Bis[1-(isopropylideneamino)guanidinium] bis(3-nitrobenzoate) monohydrate

The asymmetric unit of the title salt hydrate, 2C4H11N4 +·2C7H4NO4 −·H2O, comprises two independent 1-(isopropylideneamino)guanidinium cations, two independent 3-nitrobenzoate anions and a water molecule of crystallization. There are minimal geometric differences between the two planar [maximum deviations 0.061 (2) and 0.088 (2) Å] cations, and between the two almost planar anions [C–C–C–O and C–C–N–O torsion angles of 0.3 (3) and 11.1 (4) °, respectively in the first anion and −173.7 (2) and −0.1 (4), respectively in the second anion]. Extensive O—H⋯O and N—H⋯O hydrogen bonding between all components of the structure leads to the formation of a two-dimensional array with an undulating topology in the bc plane.

The asymmetric unit of the title salt hydrate, 2C 4 H 11 N 4 + Á-2C 7 H 4 NO 4 À ÁH 2 O, comprises two independent 1-(isopropylideneamino)guanidinium cations, two independent 3-nitrobenzoate anions and a water molecule of crystallization. There are minimal geometric differences between the two planar [maximum deviations 0.061 (2) and 0.088 (2) Å ] cations, and between the two almost planar anions [C-C-C-O and C-C-N-O torsion angles of 0.3 (3) and 11.1 (4) , respectively in the first anion and À173.7 (2) and À0.1 (4), respectively in the second anion]. Extensive O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonding between all components of the structure leads to the formation of a two-dimensional array with an undulating topology in the bc plane.
Not surprisingly from the constitution of (I), there is extensive hydrogen bonding at play in the crystal structure. The most prominent intermolecular interactions are of the type O-H···O and N-H···O, Table 1. The water molecule provides two donor interactions to two benzoate-O atoms and accepts two hydrogen bond from two N8-amino groups derived from two different cations. The later interactions occur around a centre of inversion and results in the formation of eight-membered {···HNH···O} 2 synthons. The C15-guanidinium cation utilizes all five acidic-H atoms to hydrogen bond to four oxygen atoms, derived from three symmetry related benzoate anions. One H atom from each of the N3-and N4-amino groups each connects an O atom of an O1-benzoate thereby forming an eight-membered {···HNCNH···OCO} synthon. The other N3-H atom hydrogen bonds to a benzoate-O6 atom which at the same time accepts a hydrogen bond from the N5-H atom to close a S(6) ring. The other N4-H atom hydrogen bonds to a benzoate-O5 atom so that the amino-N4-H 2 bridges the same two benzoate-O atoms as does the water molecule to form an eight-membered {···HNH···O···HOH···O} synthon.
The C19-guanidinium cation also connects to five O atoms, three derived from three symmetry related benzoate groups and two water molecules; the N8-H 2 amino group bridges two water molecules, as described above. Each of amino-N7 H atoms is connected to a symmetry related O1-benzoate anion so that rows of benzoate anions along the c axis are bridged by amino-N7-H 2 groups. Finally, the N9-H links a benzoate-O5 atom. Each of the imine-N6 and -N10 atoms participates in intramolecular interactions with the N4-and N7-H atoms, respectively. The O1-benzoate forms five acceptor interactions, one from the water molecule and four from N-H. The O5-benzoate forms the same number and  Table   1 and Fig. 4.

S2. Experimental
A solution of aminoguanidinium carbonate (0.290 g, 2.1 mmol) in MeOH (15 ml) was added to a solution of 3-nitrobenzoic acid (0.350 g, 2.1 mmol) in MeOH (15 ml) and mixed. After the effervescence had subsided, the reaction mixture was refluxed for 15 min, left at room temperature overnight, and then rotary evaporated to leave a residue of The crude material was dissolved in acetone and the solution left at room temperature to produce crystals characterized as (I), m. pt. 436-435 K.

S3. Refinement
The N-and C-bound H atoms were geometrically placed with N-H = 0.88 Å and C-H = 0.95-0.98 Å, and refined as riding with U iso (H) = 1.2-1.5U eq (C). A rotating group model was used for the methyl groups. The water-bound H atoms were located from a difference map and included in the model with restraints O-H = 0.840±0. 001 Å and H1w···Hw2 = 1.39±0.01, and with U iso (H) = 1.5U eq (O).     where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.35 e Å −3 Δρ min = −0.56 e Å −3 Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.