SYNTHESIS AND CHARACTERIZATION OF BINUCLEAR OXO-VANADIUM COMPLEXES OF CARBON OXOANION LIGANDS - CRYSTAL-STRUCTURES OF THE BINUCLEAR VANADIUM(IV) COMPLEX (NH4)[V2O2(OH)(C4O4)(2)(H2O)(3)]CENTER-DOT-H2O, OF THE MIXED-VALENCE VANADIUM(V)/VANADIUM(IV)-SQUARATE SPECIES [(N-C4H9)(4)N][V2O3(C4O4)(2)(H2O)(3)]CENTER-DOT-3H2O AND [(C4H9)(4)N](4)[V4O6(C4O4)(5)(H2O)(4)]CENTER-DOT-6H2O, AND OF THE BINUCLEAR VANADIUM(IV)-OXALATE SPECIES [V2O2CL2(C2O4)(CH3OH)(4)]CENTER-DOT-2PH(4)CL

Under reducing conditions, aqueous vanadium-oxo solutions react with squaric acid to give the binuclear V(IV) species NH4[V2O2(OH)(C4O4)(2)(H2O)(3)].H2O (1.H2O) In the absence of reducing agents and upon addition of (C4H9N)(4)NBr, vanadate solutions react with squaric acid to give the binuclear mixed-valence species [(C4H9)(4)N][V2O3(C4O4)(2)(H2O)(3)].3H(2)O (2.3H(2)O). The structure of the anion [V2O3(C4O4)(2)(H2O)(3)](2-) consists of the {V2O3-(mu-H2O)}(3+) core with the vanadium sites bridged additionally by two mu-1,2-squarate ligands and with an aquo ligand on each vanadium center completing the coordination. From the filtrate are isolated 2.3H(2)O and dark brown crystals of [(C4H9)(4)N](4)[V4O6(C4O4)(5)(H2O)(4)].6H(2)O (3.6H(2)O) after 2 weeks of standing at room temperature. The tetranuclear mixed-valence V(IV)/V(V) species 3.6H(2)O exhibits a structure consisting of two binuclear [V2O3(C4O4)(H2O)(2)](0) units bridged by a (mu-1,3) squarate group. The structure thus exhibits both mu-1,2- and mu-1,3-squarate ligands. While analogous oxalate derivatives were not isolated from reactions in aqueous solvent, the binuclear V(IV) species [V2O2Cl2(C2O4)(CH3OH)(4)].2Ph(4)PCl (4.2Ph(4)PCl) was prepared by the reaction of a suitable binuclear V(IV) precursor with oxalic acid in methanol. The structural core of the neutral [V2O2Cl2(C2O4)(CH3-OH)(4)] consists of a planar {V2O2Cl2(C2O4)} unit; the methanol ligands occupy positions normal to this moiety. Crystal data: 1.H2O, monoclinic, P2(1)/n, a = 11.554(2) Angstrom, b = 6.568(1) Angstrom, c = 13.436(3) Angstrom, beta = 108.76(3)degrees, V = 965.5(5) Angstrom(3), Z = 4, D-calc = 1.638 g cm(-3), 867 reflections, R = 0.0763; 2.3H(2)O, triclinic, <P(1)over bar>, a = 11.628(2) Angstrom, b = 14.990(3) Angstrom, c = 10.746(2) Angstrom, alpha = 108.49(3)degrees, beta = 99.02(3)degrees, gamma = 98.13(3)degrees, V = 1717.5(9) Angstrom(3), Z = 2, D-calc = 1.399 g cm(-3), 2741 reflections, R = 0.0597; 3.6H(2)O, triclinic, <P(1)over bar>, a = 16.670(3) Angstrom, b = 18.440(4) Angstrom, c = 20.151(4) Angstrom, alpha = 65.96(2)degrees, beta = 69.14(3)degrees, gamma = 80.10(3)degrees, V = 5284(3) Angstrom(3), Z = 2, D-calc = 1.261 g cm(-3), 2858 reflections, R = 0.0832; 4.2Ph(4)PCl, monoclinic, P2(1)/c, a = 10.906(2) Angstrom, b = 14.724(3) Angstrom, c = 17.574(3) Angstrom, beta = 94.93(2)degrees, D-calc = 1.387 g cm(-3), 1397 reflections, R = 0.0688.