A di­hydrogen phosphate anionic network as a host lattice for cations in 1-methyl­piperazine-1,4-diium bis­(di­hydrogen phosphate) and 2-(pyridin-2-yl)pyridinium di­hydrogen phosphate-ortho­phosphoric acid (1/1)

In the salt 1-methyl­piperazine-1,4-diium bis­(di­hydrogen phosphate), C₅H₁₃N₂²⁺·2H₂PO₄^-, (I), and the solvated salt 2-(pyridin-2-yl)pyridinium di­hydrogen phosphate-ortho­phosphoric acid (1/1), C₁₀H₉N₂⁺·H₂PO₄^-·H₃PO₄, (II), the formation of O-H...O and N-H...O hydrogen bonds between the di­hydrogen phosphate (H₂PO₄^-) anions and the cations constructs a three- and two-dimensional anionic-cationic network, respectively. In (I), the self-assembly of H₂PO₄^- anions forms a two-dimensional pseudo-honeycomb-like supra­molecular architecture along the (010) plane. 1-Methyl­piperazine-1,4-diium cations are trapped between the (010) anionic layers through three N-H...O hydrogen bonds. In solvated salt (II), the self-assembly of H₂PO₄^- anions forms a two-dimensional supra­molecular architecture with open channels projecting along the [001] direction. The 2-(pyridin-2-yl)pyridinium cations are trapped between the open channels by N-H...O and C-H...O hydrogen bonds. From a study of previously reported structures, di­hydrogen phosphate anions show a supra­molecular flexibility depending on the nature of the cations. The di­hydrogen phosphate anion may be suitable for the design of the host lattice for host-guest supra­molecular systems.

S1. Introduction

The role of organic crystal engineering in metal–organic frameworks (MOFs) and coordination polymer chemistry is to create one-, two- and three-dimensional architectures in crystalline solids through the use of different tools such as hydrogen bonds, weak inter­molecular inter­actions and covalent-coordinate bonds (including metal–oxygen bonds) (Desiraju, 1991; Aakeröy, 1997; Moulton & Zaworotko, 2002). The most significant breakthrough in supra­molecular chemistry is the construction of solids having large inter­nal surface areas, ultra-low densities and uniformly structured pores, channels and layers through covalent-coordinate bonds (Moulton & Zaworotko, 2001) and noncovalent inter­actions (Beatty, 2003). This property leads to the concept of host–guest systems, where the host network remains undisassembled by the release or inclusion of guest molecules. This finds valid applications in gas or chemical storage, sensors, catalysis and ion-exchange (Tranchemontagne et al., 2009; Allendorf et al., 2009). As a continuation of research on the supra­molecular architectures of inorganic oxy-acid-based salts (Balamurugan et al., 2010), we report here the crystal structure and supra­molecular frameworks in two di­hydrogen phosphate salts, 1-methyl­piperazine-1,4-diium bis­(di­hydrogen phosphate), (I), and 2-(pyridin-2-yl)pyridinium di­hydrogen phosphate–ortho­phospho­ric acid (1/1), (II).

Di­hydrogen phosphate anions (H₂PO₄^-), via O—H···O hydrogen bonds, form inorganic substructures such as one-dimensional chains, chains of fused R₂²(8) ring motifs [see Bernstein et al. (1995) for graph-set notation], two-dimensional layers and three-dimensional cages to which the cations are linked. This paper discusses the specific nature of H₂PO₄^- anionic self-assembly, which forms a host lattice through O—H···O hydrogen bonds and where the respective cations are held within the host lattice through N—H···O hydrogen bonds. The molecular structures of salt (I) and solvated salt (II) are illustrated in Figs. 1 and 2, respectively.

S2. Experimental

S2.1. Synthesis and crystallization

Salt (I) was prepared by taking a 1:2 ratio of 1-methyl­piperazine and ortho­phospho­ric acid. To an ethano­lic solution of 1-methyl­piperazine, ortho­phospho­ric acid was added dropwise with constant stirring at 313 K. The process was continued for 30 min and the resultant mixture was kept for crystallization. Slow evaporation of the solvent led to the formation of colourless diffraction-quality crystals of (I). Solvated salt (II) was prepared by taking equimolar amounts of 2,2'-bi­pyridine and ortho­phospho­ric acid. Initially, a solution of 2,2'-bi­pyridine was prepared from a mixture of ethanol and water (50:50 v/v). To this solution, ortho­phospho­ric acid was added dropwise with constant stirring and the temperature was maintained at 318 K. The process was allowed to continue for 20 min until the solution became clear, and this was kept for crystallization. Colourless diffraction-quality crystals of (II) were obtained after one month. [Please give qu­anti­ties used, to indicate the scale of the reaction]

S2.2. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. In salt (I), one of the di­hydrogen phosphate anions is positionally disordered over two orientations. Adjacent positions of the disordered O atoms were identified from the difference electron-density map and were refined with two discrete positions of site occupancies, 0.538 (6) and 0.462 (6). The P—O bond distances of the major and minor components were made similar using suitable similarity restraints with an effective s.u. of 0.01 Å, and the anisotropic displacement parameters of the disordered components were made similar using similarity restraints with a suitable s.u. of 0.04 Ų. For salt (I) and solvated salt (II), C-bound H atoms were treated as riding, with C—H = 0.96 Å and U_iso(H) = 1.5U_eq(C) for CH₃ groups, C—H = 0.96 Å and U_iso(H) = 1.2U_eq(C) for CH groups, and C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C) for aromatic CH groups. H atoms associated with the hy­droxy O atoms were identified from the difference electron-density maps and their positions were restrained, with O—H = 0.84 (1) Å and with U_iso(H) = 1.5U_eq(O). The positions of all the H atoms associated with N atoms were identified from a difference electron-density map and were restrained, with N—H = 0.90 (1) Å.

