POLYNUCLEAR COMPLEXES OF OXO-VANADIUM AND OXO-MOLYBDENUM WITH THE DIANION OF SQUARIC ACID AS BRIDGING LIGAND - CRYSTAL-STRUCTURES OF [C(NH2)(3)](4)[V2O2F4(C4O4)(2)]CENTER-DOT-4H(2)O, [(N)BU(4)N](4)[V3O3F4(C4O4)(3)]CENTER-DOT-2H(2)O, [ET(4)N](3)[MO3O8F(C4O4)(2)], [ET(4)N](4)[MO4O10F6(C4O4)] AND [ET(4)N](3)[MO2O3CL3(C4O4)(2)]

Aqueous or methanolic solutions containing vanadium(IV), molybdenum(V) and molybdenum(VI) oxo species and fluoride ions react with squaric a cid to give the oligonuclear complexes [C(NH2)(3)](4)[V2O2F4(C4O4)(2)] . 4H(2)O (1), Cs-4[V3O3F4(C4O4)(3)]. 5H(2)O (2a), [(BU4N)-B-n](4)[V3O3 F4(C4O4)(3)]. 2H(2)O (2b), [Et(4)N](4)[Mo4O10F6(C4O4)] (3a), [Et(4)N]( 4)[Mo4O10Cl6(C4O4)] (3b), [Et(4)N]3[Mo3O8F(C4O4)(2)] (4) and [Et(4)N]( 3)[Mo2O3Cl3(C4O4)(2)] (5). The structures of compounds 1, 2a, 2b, 3a, 4 and 5 have been determined by single crystal X-ray diffraction. The [V2O2F4(C4O4)(2)](4-) ion in 1 consists of the planar V2O2F4 core with the vanadium sites bridged by two mu-1,2-squarato Ligands. The unique cone-shaped [V3O2F4(C4O4)(3)](4-) ion in 2a and 2b contains a central defect and severely distorted V3F4 cubane unit. Each vanadium atom be ars a terminal oxo ligand; pairs of vanadium atoms are bridged by mu-1 ,2-squarato ligands. The [Mo4O10F6(C4O4)](4-) ion in 3a consists of a squarate ion, which is coordinated to four metal centers. Pairs of met al atoms are bridged by mu(O)mu(F)-bridges. Two terminal oxo ligands a nd one terminal fluoro ligand complete the metal coordination. Oxo and fluoro ligands are partly disordered. The structure of the [Mo3O8F(C4 O4)2](3-) ion in 4 is related to the structure of [V3O3F4(C4O4)(3)](4- ) It consists Of a defect Mo-3(O3F) cubane unit. Two pairs of molybden um atoms are bridged by mu-1,2-squarato ligands. Terminal oxo and diox o groups complete the molybdenum coordination. The [Mo2O3Cl3(C4O4)(2)] (3-) ion in 5 exhibits a unique structure with a planar OClMo(mu-O)(mu -Cl)MoOCl core and a cis, cis-orientation of the oxygen ligands. Two m u 1,2-squarato ligands bridge the molybdenum centers above and below t he Mo2O3Cl3 plane.