4-Methoxybenzamidinium chloride monohydrate

In the cation of the title compound, C8H11N2O+·Cl−·H2O, the C—N bonds of the amidinium group are identical within experiemental error [1.305 (2) and 1.304 (2) Å], and its plane forms a dihedral angle of 25.83 (8)° with the phenyl ring. The ionic components are associated in the crystal into polymeric hydrogen-bonded supramolecular tapes stabilized by N—H+⋯Cl− and N—H+⋯Ow intermolecular hydrogen bonds, and by Ow—H⋯Cl− interactions.

In the cation of the title compound, C 8 H 11 N 2 O + ÁCl À ÁH 2 O, the C-N bonds of the amidinium group are identical within experiemental error [1.305 (2) and 1.304 (2) Å ], and its plane forms a dihedral angle of 25.83 (8) with the phenyl ring. The ionic components are associated in the crystal into polymeric hydrogen-bonded supramolecular tapes stabilized by N-H + Á Á ÁCl À and N-H + Á Á ÁOw intermolecular hydrogen bonds, and by Ow-HÁ Á ÁCl À interactions.

4-Methoxybenzamidinium chloride monohydrate Simona Irrera and Gustavo Portalone Comment
This Laboratory is currently engaged in systematic structural analysis of proton-transfer adducts containing molecules of biological interest (Portalone, 2011a;Portalone & Irrera, 2011). In this context benzamidine derivatives, which have shown strong biological and pharmacological activity (Powers & Harper, 1999;Grzesiak et al., 2000), are being used in our group as bricks for supramolecular construction (Portalone, 2010(Portalone, , 2011b(Portalone, , 2012. Indeed, these molecules are strong Lewis bases and their cations can be easily anchored onto numerous inorganic and organic anions and polyanions, largely because of the presence of four potential donor sites for hydrogen-bonding. Benzamidinium ions have also been included in a number of protein structures (Marquart et al., 1983;Sprang et al., 1987;Bode et al., 1990).
The asymmetric unit of (I) comprises one non-planar 4-methoxybenzamidinium cation, one chloride anion and one water molecule of crystallization ( Fig. 1).
In the cation the amidinium group forms a dihedral angle of 25.83 (8)° with the mean plane of the phenyl ring, which agrees with the values observed in protonated benzamidinium ions (23.2 -30.4°, Portalone, 2010Portalone, , 2012. The lack of planarity in all these systems is obviously caused by steric hindrances between the H atoms of the aromatic ring and the amidine moiety. This conformation is rather common in benzamidinium-containing small-molecule crystal structures, with the exception of benzamidinium diliturate, where the benzamidinium cation is planar (Portalone, 2010). The pattern of bond lengths and bond angles of the 4-methoxybenzamidinium cation agrees with that reported in previous structural investigations (Portalone, 2010(Portalone, , 2012. In particular the amidinium group, true to one's expectations, features similar C-N bonds [1.305 (2) and 1.304 (2) Å], evidencing the delocalization of the π electrons and their double-bond character.
Analysis of the crystal packing of (I), (Fig. 2), shows that the ions are associated in the crystal by six distinct N-H + ···Cl -, N-H + ···Ow and Ow-H···Clintermolecular hydrogen bonds (Table 1). Each amidinium unit is bound to two chloride anions by three weak hydrogen bonds (N + ···Cl -= 3.185 (2) -3.552 (2) Å) and to one water molecule by one N-H + ···Ow interaction, just forming two R 3 5 (10) and one R 1 2 (6) supramolecular synthons (Bernstein et al., 1995). Both of these R 3 5 (10) and R 1 2 (6) motifs lead to the formation of one dimensional polymeric hydrogen-bonded supramolecular tapes approximately along the crystallographic b axis. The water molecule, which plays a dual role as both donor and acceptor in hydrogen bonding interactions, acts as a bridge between tapes through the remaining two Ow-H···Clintermolecular interactions.
Experimental 4-methoxybenzamidine (1 mmol, Fluka at 96% purity) was dissolved without further purification in 6 ml of hot water and heated under reflux for 3 h. While stirring, HCl (6 mol L -1 ) was added dropwise until the pH reached 2. After cooling the solution to ambient temperature, colourless crystals suitable for single-crystal X-ray diffraction were grown by slow evaporation of the solvent over two weeks.

Refinement
All H atoms were identified in difference Fourier maps, but for refinement all C-bound H atoms were placed in calculated positions, with C-H = 0.93 Å (phenyl) and 0.96 Å (methyl), and refined as riding on their carrier atoms. The U iso values were kept equal to 1.2U eq (C, phenyl). and to 1.5U eq (C, methyl). Positional and thermal parameters of H atoms of the amidinium group and of water molecule were freely refined, giving N-H distances in the range 0.75 (2)

Figure 1
The asymmetric unit of (I), showing the atom-labelling scheme. Displacements ellipsoids are at the 50% probability level.
H atoms are shown as small spheres of arbitrary radii.    where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.22 e Å −3 Δρ min = −0.15 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.