Modification of the structure and magnetic properties of fumarato-bridged Mn coordination polymers through different dimethyl-2,2'-bipyridine co-ligands

Manganese coordination polymers {Mn(fum)(5dmb)(H2O)(2)} (n) (1) and {[Mn-2(fum)(2)(4dmb)(2)]center dot H2O} (n) (2) (fum = fumarato; 5dmb = 5,5'-dimethyl-2,2'-bipyridine; 4dmb = 4,4'-dimethyl-2,2'-bipyridine) were obtained from one-pot, solution reactions under ambient conditions. The fum ligand acquires different coordination modes in the presence of the different dmb ancillary ligands, promoting distinctive crystal structures, including divergent dimensionalities. Thus, X-ray single-crystal data reveal that complex 1 crystallizes in a monoclinic system with C2/c space group and forms an infinite one-dimensional polymer. The Mn(II) center is six-coordinated and displays a distorted octahedral configuration. In addition, the solid-state self-assembly of the polymeric structure of 1 gives rise to a two-dimensional (2D) supramolecular framework, mainly through hydrogen bonding. In contrast, complex 2 crystallizes in a monoclinic system with a Cc space group and forms an infinite 2D coordination polymer having dinuclear units. The Mn(II) center has a distorted octahedral configuration. The thermal stabilities of both coordination polymers were investigated. Variable-temperature magnetic measurements show that complex 1 is paramagnetic, while complex 2 exhibits weak antiferromagnetic coupling between adjacent Mn(II) centers.