Professor Stephen Blundell

Abstract:

Magnetism in organic diradical ion salts prepared from the diradicals, pyridine-2,6-diylbis(nitronyl nitroxide) [(2,6-PYBNN)(center dot center dot)] and phenol-2,4-diylbis(nitronyl nitroxide) [(2,4-POBNN)(center dot center dot)], were investigated by using SQUID magnetometers. The diradical cation salt (2,6-PYBNN)Cl--+(-) shows intramolecular ferromagnetic (FM) interaction with the exchange coupling constant J/k = +9.0 K and intermolecular antiferromagnetic (AFM) interaction with the Weiss constant theta = -0.75 K in the low temperature phase below 4.5 K. Although the intramolecular FM interaction is close to that observed in the neutral diradical 2,6-PYBNN.., the intermolecular AFM interaction is significantly reduced from J'/k = -57 K due probably to the increase of intermolecular distances by the incorporation of Cl- ions into the salt. We also present and discuss the magnetic behavior in the diradical cation salt (2,6-PYBNN)center dot center dot+BF4- and the diradical anion salt. (C4H9)(4)N+(2,4-POBNN)(center dot center dot-). (c) 2005 Elsevier Ltd. All rights reserved.

Abstract:

We report temperature dependent millimetre-wave spectroscopic experiments on single crystals of the organic molecular magnet 2-benzimidazolyl nitronyl nitroxide, in the range 1.4-100 K. This organic radical shows quasi one-dimensional (1-d) ferromagnetic intermolecular interactions with the intrachain exchange coupling constant J/k(B) = +22 K and interchain coupling constant J'/k(B) = 0.24 K. The linewidth of the electron spin resonance at low temperatures was seen to be considerably broadened as compared to that at higher temperatures. This is consistent with the low dimensional behaviour of the linewidth predicted theoretically. We also see a shift in resonance field at low temperatures. We also present the results of angular dependence experiments carried out at temperatures of 1.4 and 50 K, and frequency dependence experiments at 1.4 and 50 K. (c) 2005 Elsevier Ltd. All rights reserved.