S3. Results and discussion

Salt (I) crystallizes in orthorhombic space group Pbca, with one 1-methyl­piperazine-1,4-diium cation and two di­hydrogen phosphate anions in the asymmetric unit. In the crystal structure of (I), one of the di­hydrogen phosphate anions is positionally disordered over two orientations, the two discrete sites having major and minor refined occupancies of 0.538 (6) and 0.462 (6), respectively. The P atom of the di­hydrogen phosphate anion shares the same site for disordered atoms O5/O6/O7/O8 and O5'/O6'/O7'/O8', as illustrated in Fig. 1. In the tetra­hedral di­hydrogen phosphate group of (I), the protonated P—O bond distances [P1—O1 = 1.552 (2) Å and P1—O4 = 1.552 (2) Å] are, as expected, longer than the unprotonated P—O bond distances [P1—O2 = 1.4994 (19) Å and P1—O3 = 1.4902 (19) Å]. In the disordered H₂PO₄^- anion, the bond lengths and angles of the disordered components were made similar using similarity distance restraints with suitable standard uncertainity. The H atoms of both di­hydrogen phosphate anions were observed from a difference Fourier map and were refined using suitable distance restraints. The 1-methyl­piperazine-1,4-diium ring adopts a typical chair conformation.

Solvated salt (II) crystallizes in the monoclinic space group P2₁/c, with one 2, 2'-bipyridinium cation, one di­hydrogen phosphate anion and a neutral ortho­phospho­ric acid molecule in the asymmetric unit. The P—O bond distances observed in the neutral ortho­phospho­ric acid molecule [P2—O5 = 1.541 (2) Å, P2–O8 = 1.534 (2) Å and P2–O7 = 1.545 (2) Å] are longer than the other P—O distance [P2–O6 = 1.485 (2) Å], indicating the single- and double-bond character of the H₃PO₄ group. In the ionic di­hydrogen phosphate group, the protonated P—O bond distances [P1—O1 = 1.552 (2) Å and P1—O3 = 1.545 (2) Å] are, as expected, longer than the other two P—O bonds [P1–O2 = 1.496 (2) Å and P1—O4 = 1.4930 (19) Å]. The H atoms of both neutral and anionic molecules were located from a difference Fourier map and refined with suitable distance restraints. The identical P1—O2 and P1—O4 bond distances observed in the anion indicate the delocalization of negative charge between them (Demir et al., 2006).

From a study of the previously reported structures of salts of 2,2'-bi­pyridine, it is observed that the 2-(pyridin-2-yl)pyridinium cation can exist in two different geometries, depending upon the degree of protonation. In the case of singly protonated salts, the pyridine N atoms are in a cis conformation, whereas for doubly protonated salts the pyridine N atoms are in a trans conformation (Chen et al., 2005). In (II), the pyridine N atoms are in a cis conformation as the cation is singly protonated. The torsion angle between atoms N1 and N2 (N1—C5—C6—N2) is -2.8 (4)°. The C—C bond distance connecting the pyridine rings (C5—C6) is 1.478 (4) Å. This is longer than the equivalent C—C distances in the unprotonated 2-(pyridin-2-yl)pyridine molecule and doubly protonated 2-(pyridin-2-yl)pyridinium cation [Reference for these data?]. The C—N—C angle of the protonated ring [C1—N1—C5 = 123.3 (3)°] is larger than the C—N—C angle of the unprotonated ring [C6—N2—C10 = 116.9 (3)°]. These values are consistant with those reported for 2,2'-bipyridinium perchlorate (Kavitha et al., 2005).

In (I), the hydrogen bonds formed through the minor-component O atoms are not considered for discussion of the supra­molecular structure. The protonated N atoms of the 1-methyl­piperazine-1,4-diium cation are involved in three N—H···O hydrogen bonds. Two O—H···O hydrogen bonds are observed between the H₂PO₄^- anions in the asymmetric unit. The hydrogen bonds O1—H1···O7 and O8—H8···O2 connect the di­hydrogen phosphate anions to form an asymmetric R₂²(8) motif. Similar adjacent motifs are further inter­linked through O4—H4···O3ⁱ [symmetry code: (i) x + 1/2, -y + 1/2, -z] and O5—H5···O6^iv [symmetry code: (iv) x + 1/2, y, -z + 1/2] hydrogen bonds to form a supra­molecular motif of type R₆⁶(24). The distinct R₂²(8) and R₆⁶(24) motifs are fused together to construct a two-dimensional inorganic substructure extending infinitely along the (010) plane. Adjacent anionic layers of the [Which? Text missing] type are stacked infinitely along the [010] direction, with an inter-layer distance of 2.833 Å (the measured distance between the planes formed by inter­ior atoms O2). This parallel stacking of anions forms a pseudo-honeycomb-like network, creating voids with approximate dimensions of 9.13 × 8.20 Å open towards the [001] direction and depicted in Fig. 3. The 1-methyl­piperazine-1,4-diium cations are held between these inorganic layers of anions through three N—H···O hydrogen bonds, N1—H1C···O3ⁱⁱⁱ [symmetry code: (iii) -x + 1, -y + 1, -z], N1—H1D···O2 and N2—H2E···O7ⁱⁱ [symmetry code: (ii) -x + 1/2, y + 1/2, z]. Inter­estingly, the dimensions and shape of the void created by the inorganic network are sufficient to accommodate the 1-methyl­piperazine-1,4-diium cations. The combination of O—H···O and N—H···O hydrogen bonds results in an anion–cation host–guest structure, where the di­hydrogen phosphate anions act as hosts and the 1-methyl­piperazine-1,4-diium cation act as guests (Fig. 3).

