(2-Pyridylmethyl)ammonium pyridine-2-carboxylate: the product of oxidative degradation of bis(2-pyridylmethyl)amine

The title compound, C₆H₉N₂⁺·C₆H₄NO₂^-, has been formed by oxidative degradation of neat bis(2-pyridyl­methyl)­amine. Hydro­gen bonds link the ions into infinite chains along the a axis.

S1. Comment

The amine bis(2-pyridylmethyl)amine is a versatile synthetic intermediate widely used in the preparation of polypyridyl ligands. The amine is usually distilled prior to use, and during the course of our studies in this field (Døssing et al., 1996, 1997), it has puzzled us that colourless needles begin to form after a couple of months' storage of the distilled amine. In order to characterize the decomposition product, a single-crystal was subjected to structure determination, which showed that the title salt, (I), consisting of a (2-pyridylmethyl)ammonium cation and a pyridine-2-carboxylate anion, had formed. A possible mechanism for the formation of (I) is shown below. \sch

In support of this mechanism, close scrutiny of a ¹H NMR spectrum of a concentrated solution of aged bis(2-pyridylmethyl)amine in CD₃CN indeed revealed the presence of low intensity peaks that could originate from pyridine-2-carboxaldehyde (7.61, 7.91, 8.77 and 10.00 p.p.m. in CD₃CN). It is important to emphasize that these peaks are absent in a spectrum of freshly distilled bis(2-pyridylmethyl)amine. The presence of traces of impurities might catalyse the oxidative degradation. A similar (Fe^III-promoted) oxidative degradation of a polypyridyl compound has been reported by Renz et al. (1999).

The Cambridge Structural Database (Allen et al., 1993) contains numerous structural reports of the pyridine-2-carboxylate anion, whereas the structure of the (2-pyridylmethyl)ammonium cation has no precedent. The bond lengths and angles in the cation and anion are normal. The pyridyl rings of the two ions are almost orthogonal [87.4 (5)°].

The structure of (I) shows four hydrogen bonds (Table 1) linking the ions into infinite chains along the a axis. The anion carboxylic O atoms and the pyridyl N atom act as hydrogen-bond acceptors, with the donor being the aliphatic N atom in the cation.

Related literature

For related literature, see: Allen & Kennard (1993); Døssing et al. (1996, 1997); Larsen et al. (1986); Renz et al. (1999).

S2. Experimental

Freshly distilled bis(2-pyridylmethyl)amine (Larsen et al., 1986) was left in a closed flask for about three months, during which colourless needles of (I) formed. The mother liquor was decanted off and the crystals were washed with diethyl ether and air dried.

Computing details

Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: DREADD (Blessing, 1987); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. The molecular view of (I), with displacement ellipsoids drawn at the 50% probability level and H atoms shown as spheres of arbitrary radii.

(2-Pyridylmethyl)ammonium pyridine-2-carboxylate

Crystal data

C6H9N2^+·C6H4NO2^−	F(000) = 488
Mr = 231.25	Dx = 1.307 Mg m^−3
Monoclinic, P21/c	Cu Kα radiation, λ = 1.54180 Å
a = 6.4233 (9) Å	Cell parameters from 20 reflections
b = 9.0728 (18) Å	θ = 39.3–43.8°
c = 20.265 (3) Å	µ = 0.75 mm^−1
β = 95.700 (11)°	T = 122 K
V = 1175.1 (3) Å^3	Needle, colourless
Z = 4	0.19 × 0.06 × 0.02 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	Rint = 0.025
Radiation source: fine-focus sealed tube	θmax = 75.0°, θmin = 4.4°
Graphite monochromator	h = −8→8
ω/2θ scans	k = 0→11
4776 measured reflections	l = 0→25
2412 independent reflections	5 standard reflections every 167 min
2140 reflections with I > 2σ(I)	intensity decay: 4.5%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.033	All H-atom parameters refined
wR(F^2) = 0.119	w = 1/[σ^2(Fo^2) + (0.1P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.00	(Δ/σ)max < 0.001
2412 reflections	Δρmax = 0.29 e Å^−3
207 parameters	Δρmin = −0.18 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0120 (14)

