SYNTHESES, CRYSTAL-STRUCTURES, AND PROPERTIES OF NOVEL HETEROOCTAMETALLIC CLUSTERS NA2M2'[M3O4(O2CET)(8)](2) (M'=FE, CR, MO M-3=MO-3, MOW2,W-3)

A mixture of Na2MO4, M(CO)(6), FeCl3.6H(2)O, and (EtCO)(2)O was heated at 120 degrees C to produce the heterooctanuclear clusters Na2Fe2[M3O 4-(O2CEt)(8)](2) (M=Mo, 1; W, 2). The bioxo-capped clusters Na[M3O2(O2 CEt)(9)] (M-3=MoW2, W-3) were treated with Fe(CO)(5), Cr(CO)(6), and M o(CO)(6) in (EtCO)(2)O at 120 degrees C to afford Na2M'(2)-[MoW2O4(O2C Et)(8)](2) (M'=Fe, 3; Cr, 4; Mo, 5) and Na2Mo2[W3O4(O2CEt)(8)](2) (6), respectively. The isomorphous clusters 1, 2, 5, and 6 were characteri zed by X-ray crystallography. The structures, similar to those of the analogues Na2Cr2[M3O4-(O2CEt)(8)] (M=Mo, 7; W, 8) and Na2V2[M3O4(O2CEt )(8)](2) (M = Mo, 9; W, 10), consist of two incomplete cubane-type [M3 O4(O2Et)(8)](4-) units centrosymmetrically bridged by two M'(III) meta l ions through mu-oxo and propionate groups; the resulting cluster dia nions are linked by Na+ ions into infinite chains. Clusters 1-10 do no t dissolve in water and common organic solvents at room temperature. U nlike the chromium(III) clusters 7 and 8, the iron(III) and vanadium(I II) clusters 1 and 9 are soluble in aqueous acid solution, as a result of their decomposition into isolated [Mo3O4](4+) cluster units. Tempe rature-dependent magnetic susceptibilities of 1, 2, and 7-10 were meas ured over the range 2-200 K and modeled by means of the spin-Hamiltoni an H=-2JS(1)S(2) to give spin exchange coupling constants J/k of -0.60 , -0.72, -1.76, -1.31, -4.80, and -1.46 K, respectively. These figures show that antiferromagnetic spin exchange coupling interactions betwe en the magnetic, bridging M'(III) ions are very weak. These species sh ow characteristic bands in the IR spectra at 740-820 cm(-1), which can probably be assigned to <(nu)over tilde>(M-mu-O).