Crystal structure of 2,6-di-amino-pyridinium chloride.

The asymmetric unit of the title salt, C5H8N3 (+)·Cl(-), comprises one half of the 2,6-di-amino-pyridinium cation (the other half being completed by the application of mirror symmetry) and one Cl(-) counter-anion, also located on the mirror plane. The amino N atom shows a significant pyramidalization, with a dihedral angle of 30.4 (14)° between the least-squares planes of the amino group and the non-H atoms of the 2,6-di-amino-pyridinium moiety. In the crystal, the cationic mol-ecules and Cl(-) counter-anions are arranged in sheets parallel to (001) consisting of alternating polar and non-polar parts associated with the the Cl(-) anions, pyridinium and amino moieties, and the pyridine rings, respectively. N-H⋯Cl inter-actions within the polar part, as well as slipped π-π inter-actions in the non-polar part, help to establish the three-dimensional network.

Chemical context

Pincer compounds are an important class of chelating ligands, and their metal complexes have attracted tremendous inter­est due to their high stability, activity, variability and applicability in organic synthesis and catalysis (Szabo & Wendt, 2014 ▸). Whereas a plethora of (mostly) precious transition-n class="Chemical">metal pincer complexes has been reported, information on group 6 pincer complexes is rather scarce. During a project aimed at the preparation and characterization of group 6 PNP pincer compounds (Öztopcu et al., 2013 ▸; de Aguiar et al., 2014 ▸; Mastalir et al., 2016 ▸), crystals of the title salt, C5H8N3 +·Cl−, were obtained accidentally through hydrolysis of the employed ligand N,N’-bis­(diiso­propyl­phosphino)-2,6-di­amino­pyridine in the presence of CrCl3·6H2O. Here we report on the crystal structure of this salt.

Structural commentary

The cation of the title structure is protonated at the pyridine n class="Chemical">N atom (Fig. 1 ▸). The asymmetric unit comprises half a mol­ecule of the 2,6-di­amino­pyridinium cation, with a mirror plane running through the pyridinium group (N1—H1N1) and the para-C—H group (C3—H1C3); the Cl− anion is also located on the mirror plane. In agreement with other 2,6-di­amino­pyridinium cations, the C—N(H)+—C angle involving the pyridinium group is enlarged [C1—N1—C1i = 123.37 (8)°; symmetry code: (i) x, −y, z] whereas the angle between the pyridinium N atom and the C atom in the ortho position (bearing the amino group) and in the meta position is reduced [N1—C1—C2 = 118.83 (6)°]. This situation is reversed in 2,6-di­amino­pyridine due to the non-protonated ring N atom in this structure (Schwalbe et al., 1987 ▸). A common feature of the non-protonated 2,6-di­amino­pyridine mol­ecule and the 2,6-di­amino­pyridinium cation is a significant pyramidalization of the amino N atom. In the title structure, the bond angle sum at this atom (N2) deviates with 349.0° clearly from the expected 360° for an ideal trigonal–planar group. The pyramidalization is also reflected by the dihedral angle of 30.4 (14)° between the least-squares planes of the amino group and the non-H atoms of the 2,6-di­amino­pyridinium moiety.

Figure 1

The mol­ecular structure of the cation and the inorganic anion in the title structure. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry code: (i) x, −y, z.]

Supra­molecular features

The pyridinium n class="Chemical">N1—H1N1 group is the donor of a nearly linear hydrogen bond to the Cl− counter anion (Table 1 ▸). The amino group also participates in the formation of N—H⋯Cl hydrogen bonds, albeit of explicit weaker nature. One hydrogen atom (H2N2) is clearly involved in hydrogen bonding with an H2N2⋯Cl1 distance of 2.63 Å and an N2—H2N2⋯Cl1 angle of 157°. Although the D⋯A contact involving the second hydrogen atom, H2N2, is 0.04 Å shorter than that of the other hydrogen bond of this group, the comparatively long H1N2⋯Cl distance of 2.88 Å and the very small N2—H1N2⋯Cl1 angle of 117° give room for inter­pretation whether or not this is a real hydrogen bond.

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1N1⋯Cl1	0.90 (2)	2.18 (2)	3.0790 (11)	175.6 (19)
N2—H2N2⋯Cl1i	0.833 (13)	2.628 (13)	3.4086 (8)	156.5 (12)
N2—H1N2⋯Cl1ii	0.875 (13)	2.877 (13)	3.3601 (8)	116.8 (2)

Symmetry codes: (i) ; (ii) .