In the crystal structure of (II), the supra­molecular anionic framework is formed by five O—H···O hydrogen bonds. The centrosymmetrically related H₂PO₄^- anions are linked through an O1—H1A···O4ⁱ [symmetry code: (i) -x, -y + 1, -z + 1] hydrogen bond to form the common R₂²(8) motif, occupying the crystallographic inversion centre at (x, 1/2, 1/2). Four such symmetry-related motifs are connected through an O3—H3A···O4ⁱⁱ [symmetry code: (ii) x, -y + 1/2, z - 1/2] hydrogen bond to form an R₆⁶(20) ring motif lying along (0, y, 1/2). The motifs of this type are further linked through the hydrogen bonds O5—H5A···O2, O7—H7A···O2ⁱⁱ [symmetry code: (ii) x, -y + 1/2, z - 1/2] and O8—H8A···O6ⁱⁱⁱ [symmetry code: (iii) x, -y + 1/2, z + 1/2], generating a two-dimensional inorganic substructure extending along the (100) plane. This two-dimensional H₂PO₄^- anionic network is built from the fusion of R₃³(13), R₂³(10), R₆⁶(20) and R₂²(8) motifs. Inter­estingly, the anionic framework forms open channels projected along the [001] direction, as illustrated in Fig. 4. The separation distance of the channel path is approximately 8.11 Å. The channels created within the anionic network are capable of holding foreign molecules. The 2-(pyridin-2-yl)pyridinium cations are trapped between these inorganic channels through an N1—H1B···O6 hydrogen bond and by a C2—H2···O4^iv [symmetry code: (iv) x, y, z - 1] inter­action. The size of the molecular channels within the anionic framework is sufficiently large to hold the 2-(pyridin-2-yl)pyridinium cations, as illustrated in Fig. 4.

A list of structures closely related to those of (I) and (II) has been retrieved from the Cambridge Structural Database (CSD; Version 5.31, Groom & Allen, 2014) and compared with regard to their supra­molecular frameworks. It is observed that piperazinium bis­(di­hydrogen phosphate) (CSD refcode HEWZIT; Jensen et al., 2007), 2-methyl­piperazinedium di­hydrogen phosphate (DOXBAT; Choudhury et al., 2000), N,N'-di­methyl­pipearzinedium di­hydrogen phosphate (DOXJOP; Choudhury et al., 2000), ethyl­enedi­ammonium bis­(di­hydrogen monophosphate) (KAGCEA; Kamoun et al., 1989), methyl­guanidinium di­hydrogen phosphate (MGUNAP10; Cotton et al., 1973) and cyclo­hexane-1,4-di­ammonium di­hydrogen phosphate (YEYDEM; Dakhlaoui et al., 2007) display an anionic network similar to that observed in salt (I). It is of inter­est to note that the H₂PO₄^- anionic layers in all the above-mentioned structures are built from distinct R₂²(8) and R₆⁶(24) structural motifs, the parallel stacking of which forms cavities of different dimensions, shapes and inter­layer distances. Depending on the size and nature of the cations, the void size, shape and cavities in the H₂PO₄^- anionic layers become flexible themselves to accommodate the cations. In the crystal structure of pyridinium di­hydrogen phosphate phospho­ric acid (VEGKIB; Masse & Tordjman, 1990), the di­hydrogen phosphate anions and phospho­ric acid molecules form a three-dimensional network which creates molecular channels along the [100] direction. The pyridinium cations are trapped in these molecular [100] channels through N—H···O hydrogen bonds. A three-dimensional cage of di­hydrogen phosphate anions is observed in the crystal structure of imidazolium di­hydrogen orthophosphate (IMDAZP10; Blessing, 1986), in which the imidazolium cations are trapped through two N—H···O hydrogen bonds. In tetra­methyl­ammonium di­hydrogen phosphate hemihydrate, the water molecules act as a bridge between the H₂PO₄^- anionic networks to form a three-dimensional cage-type architecture where the tetra­methyl­ammonium cations are trapped within the cage through weak C—H···O inter­actions [Reference?]. Inter­estingly, in the structure of trans-1,2-bis­(4-pyridinium)ethene bis­(di­hydrogen phosphate) dihydrate (XEPREQ; Yilmaz et al., 2006) and 4,4'-bipyridinium bis­(di­hydrogen phosphate) (CAZKUK; Dorn et al., 2005), di­hydrogen phosphate forms anionic layers and the trans-1,2-bis­(4-pyridinium)ethene (in XEPREQ) or 4,4'-bipyridinium (in CAZKUK) cations act as pillars between the anionic layers to construct the host lattice. In both XEPREQ and CAZKUK, O—H···O hydrogen-bonded chains of water molecules act as guests that are trapped in the molecular host lattice, forming a host–guest system.

From the above observations, it is understood that di­hydrogen phosphate anions display a supra­molecular flexibility with respect to the nature of the cations. Also, di­hydrogen phosphate anions can be used in the design of a host lattice in a host–guest supra­molecular system.

Computing details

For both compounds, data collection: APEX2 (Bruker, 2004); cell refinement: APEX2 and SAINT (Bruker, 2004); data reduction: SAINT and XPREP (Bruker, 2004); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2008); software used to prepare material for publication: PLATON (Spek, 2009).

