Synthesis, crystal structures, and magnetic properties of cyano-bridged heterobimetallic chains based on [(Tp)Fe(CN)3]-

With the use of the tailored cyanometalate precursor, (Bu4N)[(Tp)Fe(CN)(3)] (Tp = Tris(pyrazolyl)hydroborate) as the building block to react with fully solvated Cu-II, Co-II, and Ni-II cations, four one-dimensional (1D) heterobimetallic cyano-bridged chain complexes of squares, [(Tp)(2)Fe-2(III)(CN)(6)Cu(CH3OH)center dot 2CH(3)OH](n)(1), [(Tp)(2)Fe-2(III)(CN)(6)Cu(DMF)center dot DMF]n (2), [(Tp)(2)Fe-2(III)(CN)(6)M(CH3OH)(2)center dot 2CH(3)OH](n) (M = Co (3) and Ni (4)), have been prepared. In complexes 1 and 2, the Cu-II ions are pentacoordinated in the form of a slightly distorted square-based pyramid, and they are linked by distorted octahedrons of [(Tp)Fe(CN)(3)]- to form 1D chains of squares. In complexes 3 and 4, both the central CoII and NiII ions have a slightly distorted octahedral coordination geometry, and they are bridged by [(Tp)Fe(CN)(3)]- to form similar 1D chains of squares. There are weak interchain pi-pi stacking interactions through the pyrazolyl groups of the Tp ligands for complexes 3 and 4. The crystal structures and magnetic studies demonstrate that complexes 1 and 2 exhibit intrachain ferromagnetic coupling and single-chain magnets behavior, and the blocking temperature is ca. 6 K for complex 1 and ca. 3 K for complex 2. Complexes 3 and 4 show significant metamagnetic behavior, where the cyanides mediate the intrachain ferromagnetic coupling between Fe-III and Co-II or Ni-II ions and the interchain pi-pi stacking interactions lead to antiferromagnetic couplings. The field dependence of the magnetization measurements shows that the critical field is around 1 kOe for complex 3 and 0.8 kOe for complex 4 at 1.8 K.