Tetrakis(2-amino-5-chloropyridinium) dihydrogen cyclohexaphosphate

In the crystal structure of the title compound, 4C5H6ClN2 +·H2P6O18 4−, the [H2P6O18]4− anions are interconnected by O—H⋯O hydrogen bonds, leading to the formation of infinite ribbons extending along the a-axis direction. These ribbons are linked to the organic cations, via N—H⋯O and C—H⋯O hydrogen bonds, into a three-dimensional network. The six P atoms of the [H2P6O18]4− anion form a chair conformation. The complete cyclohexaphosphate anion is generated by inversion symmetry.

Supporting information for this paper is available from the IUCr electronic archives (Reference: FJ2662).

Comment
Research in organic-inorganic materials has experienced considerable growth in recent years for the purpose of generating desirable properties and functionalities. An important strategy employed in studying such systems has been to take advantage of hydrogen-bond interactions between organic cations and inorganic anions, since they have been recognized as the most powerful force to generate supramolecular network in one, two and three dimensions (Ozin, 1992, Teraski et al., 1987. In this context, our aims have been focused on the organic salts of cyclohexaphosphates systems. The title compound (I) provides another example of these kinds of materials.
The partial three-dimensional plot in Figure 1 illustrates the geometrical configuration of the [H 2 P 6 O 18 ] 4ring and the two independent organic cations [C 5 H 6 ClN 2 ] + in the (I) structure. The dihydrogen-cyclohexaphosphate anions are connected through strong hydrogen bonds characterized by short distances (d O···O = 2.418 (3) Å) leading to the formation of infinite and parallel [H 2 P 6 O 18 ] n 4slabs ( Figure 2). It is worth noting that the strong H-bond between phosphoric rings (Table 1) (d O···O < 2.73 Å) is rather observed in cyclohexaphosphates.
Two crystallographically independent cations coexist in this structure. They are arranged in pairs and anchored onto the anionic ribbons via N-H···O and C-H···O hydrogen bonds to keep up the three-dimensional network cohesion ( Figure   3, Figure 4).
The [H 2 P 6 O 18 ] 4-, group with chair conformation shows its standard geometry, the longest bonds length ranging between 1.580 (2) and 1.608 (2) Å, correspond to the bridging oxygen atom, the intermediate one, P1-O1 = 1.502 (2) Å, correspond to the P-OH bonding and the shortest ones spreading between 1.460 (2) and 1.498 (2) Å, correspond to the external oxygen atoms. The P-P-P angles of 111.0 (1), 120.5 (1) and 125.1 (4)° show that the rings are slightly distorted from the ideal threefold symmetry. The P-P distances as well as P-O-P or O-P-O angles show that these features are similar to those commonly observed in condensed phosphate anions (Bel Haj Salah et al., 2014, Khedhiri et al., 2012, Khedhiri et al., 2007, Amri et al., 2009, Abid et al., 2012. Despite the limited number of organic cation cyclohexaphosphates (about forty related structures), we can distinguish only few acidic cyclohexaphosphates such as the title compound (I).
The examination of pyridinium rings shows that these units are planar with mean deviation of 0.0036 and 0.0038 Å from least-square plane defined by the six constituent atoms. The average C-N distances in pyridinium rings is 1.353 Å and the C-C bond lengths are 1.380 Å. The latter value, being shorter than 1.39-1.41 Å, reported for non-substituent pyridine, may indicate some aromatic bond characters (Bak et al., 1959). These values are in accordance with those observed in others compounds (Hemissi et al., 2010, Toumi Akriche et al., 2010, Akriche et al., 2005. The inter-planar distance between the pyridine rings is in the vicinity of 4.00 Å, which is significantly longer than 3.80 Å for the p-p interaction (Janiak, 2000). In addition to electrostatic and van der Waals interactions, the structure is further stabilized with a three-dimensional network of O-H···O, N-H···O and the weaker C-H···O hydrogen bonds (Table 1, Figure 3).

Experimental
Single crystals of the title compound were prepared in two steps. In the first one, 50 ml of an aqueous solution of cyclohexaphosphoric acid was prepared by protonation of 4 g of Li 6 P 6 O 18 , obtained by the Schulke process (Schulke et al., 1985), with an ion exchange resin (Amberlite IR 120). In the second one, the frech acidic solution (20 ml, 2.6 mmol) was immediately neutralized with a solution of 2-amino-5-chloropyridine (2.8 mmol in 10 ml of ehanol) under continuous stirring. Good quality of prismatic-shaped crystals were obtained after a slow evaporation during few days at ambient temperature

Refinement
All H atoms were found in difference Fourier synthesis and refined in isotropic approximation     Projection of the structure along the b direction 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.