Crystal Structure of a Cyclohexylammonium Salt of the N-(2,2-Difluoro-2-phosphonoethanethioyl)aspartate: A Difluorinated N-(Phosphonoacetyl)- L -aspartate (PALA) Thio Analogue

The title compound, a cyclohexylammonium salt of N-(2,2-difluoro-2-phosphonoethanethioyl)aspartate, {(C6H4F2NO7PS)4-. 4[(C6H11-NH3)+]} crystallizes in the triclinic space group P1 with the following cell parameters: a = 11.335(2)A, b = 12.849(3)A, c = 14.353(3)A, α = 83.14(3)°, β = 86.75(3)°, γ = 84.81(3)°, V = 2064.7(7)A3, Z = 1 and Dx = 1.184 g cm-3. The structure was refined to a final R value of 0.0745 for 5790 reflections [I>2σ(I)]. This structure consists of two anionic N-(2,2-difluoro-2-phophonoethanethioyl)aspartate moieties and eight cationic cyclohexylammonium entities; among them, three are disordered. In addition, one water and one ethanol molecules are present. X-ray analysis shows that it possesses a sandwich-type layer structure, consisting of mutually stacking polar layers with an important hydrogen-bonding network and hydrophobic layers consisting of disordered cyclohexyl parts of cationic moieties.