Molecular self-assemblies of a π-conjugated redox-active bipyridinium cation with magnetic dimetallic oxalate-bridged trimeric clusters

A series of molecular assemblies constructed from a π-conjugated redox-active bipyridinium cation, 1,4-bis(4′-pyridyl-1′-pyridinio) phthalazine (Bpyph), and magnetic dimetallic oxalate-bridged trimeric clusters, has been synthesized and characterized by elemental analysis, IR, TGA, X-ray single-crystal diffraction and magnetic susceptibility studies. The molecular assemblies formulated as (Bpyph)₂{M^II(H₂O) ₂[M^III(C₂O₄)₃] ₂}·12.5H₂O [for M^III = Fe; M ^II = Mn (1) or Co (2); for M^III = Cr; M^II = Mn (3) or Co(4)] are isostructural, their structures feature an alternative arrangement of Bpyph²⁺ cations and the linear trimeric oxalate complexes {M^II(H₂O)₂[M^III(C ₂O₄)₃]₂} along all three crystallographic axes, in which the dimetallic trimers form two distinct homo-chiral helices along the b axis via intermolecular hydrogen bonding interactions. Within each trimeric cluster, the two M^III sites have opposite chirality (Δ and Λ). Studies on the magnetic properties reveal the presence of antiferromagnetic exchange interactions within the trimeric clusters for the Fe₂M and ferromagnetic for the Cr ₂M series.