Cold and Liquid Crystal Properties of Square‐Planar Copper(II) Versus Nickel(II)‐ Iminophenolate/Naphthalen‐2‐Olate Schiff Base Complexes
Imdadul Haque, Mohammed Enamullah, Amina Khan Resma, Nisat Taslum Jhumur, Dennis Woschko, Abdulrahman Mohabbat, Jan van Leusen, Paul Kögerler, Christoph Janiak
Abstract
Abstract Reaction of the phenolate or naphthalen‐2‐olate based Schiff base ligands, ( E )‐1‐((2‐ethylphenylimino)methyl)phenol (HL1) or ( E )‐1‐((2‐ethylphenylimino)methyl)naphthalen‐2‐ol (HL2) with nickel(II) and copper(II) acetate provides the complexes bis[( E )‐1‐((2‐ethylphenylimino)methyl)phenolato‐ĸ 2 N,O]Ni/Cu(II), [Ni(L1) 2 ] ( 1 ) and [Cu(L1) 2 ] ( 2 ), or bis[( E )‐1‐((2‐ethylphenylimino)methyl)naphthalen‐2‐olato‐ĸ 2 N,O]Ni/Cu(II), [Ni(L2) 2 ] ( 3 ) and [Cu(L2) 2 ] ( 4 ), respectively. Single crystal X‐ray structure determinations for 1 , 3 and 4 reveal N 2 ,O 2 ‐metal coordination of two chelating Schiff base ligands in a square‐planar geometry. Powder X‐ray diffractograms confirm the phase purity of the bulk microcrystalline samples. Thermal analyses by differential scanning calorimetry (DSC) and polarized light microscopic (PLM) indicate the copper(II) complexes to exhibit cold crystal ( 2 ) and liquid crystal ( 4 ) property. Cyclic voltammograms suggest an irreversible electrochemical process with two one electron charge transfer processes in N,N ‐dimethylformamide. Variable temperature magnetic measurements at the solid‐state prove the diamagnetic nature of the low‐spin Ni 2+ centres in 1 or 3 , as expected from the square‐planar coordination geometry with rather strong ligands. The complexes expose medium level of antioxidant activity in methanol. Optimized geometry and excited state property by DFT/TD‐DFT correspond well to the experimental results of the electronic and molecular structure at the ground state.