Nickel(II), copper(II), and zinc(II) complexes of penta-azamacrocyclic ligands. Crystal and molecular structure of 3,6,9,12-tetramethyl-3,6,9,12,18-penta-azabicyclo[12.3.1]octadeca-1(18),14,16-trienezinc(II) perchlorate

Abstract

The three related penta-azamacrocyclic ligands 6,9-dimethyl-2,13-dioxo-3,6,9,12,18-penta-azabicyclo[12.3.1]octadeca-1(18),14,16-triene (L¹), 6,9-dimethyl-3,6,9,12,18-penta-azabicyclo[12.3.1]octadeca-1 (18),14,16-triene (L²), and 3,6,9,12-tetramethyl-3,6,9,12,18-penta-azabicyclo[12.3.1]octadeca-1(18),14,16-triene (L³), have been prepared. The complexes [M(L)(dmso)][ClO₄]₂(dmso = dimethyl sulphoxide; L = L², M = Ni or Zn; L = L³, M = Ni) and [M(L)][ClO₄]₂(L = L², M = Cu; L = L³, M = Cu or Zn) have been isolated. The Ni²⁺ complexes are high-spin and six-co-ordinate, and the Cu²⁺ complexes five-co-ordinate. ¹³C N.m.r. spectroscopy shows [Zn(L²)(dmso)][ClO₄]₂ to be a 2 : 1 mixture of two species, one symmetric and the other asymmetric, whilst in [Zn(L³)][ClO₄]₂ only ca. 10% of the asymmetric species is present in nitromethane solution. X-Ray crystallography has been used to dermine the structure of the symmetric isomer of [Zn(L³)][ClO₄]₂{R= 0.039 for 1 816 observed [I/σ(I) 3.0] diffractometer collected reflections}; it reveals distorted trigonal-bipyramidal geometry about the zinc ion, and an approximate C₂ rotation axis passing through the zinc and pyridine N atoms, and bisectinig the macrocyclic C–C bond furthest removed from the pyridine ring [Zn–N 1.999(4)–2.252(5)Å].