  The magnetic properties of the first odd-member antiferromagnetic ring
comprising eight chromium(III) ions, S=3/2 spins, and one nickel(II) ion, S=1
spin, are investigated. The ring possesses an even number of unpaired electrons
and a S=0 ground state but, due to competing AF interactions, the first excited
spin states are close in energy. The spin frustrated ring is visualized by a
Moebius strip. The ?knot? of the strip represents the region of the ring where
the AF interactions are more frustrated. In the particular case of this
bimetallic ring electron paramagnetic resonance (EPR) has unambiguously shown
that the frustration is delocalized on the chromium chain, while the
antiparallel alignment is more rigid at the nickel site.
