Manganese Oxydiacetate Complexes: Synthesis, Structure and Magnetic Properties

Abstract

The aerobic aqueous solution syntheses and structures of monomeric and polymeric MnII complexes containing the oxydiacetate ligand [O(CH2COO)22− = oda] are reported. The magnetic properties of the polymeric products have also been investigated. The initially obtained species [{Mn(oda)(H2O)}·H2O]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)}·4H2O]n (2), [Mn(oda)(bipy)(H2O)]·2H2O (3) and [Mn(oda)(terpy)]·2H2O (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 1 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 MnII 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

A Cubic 3d–4f Structure with Only Ferromagnetic Gd–Mn Interactions

“…There are only a few compounds in which water molecules occupy the axial position of the manganese coordination sphere, whereas such coordination is much more common for copper. The relative amounts of the lanthanide, transition metal, and ligand present in both structures are same as in [Mn 3 Gd 2 (oda) 6 -(H 2 O) 6 ]. The greater preference of Mn 2+ for regular octahedral coordination over 4 + 2 coordination must be important for the formation of the cubic network.…”

“…The greater preference of Mn 2+ for regular octahedral coordination over 4 + 2 coordination must be important for the formation of the cubic network. Nevertheless, the LnMn compound [Mn 3 Ln 2 (dipic) 6 (H 2 O) 6 ] (dipicH 2 = pyridine-2,6-dicarboxylic acid) crystallized in a hexagonal lattice with two water molecules occupying the axial positions of the manganese atom.…”

“…[7] In all cases, the free oxygen of the [Ln(oda) 3 ] 3À moiety is coordinated to the transition metal. The coordination sphere of the transition metal consists of four carboxylate oxygen atoms from the [Ln(oda) 3 ] 3À unit and two water molecules coordinated in the axial positions, leading to the formation of [M 3 Ln 2 (oda) 6 -(H 2 O) 6 ] (M = Cu, Zn), a neutral, porous 3D network structure. Furthermore, the acetate group bridging M and Ln ions is in a syn-anti conformation.…”

“…However the carbon atoms of the oda ligand project into these channels, alternatively narrowing and broadening it, resulting in two types of cavities. The bigger cavity is occupied by the [Mn(H 2 O) 6 ] 2+ unit, which acts as an counterion to neutralize the charge of the MOF, while the smaller cavity is filled with solvent water molecules which are hydrogen-bonded to the carboxylate oxygen atom of oda. The ability of [Mn(H 2 O) 6 ] 2+ to act as a cation in MOF has been reported.…”

“…[2] Though much work has been done with lanthanides and copper, there are only a few coordination networks with lanthanide(III) and manganese(II) centers. [3,4] Oxydiacetic acid (O(CH 2 CO 2 H) 2 , odaH 2 ), a multidentate ligand with five coordination sites, forms a number of MOF structures with lanthanides [5] and transition-metal ions [6] as well as 3d-4f composites. [7] Herein, we report the synthesis, structure, and magnetic properties of [{Mn(H 2 O) 6 }{MnGd(oda) 3 } 2 ]·6 H 2 O (1), which is the first cubic gadolinium-manganese 3D MOF with a ferromagnetic interaction.…”