A CONCEPT FOR THE SYNTHESIS OF 3-DIMENSIONAL HOMOMETALLIC AND BIMETALLIC OXALATE-BRIDGED NETWORKS [M(2)(OX)(3)](N) - STRUCTURAL, MOSSBAUER, AND MAGNETIC STUDIES IN THE FIELD OF MOLECULAR-BASED MAGNETS

The tris-chelated [M(II)(bpy)(3)](2+) cations, where M(II) is a divalent transition metal and bpy is 2,2'-bipyridine, cause a remarkable crystallization of anionic three-dimensional (3D) coordination polymers of oxalate-bridged metal complexes [M(2)(ox)(3)](2n-)(n). With these cations, which are appropriate in charge, size, and symmetry, two types of stoichiometric units of the anionic 3D networks, with metals in different valence states, can be distinguished: [M(2)(II)(ox)(3)](2-) and [M(I)M(III)(ox)(3)](2-). Results of a structural analysis of compounds within each of the two isomorphous series are discussed: [Ni-II(bpy)(3)][Mn-2(II)(ox)(3)] (3), cubic, merohedrically twinned, P4(1)32/P4(3)32, a = 15.579(2) Angstrom, Z = 4; [Fe-II(bpy)(3)] [NaFeIII(ox)(3)] (4), cubic, P2(1)3, a = 15.507(3) Angstrom, Z = 4; [Fe-II(bpy)(3)][LiCrIII(ox)(3)] (5), cubic, P2(1)3, a = 15.262(4) Angstrom, Z = 4. The Mossbauer spectra of the iron-containing compounds [Fe-II(bpy)(3)][Fe-2(II)(ox)(3)] (1) and [Fe-II(bpy)(3)][Mn-2(II)(ox)(3)] (2) and type 4 but LiFeIII are consistent with the stoichiometric formula and the corresponding iron valence states. The straightforward synthetic approach and easy crystallization behavior, as well as the variety of metal combinations within the 3D networks, fender these systems valuable candidates for studies in the field of molecular-based magnets. They fulfill the requirements of three-dimensional connectivity as well as accessibility to detailed structural characterization. The magnetic susceptibility data in the temperature range 2-300 K of 1, 2 and type 4 but LiFeIII are presented and the results should be taken as a starting point for more extended systematical studies. 1 and 2 reveal antiferromagnetic ordering behavior, indicated by a negative Weiss constant theta of -28 and -33 K, whereas the LiFeIII compound exhibits the expected behavior of single iron(III) ions. Further extensions to possible networks of the types [M(II)M(III)(ox)(3)](1n-)(n) and [M(I)M(II)(ox)(3)](3n-)(n) are discussed.