Figures

	Fig. 1. The molecular structure of salt (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. One of the H2PO4^- anions is positionally disordered, with site occupancies of 0.538 (6) and 0.462 (6); the two components are differentiated by solid and open bonds. Double-dashed lines represent hydrogen bonds.
	Fig. 2. The molecular structure of hydrated salt (II), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. Double-dashed lines represent hydrogen bonds.
	Fig. 3. Part of the crystal structure of salt (I), showing the formation of the pseudo-honeycomb-like anionic host lattice built through O—H···O hydrogen bonds (top), and the trapping of 1-methylpiperazine-1,4-diium cations through N—H···O hydrogen bonds (bottom). Both hydrogen-bond types are represented by grey dotted lines.
	Fig. 4. Part of the crystal structure of solvated salt (II), showing the formation of two-dimensional anionic open channels built through O—H···O hydrogen bonds (top) and the trapping of 2-(pyridin-2-yl)pyridinium cations through N—H···O and O—H···O hydrogen bonds (bottom). Both hydrogen-bond types are represented by grey dotted lines.

(I) 1-Methylpiperazine-1,4-diium bis(dihydrogen phosphate)

Crystal data

C5H14N2^2+·2H2PO4^−	Dx = 1.582 Mg m^−3
Mr = 296.15	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 4348 reflections
a = 7.1305 (5) Å	θ = 2.9–29.2°
b = 12.5719 (10) Å	µ = 0.38 mm^−1
c = 27.745 (2) Å	T = 296 K
V = 2487.1 (3) Å^3	Block, colourless
Z = 8	0.30 × 0.25 × 0.20 mm
F(000) = 1248

Data collection

Bruker Kappa APEXII CCD area-detector diffractometer	2703 independent reflections
Radiation source: fine-focus sealed tube	1903 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.044
ω and ϕ scans	θmax = 27.0°, θmin = 1.5°
Absorption correction: multi-scan (SADABS; Bruker, 2004)	h = −8→9
Tmin = 0.884, Tmax = 0.938	k = −12→16
11897 measured reflections	l = −29→35

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.041	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.111	H atoms treated by a mixture of independent and constrained refinement
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0488P)^2 + 1.3101P] where P = (Fo^2 + 2Fc^2)/3
2703 reflections	(Δ/σ)max < 0.001
222 parameters	Δρmax = 0.37 e Å^−3
52 restraints	Δρmin = −0.33 e Å^−3

Special details

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 F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
C1	0.3872 (4)	0.6190 (2)	0.11550 (9)	0.0453 (7)
H1A	0.2926	0.6735	0.1110	0.054*
H1B	0.5087	0.6535	0.1169	0.054*
C2	0.3511 (3)	0.5612 (2)	0.16204 (9)	0.0423 (6)
H2A	0.4507	0.5102	0.1677	0.051*
H2B	0.3510	0.6117	0.1885	0.051*
C3	0.1627 (4)	0.4307 (2)	0.11857 (9)	0.0434 (6)
H3A	0.0402	0.3973	0.1170	0.052*
H3B	0.2555	0.3752	0.1231	0.052*
C4	0.2009 (3)	0.4877 (2)	0.07180 (9)	0.0441 (6)
H4A	0.2034	0.4367	0.0456	0.053*
H4B	0.1013	0.5384	0.0655	0.053*
C5	0.1304 (4)	0.4485 (2)	0.20676 (10)	0.0562 (8)