In the crystal (Figs. 2 ▸ and 3 ▸), the cationic mol­ecules and anions are arranged into layers with alternating polar and non-polar parts extending parallel to (001). Adjacent polar parts, comprising the Cl− anions and the pyridinium and amino moieties, are linked through n class="Chemical">N—H⋯Cl hydrogen bonds into sheets with a thickness of ≃ c/2. The non-polar parts, i.e. the pyridine rings, inter­act through slipped π–π stacking along [001] with a centroid-to-centroid distance of 3.5129 (6) Å; the corresponding plane-to-plane distance between the pyridine rings is 3.344 Å.

Figure 2

Crystal packing of the organic and inorganic components in the title structure in a projection along [001]. N—H⋯Cl hydrogen bonds involving the pyridinium group are shown as magenta dotted lines and those involving the amino group are shown as orange dotted lines.

Figure 3

Crystal packing of the organic and inorganic components in the title structure in a projection along [100]. The colour code of the inter­molecular inter­actions is as in Fig. 2 ▸.

Database survey

A search in the CSD (Groom & Allen, 2014 ▸; CSD Version 5.31) revealed 87 different salts containing the 2,6-di­amino­n class="Chemical">pyridinium cation, with the majority of cases in the form of organic anions (46 representatives), followed by complex metal anions (31 representatives). Two structures are reported that contain additional metal cations and inorganic anions, and eight representatives are compiled with inorganic anions only, including the SiF6 2− salt (CSD code FOSXER; Gelmboldt et al., 2009 ▸), the Br− salt (GOLMIF; Turrell et al., 2010 ▸), the BF4 − salt (IFOQAW; Benito-Garagorri et al.; 2007 ▸), the Br− salt monohydrate (ILINEW; Haddad & Al-Far, 2003 ▸), the hydrogensulfate sulfate salt (KORRAM; Said & Naili, 2014 ▸), the ClO4 − salt (MIGWOP; Jazdoń et al., 2007 ▸), the H2PO4 − salt (QEDHUE; Yu, 2012 ▸) and the NO3 − salt (XAKVAG; Kristiansson, 2000 ▸). It should be noted that the chemically most related anhydrous Br− salt crystallizes in space group I 2d and hence shows no isotypism with the title Cl− salt.

Synthesis and crystallization

N,n class="Chemical">N’-bis­(diiso­propyl­phosphino)-2,6-di­amino­pyridine (0.2 g, 0.53 mmol) was dissolved in dry tetra­hydro­furan (5 ml) under argon atmosphere. CrCl3·6H2O (0.134 g, 0.51 mmol) was added and the resulting mixture stirred for 4 h at room temperature. The formed purple solid was filtered off, washed with dry diethyl ether and dried. The solid was redissolved in aceto­nitrile for crystallization initiated by solvent diffusion with diethyl ether. The title compound grew in the form of yellow crystals as the only solid product. We assume that the Lewis acid CrCl3 in combination with water is able to cleave the P—N bond of the pincer compound accompanied by an in situ formation of HCl which eventually yields the title compound.

Refinement

All H atoms were clearly discernible from difference Fourier maps and were refined freely. Crystal data, data collection and structure refinement details are summarized in Table 2 ▸.

Table 2

Experimental details

Crystal data
Chemical formula	C5H8N3+·Cl−
M r	145.6
Crystal system, space group	Monoclinic, C2/m
Temperature (K)	100
a, b, c (Å)	10.8046 (10), 9.0459 (9), 6.8108 (7)
β (°)	96.710 (2)
V (Å3)	661.11 (11)
Z	4
Radiation type	Mo Kα
μ (mm−1)	0.48
Crystal size (mm)	0.52 × 0.38 × 0.23
Data collection
Diffractometer	Bruker Kappa APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2014 ▸)
T min, T max	0.80, 0.90
No. of measured, independent and observed [I > 3σ(I)] reflections	9529, 1538, 1407
R int	0.031
(sin θ/λ)max (Å−1)	0.808
Refinement
R[F 2 > 3σ(F)], wR(F), S	0.024, 0.038, 2.24
No. of reflections	1538
No. of parameters	64
H-atom treatment	All H-atom parameters refined
Δρmax, Δρmin (e Å−3)	0.49, −0.18

Computer programs: APEX2 (Bruker, 2014 ▸), SAINT (Bruker, 2014 ▸), SUPERFLIP (Palatinus & Chapuis, 2007 ▸), JANA2006 (Petříček et al., 2014 ▸), XP in SHELXTL (Sheldrick, 2008 ▸), Mercury (Macrae et al., 2006 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S2056989016002425/hb7564sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989016002425/hb7564Isup2.hkl

Click here for additional data file.

