THE rational design of molecular compounds that exhibit spontaneous ma
gnetic ordering might enable one to tailor magnetic properties ties fo
r specific applications in magnetic memory devices(1-4). In such mater
ials synthesized previously(5-17), however, the underlying weak magnet
ic interactions are incapable of maintaining ordering at ambient tempe
ratures. One remarkable exception is a compound derived from vanadium
and tetracyanoethylene(18), but the material is amorphous and fragile,
and consequently the molecular interactions responsible for its strik
ing properties are not understood. Here we demonstrate another route t
o the synthesis of a room-temperature organometallic magnet, in which
we combine a hexacyanometalate [M(CN)6](q-) with a Lewis acid L(p+). I
f L and M are transition-metal ions, then the orbital interactions in
the resulting compound can be described by well understood principles(
21-24), and it is therefore possible to choose the metals to tune the
compound's magnetic properties-in particular, the magnetic ordering (C
urie) temperature T-c(refs 21-26). We have synthesized a room-temperat
ure magnetic material (T-c=315 K) that belongs to the Prussian blue fa
mily of compounds(27) (where M is chromium and L is vanadium), demonst
rating that transition-metal hexacyano complexes are promising compone
nts for the construction of molecule-based high-T-c magnets.