Zwitterionic 5-(1-piperidiniomethyl)-1H-tetrazolide

The title compound, C₇H₁₃N₅, a tetrazole analogue of betaines, exists as a zwitterion, with the H atom of the tetrazole ring being transferred to the piperidine ring N atom. The tetrazole ring symmetry is close to C_2v, which suggests strong charge delocalization in the N-C-N fragment of the ring. There are classical hydrogen bonds in the structure which are responsible for the formation of two-membered aggregates.

S1. Comment

Tetrazole and its 5-substituted derivatives attract research attention in the field of bioorganic and medicinal chemistry, due to the isosterity and acidity of the N-unsubstituted tetrazole ring being comparable with those of the carboxylic acid group (Butler, 1996). 5-Monosubstituted tetrazoles with an aminomethyl substituent represent an interesting class of tetrazole analogues of α-aminoacids. One should expect that such compounds may exist in the form of a zwitterion. In this paper, we report the molecular and crystal structures of the title compound, (I) (Fig. 1). No crystal data were found for 5-(α-aminomethyl)tetrazoles (Cambridge Structural Database, Version 5.23 of September 2002; Allen, 2002). \sch

As was expected, compound (I) exists as a zwitterion, with the H atom of the tetrazole ring being transferred to the piperidine ring N atom. The main geometrical features of (I) are given in Table 1.

As can be seen in Fig. 1, the tetrazole ring in (I) is rather symmetrical. The C5—N1 and C5—N4 bond lengths are practically the same, and the N1—N2 bond length is equal to the value for N3—N4. The N2—N3 bond is the shortest in the ring. Bond symmetry is supported by angle symmetry (Table 1). Moreover, the tetrazole ring is essentially planar to within 0.0019 (6) Å. Thus, the ring symmetry is close to C_2v. Taking into account the essential difference between the C5—N1 and C5—N4 bond lengths in 5-substituted tetrazoles, one can conclude that there is strong charge delocalization in the N1—C5—N4 fragment of (I).

The protonation at the N7 atom leads to an increase in the N7—C distances and to the angles at N7 being close to tetrahedral (Table 1). The piperidine ring adopts a chair conformation, with the H atom at N7 in the axial position, whereas the bulky substituent is located in the equatorial position.

Inspection of the packing structure of (I) reveals classical N7—H7···N4 hydrogen bonds (Table 2). These are responsible for the formation of two-membered aggregates (Fig.2), additionally stabilized by weak C9—H9B···N3 interactions (Table 2). Only non-classical hydrogen bonds (Table 2), together with van der Waals interactions, exist between the above aggregates in the structure of (I).

It should be noted that the title compound is the second structurally characterized tetrazole analogue of betaines after 5-(2'-dimethylaminoethyl)tetrazole (Chertanova et al., 1988). The main features of the tetrazole ring geometry of the latter compound are close to those found for (I).

S2. Experimental

The title compound was synthesized by the aminomethylation of tetrazole with piperidine and formaldehyde, according to the method described by Karavai & Gaponik (1991). The compound decomposes at 528 K. Single crystals of (I) were grown by slow evaporation in air of an ethyl alcohol solution of the title compound. Spectroscopic analysis: ¹H NMR [100 MHz, (CD₃)₂SO, δ, p.p.m.]: 1.30–1.82 (m, 6H, 3CH₂), 3.00 (t, 4H, 2CH₂), 4.25 (s, 2H, CH₂).

S3. Refinement

H-atom positions were found from the difference Fourier map and all associated parameters were refined freely. Refined C—H distances were in the range 0.95 (2)–1.01 (2) Å.

Computing details

Data collection: R3m Software (Nicolet, 1980); cell refinement: R3m Software; data reduction: R3m Software; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and PLATON (Spek, 1999); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of the molecular structure of (I). Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. The crystal structure of (I) viewed along the a axis. Dashed lines indicate classical N—H···N hydrogen bonds.

