Molecular magnetic materials and small clusters containing N-donor chelated metal species combined with hexacyanometallate, tris-oxalatometallate, and related bridging groups

New molecular-based ferromagnetic materials based on the hexacyanoferrate(III) building block are described. They are formed by reaction of bispyrazolylmethane (bpm) chelates of copper(II) and nickel(II) with K-3[Fe(CN)(6)] and have formulae [Ni-II(bpm)(H2O)(2)](3) [Fe-III(CN)(6)](2).2H(2)O (1) and K[Cu-II(bpm)][Fe-III(CN)(6)] (2). Detailed studies of their magnetic susceptibilities and magnetizations showed that long-range ordering occurs at 19K for 1 and 10K for 2. Attempts to make bimetallic oxalato compounds having 1D, 2D or 3D-bridged structures, and incorporating cationic trispyrazolylmethane (tpm) metal chelates, led unexpectedly to double salt formation. The crystal structures of three of these hydrated materials [Cu(tpm)(2)](3)[Cr(C2O4)(3)](2).20H(2)O (4), [Fe-II(tpm)(2)](3)[Fe-III(C2O4)(3)](2).20H(2)O (5), [Cu-II(Me(2)tpm)(2)](3)[Fe-III(C2O4)(3)].20H(2)O (7) all show the individual cationic and anionic molecules with H-bonded water intermolecular contacts occurring between [M(C2O4)(3)](3-) groups. These contacts are deemed responsible for the weak exchange effects noted at low temperatures in the susceptibilities of these compounds. 5 is rather novel in that it shows spin-crossover behaviour of the [Fe-II(tpm)(2)](2+) centres above 250K whilst displaying field-dependent weak exchange effects below 20K. Finally, the importance of measuring multifield/multitemperature magnetization data on small clusters is stressed.