Cobalt 2-pyrazinephosphonates: syntheses,structures, and magnetic properties

Reactions of Co(ClO₄)₂·6H₂O with 2-pyrazinephosphonic acid (2-paPO₃H₂) under two different hydrothermal conditions gave two new cobalt 2-pyrazinephosphonates, Co(2-paPO₃H)₂ (1) and Co(2-paPO₃)(H₂O) (2). Compound 1 was obtained at 160 °C, while 2 was obtained at 180 °C. In 1, two Co(II) units are bridged by two O–P–O’s into a dimer and the dimers are linked by pyrazinyl groups into a 1-D double chain. In 2, the {CoO₄N₂} and {CPO₃} polyhedra are interconnected via edge and corner-sharing into a metal phosphonate layer, and the layers are pillared by pyrazinyl groups into a 3-D network. Variable-temperature magnetic susceptibility studies reveal that both complexes have weak antiferromagnetic coupling between Co(II) ions.