Preparation of 1,4,8,11-tetrakis(2-pyridylmethyl)-1,4,8,11-tetra-azacyclotetradecane (L1) and a binuclear complex with copper(II). X-Ray structure of [Cu2L1Br2][ClO4]2

Abstract

The 14-membered tetra-azamacrocyclic ligand 1,4,8,11-tetra-azacyclotetradecane has been functionalised at the four N atoms with pendant 2-pyridylmethyl groups to give a new potentially octadentate ligand, L¹. The binuclear copper(II) complex [Cu₂L¹Br₂][ClO₄]₂ has been isolated, and its structure determined by X-ray crystallography. The deep green crystals are monoclinic, space group P2₁/c, with a= 9.029(1), b= 21.120(5), c= 11.376(2)Å, β= 111.47(1)°, and Z= 2. The structure was solved by the heavy-atom method to a final R value of 0.037 for 2 264 reflections with I/σ(I) > 3.0. All eight N atoms are co-ordinated in an exo structure in which each copper atom is five-co-ordinate, bonding to a bromide ion and four N atoms (two from adjacent pyridyl groups and two from one of the NCH₂CH₂N portions of the macrocyclic ring). The Cu–Br bond length is 2.412(1)Å and Cu–N bond lengths are in the range 1.996(4)–2.147(4)Å. The Cu–Cu distance is 5.74(1)Å, and this together with the magnetic susceptibility at room temperature indicates that there is no appreciable interaction between the two copper centres.