Co-ordination of 1,4,7,10-tetraazacyclotridecane ([13]aneN4) to nickel(III). Crystal structure of [Ni([13]aneN4)Br2]Br

Abstract

The crystal structure of [Ni([13]aneN₄)Br₂]Br ([13]aneN₄= 1,4,7,10-tetraazacyclotridecane) has been determined by single-crystal X-ray diffraction: tetragonal, space group P4₂ with a= 7.8502(9), c= 12.464(2)Å and Z= 2. The Ni atom on the crystallographic two-fold axis is surrounded octahedrally by a square-planar array of four N atoms from the macrocycle with two bromide ions occupying the axial positions. The carbon atoms of the macrocycle are too disordered to be depicted because of the unexpected crystallographic symmetry. The tetragonal co-ordination geometry found in this complex is consistent with that proposed on the basis of the ESR spectrum in dimethyl sulphoxide. The correlation between the in-plane Ni–N and axial Ni–Br distances is discussed in terms of the size of the aperture in the cyclic ligand.