Transition Metal Azolates from Metallocenes. 2. Synthesis, X-ray Structure, and Magnetic Properties of a Three-Dimensional Polymetallic Iron(II) Imidazolate Complex, a Low-Temperature Weak Ferromagnet

The reaction of ferrocene with molten imidazole at 150 °C
yielded pale yellow crystals of composition
[Fe3(imid)6(imidH)2]x.
Crystals of
[Fe3(imid)6(imidH)2]x
are monoclinic, a = 10.5912(9), b =
12.958(2), c = 10.617(1) Å; β = 92.696(9)°; Z = 2; space group
P21/c. The structure was solved
by Patterson methods and refined by
full-matrix least-squares procedures to R = 0.033 and
Rw = 0.031 for 2260 reflections
with I ≥ 3σ(F2). The
structure
consists of chains of tetrahedral iron centers cross-linked via
octahedral iron ions to generate a 3-D array. All of
the
iron centers are bridged to four other metal centers via imidazolate
ions, the two remaining (trans) coordination
positions of the octahedral centers being occupied by neutral imidazole
molecules. Magnetic susceptibilities on
powdered samples were measured over the temperature range 2−300 K and
at fields ranging from 0 to 55 000 G.
The compound exhibits antiferromagnetic coupling along chains of
tetrahedrally coordinated iron centers. A canted
spin structure leads to weak ferromagnetism at temperatures below a
magnetic phase transition temperature of 17 K.
Upon cycling the applied magnetic field between +55 000 and
−55 000 G at 4.8 K, a hysteresis loop was obtained
with a remnant magnetization of 2500 cm3 G
mol-1 and a coercive field of 200
G.