Guanidinium 2-phenylacetate

In the structure of the title salt, CH6N3 +·C8H7O2 −, the guanidinium cation gives three cyclic hydrogen-bonding interactions with O-atom acceptors of three independent phenylacetate anions, one R 2 2(8) and two R 2 1(6), giving one-dimensional columnar structures which extend down the 42 axis in the tetragonal cell. Within these structures, there are solvent-accessible voids of volume 86.5 Å3.

In the structure of the title salt, CH 6 N 3 + ÁC 8 H 7 O 2 À , the guanidinium cation gives three cyclic hydrogen-bonding interactions with O-atom acceptors of three independent phenylacetate anions, one R 2 2 (8) and two R 2 1 (6), giving onedimensional columnar structures which extend down the 4 2 axis in the tetragonal cell. Within these structures, there are solvent-accessible voids of volume 86.5 Å 3 .

Comment
The known structures of the guanidinium salts of simple monocyclic aromatic carboxylic acids comsist of those with benzoic acid (Pereira Silva et al., 2007), 4-aminobenzoic acid (Pereira Silva et al., 2010), 4-nitrobenzoic acid (Kleb et al., 1998) and 3-nitrobenzoic acid (Smith & Wermuth, 2010). In these anhydrous structures the guanidinium cation is usually involved in cyclic hydrogen-bonding associations through N-H···O carboxyl links [graph sets R 2 2 (8) or R 2 1 (6) (Etter et al., 1990)] giving most commonly three-dimensional structures. The structure of the guanidinium salt of phenylacetic acid had not been previously reported so we carried out the 2:1 stoichiometric reaction of phenylacetic acid with guanidinium carbonate in aqueous ethanol solution, providing colourless crystals of the title compound, CH 6 N 3 + C 8 H 7 O 2 -(I) when recrystallized from water.
In the structure of (I) (

Experimental
The title compound was synthesized by heating together under reflux for 10 minutes 1 mmol of phenylacetic acid and 0.5 mmol of guanidinium carbonate in 50 ml of 50% ethanol-water. After concentration to ca 30 ml, room temperature evaporation of the hot-filtered solution gave a colourless powder which was recrystallized from a minimum volume of water, giving on total evaporation, crystal plates of (I) (m.p. 443 K), from which a specimen suitable for X-ray analysis was cleaved.

Refinement
Hydrogen atoms involved in hydrogen-bonding interactions were located by difference methods and their positional and isotropic displacement parameters were refined. The H atoms were included in the refinement in calculated positions (C-H aromatic = 0.93 Å and C-H aliphatc = 0.97 Å) and treated as riding, with U iso (H) = 1.2U eq (C).
supplementary materials sup-2 Figures   Fig. 1. Molecular configuration and atom naming scheme for the guanidinium cation and the phenylacetate anion in (I). Inter-species hydrogen bonds are shown as dashed lines. Displacement ellipsoids are drawn at the 40% probability level. Fig. 2. The hydrogen-bonding extensions of the basic asymmetric unit in the structure of (I), showing the three cyclic cation-anion hydrogen-bonding associations as dashed lines. Nonassociative hydrogen atoms are deleted. For symmetry codes, see Table 1. as those based on F, and R-factors based on ALL data will be even larger.