Dinuclear and hexanuclear iron(III) oxide complexes with a bis(bipyridine) ligand:: A new [Fe6(μ3-O)4]10+ core

The use of the bis(bipyridine) ligand L (1,2-bis(2,2'-bipyridyl-6-yl)ethane) has yielded new dinuclear and hexanuclear complexes. The FeCl3/NaO2CPh/L (4:4:1) reaction system in MeCN gives red-brown [Fe6O4Cl4(O2CPh)(4)L-2][FeCl4](2) (1). The same reaction system in a 3:3:1 ratio in MeOH gives orange [Fe-2(OMe)(2)Cl-2(O2CPh)L][FeCl4] (2). Complex 1.2MeCN: monoclinic, P2(1)/a, a = 15.317(2) Angstrom, b = 18.303(3) Angstrom, c = 16.168(3) Angstrom, beta = 108.91(1)degrees and Z = 2. Complex 2: triclinic, <P(1)over bar>, a = 14.099(6) Angstrom, b = 18.510(7) Angstrom, c = 7.108(3) Angstrom, alpha = 96.77(2)degrees, beta = 99.45(2)degrees, gamma = 81.16(2)degrees, and Z = 2. Tne cation of 1 consists of a near-planar [Fe-6(mu(3)-O)(4)](10+) core that can be described-as three edge-fused [Fe2O2] rhombs to which are attached two additional Fe atoms. The cation of 2 contains a [Fe-2(mu-OMe)(2)(mu-O2CPh)](3+) core. In both cations, the L group acts as a bridging ligand across an Fe-2 unit, with the bpy rings essentially parallel. Variable-temperature solid-state magnetic-susceptibility studies of 1 and 2 in the 2.00-300 K range reveal that for both complexes the data are consistent with an S = 0 cation and S = 5/2 [FeCl4](-) anions. These conclusions were confirmed by magnetization vs field studies in the 2.00-4.00 K and 10.0-50.0 kG ranges. Fitting of the-data for 2 to the appropriate theoretical equation for an equimolar composition of Fe-2 cations and [FeCl4](-) anions allowed the exchange interaction in the cation to be determined as J = -10.5 cm(-1) (H = -2JS(1)S(2)) with g held at 2.00. The obtained J value is consistent: with that predicted by a previously published magnetostructural relationship.