H5A	0.2247	0.3952	0.2119	0.084*
H5B	0.0093	0.4153	0.2052	0.084*
H5C	0.1327	0.4986	0.2329	0.084*
N1	0.3829 (3)	0.54409 (18)	0.07425 (8)	0.0362 (5)
N2	0.1686 (3)	0.50511 (17)	0.16047 (7)	0.0346 (5)
P1	0.68047 (9)	0.31207 (5)	0.04786 (2)	0.03558 (19)
O1	0.6518 (4)	0.19420 (17)	0.06280 (7)	0.0603 (6)
H1	0.633 (5)	0.185 (3)	0.0918 (5)	0.091*
O2	0.6393 (3)	0.38734 (15)	0.08842 (6)	0.0495 (5)
O3	0.5659 (3)	0.33198 (16)	0.00384 (7)	0.0579 (6)
O4	0.8929 (3)	0.32405 (18)	0.03700 (9)	0.0643 (7)
H4	0.944 (5)	0.275 (2)	0.0217 (13)	0.096*
P2	0.63383 (9)	0.22606 (6)	0.19152 (2)	0.0402 (2)
O5	0.7523 (9)	0.1778 (5)	0.2297 (2)	0.108 (3)	0.538 (6)
H5	0.8675 (17)	0.186 (9)	0.226 (3)	0.161*	0.538 (6)
O6	0.4467 (6)	0.2565 (4)	0.21033 (19)	0.0825 (19)	0.538 (6)
O7	0.6215 (14)	0.1469 (6)	0.1506 (3)	0.0492 (19)	0.538 (6)
O8	0.7374 (8)	0.3271 (4)	0.17205 (16)	0.0567 (14)	0.538 (6)
H8	0.691 (8)	0.347 (4)	0.1462 (14)	0.085*	0.538 (6)
O5'	0.8435 (6)	0.2045 (6)	0.2003 (2)	0.075 (2)	0.462 (6)
H5'	0.881 (5)	0.227 (8)	0.2266 (17)	0.113*	0.462 (6)
O6'	0.5381 (7)	0.2031 (5)	0.23876 (19)	0.091 (2)	0.462 (6)
O7'	0.5715 (18)	0.1610 (6)	0.1500 (4)	0.075 (4)	0.462 (6)
O8'	0.6166 (12)	0.3451 (4)	0.18005 (19)	0.078 (2)	0.462 (6)
H8'	0.681 (13)	0.361 (3)	0.156 (3)	0.117*	0.462 (6)
H2E	0.079 (3)	0.5554 (16)	0.1574 (10)	0.047 (8)*
H1C	0.400 (4)	0.582 (2)	0.0470 (7)	0.065 (10)*
H1D	0.478 (3)	0.4976 (19)	0.0770 (11)	0.062 (9)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0515 (15)	0.0399 (16)	0.0446 (16)	−0.0115 (12)	0.0105 (13)	−0.0068 (12)
C2	0.0427 (13)	0.0509 (17)	0.0334 (14)	−0.0077 (12)	−0.0003 (11)	−0.0099 (12)
C3	0.0469 (14)	0.0391 (16)	0.0442 (16)	−0.0080 (11)	0.0008 (12)	−0.0049 (12)
C4	0.0438 (14)	0.0521 (17)	0.0364 (15)	−0.0033 (12)	−0.0047 (11)	−0.0044 (13)
C5	0.0652 (18)	0.061 (2)	0.0430 (18)	−0.0041 (15)	0.0084 (14)	0.0138 (14)
N1	0.0411 (11)	0.0391 (13)	0.0284 (12)	0.0047 (9)	0.0034 (9)	0.0026 (9)
N2	0.0359 (10)	0.0340 (12)	0.0340 (11)	0.0020 (9)	0.0027 (9)	0.0023 (9)
P1	0.0373 (3)	0.0403 (4)	0.0291 (4)	−0.0013 (3)	−0.0016 (3)	0.0028 (3)
O1	0.1013 (17)	0.0436 (12)	0.0362 (11)	−0.0046 (11)	0.0007 (12)	0.0044 (9)
O2	0.0667 (12)	0.0457 (12)	0.0361 (10)	0.0183 (9)	0.0056 (9)	0.0044 (8)
O3	0.0646 (13)	0.0645 (14)	0.0446 (12)	−0.0200 (10)	−0.0221 (10)	0.0191 (10)
O4	0.0402 (11)	0.0703 (17)	0.0823 (17)	−0.0064 (10)	0.0087 (10)	−0.0349 (12)
P2	0.0379 (3)	0.0534 (5)	0.0293 (4)	−0.0075 (3)	0.0010 (3)	0.0030 (3)
O5	0.113 (5)	0.111 (4)	0.099 (5)	−0.044 (4)	−0.060 (4)	0.067 (3)
O6	0.086 (3)	0.088 (4)	0.074 (4)	0.025 (3)	0.046 (3)	0.017 (3)
O7	0.060 (4)	0.048 (3)	0.039 (3)	−0.004 (3)	0.008 (2)	0.004 (2)
O8	0.074 (3)	0.053 (3)	0.043 (3)	−0.027 (2)	−0.019 (2)	0.010 (2)
O5'	0.049 (3)	0.109 (5)	0.067 (4)	0.035 (3)	−0.010 (3)	−0.016 (3)
O6'	0.062 (3)	0.157 (6)	0.054 (3)	0.000 (3)	0.025 (3)	0.028 (3)
O7'	0.103 (8)	0.087 (7)	0.034 (4)	−0.070 (6)	−0.010 (4)	0.007 (4)
O8'	0.130 (6)	0.061 (3)	0.042 (3)	0.045 (4)	0.003 (4)	0.005 (2)

