Metal binding of polyalcohols .4. Structure and magnetism of the hexanuclear, mu(6)-oxo-centered [OFe6(H-(3)thme)(3)(OCH3)(3)Cl-6](2-) (thme=1,1,1-tris(hydroxymethyl)ethane)

The addition of [N(CH3)(4)]OH to a methanolic solution of FeCl3 and thme (thme = 1,1,l-tris(hydroxymethyl)ethane) yielded [N(CH3)(4)](2)[OFe6(H(-3)thme)3(OCH3)(3)Cl-6]. 2H(2)O (1) Crystal data: C26H64Cl6Fe6N2O15, trigonal space group P31c, a = 12.459(2) Angstrom, c = 18.077(4) Angstrom, Z = 2. The complex anion exhibits the well-known mu(6)-O-Fe-6-(mu(2)-OR)(12) structure with three mu(2)-methoxo bridges, three triply deprotonated H(-3)thme ligands, where each alkoxo group bridges two Fe-III centers, and six terminally coordinating Cl- ligands. In contrast to two previously described ferric complexes with an analogous structure of the complex core, compound 1 is stable in air. Variable-temperature magnetic susceptibility measurements established antiferromagnetic exchange coupling interactions with J(trans)(Fe-mu(6)-O-Fe) = 24.5 cm(-1), J(cis)(Fe-mu(2)-O-thme-Fe) = 11.5 cm(-1), and J(cis)'(Fe-mu(2)-OCH3-Fe) = 19.5 cm(-1). The unexpectedly high value for J(trans) is explained by means of a superexchange pathway and is discussed for a simplified model by using MO calculations at the extended Huckel level.