Syntheses, Crystal Structures, and Properties of Novel Heterooctametallic Clusters Na2M'2[M3O4(O2CEt)8]2 (M' = Fe, Cr, Mo; M3 = Mo3, MoW2, W3)

A mixture of Na2 MO4 , M(CO)6 , FeCl3 ·6H2 O, and (EtCO)2 O was heated at 120°C to produce the heterooctanuclear clusters Na2 Fe2 [M3 O4 -(O2 CEt)8 ]2 (M = Mo, 1; W, 2). The bioxo-capped clusters Na[M3 O2 (O2 CEt)9 ] (M3 = MoW2 , W3 ) were treated with Fe-(CO)5 , Cr(CO)6 , and Mo(CO)6 in (EtCO)2 O at 120°C to afford Na2 M'2 -[MoW2 O4 (O2 CEt)8 ]2 (M' = Fe, 3; Cr, 4; Mo, 5) and Na2 Mo2 [W3 O4 (O2 CEt)8 ]2 (6), respectively. The isomorphous clusters 1, 2, 5, and 6 were characterized by X-ray crystallography. The structures, similar to those of the analogues Na2 Cr2 [M3 O4 -(O2 CEt)8 ] (M = Mo, 7; W, 8) and Na2 V2 [M3 O4 (O2 CEt)8 ]2 (M = Mo, 9; W, 10), consist of two incomplete cubane-type [M3 O4 (O2 Et)8 ](4-) units centrosymmetrically bridged by two M'(III) metal ions through μ-oxo and propionate groups; the resulting cluster dianions are linked by Na(+) ions into infinite chains. Clusters 1-10 do not dissolve in water and common organic solvents at room temperature. Unlike the chromium(III) clusters 7 and 8, the iron(III) and vanadium(III) clusters 1 and 9 are soluble in aqueous acid solution, as a result of their decomposition into isolated [Mo3 O4 ](4+) cluster units. Temperature-dependent magnetic susceptibilities of 1, 2, and 7-10 were measured over the range 2-200 K and modeled by means of the spin-Hamiltonian H = - 2JS1 S2 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 between the magnetic, bridging M'(III) ions are very weak. These species show characteristic bands in the IR spectra at 740-820 cm(-1) , which can probably be assigned to ṽ(M-μ-O).