A Comparative Structural and Magnetic Study of Three Compounds Based on the Cluster Unit M4Cl8(THF)6 (M=Mn, Fe, Co)

Abstract

Treatment of anhydrous MCl2 phases with THF under refluxing conditions leads to excision of the clusters M4Cl8(THF)6 (M=Fe (1), Co (3)) and dimensional reduction to the chain of clusters, {Mn4Cl8(THF)6(Mn(THF)2Cl2}∞, (2). All three compounds were isolated in high yields as crystalline materials and subjected to comprehensive magnetic studies. X-ray structures of the three compounds were performed to verify the nature of the compounds, but only the Mn derivative is discussed in detail due to the fact that the structures of the Fe and Co clusters were reported earlier. The molecular structures of M4Cl8(THF)6 (M=Fe, Co) consist of a rhombic arrrangement of metal ions with two octahedral and two pseudo-five-coordinate metal sites. The four outer edges of the cluster are each spanned by a chloride bridge, while the short diagonal is bridged by two chloride ions. The remainder of the coordination sites are occupied by two terminal chlorides and six THF solvent molecules. The 1D compound {Mn4Cl8(THF)6(Mn(THF)2Cl2}∞, (2), is related to (1) and (3) in that the core of the structure is the same, but in this case the M4Cl8(THF)6 units are linked by MnCl2(THF)2 bridges. The magnetic susceptibility data for Fe4Cl8(THF)6 (1) and Co4Cl8(THF)6 (3) in the high-temperature range are indicative of the presence of ferromagnetic and antiferromagnetic interactions respectively. Fitting of the data to anisotropic exchange models provided information on the intramolecular exchange parameters. In the low-temperature region, cooperative behavior was observed as a consequence of the presence of significant intercluster interactions. The Fe derivative behaves as a metamagnet, while the Co derivative is a weak ferromagnet below 3.5 K. In contrast to (1) and (3), the magnetic properties of {Mn4Cl8(THF)6(Mn(THF)2Cl2}∞, (2), are indicative of the presence of antiferromagnetic exchange interactions within the cluster as well as between the neighboring clusters that lead to a nonmagnetic ground state.