Metal Binding of Polyalcohols. 4. Structure and Magnetism of the Hexanuclear, μ6-Oxo-Centered [OFe6(H-3thme)3(OCH3)3Cl6]2- (thme = 1,1,1-Tris(hydroxymethyl)ethane)

The addn. of [NMe4]OH to a methanolic soln. of FeCl3 and thme (thme = 1,1,1-tris(hydroxymethyl)ethane) yielded [NMe4]2[OFe6(H-3thme)3(OCH3)3Cl6]·2H2O. Crystal data: C26H64Cl6Fe6N2O15, trigonal space group P31c, a = 12.459(2), c = 18.077(4) Å, Z = 2. The complex anion exhibits the known μ6-O-Fe6-(μ2-OR)12 structure with three μ2-methoxo bridges, three triply deprotonated H-3thme ligands, where each alkoxo group bridges two FeIII centers, and six terminally coordinating Cl- ligands. In contrast to two previously described ferric complexes with an analogous structure of the complex core, this compd. is stable in air. Variable-temp. magnetic susceptibility measurements established antiferromagnetic exchange coupling interactions with Jtrans(Fe-μ6-O-Fe) = 24.5 cm-1, Jcis(Fe-μ2-Othme-Fe) = 11.5 cm-1, and Jcis'(Fe-μ2-OCH3-Fe) = 19.5 cm-1. The unexpectedly high value for Jtrans is explained by a superexchange pathway and is discussed for a simplified model by using MO calcns. at the extended Hueckel level.