Crystal Structures of Ammonium Propionates: (NH4)[HProp2] and (NH4)Prop (Prop– = C2H5COO–)

Two crystalline compounds - (NH 4 )HProp 2 and (NH 4 )Prop (HProp = C 2 H 5 COOH) are obtained by the interaction of ammonia with propionic acid. Their crystal structures are determined by X-ray diffraction. Both compounds crystallize in the monoclinic crystal system (space groups C 2/ c and P 2 1 / n respectively) and consist of alternating and Prop – ions (or hydrogen-bonded pairs Prop–H⋯Prop – ) organized into a 3D framework via hydrogen bonds. The structural feature of the (NH 4 )HProp 2 compound, namely, the positional disorder of acidic hydrogen atoms between carboxyl groups of propionate anions, is studied by maximum entropy and DFT methods. Similar to homologous ammonium carboxylates, (NH 4 )Prop is extremely unstable under atmospheric conditions whereas (NH 4 )HProp 2 acidic salt is stable during storage and can be used for the further synthesis of metal propionates.