A general synthetic approach to rationalize the solution preparative chemistry of oxovanadium phosphates containing organic species as structural directing agents is presented. Careful attention is payed to the hydrolysis and condensation processes involving the ionic species in solution, and a simple restatement of the partial charge model (PCM) has been used in order to organize the experimental results. The structure of a new V(IV)-Fe(III) bimetallic oxovanadium phosphate, [H3N(CH2)(2)NH3](2)[H3N(CH2)(2)NH2] [Fe-III(H2O)(2)((VO)-O-IV)(8)(OH)(4)(HPO4)(4)(PO4)(4)].-4H(2)O, has been determined by X-ray single crystal diffraction methods. This compound crystallizes in the monoclinic system, space group P2(1)/n and the cell dimensions are as follows : a = 14.383(3) Angstrom, b = 10.150(2) Angstrom, c = 18.355(4) Angstrom, and beta = 90.39(3)degrees (Z = 2). The existence of a complex intercrossing channel system, including a very large channel of 18.4 Angstrom of diameter (in which both water molecules and ethylenediamine species are located), is the more interesting feature of this structure. Thermal decomposition, including the dehydration/rehydration process, has been studied by thermal analysis and variable temperature X-ray powder diffraction techniques. A complementary SEM study of the different intermediate decomposition products is presented.