π–π interaction leading to an inversion-symmetric complex pair of Λ- and Δ-bis[N-2-(R-pyridyl)-2-oxo-1-naphthaldiminato-κ2N,O]zinc(II)

Abstract

The Schiff base ligands N-2-(R-pyridyl)-2-hydroxy-1-naphthaldimine (HL) react with the zinc(II) nitrate or acetate to give the Λ- and Δ-bis[N-2-(R-pyridyl)-2-oxo-1-naphthaldiminato-κ2N,O]zinc(II), [Zn(L)2] {R = H (1), 4/6-CH3 (2/3)}. EI-mass spectra show the molecular ion peaks at 558 (1) and 586 (2 or 3). Molecular structure determination for 2·0.5CH2Cl2 crystal reveals that two molecules of the N^O-chelate ligands form a tetrahedral N2O2-coordination sphere around the zinc atom, in which one of the pyridyl-N atom is located towards the metal atom at a close contact ([Zn1…N2] = 2.674 Å). Packing analysis explores that one of the Zn-chelate ring metallacycles forms a reciprocal and rather strong π–π interaction (Cg⋯g = 3.517 Å) with the pyridyl ring of an adjacent molecule and vice versa, and results in an inversion-symmetric complex pair with opposite Λ- and Δ-configurations at the metal centre. The packing analysis is further supported by quantitative analysis of intermolecular interactions with the Hirshfeld surface. The optimized structure and excitation state properties by DFT/TDDFT support the solid state molecular structure and electronic spectra in solution, respectively.