Manganese Oxydiacetate Complexes: Synthesis, Structure and Magnetic Properties

The aerobic aqueous solution syntheses and structures of monomeric and polymeric Mn-II complexes containing the oxydiacetate ligand [O(CH2COO)(2)(2-)= oda] are reported. The magnetic properties of the polymeric products have also been investigated. The initially obtained species [{Mn(oda)(H2O)}(H2O)-H-.](n) (1) has been reacted with bidentate or tridentate N-donor ligands such as o-phenanthroline (phen), 2,2'-bipyridine (bipy) and 2,2':6,2"-terpyridine (terpy) to give the complexes [{Mn(oda)(phen)}(.)4H(2)O](n) (2), [Mn(oda)(bipy)(H2O)](.)2H(2)O (3) and [Mn(oda)(terpy)](.)2H(2)O (4), respectively. Species 1-4 are the first Mn-oda structures determined by X-ray methods. In all cases, the oda acts as a tridentate ligand toward one metal and adopts the typical planar arrangement. However, while the 3 and 4 are monomers, 2 and I are polymers as oda exploits both atoms of its carboxylate groups to coordinate other metals; 1 consists of a three-dimensional diamond-type network, while 2 is one-dimensional, consisting of an extended chain of {Mn(oda)(phen)} subunits. For both compounds, magnetic susceptibility measurements down to 2 K showed only weak antiferromagnetic interactions between high-spin Mn-II ions. Despite the expectedly similar coordinating capabilities of N-donor ligands, the bipy complex 3 is a monomer with the six-coordination completed by one water ligand. The tridentate nature of simultaneously present oda and terpy ligands excludes the coordination of water in complex 4, the geometry of which is distorted from the octahedron, most likely due to a peculiar packing effect. Finally, the known five-coordinate complex [MnCl2(terpy)] (5), a side product of our synthetic experiments, has also been structurally characterized.