Geometric parameters (Å, º)

C1—N1	1.482 (3)	P1—O2	1.4994 (19)
C1—C2	1.503 (4)	P1—O4	1.552 (2)
C1—H1A	0.9700	P1—O1	1.552 (2)
C1—H1B	0.9700	O1—H1	0.822 (10)
C2—N2	1.481 (3)	O4—H4	0.830 (10)
C2—H2A	0.9700	P2—O7'	1.481 (5)
C2—H2B	0.9700	P2—O6	1.483 (4)
C3—N2	1.493 (3)	P2—O5	1.484 (4)
C3—C4	1.507 (4)	P2—O6'	1.506 (4)
C3—H3A	0.9700	P2—O7	1.512 (5)
C3—H3B	0.9700	P2—O8'	1.535 (5)
C4—N1	1.480 (3)	P2—O5'	1.539 (4)
C4—H4A	0.9700	P2—O8	1.566 (4)
C4—H4B	0.9700	O5—H5	0.834 (11)
C5—N2	1.493 (3)	O5—H5'	1.11 (8)
C5—H5A	0.9600	O8—H8	0.828 (11)
C5—H5B	0.9600	O8—H8'	0.74 (8)
C5—H5C	0.9600	O5'—H5	0.77 (4)
N1—H1C	0.903 (10)	O5'—H5'	0.826 (11)
N1—H1D	0.900 (10)	O8'—H8	1.08 (6)
N2—H2E	0.903 (10)	O8'—H8'	0.833 (11)
P1—O3	1.4902 (19)
N1—C1—C2	110.7 (2)	O3—P1—O1	107.87 (12)
N1—C1—H1A	109.5	O2—P1—O1	112.10 (11)
C2—C1—H1A	109.5	O4—P1—O1	105.85 (14)
N1—C1—H1B	109.5	P1—O1—H1	114 (3)
C2—C1—H1B	109.5	P1—O4—H4	117 (3)
H1A—C1—H1B	108.1	O7'—P2—O6	98.4 (6)
N2—C2—C1	110.8 (2)	O7'—P2—O5	120.0 (5)
N2—C2—H2A	109.5	O6—P2—O5	111.5 (3)
C1—C2—H2A	109.5	O7'—P2—O6'	115.8 (6)
N2—C2—H2B	109.5	O6—P2—O6'	48.3 (2)
C1—C2—H2B	109.5	O5—P2—O6'	63.8 (4)
H2A—C2—H2B	108.1	O7'—P2—O7	15.3 (7)
N2—C3—C4	111.6 (2)	O6—P2—O7	112.5 (4)
N2—C3—H3A	109.3	O5—P2—O7	107.5 (4)
C4—C3—H3A	109.3	O6'—P2—O7	120.1 (5)
N2—C3—H3B	109.3	O7'—P2—O8'	110.7 (4)
C4—C3—H3B	109.3	O6—P2—O8'	75.5 (4)
H3A—C3—H3B	108.0	O5—P2—O8'	126.3 (4)
N1—C4—C3	110.3 (2)	O6'—P2—O8'	109.3 (3)
N1—C4—H4A	109.6	O7—P2—O8'	118.8 (5)
C3—C4—H4A	109.6	O7'—P2—O5'	108.5 (5)
N1—C4—H4B	109.6	O6—P2—O5'	149.7 (3)
C3—C4—H4B	109.6	O5—P2—O5'	42.4 (3)
H4A—C4—H4B	108.1	O6'—P2—O5'	105.6 (3)
N2—C5—H5A	109.5	O7—P2—O5'	93.4 (4)
N2—C5—H5B	109.5	O8'—P2—O5'	106.4 (4)
H5A—C5—H5B	109.5	O7'—P2—O8	108.8 (6)
N2—C5—H5C	109.5	O6—P2—O8	109.6 (3)
H5A—C5—H5C	109.5	O5—P2—O8	108.0 (3)
H5B—C5—H5C	109.5	O6'—P2—O8	132.0 (3)
C4—N1—C1	110.97 (19)	O7—P2—O8	107.6 (4)
C4—N1—H1C	109.4 (19)	O8'—P2—O8	34.4 (3)
C1—N1—H1C	108 (2)	O5'—P2—O8	74.9 (3)
C4—N1—H1D	110.8 (19)	P2—O5—H5	115 (2)
C1—N1—H1D	109.3 (19)	P2—O5—H5'	101 (4)
H1C—N1—H1D	108 (3)	H5—O5—H5'	27 (9)
C2—N2—C3	110.24 (18)	P2—O8—H8	111 (2)
C2—N2—C5	111.2 (2)	P2—O8—H8'	115 (6)
C3—N2—C5	111.5 (2)	H8—O8—H8'	24 (6)
C2—N2—H2E	106.9 (17)	P2—O5'—H5	115 (2)
C3—N2—H2E	110.3 (17)	P2—O5'—H5'	113 (2)
C5—N2—H2E	106.6 (17)	H5—O5'—H5'	38 (10)
O3—P1—O2	113.70 (12)	P2—O8'—H8	99 (3)
O3—P1—O4	111.07 (13)	P2—O8'—H8'	111 (2)
O2—P1—O4	105.99 (11)	H8—O8'—H8'	14 (5)
N1—C1—C2—N2	−57.6 (3)	C1—C2—N2—C3	56.5 (3)
N2—C3—C4—N1	56.0 (3)	C1—C2—N2—C5	−179.4 (2)
C3—C4—N1—C1	−56.5 (3)	C4—C3—N2—C2	−56.0 (3)
C2—C1—N1—C4	57.6 (3)	C4—C3—N2—C5	179.9 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O4—H4···O3^i	0.83 (1)	1.75 (1)	2.580 (3)	173 (4)
N2—H2E···O7^ii	0.90 (1)	1.85 (2)	2.745 (10)	174 (2)
N1—H1C···O3^iii	0.90 (1)	1.79 (1)	2.693 (3)	175 (3)
O5—H5···O6^iv	0.83 (1)	2.06 (10)	2.381 (7)	102 (8)
O1—H1···O7	0.82 (1)	1.70 (2)	2.516 (10)	169 (4)
O8—H8···O2	0.83 (1)	1.72 (2)	2.539 (4)	169 (6)
N1—H1D···O2	0.90 (1)	1.83 (1)	2.717 (3)	169 (3)

Symmetry codes: (i) x+1/2, −y+1/2, −z; (ii) −x+1/2, y+1/2, z; (iii) −x+1, −y+1, −z; (iv) x+1/2, y, −z+1/2.

(II) 2-(Pyridin-2-yl)pyridinium dihydrogen phosphate–orthophosphoric acid (1/1)

Crystal data

C10H9N2^+·H2PO4^−·H3PO4	F(000) = 728
Mr = 352.17	Dx = 1.552 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 17.3885 (7) Å	Cell parameters from 3870 reflections
b = 10.4019 (5) Å	θ = 2.3–25.2°
c = 8.3927 (3) Å	µ = 0.33 mm^−1
β = 96.881 (3)°	T = 296 K
V = 1507.08 (11) Å^3	Block, colourless
Z = 4	0.30 × 0.25 × 0.20 mm

Data collection

Bruker Kappa APEXII CCD area-detector diffractometer	2889 independent reflections
Radiation source: fine-focus sealed tube	2096 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.042
ω and ϕ scans	θmax = 25.8°, θmin = 2.3°
Absorption correction: multi-scan (SADABS; Bruker, 2004)	h = −20→21
Tmin = 0.898, Tmax = 0.947	k = −12→12
13052 measured reflections	l = −10→10

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.039	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.104	H atoms treated by a mixture of independent and constrained refinement
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0384P)^2 + 1.3728P] where P = (Fo^2 + 2Fc^2)/3
2889 reflections	(Δ/σ)max < 0.001
218 parameters	Δρmax = 0.50 e Å^−3
6 restraints	Δρmin = −0.32 e Å^−3

