Diethylammonium 4-hydroxybenzoate

In the crystal structure of the title compound, C4H12N+·C7H5O3 −, the cations and anions are linked by N—H⋯O and O—H⋯O hydrogen bonds, leading to the formation of a three-dimensional network.

In the crystal structure of the title compound, C 4 H 12 N + Á-C 7 H 5 O 3 À , the cations and anions are linked by N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds, leading to the formation of a three-dimensional network.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FL2305).

Comment
In recent years, study of co-crystals has attracted a great many chemists' interest since they can be exploited to improve the physical and/or chemical properties of active pharmaceutical ingredients (APIs). The hydrogen bonds in co-crystals have been widely used to design and synthesize one-, two-and three-dimensional supramolecular compounds (Aakeroÿ et al., 2002).Research into hydrogen bonds experienced a stagnant period in the 1980 s, but re-opened around 1990, and has been in rapid development since then. 4-Hydroxybenzoic acid is a good hydrogen bond donor and can form co-crystals with other organic molecules (Vishweshwar et al., 2003). In this paper, we used 4-Hydroxybenzoic acid and diethylamine to synthesize the co-crystal compound (I).
Compound (I) consists of a diethylamine cation and a 4-hydroxybenzoic acid anion ( Fig. 1), therefore, it is a molecular salt. The -NH2 groups of the cations act as hydrogen-bond donors to the O atoms of the carboxyl group of the anions.
Moreover, the hydroxyl H atom of the anions also act as hydrogen-bond donors to tone of the O atoms of a neighboring carboxyl group of the 4-hydroxybenzoic acid anions to form a three-dimension network ( Fig. 2 and Table 1). One of the H atoms of the -NH2 group links to both O atoms of the -COOH group in an adjacent molecule via two N-H···O bonds such that two cations and two anions are linked by hydrogen bonds to form an eight-membered ring.

Experimental
All reagents were commercially available and of analytical grade. 4-Hydroxybenzoic acid (0.78 mmol, 0.108 g) and diethylamine (0.78 mmol, 0.057 g) were dissolved in ethanol (15 ml). The mixture was stirred for 10 min at room temperature and then filtered. Colorless crystals suitable for data collection were obtained after several days.

Refinement
The H atoms bonded to C atoms were positioned geometrically and refined as riding, with C-H = 0.93-0.97 Å and U iso (H) = 1.2 or 1.5 U eq (C) while the H atoms bonded to the N atom and the hydroxy group were located in a difference Fourier map, with N-H = 0.90 Å and O-H = 0.82 Å and then refined with a riding model as was used for the H atoms on the C atoms.