Copper(II) Complexes of Substituted Macrobicyclic Hexaamines

Abstract

The hexaamine complexes [M{(NH3)2sar}]4+ and [M{(NMe3)2sar}]4+ (M = Cu(II), Zn(II); sar = 3,6,10,13,16,−19-hexaazabicyclo[6.6.6]icosane) have been synthesized and characterized both spectroscopically and structurally. X-ray crystal structural analyses of [Cu{(NH3)2sar}](NO3)4·H2O (monoclinic, P21, a 12.311(3) Å, b 12.338(4) Å, c 8.574(3) Å, β 93.91(3)·, Z = 2), [Zn{(NH3)2sar}](N03)4·H2O (monoclinic, P21 a 12.365(4) Å, b 12.396(7) Å, c 8.587(4) Å, β 94.13(3)·, Z = 2), [Cu{(NMe3)2sar}](ClO4)4 (hexagonal P62c, a 8.689(2) Å, c 27.927(2) Å, Z = 2), and [Zn{(NMe3)2sar}](ClO4)4 (hexagonal, P62c, a 8.669(5) Å, c 27.998(5) Å, Z = 2) are reported. Visible-near-infrared absorption, circular dichroism, magnetic circular dichroism, and electron paramagnetic resonance spectroscopic studies reveal distorted CuN6 chromophores. Trigonal’distortions arise from steric requirements of the ligands, whereas tetragonal distortions result from Jahn-Teller coupling in the Cu(II) complexes. X-ray crystallographic studies of these copper(II) complexes revealed partially averaged ([Cu{(NH3)2sar}]4+) and completely averaged ([Cu{(NMe3)2sar}]4+) geometries as a result of both static disorder and dynamic processes throughout each lattice. Partial resolution of [Cu{(NMe3)2sar}]4+ into its enantiomeric forms was achieved to give the first stable chiral molecule where Cu(II) is the stereogenic atom. In the absence of Jahn-Teller coupling characteristic of their Cu(II) relatives, the analogous Zn(II) complexes exhibited high-symmetry structures both in solution and in the solid state. Show more