Bis(N,N′,N′′-triisopropylguanidinium) fumarate–fumaric acid (1/1)

The asymmetric unit of the title compound, C10H24N3 +·0.5C4H2O4 2−·0.5C4H4O4, comprises a triisopropylguanidinium cation, half of a fumarate dianion and half of a fumaric acid molecule; both the fumarate dianion and the fumaric acid molecule are located on inversion centres. In the crystal, intermolecular O—H⋯O hydrogen bonds between the carboxyl groups of the fumaric acid molecules and the carboxylate groups of the fumarate anions lead to the formation of a hydrogen-bonded supramolecular twisted chain along the b axis. The triisopropylguanidinium cations interact with the fumarate–fumaric acid chains via extensive N—H⋯O and C—H⋯O hydrogen bonds, leading to a ladder arrangement, with the cation being the rungs that bridge three curled chains of fumarate–fumaric acid. The crystal packing is stabilized by N—H⋯O and C—H⋯O (cation⋯fumarate/fumaric) and O—H⋯O (fumarate⋯fumaric) hydrogen bonds, consolidating a three-dimensional network.

The asymmetric unit of the title compound, C 10 H 24 N 3 + Á-0.5C 4 H 2 O 4 2À Á0.5C 4 H 4 O 4 , comprises a triisopropylguanidinium cation, half of a fumarate dianion and half of a fumaric acid molecule; both the fumarate dianion and the fumaric acid molecule are located on inversion centres. In the crystal, intermolecular O-HÁ Á ÁO hydrogen bonds between the carboxyl groups of the fumaric acid molecules and the carboxylate groups of the fumarate anions lead to the formation of a hydrogen-bonded supramolecular twisted chain along the b axis. The triisopropylguanidinium cations interact with the fumarate-fumaric acid chains via extensive N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, leading to a ladder arrangement, with the cation being the rungs that bridge three curled chains of fumarate-fumaric acid. The crystal packing is stabilized by N-HÁ Á ÁO and C-HÁ Á ÁO (cationÁ Á Áfumarate/ fumaric) and O-HÁ Á ÁO (fumarateÁ Á Áfumaric) hydrogen bonds, consolidating a three-dimensional network.

Experimental
Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL. In connection with ongoing studies of the structural aspects of N,N′,N"-trisubstituted guanidinium salts (Said et al., 2011), we herein report the crystal structure of the title compound (Fig. 1). The bond distances and bond angles in the title compound agree very well with the corresponding bond distances and bond angles reported in a similar compound earlier (Said et al., 2005). The central guanidinium fragment of the cation is planar (sum of NCN angles is 360°).  Table 1). This type of carboxyl-carboxylate interaction has been reported in the several crystal structures containing fumarate-fumaric acid species with different cations (Hemamalini & Fun, 2010, Büyükgüngör et al., 2004 indicating the stability of such a supramolecular motif. The triisopropyl guanidinium cations are bridging three fumarate-fumaric curled chains via extensive N-H···O hydrogen bonds (Table 1), forming triply bridged twisted chains, leading to a ladder type arrangement with guanidinium cation forming rungs (Fig. 2). The extensive hydrogen bonding interactions between the fumarate-fumaric acid chains and the ladder of guanidinium rungs along the b-axis consolidate the three-dimensional network.
Experimental N,N′,N"-Triisopropylguanidine was prepared according to literature methods (Ong et al., 2003). In a round bottom flask, a mixture fumaric acid (0.395 mmol) and N,N′,N"-triisopropylguanidine (0.395 mmol was dissolved in THF (10 ml). The reaction mixture was stirred, and a colorless precipitate formed over the next few minutes. The solid was removed by filtration and the product was crystallized from a mixture of THF:methanol (1:2) to give colorless crystals of the title compound (92% yield).

Refinement
Hydrogen atoms were included in calculated positions and refined as riding on their parent atoms with N-H = 0.88 Å, O -H = 0.84 Å and C-H = 0.95-1.0 Å and U iso (H) = 1.2U eq (non-methyl C/N) or 1.5U eq (methyl C/O). Due to the quality of crystal we did not observe significant diffraction data past 0.95 Å resolution, therefore the data set was trimmed to that value to reduce data to noise ratio and improve the quality of the final refinement.

Figure 1
The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are presented as small spheres of arbitrary radius. Symmetry operations: (i) 2 -x,-y, 1 -z; (ii) -x, 1 -y, 1 -z.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.22 e Å −3 Δρ min = −0.18 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.013 (2) Special details Experimental. Data collection is performed with three batch runs at phi = 0.00 ° (650 frames), at phi = 120.00 ° (650 frames), and at phi = 240.00 ° (650 frames). Frame width = 0.30 ° in omega. Data is merged, corrected for decay (if any), and treated with multi-scan absorption corrections (if required). All symmetry-equivalent reflections are merged for centrosymmetric data. Friedel pairs are not merged for noncentrosymmetric data. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.