A crystalline product of the reaction of adenosine with vanadate has been obtained from aqueous solution. Its structure has been determined from X-ray diffraction studies and this structure related to the products of equilibration in aqueous solution. The crystalline product was found to contain two vanadium nuclei and two adenosine moieties in a dimeric structure. Each vanadium was coordinated in an irregular pentacoordinate arrangement. H-1 and V-51 timecourse NMR studies at reduced temperature in acetone/water solvent provided strong evidence that the crystal structure was maintained in solution and that related structures were the source of the other major products found in equilibrated solutions. Crystal structure of [NEt(4)](2)[{VO(2)Ad}(2)]. 4.74H(2)O : monoclinic, space group P2(1); Z = 2; a = 13.676(2) Angstrom; b = 11.625(2) Angstrom; c = 15.306(2) Angstrom; beta = 95.525(9)degrees; V = 2422.0 Angstrom(3); T = 200 K; R(F) = 0.029 for 4400 data (I-0 greater than or equal to 2.5 sigma(I-0)) and 652 variables.