High pressure ESR and other complementary studies of copper trimers with the quartet spin ground state

Abstract

The intriguing, earlier observed, temperature shift of the X-band ESR magnetic field H res was studied for powder samples of linear Cu 3EtBz·2MeOH and Cu 3BuNaEs·2MeOH trimeric Cu(II) complexes. For Cu 3BuNaEs·2MeOH, H res changes dramatically at ∼100 K, where a crystallographic phase transition was found by X-ray diffraction. For Cu 3EtBz·2MeOH, ESR measurements were performed under high pressure. It was observed that H res decreases with increasing pressure but the linewidth increases. Far-infrared absorption measurements were performed as a function of temperature for Cu 3EtBz·2MeOH and Cu 3BuNaEs·2MeOH. No clear change of vibration frequencies with temperature was observed. These results agree with the earlier interpretation that the temperature shift of H res is caused by the thermal averaging of ESR lines due to the short spin-lattice relaxation time.