An X-ray structural and thermodynamic investigation of the blue and red forms of (C-meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane)copper(II) perchlorate

Abstract

Copper(II) forms two products with C-meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane (L¹), a red and a blue complex. The crystal structures of both complexes (as perchlorates) have been determined. The red complex [Monoclinic, space group P2₁/c, a= 8.47(1), b= 9.26(1), c= 16.61 (2)Å, β= 112.3(3)°] has been solved by heavy-atom methods and refined to R= 0.048. It contains tetragonally distorted octahedral coordination for the copper atom (Cu–N 2.02, 2.06; Cu–O 2.59 Å). The blue complex [Monoclinic, P2₁, a= 8.71 (1), b= 15.68(2), c= 9.44(1)Å, β= 107.98(2)°] is pseudosymmetric and could not be completely refined (R= 0.22). It is likely that it is also octahedral, the main difference from the red complex being the inversion of the chiral nitrogen atom at N(8). The enthalpy difference between the two complexes has been determined (14.9 kJ mol^–1) and compared to the difference in stability constants. Thermodynamic, conductimetric, and spectral data are considered in the light of the likely structures for both complexes.