The reactions of the dimers [Ru(eta(6)-arene)Cl-2](2)] (arene = C6H5Me, p-MeC(6)H(4)i-Pr or C6Me6) with (n-Bu4N)(2)[Mo2O7] have been investigated in methanol or acetonitrile, in some cases in the presence of MeC(CH2OH)(3). A series of complexes with various nuclearities, [{Ru(eta(6)-arene)} Mo2O4 {MeC(CH2O)(3))(2)] and [{Ru(eta(6)-arene)}(Mo2O6)-Mo-2(OMe)(4)] (arene = p-MeC(6)H(4)i-Pr), (n-Bu4N)(2)[{Ru(eta(6)-arene)}(2)Mo6O20(OMe)(2)] (arene = C6H5Me or C6Me6) and (n-Bu4N)(2)[{Ru(eta(6)-arene)}(2)Mo6O18{MeC(CH2O)(3)}(2)] (arene = C6Me6), has been obtained. The crystal structures of these compounds have been determined by X-ray crystallography. The clusters [{Ru(eta(6)-arene)}Mo2O4[MeC(CH2O)(3)}(2)], [(Ru(eta(6)-arene)}(2)Mo2O6(OMe)(4)], [{Ru(eta(6)-arene)}(2)Mo6O20(OMe)(2)](2-) and [{Ru(eta(6)-arene)}(2)Mo6O18{MeC(CH2O)(3)}(2)](2-) were derived from known oxoalkoxopolymolybdates, [Mo3O6(OMe){MeC(CH2O)(3)}(2)](-), [Mo4O10(OMe)(6)](2-), [Mo8O24(OMe)(4)](4-) and [Mo8O20(OMe)(4){MeC(CH2O)(3)}(2)](2-), respectively, through the formal replacement of d(0)-fac-{MoO2(OMe)}(+) groups by topologically equivalent [Ru(eta(6)- arene)}(2+) units and, for the octanuclear trisalkoxo derivatives, by further substitution of two oxo ligands for the two remaining methoxo ligands. (C) 2003 Elsevier B.V. All rights reserved.