Magnetism of novel organic heterospin composite systems in supramolecular complexes of nitronyl nitroxide

The authors have shown from theoretical calculations that a one-dimensional molecular assemblage composed of ground-state singlet biradicals and S = 1/2 monoradicals has three kinds of ground states; two with seemingly ferrimagnetic spin alignments and one with a spinless (diamagnetic) state. The energy preference of the three states depends on the relative ratios of the intra- and intermolecular magnetic interactions. This gives a quantum switching device, in which a conversion of the spin state is controlled by external perturbation such as pressure and magnetic field. As a model system for the magnetic switching device, we have designed and synthesized organic coordination compound of an anionic biradical (1−) with a singlet (S = 0) ground state and a Na+-15-crown-5-ether derivative of nitronylnitroxide monoradical (2), 2,5-Bis(1 -oxyl-3-oxido-dihydroxy-4,4,5,5-tetramethyl imidazolin-2-yl)phenol-Sodium(4-(1 -oxyl-3-oxido-dihydroxy-4,4,5,5-tetramethyl imidazolin-2-yl)-15-crown-5) Salt, [Na2]+1−. Possible occurrence of the exotic ferrimagnetic spin alignment in the complex salt [Na2]+1− is discussed from magnetic susceptibility measurements. A novel 18-crown-6-ether substituted nitronyl nitroxide monoradical 3 has also been synthesized as a building block for organic ferrimagnet. The intermolecular interaction of 3 was found to be antiferromagnetic from magnetic susceptibility measurements.