METAL-HYDROXYCARBOXYLATE INTERACTIONS - SYNTHESES AND STRUCTURES OF K-2[VO2(C6H6O7)](2)CENTER-DOT-4H(2)O AND (NH4)(2)[VO2(C6H6O7)](2)CENTER-DOT-2H(2)O

Potassium and ammonium dimeric (citrato)dioxovanadium(V) hydrate K-2[V O2(H(2)cit)](2) . 4H(2)O 1 and (NH4)(2)[VO2(H(2)Cit)](2) . 2H(2)O 2 (H (4)Cit = citric acid) have been prepared and characterized by X-ray st ructure analyses. Vanadate 1 crystallizes in the monoclinic space grou p P2(1)/n (No. 14) with unit cell parameters: a = 9.304(2), b = 11.756 (2), c = 11.911(2)Angstrom, beta = 111.72(3)degrees, and D-c = 1.911g/ cm(3), Z = 2; Vanadate 2 also crystallizes in the monoclinic space gro up P2(1)/n with unit cell parameters: a = 9.719(2), b = 11.111(3), c = 11.294(2)Angstrom beta = 109.03(2)degrees, and D-c = 1.781g/cm(3), Z = 2. Each dimer contains a centro-symmetric planar four-member V2O2 ri ng with two exocyclic citrate entities coordinated by the oxygen atoms of the hydroxy- and alpha-carboxylate ligands, while the other two be ta-carboxylate groups remain uncomplexed. Principal dimensions of the V-O bonds are 1.986(4)(av) (hydroxy) and 1.980(3)Angstrom(alpha-carbox yl) for vanadate 1, 1.988(2)(av) (hydroxy) and 1.974(3)Angstrom(alpha- carboxyl) for vanadate 2.