Structural studies on co-ordinated macrocyclic ligands. Part III. Preparations and crystal structure analyses of salts of the nickel(II) complex C-rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane, [Ni(tetb)]2+, in the α-, β-, and γ-configurations

Abstract

The preparations and X-ray structural analyses of three configurational isomers of the [Ni(tetb)]²⁺ complex cation are described: [Ni(α-tetb)](ClO₄)₂, a= 19·298(9), b= 17·34(1), c= 14·078(6)Å, space group Pbca; (Ni)(β-tetb)ZnCl₄,H₂O, a= 19·442(8), b= 9·926(4), c= 12·657(7)Å, space group Pna2₁: [Ni(γ-tetb)](ClO₄)₂, a= 17·08(2), b= 9·01(1). c= 8·19(1)Å,β= 107·1(2)°, space group P2₁/a. The structures of the α- and β-isomer were solved from diffractometer data and of the γ-isomer from photographic data by the heavy-atom method. The structures were refined by least-squares techniques to R 0·071 (α,1 536 reflections), 0·039 (β, 1698 reflections), and 0·075 (γ, 1184 reflections). All are co-ordinatively planar and thus strained with respect to the preferred conformation attained by co-ordination of the ligand to adjacent octahedral sites. The strain induced in the macrocycle is particularly manifest in the α-isomer in the distortion of both six-membered chelate rings, in the β-isomer by the distortion of the five-membered rings, and in the γ-isomer by distortion of just one six-membered ring. Details of these deviations from preferred geometry are presented and discussed.