Bis(ethanolaminium) succinate–succinic acid (1/1)

The asymmetric unit of the title compound, 2C2H8NO+·C4H4O4 2−·C4H6O4, consists of half a succinate anion, half a succinic acid molecule and one ethanolaminium cation. The succinate anion and succinic acid molecule, both of which are located on inversion centres, are linked by O—H⋯O hydrogen bonds, forming a chain along the [20] direction. The chain and the ethanolaminium cation are further connected by O—H⋯O and N—H⋯O hydrogen bonds.

The asymmetric unit of the title compound, 2C 2 H 8 NO + Á-
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: IS2756).
As shown in Fig. 1, the asymmetric unit is composed of one ethanolaminium cation, half a succinate anion, and half a succinic acid molecule. The succinate anion and succinic acid molecule are linked by an O2-H2···O4 hydrogen bond (  (Borthwick, 1980). This is mixed mode of succinate and succinic acid, and is similar to those observed in other cases (Prasad & Vijayan, 1990;Li et al., 2003;Bruno et al., 2004).
The succinate anion and the succinic acid molecule are arranged almost in the same layers (Fig. 2), and the ethanolaminium cation are sandwiched between the layers by O-H···O and N-H···O hydrogen bonds (Table 1).

Experimental
Succinic acid (5.1 g) and ethanolamine (2.4 g), in a molar ratio of 1:1, were mixed and dissolved in sufficient ethanol by heating to 373 K, at which point a clear solution resulted. The system was then cooled slowly to room temperature. Crystals of (I) (4.3 g) were formed, collected and washed with ethanol.