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
C1	0.18390 (16)	0.33894 (11)	0.38952 (5)	0.0202 (2)
C2	0.02792 (15)	0.28040 (11)	0.33368 (5)	0.0196 (2)
C3	0.09091 (19)	0.18135 (12)	0.28715 (6)	0.0270 (3)
C4	−0.30398 (18)	0.29114 (14)	0.28076 (5)	0.0292 (3)
C5	−0.25469 (19)	0.19433 (14)	0.23157 (6)	0.0309 (3)
C6	−0.0539 (2)	0.13815 (13)	0.23503 (6)	0.0324 (3)
C7	0.75862 (17)	0.24344 (12)	0.50895 (6)	0.0261 (3)
C8	0.58952 (17)	0.20647 (11)	0.55274 (5)	0.0229 (3)
C9	0.5797 (2)	0.06513 (13)	0.57965 (6)	0.0309 (3)
C10	0.4236 (2)	0.03386 (13)	0.61969 (6)	0.0348 (3)
C11	0.2816 (2)	0.14310 (15)	0.63175 (6)	0.0332 (3)
C12	0.30333 (18)	0.28077 (13)	0.60322 (6)	0.0287 (3)
O1	0.11368 (12)	0.42770 (9)	0.42944 (4)	0.0274 (2)
O2	0.36799 (12)	0.29485 (9)	0.39017 (4)	0.0283 (2)
N1	−0.16701 (14)	0.33402 (11)	0.33111 (4)	0.0246 (2)
N2	0.45458 (14)	0.31311 (10)	0.56429 (4)	0.0236 (2)
N3	0.71603 (14)	0.38256 (10)	0.47272 (4)	0.0203 (2)
H3	0.239 (3)	0.1468 (18)	0.2917 (8)	0.041 (4)*
H4	−0.449 (3)	0.3261 (19)	0.2794 (8)	0.046 (4)*
H5	−0.360 (3)	0.1641 (18)	0.1959 (8)	0.041 (4)*
H6	−0.017 (2)	0.0712 (19)	0.2007 (8)	0.045 (4)*
H1N3	0.725 (2)	0.4624 (18)	0.5029 (8)	0.036 (4)*
H2N3	0.585 (3)	0.3764 (17)	0.4482 (8)	0.037 (4)*
H3N3	0.821 (3)	0.3990 (17)	0.4453 (8)	0.038 (4)*
H7A	0.898 (3)	0.2511 (19)	0.5348 (8)	0.038 (4)*
H7B	0.770 (3)	0.163 (2)	0.4775 (9)	0.045 (4)*
H9	0.679 (2)	−0.0096 (18)	0.5697 (7)	0.036 (4)*
H10	0.407 (2)	−0.0658 (18)	0.6390 (8)	0.046 (4)*
H11	0.173 (3)	0.1250 (19)	0.6597 (9)	0.051 (5)*
H12	0.207 (2)	0.3641 (16)	0.6127 (7)	0.028 (3)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0193 (5)	0.0209 (5)	0.0208 (5)	−0.0019 (4)	0.0035 (4)	−0.0009 (4)
C2	0.0202 (5)	0.0203 (5)	0.0188 (5)	−0.0030 (4)	0.0037 (4)	0.0010 (4)
C3	0.0294 (6)	0.0246 (5)	0.0270 (6)	0.0016 (4)	0.0026 (4)	−0.0049 (4)
C4	0.0216 (5)	0.0421 (6)	0.0233 (6)	−0.0034 (5)	0.0001 (4)	0.0005 (5)
C5	0.0323 (6)	0.0379 (6)	0.0214 (5)	−0.0095 (5)	−0.0025 (4)	−0.0001 (4)
C6	0.0424 (7)	0.0287 (6)	0.0258 (6)	−0.0036 (5)	0.0025 (5)	−0.0085 (4)
C7	0.0228 (5)	0.0225 (5)	0.0330 (6)	0.0056 (4)	0.0023 (4)	−0.0002 (4)
C8	0.0244 (5)	0.0219 (5)	0.0214 (5)	−0.0001 (4)	−0.0032 (4)	−0.0013 (4)
C9	0.0420 (7)	0.0220 (5)	0.0279 (5)	0.0028 (5)	−0.0010 (5)	0.0005 (4)
C10	0.0512 (8)	0.0245 (5)	0.0280 (6)	−0.0076 (5)	−0.0002 (5)	0.0052 (4)
C11	0.0364 (7)	0.0367 (6)	0.0265 (6)	−0.0097 (5)	0.0030 (5)	0.0043 (5)
C12	0.0259 (5)	0.0326 (6)	0.0280 (6)	−0.0002 (4)	0.0038 (4)	0.0046 (4)
O1	0.0206 (4)	0.0339 (4)	0.0279 (4)	−0.0012 (3)	0.0036 (3)	−0.0131 (3)
O2	0.0199 (4)	0.0341 (4)	0.0307 (4)	0.0027 (3)	0.0008 (3)	−0.0085 (3)
N1	0.0197 (4)	0.0326 (5)	0.0219 (5)	−0.0014 (3)	0.0036 (3)	−0.0015 (4)
N2	0.0229 (5)	0.0237 (5)	0.0240 (5)	0.0006 (3)	0.0012 (3)	0.0024 (3)
N3	0.0178 (4)	0.0221 (4)	0.0213 (4)	0.0006 (3)	0.0035 (3)	−0.0026 (3)

