Structure of ammonium hydrogen succinate above and below the phase transition around 170K

Abstract

For crystals of ammonium hydrogen succinate it is known that the space group is P{\bar 1} with Z = 2 at 293 K and the second-order phase transition occurs around 170 K. X-ray crystal structure analyses above and below 170 K have been carried out in order to study the change in mode of short hydrogen bonds between the hydrogen succinate ions. The space group was determined to be P{\bar 1} at 150 and 190 K by structure analysis. No ordering of the H-atom positions in the short hydrogen bonds occurs by the phase transition. The hydrogen bonds show a decrease in the O...O distances with a decrease in temperature from 290 to 190 K, but no significant change in the geometries between 190 and 150 K. Disorder of the NH4 + ion is not observed at 297, 190 and 150 K. Significant change through the phase transition is found only in the geometry of one of the N—H...O hydrogen bonds between ammonium and hydrogen succinate ions.

Crystal Structure of a New Ordered form of Ammonium Hydrogen Succinate NH4HC4H4O4

“…The main interatomic distances and bond angles are gathered in Table 3. It could be noted that in the disordered form, the two carboxylic groups are equivalent with C-O bond lengths of ≈ 1.28 Å (corresponding to the bond between carbonyl carbon atom and hydroxyl group) and ≈ 1.24 Å (corresponding to the carbonyl group) [7]. These values are in agreement with the statistical distribution of hydrogen atom on the two carboxylic group in the disordered form and with its ordering position in the ordered form.…”

“…Ammonium interacts with four different hydrogen succinate molecules through the non-protonated oxygen atoms of the carboxyl groups (Figure 3), leading to the formation of four N-H···O hydrogen bonds (Table 4). Hence, in the ordered form the structural stability is achieved by one O-H···O and four N-H···O hydrogen bonds (Table 4), instead of two O-H···O and five N-H···O hydrogen bonds in the disordered form [7]. These different hydrogen bond networks are mainly explained by the different conformations of the hydrogen succinate molecules, trans in the ordered form and gauche in the disordered one, leading to different geometries of the molecule.…”

“…Their analysis by X-ray diffraction at room temperature indicates the crystallization of the title compound NH4HC4H4O4 in a new structural form also of triclinic symmetry. This new form, called ordered form, is characterized by the localization of hydrogen atom belonging to the carboxyl group on one crystallographic site, on the contrary to the other form, called disordered form, where this hydrogen atom is statistically distributed on two distinct crystallographic sites [6][7][8]. The crystal structure of the new ordered ammonium hydrogen succinate form is reported here and compared to that of the disordered one.…”

“…Numerous molecular assemblies stabilized by the existence of very short O-H···O hydrogen bonds are reported in acidic salts of succinic acid MHC4H4O4 family (M = Li + [1], Na + [2,3], K + [4], Rb + [2], Cs + [5], NH4 + [6][7][8], {(C4H4)(NH3 + )2}1/2 [9], (CH3)NH3 + [10], (C2H5)NH3 + [11], (C3H5)NH3 + [12], (C7H7O)NH3 + [13], (C8H15)NH3 + [14], (C17H22NO)NH + [15], (CH3)2NH2 + [10], (C2H5)2NH2 + [11], (C2H5O)3NH + [16,17], (C2H5)4N + [18]). Among these salts, the triclinic ammonium hydrogen succinate compound NH4HC4H4O4 evidences a second order phase transition around 170 K [6][7][8]. It was shown that this structural phase transition modifies the geometry of the hydrogen bonds between ammonium and hydrogen succinate ions, but is neither related to the loss of the center of symmetry or the formation of a superstructure, nor related to the breaking of hydrogen bonds or to the crystallographic reorganization of the hydrogen atom belonging to the carboxyl group [7,8].…”

“…Among these salts, the triclinic ammonium hydrogen succinate compound NH4HC4H4O4 evidences a second order phase transition around 170 K [6][7][8]. It was shown that this structural phase transition modifies the geometry of the hydrogen bonds between ammonium and hydrogen succinate ions, but is neither related to the loss of the center of symmetry or the formation of a superstructure, nor related to the breaking of hydrogen bonds or to the crystallographic reorganization of the hydrogen atom belonging to the carboxyl group [7,8].…”