Synthesis and characterization of a di-N-hydroxyethylated tetraaza macrocycle and its nickel(II) and copper(II) complexes: Crystal structure of the nickel(II) complex

The one-step reaction of 3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.0^7,12]docosane (L¹) with 2-bromoethanol produced the macrocycle 2,13-bis(2-hydroxyethyl)-5,16-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.0 ^7,12]docosane (L²) in which two 2-hydroxyethyl groups are appended. The nickel(II) and copper(II) complexes of L² have been prepared and characterized. The crystal structure of [NiL²][ClO₄]₂ shows that the complex is exactly centrosymmetric and the metal centre has a slightly distorted octahedral geometry with two oxygen atoms of the pendant arms at the axial positions. However, spectra and redox potentials of [CuL²][ClO₄]₂ indicate that the complex has a planar geometry without co-ordination of the pendant arms. The macrocycle L² reacts more slowly with copper(II) ion than does L¹ and the resulting complex dissociates very slowly even at low pH. Crystal data for [NiL²][ClO₄]₂: monoclinic, space group P2₁/n, a = 9.128(2), b = 18.141(3), c = 9.256(2) Å, β = 101.69(1)°, Z = 2, R = 0.057 and R′ = 0.060 for 1993 independent reflections with I > 3σ(I).