Synthesis, crystal structures and electronic properties of Schiff base nickel (II) complexes: Towards solvatochromism induced by a photochromic solute

• DOI: 10.1016/j.poly.2005.06.019
• Publication Date: 2005-08-04T19:54:58Z
• Authors: Takashiro Akitsu; Yasuaki Einaga
• Keywords: Solvatochromism; Coordination geometry; Bathochromic shift

Abstract Two new mononuclear nickel (II) complexes incorporating Schiff base ligands, bis(N-R-1-phenylethyl- or N-2-propyl-3,5-dichlorosalicydenaminato)nickel (II), have been synthesized and characterized. The former chiral brown paramagnetic complex adopts a compressed tetrahedral [NiN2O2] coordination geometry of Λ(R,R) absolute configuration with the coordination bond angles of N–Ni–N = 116.3(2)° and O–Ni–O = 141.4(2)°. On the other hand, the latter green diamagnetic complex adopts a square planar trans-[NiN2O2] coordination geometry. It is revealed that flexible distortion of the [NiN2O2] coordination environment and the overall dipole moment of the complexes are affected by both electronic withdrawing Cl-substituents and steric factors of the ligands. A structural phase transition occurs by heating in the solid state for both complexes. Negative solvatochromism relating to d–d and π–π* transitions can be observed, depending on the polarity of the solvents in which these complexes are dissolved. Furthermore, we have attempted to design a supramolecular solvatochromism system induced by a photochromic solute, that is a CHCl3 solution of the chiral Ni(II) complex and polar 4-hydroxyazobenzene solute. After UV light irradiation, we have successfully observed slight spectral changes of the π–π* bands in absorption and CD spectra due to conformational change of the R-1-phenylethylamine moieties of the chiral ligands.