A novel synthetic route was elaborated to obtain Cu/V10O28 compounds in a one-pot procedure based on a "direct synthesis" approach using water or dmf as a solvent and ethylenediamine as a ligand. The crystalline compounds (H(2)en)(2)[Cu(en)(2)(H2O)(2)][V10O28]center dot 4H(2)O (1), (H3O)(2)[{Cu(en)(2)(H2O))(2)V10O28]center dot 3H(2)O (2), [(Cu(en)(2)}(3)(V10O28)]center dot 6H(2)0 (3) and (H(2)en)(3)[V10O28]center dot 2H(2)O (4), with copper-to-vanadium ratios of 1:10, 2:10, 3:10 and 0:10, respectively, were isolated and characterized by single-crystal X-ray analysis, FTIR, magnetic measurements and EPR spectroscopy. As proven by EPR measurements on the reaction solutions, the reactions pass through the formation of V(IV) species. However, from BVS analysis of the crystal structures, it is clear that all V atoms in the final products have the +5 oxidation state. A probable mechanism of the reactions taking place during the synthesis was proposed based on additional synthetic experiments and EPR data. The vibrational spectra of the V10O286- adducts with water, ammonia, H(2)en(2+) and copper complex species, as well as differently protonated decavanadates, were simulated based on quantum-chemical calculations, allowing the assignment of additional bands in the 990-970 cm(-1) region to the (delta(VOH) vibrations and modes arising due to strong H-bonding of protic molecules to the decavanadate moiety.