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 degrees C yielded pale yellow crystals of composition [Fe-3(imid)(6)(imidH)(2)](x). Crystals of [Fe-3(imid)(6)(imidH)(2)](x) are monoclinic, a = 10.5912(9), b = 12.958(2), c = 10.617(1) Angstrom; beta = 92.696(4)degrees; Z = 2; space group P2(1)/c. The structure was solved by Patterson methods and refined by full-matrix least-squares procedures to R = 0.033 and R-w = 0.031 for 2260 reflections with I greater than or equal to 3 sigma(F-2). 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 cm(3) G mol(-1) and a coercive field of 200 G.