A NOVEL TETRANUCLEAR [CRIII2MNIII2(MU(3)-O)2]8-STATE( CORE WITH AN S(T)=0 SPIN GROUND)

The reaction of [Cr(III)L(MeOH3)3]3 +ions with Mn(III)(salox) units (L = 1,4,7-trimethyl-1,4,7-triazacyclononane; salox = salicylaldehyde ox ime) produced in situ in methanol, yielded, in the presence of a small amount of triethylamine and NaClO4, the complex I)2(mu-OMe)2(mu3-O)2( salox)2Mn(III)2][ClO4]2.3H2O. It has been characterized on the basis o f elemental analysis, IR spectroscopy and variable-temperature (4-278 K) magnetic susceptibility measurements. The molecular structure estab lished by X-ray diffraction consists of a [Cr(III)2(mu3-O)2Mn(III)2]8 butterfly core with the chromium(III) ions representing the wing-tips , and high-spin manganese(III) ions the 'body' ions in the tetranuclea r core. The magnetic susceptibility measurements revealed a diamagneti c (S(T) = 0) ground state with antiferromagnetic exchange interactions J(CrMn) = -11.7 cm-1 and J(MnMn) = -1 3.0 cm-1. The ground state is t he result of spin frustration of the 'body' manganese(III) ions. In ot her words, owing to the topology of the tetranuclear complex, which ca n be viewed as being made up of two edge-shared triangular units, the ground state represents the lowest possible spin state for this electr onic configuration when both interactions are antiferromagnetic.