DINUCLEAR AND HEXANUCLEAR IRON(III) OXIDE COMPLEXES WITH A BIS(BIPYRIDINE) LIGAND - A NEW [FE-6(MU(3)-O)(4)](10+) CORE

The use of the bis(bipyridine) ligand L (1,2-bis(2,2'-bipyridyl-6-yl)e thane) has yielded new dinuclear and hexanuclear complexes. The FeCl3/ NaO2CPh/L (4:4:1) reaction system in MeCN gives red-brown [Fe6O4Cl4(O2 CPh)(4)L-2][FeCl4](2) (1). The same reaction system in a 3:3:1 ratio i n MeOH gives orange [Fe-2(OMe)(2)Cl-2(O2CPh)L][FeCl4] (2). Complex 1.2 MeCN: monoclinic, P2(1)/a, a = 15.317(2) Angstrom, b = 18.303(3) Angst rom, c = 16.168(3) Angstrom, beta = 108.91(1)degrees and Z = 2. Comple x 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 consis ts 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 addition al 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-temper ature 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 an d 10.0-50.0 kG ranges. Fitting of the-data for 2 to the appropriate th eoretical equation for an equimolar composition of Fe-2 cations and [F eCl4](-) anions allowed the exchange interaction in the cation to be d etermined as J = -10.5 cm(-1) (H = -2JS(1)S(2)) with g held at 2.00. T he obtained J value is consistent: with that predicted by a previously published magnetostructural relationship.