Special details

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 F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
P1	0.07564 (4)	0.34398 (7)	0.48852 (8)	0.03173 (19)
O1	0.07103 (13)	0.4568 (2)	0.3667 (3)	0.0556 (6)
H1A	0.0313 (14)	0.503 (3)	0.365 (5)	0.083*
O2	0.15907 (11)	0.3051 (2)	0.5129 (3)	0.0502 (5)
O3	0.02501 (14)	0.2337 (2)	0.4098 (3)	0.0631 (7)
H3A	0.040 (2)	0.198 (4)	0.329 (3)	0.095*
O4	0.04158 (10)	0.37956 (17)	0.6375 (2)	0.0377 (5)
P2	0.31209 (4)	0.30542 (7)	0.28136 (9)	0.03426 (19)
O5	0.25756 (12)	0.4033 (2)	0.3480 (3)	0.0470 (5)
H5A	0.2222 (15)	0.375 (3)	0.398 (4)	0.070*
O6	0.34137 (11)	0.36379 (18)	0.1388 (2)	0.0413 (5)
O7	0.26692 (12)	0.17850 (19)	0.2475 (2)	0.0441 (5)
H7A	0.2270 (13)	0.182 (3)	0.181 (3)	0.066*
O8	0.37932 (11)	0.2708 (2)	0.4096 (2)	0.0493 (5)
H8A	0.366 (2)	0.227 (3)	0.484 (3)	0.074*
N1	0.25500 (15)	0.5909 (2)	0.0523 (3)	0.0458 (6)
N2	0.37702 (16)	0.6835 (3)	0.2320 (3)	0.0564 (7)
C1	0.1943 (2)	0.5302 (3)	−0.0257 (4)	0.0596 (9)
H1	0.1919	0.4409	−0.0239	0.072*
C2	0.1363 (2)	0.5983 (4)	−0.1076 (5)	0.0674 (10)
H2	0.0933	0.5568	−0.1609	0.081*
C3	0.1419 (2)	0.7300 (3)	−0.1106 (5)	0.0664 (10)
H3	0.1029	0.7782	−0.1681	0.080*
C4	0.20447 (19)	0.7905 (3)	−0.0295 (4)	0.0547 (8)
H4	0.2081	0.8796	−0.0316	0.066*
C5	0.26220 (16)	0.7188 (3)	0.0555 (3)	0.0391 (6)
C6	0.33146 (17)	0.7716 (3)	0.1529 (4)	0.0419 (7)
C7	0.3466 (2)	0.9001 (3)	0.1633 (5)	0.0639 (10)
H7	0.3135	0.9587	0.1066	0.077*
C8	0.4116 (2)	0.9416 (4)	0.2589 (6)	0.0812 (13)
H8	0.4230	1.0288	0.2686	0.097*
C9	0.4590 (2)	0.8531 (4)	0.3390 (5)	0.0761 (12)
H9	0.5037	0.8785	0.4033	0.091*
C10	0.4397 (2)	0.7263 (4)	0.3233 (5)	0.0697 (11)
H10	0.4721	0.6664	0.3795	0.084*
H1B	0.2944 (14)	0.543 (3)	0.100 (4)	0.074 (12)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.0301 (4)	0.0348 (4)	0.0298 (4)	0.0041 (3)	0.0017 (3)	0.0003 (3)
O1	0.0557 (14)	0.0621 (15)	0.0529 (13)	0.0241 (11)	0.0222 (11)	0.0248 (11)
O2	0.0336 (11)	0.0677 (14)	0.0487 (12)	0.0136 (10)	0.0026 (9)	0.0072 (11)
O3	0.0671 (15)	0.0721 (16)	0.0533 (14)	−0.0262 (13)	0.0202 (12)	−0.0269 (12)
O4	0.0430 (11)	0.0402 (11)	0.0300 (10)	0.0100 (9)	0.0048 (8)	0.0032 (8)
P2	0.0330 (4)	0.0377 (4)	0.0314 (4)	−0.0008 (3)	0.0009 (3)	−0.0012 (3)
O5	0.0445 (12)	0.0425 (12)	0.0563 (14)	0.0004 (10)	0.0160 (10)	−0.0061 (10)
O6	0.0454 (11)	0.0444 (11)	0.0339 (11)	−0.0018 (9)	0.0049 (9)	0.0010 (9)
O7	0.0486 (12)	0.0386 (11)	0.0431 (12)	−0.0049 (9)	−0.0026 (9)	−0.0011 (9)
O8	0.0372 (11)	0.0694 (15)	0.0396 (12)	−0.0049 (10)	−0.0019 (9)	0.0120 (10)
N1	0.0470 (15)	0.0375 (14)	0.0504 (15)	0.0044 (12)	−0.0046 (12)	0.0000 (11)
N2	0.0503 (16)	0.0518 (16)	0.0634 (18)	0.0069 (13)	−0.0093 (14)	0.0033 (13)
C1	0.062 (2)	0.0433 (18)	0.069 (2)	0.0004 (16)	−0.0094 (18)	−0.0097 (16)
C2	0.053 (2)	0.061 (2)	0.081 (3)	0.0008 (17)	−0.0198 (19)	−0.0180 (19)
C3	0.058 (2)	0.058 (2)	0.076 (3)	0.0144 (17)	−0.0216 (19)	−0.0053 (18)
C4	0.056 (2)	0.0398 (17)	0.065 (2)	0.0082 (15)	−0.0083 (17)	0.0030 (16)
C5	0.0432 (16)	0.0370 (16)	0.0371 (15)	0.0030 (12)	0.0046 (13)	0.0013 (12)
C6	0.0392 (16)	0.0431 (17)	0.0434 (17)	0.0023 (13)	0.0050 (13)	0.0011 (13)
C7	0.057 (2)	0.0446 (19)	0.085 (3)	−0.0003 (16)	−0.0091 (19)	−0.0011 (18)
C8	0.064 (2)	0.057 (2)	0.119 (4)	−0.007 (2)	−0.005 (2)	−0.017 (2)
C9	0.042 (2)	0.084 (3)	0.098 (3)	0.001 (2)	−0.0092 (19)	−0.028 (2)
C10	0.051 (2)	0.076 (3)	0.077 (3)	0.0159 (19)	−0.0143 (19)	−0.004 (2)

