Interpenetrated (8,3)-c and (10,3)-b Metal–Organic Frameworks Based on {Fe^III₃} and {Fe^III₂Co^II} Pivalate Spin Clusters

Abstract

Two new magnetic cluster-based 3D coordination polymers consisting of μ3-oxo-centered cationic homometallic [FeIII3O(O2CCMe3)6]+ or neutral heterometallic [FeIII2CoIIO(O2CCMe3)6] coordination clusters bridged by different N,N′-donor ligands into three-dimensional networks of {[Fe3O(O2CCMe3)6(4,4′-bpy)1.5](OH)·0.75(CH2Cl2)·x(H2O)}n (1, x ≈ 8) and {[Fe2CoO(O2CCMe3)6(bpe)0.5(pyz)]}n (2) (where 4,4′-bpy = 4,4′-bipyridine; bpe = 1,2′-bis(4-pyridyl)ethylene; pyz = pyrazine) have been prepared under solvothermal conditions. Single-crystal X-ray diffraction studies reveal the existence of a 6-fold interpenetrated network with rare (8,3)-c (etc) topology for 1 and a 3-fold interpenetrated network with (10,3)-b (ths) topology for 2. The interpenetration effectively results in very low BET surface areas, and the compounds have to be regarded as nonporous. Magnetic studies of 1 and 2 point to both ferro- and antiferromagnetic intra- and intercluster exchange interactions between the isotropic FeIII and the strongly anisotropic CoII spin centers. 57Fe Mössbauer spectroscopy confirms the uniform ferric (+III) valence state in both 1 and 2, and low-temperature data for 1 point toward distinct hyperfine fields for the Fe sites.