COMPOSITIONAL AND GEOMETRICAL-ISOMERS OF 15-METALLACROWN-5 COMPLEXES

Two mixed valent, hexanuclear manganese clusters of general compositio n cetate)2[Mn(III)(salicylhydroximate)]5(pyridine)6, Mn(II)(OAC)2(15-M C(Mn3+N)-5) have been prepared in almost-equal-to 70% yield. Structura l characterization of these complexes using X-ray crystallography prov ides the first examples of 15 membered ring metallacrowns. A 15 member ed chelate ring is constructed of five [Mn(III)-N-O] linkages. The fiv e manganese(III) ions are designated Mn(1)-Mn(5). The Mn(1), Mn(2) and Mn(3) atoms adopt propeller configurations with LAMBDA,DELTA,LAMBDA a bsolute stereochemistry, respectively. The Mn(4) and Mn(5) atoms are r estricted to planar configurations. Both complexes contain a seven coo rdinate manganese(II) [Mn(6)] encapsulated in the core of this 15 memb ered ring. The Mn(6) polyhedron is best described using an 8 coordinat e reference frame in which one of the vertices of a trigonal faced dod ecahedron is vacant. The Mn(6) coordination sphere contains five hydro ximate oxygen donors, provided by the metallacrown ring, and two oxyge ns from acetates that bridge between ring manganese(III) and the encap sulated manganese(II). Two geometrical isomers are formed that differ in the bridging acetate modes. In 1, the bridging acetate forms a bifu rcated bridge between Mn(2) and Mn(6) while complex 2 has a bifurcated acetate bridge between Mn(5) and Mn(6). A compositional isomer, Mn(II )(acetate)(HSal)(15-MC(Mn3+N)-5), 4, which substitutes the carboxylate function of salicylate for one of the acetates has also been prepared . This isomer adopts the same bifurcation mode, using the salicylate c arboxylate, as complex 2. Studies to define the solution integrity of the metallacrowns are presented in addition to the solid state structu res.