Geometric parameters (Å, º)

P1—O4	1.4930 (19)	C1—C2	1.352 (5)
P1—O2	1.496 (2)	C1—H1	0.9300
P1—O3	1.545 (2)	C2—C3	1.374 (5)
P1—O1	1.552 (2)	C2—H2	0.9300
O1—H1A	0.841 (10)	C3—C4	1.366 (5)
O3—H3A	0.840 (10)	C3—H3	0.9300
P2—O6	1.485 (2)	C4—C5	1.379 (4)
P2—O8	1.534 (2)	C4—H4	0.9300
P2—O5	1.541 (2)	C5—C6	1.478 (4)
P2—O7	1.545 (2)	C6—C7	1.363 (4)
O5—H5A	0.839 (10)	C7—C8	1.376 (5)
O7—H7A	0.836 (10)	C7—H7	0.9300
O8—H8A	0.836 (10)	C8—C9	1.357 (5)
N1—C1	1.333 (4)	C8—H8	0.9300
N1—C5	1.336 (4)	C9—C10	1.363 (5)
N1—H1B	0.897 (10)	C9—H9	0.9300
N2—C10	1.331 (4)	C10—H10	0.9300
N2—C6	1.335 (4)
O4—P1—O2	115.32 (11)	C3—C2—H2	120.6
O4—P1—O3	106.21 (12)	C4—C3—C2	120.2 (3)
O2—P1—O3	110.56 (14)	C4—C3—H3	119.9
O4—P1—O1	111.71 (11)	C2—C3—H3	119.9
O2—P1—O1	105.52 (12)	C3—C4—C5	119.8 (3)
O3—P1—O1	107.32 (14)	C3—C4—H4	120.1
P1—O1—H1A	115 (3)	C5—C4—H4	120.1
P1—O3—H3A	118 (3)	N1—C5—C4	117.9 (3)
O6—P2—O8	110.82 (11)	N1—C5—C6	116.7 (3)
O6—P2—O5	107.92 (12)	C4—C5—C6	125.4 (3)
O8—P2—O5	110.54 (13)	N2—C6—C7	122.9 (3)
O6—P2—O7	114.65 (11)	N2—C6—C5	114.6 (3)
O8—P2—O7	104.84 (12)	C7—C6—C5	122.5 (3)
O5—P2—O7	108.03 (12)	C6—C7—C8	118.9 (3)
P2—O5—H5A	118 (3)	C6—C7—H7	120.5
P2—O7—H7A	117 (2)	C8—C7—H7	120.5
P2—O8—H8A	113 (3)	C9—C8—C7	118.9 (4)
C1—N1—C5	123.3 (3)	C9—C8—H8	120.5
C1—N1—H1B	118 (2)	C7—C8—H8	120.5
C5—N1—H1B	118 (2)	C8—C9—C10	118.7 (4)
C10—N2—C6	116.9 (3)	C8—C9—H9	120.6
N1—C1—C2	120.0 (3)	C10—C9—H9	120.6
N1—C1—H1	120.0	N2—C10—C9	123.7 (4)
C2—C1—H1	120.0	N2—C10—H10	118.2
C1—C2—C3	118.8 (3)	C9—C10—H10	118.2
C1—C2—H2	120.6
C5—N1—C1—C2	0.3 (5)	N1—C5—C6—N2	−2.8 (4)
N1—C1—C2—C3	1.1 (6)	C4—C5—C6—N2	176.2 (3)
C1—C2—C3—C4	−1.2 (6)	N1—C5—C6—C7	178.5 (3)
C2—C3—C4—C5	0.0 (6)	C4—C5—C6—C7	−2.5 (5)
C1—N1—C5—C4	−1.5 (5)	N2—C6—C7—C8	0.1 (6)
C1—N1—C5—C6	177.6 (3)	C5—C6—C7—C8	178.8 (3)
C3—C4—C5—N1	1.3 (5)	C6—C7—C8—C9	0.5 (6)
C3—C4—C5—C6	−177.7 (3)	C7—C8—C9—C10	−0.9 (6)
C10—N2—C6—C7	−0.3 (5)	C6—N2—C10—C9	−0.1 (6)
C10—N2—C6—C5	−179.1 (3)	C8—C9—C10—N2	0.7 (7)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···O4^i	0.84 (1)	1.76 (1)	2.592 (3)	171 (4)
O3—H3A···O4^ii	0.84 (1)	1.80 (2)	2.617 (3)	164 (4)
O7—H7A···O2^ii	0.84 (1)	1.74 (1)	2.557 (3)	167 (4)
O8—H8A···O6^iii	0.84 (1)	1.69 (1)	2.529 (3)	178 (4)
O5—H5A···O2	0.84 (1)	1.71 (1)	2.542 (3)	173 (4)
N1—H1B···O6	0.90 (1)	2.05 (2)	2.847 (3)	147 (3)
C2—H2···O4^iv	0.93	2.59	3.409 (4)	147

Symmetry codes: (i) −x, −y+1, −z+1; (ii) x, −y+1/2, z−1/2; (iii) x, −y+1/2, z+1/2; (iv) x, y, z−1.