Chemical preparation, crystal structure and vibrational study are reported for a new diphenylhydrazine dihydrogenophosphate monocrystal DPHDP (C6H9N2)2H2P2O7 .This organic cationic diphosphate (C6H9N2)2H2P2O7 was synthesized by the method of ion exchange resin. (C6H9N2)2H2P2O7 crystallizes in the monoclinic system, with a merit factor of 0.0285, space group P21/c, a = 7,1991 (2) Å, b = 8,0209 (4) Å, c =31,2070(2) Å, β = 93,577(1)°, Z = 4, V = 1798.5 (1) Å3. The crystal structure was refined down to R = 0.027, R = 0.069 for 1830 reflections satisfying criterion I ≥ 2σ (I). The structural resolution shows the existence of H2P2O72- ion chains linked together by hydrogen bonds. The organic cations C6H9N2+ and the phosphate chains are linked together by hydrogen bonds. Diphosphate group adopt an eclipsed configuration. A network of O-H... O hydrogen bonds reinforce the cohesion of the structure. The vibrational study by IR absorption spectroscopy of the title compound reveals the presence of three bands and conﬁrms the existence of non-equivalent positions of water molecules in the structure.
(C6H9N2)2H2P2O7 is a non linear optical NLO product as it is not centrosymetric.