The physicochemical behavior of a substance is fundamentally governed by its crystal structure and can be precisely tuned through isostructural chemical substitution. This atomic replacement typically occurs among atoms or ions within the same group or block of the periodic table, characterized by similar ionic radii, oxidation states, and electronegativity profiles. However, when such substitutions involve elements across different periodic blocks with distinct electronic configurations, they enable non-traditional routes for tuning material properties, often deviating from conventional structure-property relationships. In the present investigation, a novel organic vanadyl phosphate complex, [(VIVO)3(PO4)2(dien)3] (1) (dien = diethyltriamine, C4H13N3), was successfully synthesized through a hydrothermal reaction involving dien, NH₄VO₃, and Na3PO4 in aqueous medium, achieved by substituting a p-block element (phosphorus) for a d-block element (vanadium) in the prototype structure. Single-crystal X-ray diffraction analysis revealed that compound 1 maintains isostructural characteristics with its mixed-valence vanadium analogue, [V5O11(dien)3], wherein the [VVO4] moiety is replaced by the [PO4] tetrahedron. The incorporation of phosphorus and vanadium in compound 1, along with their respective oxidation states, was verified through comprehensive spectroscopic and analytical techniques. The results revealed that compound 1 exhibits substantial differences in physical properties, particularly in magnetic response and thermal stability, compared to its structural analogue.