Syntheses, Crystal Structures, and Properties of Novel Heterooctametallic Clusters Na 2 M' 2 [M 3 O 4 (O 2 CEt) 8 ] 2 (M' = Fe, Cr, Mo; M 3 = Mo 3 , MoW 2 , W 3 )

A mixture of Na 2 MO 4 , M(CO) 6 , FeCl 3 ·6H 2 O, and (EtCO) 2 O was heated at 120°C to produce the heterooctanuclear clusters Na 2 Fe 2 [M 3 O 4 ‐(O 2 CEt) 8 ] 2 (M = Mo, 1 ; W, 2 ). The bioxo‐capped clusters Na[M 3 O 2 (O 2 CEt) 9 ] (M 3 = MoW 2 , W 3 ) were treated with Fe‐(CO) 5 , Cr(CO) 6 , and Mo(CO) 6 in (EtCO) 2 O at 120°C to afford Na 2 M' 2 ‐[MoW 2 O 4 (O 2 CEt) 8 ] 2 (M' = Fe, 3 ; Cr, 4 ; Mo, 5 ) and Na 2 Mo 2 [W 3 O 4 (O 2 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 Na 2 Cr 2 [M 3 O 4 ‐(O 2 CEt) 8 ] (M = Mo, 7 ; W, 8 ) and Na 2 V 2 [M 3 O 4 (O 2 CEt) 8 ] 2 (M = Mo, 9 ; W, 10 ), consist of two incomplete cubane‐type [M 3 O 4 (O 2 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 [Mo 3 O 4 ] 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 = – 2 JS 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 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).