Geometric parameters (Å, º)

C1—O2	1.2472 (13)	C7—H7A	0.995 (17)
C1—O1	1.2564 (13)	C7—H7B	0.976 (18)
C1—C2	1.5299 (14)	C8—N2	1.3351 (14)
C2—N1	1.3395 (14)	C8—C9	1.3974 (15)
C2—C3	1.3914 (15)	C9—C10	1.3807 (18)
C3—C6	1.3924 (16)	C9—H9	0.967 (16)
C3—H3	0.995 (16)	C10—C11	1.3853 (19)
C4—N1	1.3370 (14)	C10—H10	0.995 (17)
C4—C5	1.3884 (17)	C11—C12	1.3894 (17)
C4—H4	0.985 (17)	C11—H11	0.954 (19)
C5—C6	1.3821 (18)	C12—N2	1.3435 (14)
C5—H5	0.979 (17)	C12—H12	1.006 (15)
C6—H6	0.970 (17)	N3—H1N3	0.946 (16)
C7—N3	1.4724 (14)	N3—H2N3	0.933 (16)
C7—C8	1.5071 (15)	N3—H3N3	0.927 (17)
O2—C1—O1	126.84 (10)	N2—C8—C9	122.80 (11)
O2—C1—C2	116.55 (9)	N2—C8—C7	117.40 (9)
O1—C1—C2	116.61 (9)	C9—C8—C7	119.80 (10)
N1—C2—C3	122.81 (10)	C10—C9—C8	118.78 (11)
N1—C2—C1	116.34 (9)	C10—C9—H9	120.8 (9)
C3—C2—C1	120.80 (9)	C8—C9—H9	120.4 (9)
C2—C3—C6	118.57 (11)	C9—C10—C11	119.09 (11)
C2—C3—H3	118.7 (9)	C9—C10—H10	121.9 (10)
C6—C3—H3	122.7 (9)	C11—C10—H10	118.9 (10)
N1—C4—C5	123.50 (11)	C10—C11—C12	118.34 (11)
N1—C4—H4	118.6 (10)	C10—C11—H11	120.9 (11)
C5—C4—H4	117.8 (10)	C12—C11—H11	120.8 (11)
C6—C5—C4	118.37 (10)	N2—C12—C11	123.32 (11)
C6—C5—H5	120.6 (10)	N2—C12—H12	116.1 (8)
C4—C5—H5	121.1 (10)	C11—C12—H12	120.5 (8)
C5—C6—C3	118.98 (11)	C4—N1—C2	117.76 (9)
C5—C6—H6	119.1 (10)	C8—N2—C12	117.68 (10)
C3—C6—H6	121.9 (10)	C7—N3—H1N3	109.7 (9)
N3—C7—C8	112.05 (9)	C7—N3—H2N3	109.1 (10)
N3—C7—H7A	108.4 (10)	H1N3—N3—H2N3	112.7 (13)
C8—C7—H7A	111.7 (9)	C7—N3—H3N3	109.1 (10)
N3—C7—H7B	109.6 (10)	H1N3—N3—H3N3	105.1 (13)
C8—C7—H7B	109.0 (10)	H2N3—N3—H3N3	111.1 (13)
H7A—C7—H7B	105.8 (14)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N3—H1N3···O1^i	0.946 (16)	1.913 (16)	2.7672 (13)	149.0 (13)
N3—H2N3···O2	0.933 (16)	1.885 (17)	2.7722 (13)	157.9 (14)
N3—H3N3···N1^ii	0.927 (17)	2.396 (16)	3.0694 (13)	129.4 (13)
N3—H3N3···O1^ii	0.927 (17)	1.956 (17)	2.8117 (12)	152.5 (14)

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