuclear multifunctional lanthanide(III)‐Schiff base complexes have been synthesized and characterized by elemental analyses, FTIR, 1H NMR and UV/Vis spectroscopy. Potentially tridentate, the Schiff‐base ligand is based on a ‘salicyldimine’ core with a long and flexible alkoxy group which coordinates to lanthanide ions in its zwitterionic form via the phenolic‐oxygen with the proton shifted to the imine‐nitrogen. The chelate nitrato groups complete a nine‐coordinate geometry. The ligand is non‐mesomorphic, while coordination to Ln3+ ion induces a liquid crystalline behavior. The complexes exhibited a thermally stable highly viscous partially bilayer smectic Ad phase in the 45‐135°C temperature range. The molecular organization of the complexes in the mesophase is conjectured to be based on a cylindrical‐like dimeric structure with the three alkoxy group pointing up and three pointing down assembling laterally into a lamellae. The Schiff base ligand is a blue light emitter exhibiting a broad emission maximum at 435 nm while the lanthanide complexes show an intense green emission. The Tb3+ complex, interestingly, also showed mesophase luminescence. The ligand and its complexes of La3+, Dy3+ and Yb3+ exhibited a significant second order non‐linear optical (NLO) activity representing the first example of lanthanidomesogens to exhibit such behaviour.