PMR Studies of the Phase Transition in N,N,N′,N′-Tetramethyl-p-phenylenediamine (Wurster’s Blue) Perchlorate

The powder PMR spectra of [TMPD]+(ClO4)− were recorded in the temperature range 110–300 K. The spectra observed above 140 K consist of two widely separated simple absorption curves of intensity ratio approximately equal to 3 : 1. Spin densities on the carbon and nitrogen atoms of the cation radical were evaluated from the observed field shift ascribable to the Fermi contact interaction. The spin density distribution of the radical ion changes at the transition temperature of 189 K.