Cyanido-Bridged Fe(III)-Mn(III) Heterobimetallic Materials Built From Mn(III) Schiff Base Complexes and Di- or Tri-Cyanido Fe(III) Precursors

The reaction of [Fe-III(CN)(3)](-) (L being bpca = bis(2-pyridylcarbonyl)amidate, pcq = 8-(pyridine-2-carboxamido) quinoline) or [Fe-III(bpb)(CN)(2)](-) (bpb = 1,2-bis(pyridine-2-carboxamido)benzenate) ferric complexes with Mn-III salen type complexes afforded seven new bimetallic : cyanido-bridged Mn(III)-Fe(III) systems: [Fe(pcq)(CN)-3Mn(saltmen)(CH3OH)]center dot CH3OH (1), [Fe(bpca)(CN)(3)Mn(3-MeO-salen)center dot(OH2)]center dot CH3OH center dot H2O (2), [Fe(bpca)(CN)(3)Mn(salpen)] (3), [Fe(bpca)-(CN)(3)Mn(saltmen)] (4), [Fe(bpca)(CN)(3)Mn(5-Me-saltmen)]center dot 2CHCl(3) (5), [Fe(pcq)(CN)(3)Mn(5-Me-saltmen)]center dot 2CH(3)OH center dot 0.75H(2)O (6), and [Fe(bpb)-(CN)(3)Mn(saltmen)]center dot 2CH(3)OH (7) (with saltmen(2-) = N,N'-(1,1,2,2-tetramethylethylene)bis(salicylideneiminato) dianion, salpen(2-) = N,N'-propylenebis(salicylideneiminato) dianion, salen(2-) = N,N'-ethylenebis(salicylideneiminato) dianion). Single crystal X-ray diffraction studies were carried out for all these compounds indicating that compounds 1 and 2 are discrete dinuclear [Fe(III)-CN-Mn(III)] complexes while systems 3-7 are heterometallic chains with {-NC-Fe(III)-CN-Mn(III)} repeating units. These chains are connected through pi-pi and short contact interactions to form extended supramolecular networks. Investigation of the magnetic properties revealed the occurrence of antiferromagnetic Mn(III)center dot center dot center dot Fe(III) interactions in 1-4 while ferromagnetic Mn(III)center dot center dot center dot Fe(III) interactions were detected in 5-7. The nature of these Mn(III)center dot center dot center dot Fe(III) magnetic interactions mediated by a CN bridge appeared to be dependent on the Schiff base substituent. The packing is also strongly affected by the nature of the substituent and the presence of solvent molecules, resulting in additional antiferromagnetic interdinuclear/interchain interactions. Thus the crystal packing and the supramolecular interactions induce different magnetic properties for these systems. The dinuclear complexes 1 and 2, which possess a paramagnetic S-T = 3/2 ground state, interact antiferromagnetically in their crystal packing. At high temperature, the complexes 3-7 exhibit a one-dimensional magnetic behavior, but at low temperature their magnetic properties are modulated by the supramolecular arrangement: a three-dimensional antiferromagnetic order with a metamagnetic behavior is observed for 3, 4, and 7, and Single-Chain Magnet properties are detected for S and 6.