Synthesis and characterisation of new binuclear oxo-vanadium(IV) complexeswith a bis(bidentate)oxalate bridge. Crystal structures of the cationic and anionic complexes [V2O2(C2O4)(H2O)(6)]Cl-2 center dot 4Bu(4)NCl center dot H2O and [FeCp2*](2)[Et4N](2)[V2O2(C2O4)(NCS)(6)]

The new oxalate - vanadyl compounds [V2O2(C2O4)(H2O)(6)]Cl-2. 4Bu(4)NCl .H2 O (1) (Bu = C4H9) and [Et4N](4)[V2O2(C2O4)(NCS)(6)] (2 ') (Et = C2H5) have been synthesized starting from V2O5 and VOSO4. 5H(2)O respectively. Metathe sis of 2' with [FeCp2*]BF4 (Cp* = C-5(CH3)(5)) gave a partial substitution of the cations affording [FeCp2*](2)[Et4N](2)[V2O2(C2O4)(NCS)(6)] (2). The X-ray structures of 1 and 2 have been determined. In both complexes, which crystallise in the monoclinic space group P2(1)/c, the centrosymmetric binu clear vanadium species present a bis(bidentate)oxalate ligand and an almost planar [V2O2(C2O4)X-2] unit (X = O-(H2O) for 1 and N-(NCS) for 2) with two V=O groups located in trans positions in the equatorial plane. In both cas es, the strong V=O terminal bond (1.569(7) in 1, 1.580(7) Angstrom in 2) ha s a strong trans influence which is slightly greater in the cation of 1 tha n in the anion of 2, Magnetic susceptibility measurements indicate weak ant iferromagnetic pairwise interactions for 1, 2 and 2'. (C) 2000 Elsevier Sci ence S.A. All rights reserved.