Plate-shaped, colorless crystals were grown from a solution, originating with the reaction of P4S10 and NH4F in CH3CN. By a molar ratio of 4NH4F/P4S10, third of P4S10 reacted to Di-(acetamidinium)-difluoropentathiodiphosphate, [CH3C(NH2)2]2P2S5F2. Crystals are melting in the range of 134 – 142 °C under their decomposition. The crystal structure has been determined from three-dimensional MoKβ data, collected on a CAD-4 diffractometer. It crystallizes in the space group C2/c with four formula units in a cell of dimensions a = 10.600(5) b = 10.069(5) c = 15.129(8) Ā β = 92,35(5)° with V = 1613.4 Ā3, Do = 1,557 g.cm−3, Do 1.49 g.cm−3. The structure was solved by the direct methods program system MULTAN 82 and anisotropically refined by least-squares techniques to a final R = 0,037 based on 966 independent intensities. The hydrogen atoms were located from a difference map. The difluoropentathiodiphosphate-anion consists of two PS3F-tetrahedra which are connected together by a common sulfur atom. This bridge-atom occupies a special equivalent position on a twofold rotation axis, therefore the anion shows the point symmetry 2. Bond distances and angles within the tetrahedra have the usual values (P-Sbridge = 2,075(1) Ā, P-Sterminal = 1.951(1) and 1.944(1) Ā, P-F = 1.577(2) Ā), < P-S-P = 107.8(1)°. The nitrogen- carbon-atoms of the acetamidinium-cation are lying in plane. Bonds lengths are: CC = 1.485(5) Ā, CN = 1.301(4) and 1.280(5) Ā. There are hydrogen bonds in the structure.
