Two new ammonium diphosphates, Mn 0.5 NH 4 H 2 P 2 O 7 ·H 2 O (1) and MnNaNH 4 P 2 O 7 ·3H 2 O (2) , have been synthesized and investigated by single crystal X-ray diffraction. Compound (1) crystallizes in the triclinic space group P 1̅, and the unit cell dimensions are a = 7.0029(2) Å, b = 7.4401(2) Å, c = 7.8771(2) Å, α = 80.444(1)°, β = 71.359(1)°, γ = 87.408(1)°, V = 383.48(2) Å 3 , Z = 2; compound (2) crystallizes in the monoclinic space group Cc , with the following unit cell dimensions: a = 10.1124(4) Å, b = 16.4448(7) Å, c = 5.6000(3) Å, β = 104.304(2)°, V = 902.39(7) Å 3 , Z = 4. Final residuals are: R = 0.0281 and w R = 0.0769, by using 2356 reflections with I > 2 σ ( I ), for (1) ; R = 0.0301 and w R = 0.0682, by using 2322 reflections with I > 2 σ ( I ), for (2) . The crystal packing of Mn 0.5 NH 4 H 2 P 2 O 7 ·H 2 O consists of layers parallel to ac plane formed by MnO 6 regular octahedra, H 2 P 2 O 7 double tetrahedra and ammonium cations. Strong hydrogen bonds embed the dihydrogendiphosphate groups in the framework. The crystal packing of MnNaNH 4 P 2 O 7 ·3H 2 O is made up of layers of P 2 O 7 double tetrahedra, NaO 7 monocapped octahedra and MnO 6 regular octahedra down c . Water and ammonium cations molecules fill up the cavities between the above mentioned polyhedra. Strong hydrogen bonds complete the network.
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Capitelli et al. (2004) studied this question.