EPR Characterisation of Cu II Complexes of Poly(propylene imine) Dendromesogens: Using the Orienting Effect of a Magnetic Field

Liquid‐crystalline derivatives of poly(propylene imine) dendrimers of the 0th, 1st and 2nd generations, complexed with copper( II ) ions, were studied by EPR spectroscopy. The structures of copper( II ) complexes with different Cu II loadings x per dendrimer ligand L ( x =Cu/L) were determined. At the lowest concentration, the Cu II ions form monomeric complexes with approximately square‐planar N 2 O 2 coordination of both carbonyl oxygen and amido nitrogen atoms. At higher copper content, two kinds of Cu II complex sites with different geometries exist. The orienting effect of a high magnetic field was used to investigate the structure and magnetic properties of the copper( II ) complexes. This effect, for the first time in dendrimers, allowed the resolution of five nitrogen super‐hyperfine lines on g z components with the unusual coupling constant of a N z =35.9×10 −4 cm −1 . The combination of the magnetic parameters and the orienting effect indicates the presence of a monomeric complex with pseudotetrahedral N 2 O 2 coordination of the Cu II ion, as well as a “dimer” structure with fivefold coordination, presumably due to an N 3 O 2 environment. Higher copper loadings lead to increased exchange coupling between the complex sites.