Structural and luminescence studies of nickel(ii) and copper(ii) complexes with (1R,2R)-cyclohexanediamine derived unsymmetric Schiff base

Abstract

Unsymmetrical Schiff base obtained by the condensation reaction of (1R,2R)(-)cyclohexanediamine with 2-hydroxybenzaldehyde and 2-hydroxynaphthaldehyde was used as a ligand for copper(II) and nickel(II). The ligand and complexes were characterized by circular dichroism (CD), UV-VIS, fluorescence, IR and (1)H (NOE diff), NOESY and (13)C NMR (ligand) spectra. The X-ray crystal structures solved for (1R,2R)(-)chxn(salH)(naftalH) and Cu(II)(1R,2R)(-)chxn(sal)(naftal) revealed tetrahedral distortion of coordination sphere in the solid phase. The [Cu(1R,2R)(-)chxn(sal)(naftal)]·0.5EtOH·1.25H(2)O complex crystallized in the monoclinic chiral C2 space group with two molecules in the asymmetric unit as well as disordered ethanol and water molecules. For both molecules Cu(II) ions were found in square-planar environments and adopts conformation described as "semi-open armed", because of distinctly oriented arms according to cyclohexane ring defined by three torsion angles. The thin layers of the ligands, copper(II) and nickel(II) complexes were deposited on Si(111) by a spin coating method and characterized with scanning electron microscopy SEM/EDS and fluorescence spectra. The ligand layers exhibit the most intensive fluorescence band at 498 nm, which can be assigned to emission transition π* → n of Schiff base ligand. For copper(II) layers the most intensive band from intraligand transition at 550 nm was observed. The highest intensity band was registered for the layer obtained when rotation speed was 1000 rpm and time 20 s. The nickel(II) complex layers fluorescence spectra exhibit an intensive band at 564 nm. The emission maxima of the copper(II) and nickel(II) complexes are shifted towards longer wavelength in comparison to the free ligand layers. CD spectra of the complexes in solution are characteristic for tetrahedral planar distortion of the chelate ring. The (1)H NMR NOE diff were measured and the position of the nearest hydrogen atoms in the cyclohexane and aromatic rings were discussed, suggesting the tetrahedral distortion of the central ion of the coordination sphere in solution.

Synthesis, characterization, crystal structure and predicting the second-order optical nonlinearity of a new dicobalt(III) complex with Schiff base ligand

“…These compounds form stable and variety complexes with the majority of transition metal ions that exhibit various electronic and structure characteristics [5][6][7][8][9]. Therefore, the research area containing the coordination compounds with azomethine ligands as main characters is widely expansive especially due to their potential interest roles in various interdisciplinary fields such as: structural features [10,11], efficient different catalytic processes in various organic reactions [12][13][14], models of the metal ion coordination sites in metalloproteins or enzymes at bioinorganic chemistry [15][16][17], magnetochemistry [18][19][20], corrosion inhibitors [21] and nonlinear optical materials [22][23][24]. Second-Order NLO organic materials such as Schiff base compounds have recently attracted attention owing to their potential applications in computers, optical communication and medical imaging [25,26].…”

Structural Variety of Cobalt(II), Nickel(II), Zinc(II), and Cadmium(II) Complexes with 4,4′‐Azopyridine: Synthesis, Structure and Luminescence Properties

“…Metals such as Ni 2+ , Cu 2+ , and Co 2+ usually quench organic ligand luminescence; this is in contrast to the Zn 2+ and Cd 2+ ions, for which the effect is not present . As depicted in Figure , upon excitation at approximately λ =370 nm, two strong emission bands are observed at λ =466 and 494 nm with a weak emission band at λ =570 nm in azpy.…”

Copper(II) Schiff base complexes and their mixed thin layers with ZnO nanoparticles

“…Previously, copper(II) and nickel(II) complexes with optically active Schiff bases derived from (1R, 2R)(-)cyclohexanediamine or 2-(2-aminoethyl)pyridine were deposited by us on silicon or glass using the spin coating method. [21][22][23] The obtained thin materials exhibited fluorescence, which depends on the spin coating parameters and the molecular structure of the complexes.…”