Supporting information file. DOI: 10.1107/S2056989016002425/hb7564Isup3.cml

CCDC reference: 1452262

Additional supporting information: crystallographic information; 3D view; checkCIF report

C5H8N3+·Cl−	F(000) = 304
Mr = 145.6	Dx = 1.462 Mg m−3
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2y	Cell parameters from 6316 reflections
a = 10.8046 (10) Å	θ = 2.9–35.5°
b = 9.0459 (9) Å	µ = 0.48 mm−1
c = 6.8108 (7) Å	T = 100 K
β = 96.710 (2)°	Block, yellow
V = 661.11 (11) Å3	0.52 × 0.38 × 0.23 mm
Z = 4

Bruker Kappa APEXII CCD diffractometer	1538 independent reflections
Radiation source: X-ray tube	1407 reflections with I > 3σ(I)
Graphite monochromator	Rint = 0.031
ω– and φ–scans	θmax = 35.0°, θmin = 3.0°
Absorption correction: multi-scan (SADABS; Bruker, 2014)	h = −17→17
Tmin = 0.80, Tmax = 0.90	k = −14→14
9529 measured reflections	l = −10→10

Refinement on F	0 constraints
R[F2 > 2σ(F2)] = 0.024	All H-atom parameters refined
wR(F2) = 0.038	Weighting scheme based on measured s.u.'s w = 1/(σ2(F) + 0.0001F2)
S = 2.24	(Δ/σ)max = 0.030
1538 reflections	Δρmax = 0.49 e Å−3
64 parameters	Δρmin = −0.18 e Å−3
0 restraints

	x	y	z	Uiso*/Ueq
Cl1	0.17115 (2)	0	0.12206 (3)	0.01401 (7)
N1	0.45600 (9)	0	0.22925 (12)	0.0132 (2)
N2	0.44617 (7)	0.25682 (8)	0.22357 (10)	0.01951 (18)
C1	0.51532 (7)	0.13257 (7)	0.25660 (9)	0.01272 (16)
C2	0.64225 (7)	0.13396 (7)	0.32011 (10)	0.01334 (17)
C3	0.70393 (10)	0	0.35111 (14)	0.0136 (2)
H1C2	0.6796 (9)	0.2256 (14)	0.3421 (16)	0.019 (3)*
H1C3	0.7905 (16)	0	0.392 (2)	0.015 (3)*
H1N2	0.3742 (16)	0.2574 (17)	0.150 (2)	0.046 (4)*
H2N2	0.4841 (12)	0.3350 (15)	0.2058 (19)	0.032 (3)*
H1N1	0.3735 (19)	0	0.191 (3)	0.039 (5)*

	U11	U22	U33	U12	U13	U23
Cl1	0.01121 (13)	0.01270 (11)	0.01763 (12)	0	−0.00037 (8)	0
N1	0.0093 (4)	0.0176 (4)	0.0128 (3)	0	0.0018 (3)	0
N2	0.0192 (3)	0.0187 (3)	0.0214 (3)	0.0075 (2)	0.0056 (2)	0.0065 (2)
C1	0.0137 (3)	0.0143 (3)	0.0107 (2)	0.0025 (2)	0.0039 (2)	0.00180 (19)
C2	0.0136 (3)	0.0118 (3)	0.0149 (3)	−0.0012 (2)	0.0026 (2)	−0.00027 (19)
C3	0.0108 (4)	0.0154 (4)	0.0145 (4)	0	0.0011 (3)	0

N1—C1	1.3622 (8)	C1—C2	1.3890 (10)
N1—C1	1.3622 (8)	C2—C3	1.3872 (9)
N1—H1N1	0.90 (2)	C2—H1C2	0.927 (12)
N2—C1	1.3538 (10)	C3—H1C3	0.944 (17)
N2—H1N2	0.875 (16)	C3—C2	1.3872 (9)
N2—H2N2	0.833 (13)
C1—N1—C1	123.37 (8)	N2—C1—C2	123.35 (6)
C1—N1—H1N1	118.32 (4)	C1—C2—C3	118.60 (7)
C1—N1—H1N1	118.32 (4)	C1—C2—H1C2	117.0 (6)
C1—N2—H1N2	122.5 (10)	C3—C2—H1C2	124.4 (6)
C1—N2—H2N2	117.2 (9)	C2—C3—C2	121.75 (9)
H1N2—N2—H2N2	109.3 (13)	C2—C3—H1C3	119.12 (5)
N1—C1—N2	117.81 (7)	C2—C3—H1C3	119.12 (5)
N1—C1—C2	118.83 (6)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N1···Cl1	0.90 (2)	2.18 (2)	3.0790 (11)	175.6 (19)
N2—H2N2···Cl1i	0.833 (13)	2.628 (13)	3.4086 (8)	156.5 (12)
N2—H1N2···Cl1ii	0.875 (13)	2.877 (13)	3.3601 (8)	116.8 (2)