Polybis(4-azabenzimidazolato)-iron(II) and -cobalt(II).: 3-D single diamond-like framework materials which exhibit spin canting and ferromagnetic ordering at low temperatures

The direct reaction between ferrocene and an excess of molten 4-azabenzimidazole yielded amber-green crystals of polybis(4-azabenzimidazolato)iron(II), 1. Single crystal X-ray diffraction studies revealed tetrahedrally coordinated iron ions linked by single imidazolate bridges and forming a 3-D single diamond-like (diamondoid) extended lattice. Magnetization studies show the effects of antiferromagnetic exchange above a critical temperature, T-c=21 K, and long-range ferromagnetic ordering below this temperature, behavior that classifies 1 as a molecule-based magnet. Magnetic hysteresis studies at 4.8 K yield a coercive field, H-coer=80 G and a remnant magnetization, M-rem=2100 cm(3) G mol(-1). The isomorphous polybis(4-azabenzimidazolato)cobalt(II), 2, has also been studied. It too is a low temperature molecule-based magnet. For 2, T-c=11 K and from magnetic hysteresis studies at 10 K, H-coer=400 G and M-rem=22 cm(3) G mol(-1).