MOLECULES With large spins, and associated large magnetic moments, are
potential building blocks for magnetic materials(1). To make such mol
ecules, spin-carrying metal ions can be assembled into polynuclear com
plexes, but the coupling between the spins is usually antiferromagneti
c, leading to antiparallel alignment(2). Magnetic coupling leading to
parallel alignment occurs only rarely, and even then is usually too we
ak for the alignment to persist at ambient temperatures(3-14). Here we
report the synthesis of a tetranuclear chromium hydride cluster With
a ground state of non-zero spin (spin quantum number S = 7/2), in whic
h the intramolecular magnetic coupling is so strong that the magnetic
alignment is not disturbed appreciably even at room temperature. This
ground state cannot be explained either by simple parallel or antipara
llel alignment of spins, but can be understood in terms of antiparalle
l alignment of three Cr(III) moments with one Cr(II) moment, These fin
dings indicate that hydride ligands can mediate extremely strong magne
tic exchange interactions between metal ions, and that metal hydrides
may therefore be promising components for the construction of molecula
r magnetic materials.