A new bis(1-naphthylimino)acenaphthene compound and its Pd(II) and Zn(II) complexes: Synthesis, characterization, solid-state structures and density functional theory studies on the syn and anti isomers

A new rigid bidentate ligand, bis(1-naphthylimino)acenaphthene, L1, and its Zn(II) and Pd(II) complexes [ZnCl₂(L1)], 1, and [PdCl ₂(L1)], 2, were synthesized. L1 was prepared by the "template method", reacting 1-naphthyl amine and acenaphthenequinone in the presence of ZnCl₂, giving 1, which was further demetallated. Reaction of 1-naphthyl amine with acenaphthenequinone and PdCl₂ afforded dichloride bis(1-naphthyl)acenaphthenequinonediimine palladium, 2. L1, 1, and 2 were obtained as a mixture of syn and anti isomers. Compound 2 was also obtained by the reaction of PdCl₂ activated by refluxing it in acetonitrile followed by the addition of L1; by this route also a mixture of syn and anti isomers was obtained, but at a different rate. The solid-state structures of L1 and the anti isomer of compound 2 have been determined by single-crystal X-ray diffraction. All compounds have been characterized by elemental analyses; matrix-assisted laser desorption ionization-time-of-flight-mass spectrometry; IR; UV-vis; ¹H, ¹³C, and ¹H-¹H correlation spectroscopy; ¹H-¹³C heteronuclear single quantum coherence; ¹H-¹³C heteronuclear single quantum coherence-total correlation spectroscopy; and ¹H-¹H nuclear Overhauser effect spectrometry NMR spectroscopies when applied. Density functional theory studies showed that both conformers for [PdCl ₂(BIAN)] are isoenergetic, and they can both be obtained experimentally. However, we can predict that the isomerization process is not available in a square-planar complex, but it is possible for the free ligand. The molecular geometry is very similar in both isomers, and only different orientations for naphthyl groups can be expected.