The established biochemical potential of vanadium- has spurred considerable research interest in our lab, with specific focus on pertinent synthetic studies of vanadium(III) with a biologically relevant,. organic, dicarboxylic acid, malic acid, in:aqueous solutions. Simple reactions between VCl3 and malic acid in water, at different pH values, in the presence of H2O2, led to the crystalline dimeric complexes (Cat)(4)[VO(O-2)(C4H3O5)](2). nH(2)O (Cat K+, n = 4, 1; Cat = NH4+, n = 3, 2) and K-2[VO(O-2)(C4H4O5)](2). 2H(2)O (3). All three complexes were:characterized by elemental analysis, FT-IR, and UV/visible spectroscopies. Compound 1 crystallizes in the monoclinic space group P2(1)/c, with a 8.380(5) Angstrom, b = 9.252(5) Angstrom, c = 13.714(8) Angstrom, beta = 93.60(2)degrees, V = 1061(1) Angstrom (3), and Z = 4. Compound 2 crystallizes in the triclinic space group Pi, with a = 9.158(4) Angstrom (3), b = 9.664(4), c = 14.185(6) Angstrom, alpha = 104.81(1)degrees, beta = 90.31(1)degrees; gamma = 115.643(13)degrees, V = 1085.0(7) Angstrom (3), and Z = 2. Compound 3 crystallizes in the monoclinic space group P2(1)/c, with a 9.123(8) Angstrom, b = 9.439(8) Angstrom, c = 10.640(9) Angstrom, beta = 104.58(3)degrees, V = 887(1) Angstrom (3), and Z = 2. The X-ray structures showed that, in 1 and 2; the dimers consist of two (V-V=O)(2)O-2 rhombic units to which two malate ligands are attached. The ligands are triply deprotonated and, as such, they coordinate,to vanadium(V), promoting a pentagonal bipyramidal geometry. In 3, the dimeric (V-V=O)(2)O-2 rhombic unit persists, with the two doubly deprotonated malate ligands coordinated to the vanadium(V) ions. UV/vis and EPR spectroscopic studies on the intermediate blue solutions of the synthesis reactions of 1-3 support the existence of vanadyl-containing dimeric species. These species further react with H2O2 to yield oxidation of (V2O2)-O-IV to (V2O2)-O-V and coordination of the peroxide to vanadium(V). From the collective data on 1-3, it appears that pH acts as a decisive factor in dictating;the structural features of the isolated complexes. The details of the introduced structural differentiation in the reported complexes, and their potential relevance to vanadium(V) dicarboxylate systems in biological media are dwelled-on.