INTRAMOLECULAR LONG-RANGE ELECTRONIC SPIN-EXCHANGE COUPLING IN DIRADICALS - A NEW MAGNETIC COUPLING UNIT

A phenyl diethynyl bridge is used as a magnetic coupling unit (MCU) be tween two iminonitroxide pi-radicals. The ethynyl moiety is attached t o the central phenyl ring either in the para or in the meta position. The magnetic properties of the resulting bis-imino nitroxide diradical s (p-BIN and m-BIN) are investigated both at the molecular scale and i n the condensed phases. An intramolecular through bond spin coupling i s observed at an unusual long distance (about 20 Angstrom) in both der ivatives. However, the ground state is found to be a singlet spin stat e in both compounds. The results suggest an interplay between the spin polarization and the spin delocalization (pi-conjugation). An intermo lecular weak antiferromagnetic spin coupling is occuring in both compo unds.