Four novel polyoxotungstates have been synthesized by reaction of the sandwich type compound [Fe-4(III)(H2O)(10)(B-beta-SbW9O33)2](6-) (noted Fe-4(H2O)(10)Sb2W18) with ethylenediamine (en) and/or oxalate (ox) ligands under various conditions. The one-dimensional (1D) compound [enH(2)](3)[Fe-4(III)(H2O)(8)(SbW9O33)(2)]center dot 20H(2)O (1) is isolated at 130 degrees C and results from the elimination of two water molecules and the condensation of the polyoxotungstate precursor. The reaction of Fe-4(H2O)(10)Sb2W18 with oxalate ligands affords the molecular complex Na-14[Fe-4(III)(ox)(4)(H2O)(2)(SbW9O33)(2)] center dot 60H(2)O (2) where two organic ligands substitute four water molecules, while the same reaction in the presence of en molecules at 130 degrees C leads to the formation of the functionalized 1D chain [enH(2)](7)-[Fe-4(III)(ox)(4)(SbW9O33)(2)] center dot 14H(2)O (3) with protonated ethylenediamine counterions. Finally, at 160 degrees C a rearrangement of the Fe-4(H2O)(10)Sb2W18 polyoxotungstate is observed, and the sandwich type compound [enH(2)](5)[(Fe2Fe2II)-Fe-II(enH)(2)((FeW9O34)-W-III)(2)] center dot 24H(2)O (4) crystallizes. In 4, the heteroelement is a Fe-III ion, and the water molecules on the two outer Fe-II centers are bound to pendant monoprotonated en ligands. The four compounds have been characterized by IR spectroscopy, thermogravimetric analysis, and single crystal X-ray diffraction. A detailed study of the magnetic properties of the mixed-valent hexanuclear iron complex in 4 shows evidence of an S = 5 ground-state because of spin frustration effects. A quantification of the electronic parameters characterizing the ground state (D = +1.12 cm(-1), E/D = 0.15) confirms that polyoxotungstate ligands induce large magnetic anisotropy.