1-(1-piperidiniomethyl)-1H-tetrazolide

Crystal data

C7H13N5	Z = 2
Mr = 167.22	F(000) = 180
Triclinic, P1	Dx = 1.321 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71069 Å
a = 6.1664 (10) Å	Cell parameters from 25 reflections
b = 8.3913 (18) Å	θ = 20.4–23.3°
c = 8.6842 (17) Å	µ = 0.09 mm^−1
α = 90.062 (17)°	T = 293 K
β = 110.351 (15)°	Prism, colourless
γ = 93.176 (16)°	0.50 × 0.40 × 0.38 mm
V = 420.56 (14) Å^3

Data collection

Nicolet R3m four-circle diffractometer	Rint = 0.018
Radiation source: fine-focus sealed tube	θmax = 30.0°, θmin = 2.4°
Graphite monochromator	h = 0→8
ω/2θ scans	k = −11→11
2761 measured reflections	l = −12→11
2467 independent reflections	3 standard reflections every 100 reflections
2118 reflections with I > 2σ(I)	intensity decay: 1.7%

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)] = 0.040	Hydrogen site location: difference Fourier map
wR(F^2) = 0.118	All H-atom parameters refined
S = 1.06	w = 1/[σ^2(Fo^2) + (0.069P)^2 + 0.0378P] where P = (Fo^2 + 2Fc^2)/3
2467 reflections	(Δ/σ)max < 0.001
161 parameters	Δρmax = 0.17 e Å^−3
0 restraints	Δρmin = −0.26 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
N1	−0.23825 (15)	0.61929 (11)	0.80123 (10)	0.0448 (2)
N2	−0.41908 (15)	0.68757 (11)	0.69104 (11)	0.0479 (2)
N3	−0.38644 (14)	0.69921 (10)	0.55060 (10)	0.0438 (2)
N4	−0.18145 (13)	0.63976 (9)	0.56555 (9)	0.03756 (19)
C5	−0.09640 (14)	0.59166 (10)	0.71974 (9)	0.03267 (18)
C6	0.12905 (14)	0.51840 (11)	0.79597 (10)	0.03540 (19)
H6A	0.252 (2)	0.5757 (14)	0.7671 (15)	0.045 (3)*
H6B	0.172 (2)	0.5195 (14)	0.9139 (15)	0.039 (3)*
N7	0.12534 (11)	0.34779 (9)	0.74078 (8)	0.03126 (17)
H7	0.120 (2)	0.3488 (16)	0.6309 (17)	0.050 (3)*
C8	0.35021 (15)	0.27820 (12)	0.83978 (11)	0.0392 (2)
H8A	0.363 (2)	0.2864 (14)	0.9580 (15)	0.045 (3)*
H8B	0.474 (2)	0.3495 (16)	0.8234 (16)	0.051 (3)*
C9	0.35742 (17)	0.10701 (13)	0.78682 (13)	0.0464 (2)
H9A	0.507 (2)	0.0668 (18)	0.8596 (18)	0.062 (4)*
H9B	0.363 (2)	0.1039 (15)	0.6761 (16)	0.050 (3)*
C10	0.1508 (2)	0.00404 (14)	0.79440 (17)	0.0559 (3)
H10A	0.162 (3)	−0.0057 (19)	0.914 (2)	0.068 (4)*
H10B	0.150 (3)	−0.106 (2)	0.758 (2)	0.075 (5)*
C11	−0.07294 (18)	0.07791 (13)	0.69544 (15)	0.0495 (2)
H11A	−0.094 (2)	0.0780 (17)	0.5764 (19)	0.058 (4)*
H11B	−0.208 (3)	0.0136 (19)	0.7034 (19)	0.067 (4)*
C12	−0.07836 (14)	0.24810 (11)	0.75148 (12)	0.0377 (2)
H12A	−0.071 (2)	0.2549 (15)	0.8652 (16)	0.045 (3)*
H12B	−0.216 (2)	0.2989 (14)	0.6819 (15)	0.041 (3)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0507 (5)	0.0569 (5)	0.0382 (4)	0.0096 (4)	0.0290 (4)	0.0065 (3)
N2	0.0469 (4)	0.0559 (5)	0.0523 (5)	0.0098 (4)	0.0306 (4)	0.0087 (4)
N3	0.0402 (4)	0.0527 (5)	0.0424 (4)	0.0060 (3)	0.0189 (3)	0.0074 (3)
N4	0.0381 (4)	0.0491 (4)	0.0300 (3)	0.0030 (3)	0.0174 (3)	0.0039 (3)
C5	0.0365 (4)	0.0378 (4)	0.0284 (3)	−0.0021 (3)	0.0180 (3)	−0.0001 (3)
C6	0.0340 (4)	0.0430 (4)	0.0298 (4)	−0.0030 (3)	0.0127 (3)	−0.0015 (3)
N7	0.0283 (3)	0.0436 (4)	0.0241 (3)	0.0011 (3)	0.0121 (2)	0.0016 (2)
C8	0.0285 (4)	0.0571 (5)	0.0324 (4)	0.0046 (3)	0.0107 (3)	0.0056 (3)
C9	0.0413 (5)	0.0565 (6)	0.0460 (5)	0.0150 (4)	0.0192 (4)	0.0118 (4)
C10	0.0563 (6)	0.0474 (6)	0.0697 (7)	0.0086 (5)	0.0284 (6)	0.0137 (5)
C11	0.0430 (5)	0.0452 (5)	0.0607 (6)	−0.0031 (4)	0.0196 (5)	−0.0053 (4)
C12	0.0299 (4)	0.0449 (4)	0.0408 (4)	−0.0020 (3)	0.0162 (3)	−0.0006 (3)

