A barium dithiocyanate complex with an unusual macrocycle containing pendant arms, the amine precursor, and related copper(II) diperchlorate complexes: synthesis and structure

Abstract

The ligand 1-(p-nitrobenzylideneaminoethyl)-2-(p-nitrophenyl)imidazolidine (L¹) was synthesized by condensation of p-nitrobenzaldehyde and diethylenetriamine. Reaction of L¹ with 2-chloromethylpyridine yielded 1-(p-nitrobenzylideneaminoethyl)-2-(p-nitrophenyl)-3-(2′- pyridylmethyl) imidazolidine (L²), which by hydrolysis gave 7-(2′-pyridyl)-3,6-diazaheptylamine (L³). Crystals of L² are monoclinic, space group P2₁/_n, with a= 21.050(5), b= 7.935(6), c= 13.529(6)Å, and β= 94.01 (3)°. The structure, determined by X-ray crystallography, was refined to a final R of 0.054 based on 2 646 observed reflections, The molecule shows the expected imidazolidine ring with normal bond lengths and angles. The behaviour in solution and the stereospecific assignments for the methylene protons of L² were studied by ¹H n.m.r. spectroscopy. The reaction of the polyamine L³ with Cu(ClO₄)₂ produced [CuL³(ClO₄)₂]. Crystals are orthorhombic, space group P2₁2₁2₁, with a= 14.295(6), b= 13.143(6), and c= 9.068(6)Å. The structure was determined by X-ray crystallography and refined to a final R of 0.079 based on 1 068 observed reflections. The quadridentate ligand is equatorially bonded to Cu²⁺ through the N atoms. Two axial Cu ⋯ O contacts with the ClO₄^– anions complete the tetragonally elongated octahedral environment around the copper ion. Reaction of L³ with 4-chloro-2,6-diformylphenol in the presence of Ba(SCN)₂ gave a macrocyclic complex [BaL⁴(SCN)₂]. Crystals are orthorhombic, space group Pbcn, with a= 15.759(6), b= 14.124(6), and c= 19.393(5)Å. The structure was determined by X-ray crystallography and refined to a final R of 0.075 based on 1 270 observed reflections. The neutral macrocycle is co-ordinated to the Ba²⁺ ion through four N and two O atoms. Two SCN^– ions complete the co-ordination polyhedron around the metal. The Ba²⁺ ion lies on a crystallographic two-fold axis so that the molecular symmetry is C2.