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 divale nt transition metal and bpy is 2,2'-bipyridine, cause a remarkable cry stallization of anionic three-dimensional (3D) coordination polymers o f oxalate-bridged metal complexes [M(2)(ox)(3)](2n-)(n). With these ca tions, which are appropriate in charge, size, and symmetry, two types of stoichiometric units of the anionic 3D networks, with metals in dif ferent 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 compound s 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)][LiCr III(ox)(3)] (5), cubic, P2(1)3, a = 15.262(4) Angstrom, Z = 4. The Mos sbauer spectra of the iron-containing compounds [Fe-II(bpy)(3)][Fe-2(I I)(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 corres ponding iron valence states. The straightforward synthetic approach an d easy crystallization behavior, as well as the variety of metal combi nations within the 3D networks, fender these systems valuable candidat es for studies in the field of molecular-based magnets. They fulfill t he requirements of three-dimensional connectivity as well as accessibi lity to detailed structural characterization. The magnetic susceptibil ity data in the temperature range 2-300 K of 1, 2 and type 4 but LiFeI II are presented and the results should be taken as a starting point f or more extended systematical studies. 1 and 2 reveal antiferromagneti c ordering behavior, indicated by a negative Weiss constant theta of - 28 and -33 K, whereas the LiFeIII compound exhibits the expected behav ior 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.