Geometric parameters (Å, º)

N1—C5	1.3313 (11)	C8—H8A	1.004 (13)
N1—N2	1.3480 (13)	C8—H8B	0.994 (14)
N2—N3	1.3062 (12)	C9—C10	1.5203 (16)
N3—N4	1.3489 (11)	C9—H9A	0.995 (15)
N4—C5	1.3293 (11)	C9—H9B	0.975 (14)
C5—C6	1.4847 (12)	C10—C11	1.5156 (16)
C6—N7	1.5058 (12)	C10—H10A	1.018 (17)
C6—H6A	0.979 (13)	C10—H10B	0.978 (17)
C6—H6B	0.965 (12)	C11—C12	1.5141 (14)
N7—C12	1.5003 (11)	C11—H11A	0.996 (15)
N7—C8	1.5048 (11)	C11—H11B	0.988 (16)
N7—H7	0.943 (14)	C12—H12A	0.974 (13)
C8—C9	1.5156 (15)	C12—H12B	0.975 (12)
C5—N1—N2	104.73 (7)	C8—C9—C10	111.64 (9)
N3—N2—N1	109.69 (8)	C8—C9—H9A	107.3 (9)
N2—N3—N4	108.96 (8)	C10—C9—H9A	111.7 (9)
C5—N4—N3	105.17 (7)	C8—C9—H9B	109.9 (8)
N4—C5—N1	111.45 (8)	C10—C9—H9B	110.3 (8)
N4—C5—C6	125.48 (7)	H9A—C9—H9B	105.9 (11)
N1—C5—C6	123.06 (7)	C11—C10—C9	110.14 (9)
C5—C6—N7	113.13 (7)	C11—C10—H10A	110.1 (9)
C5—C6—H6A	111.2 (7)	C9—C10—H10A	109.1 (9)
N7—C6—H6A	105.7 (7)	C11—C10—H10B	110.6 (10)
C5—C6—H6B	110.0 (7)	C9—C10—H10B	112.8 (10)
N7—C6—H6B	107.5 (7)	H10A—C10—H10B	104.1 (13)
H6A—C6—H6B	109.1 (10)	C12—C11—C10	111.69 (9)
C12—N7—C8	111.25 (7)	C12—C11—H11A	108.4 (8)
C12—N7—C6	112.71 (7)	C10—C11—H11A	110.9 (8)
C8—N7—C6	109.07 (7)	C12—C11—H11B	109.6 (9)
C12—N7—H7	109.4 (8)	C10—C11—H11B	110.5 (9)
C8—N7—H7	106.6 (8)	H11A—C11—H11B	105.6 (12)
C6—N7—H7	107.6 (8)	N7—C12—C11	110.50 (8)
N7—C8—C9	111.24 (8)	N7—C12—H12A	106.9 (7)
N7—C8—H8A	106.5 (7)	C11—C12—H12A	112.3 (7)
C9—C8—H8A	111.7 (7)	N7—C12—H12B	106.1 (7)
N7—C8—H8B	105.8 (7)	C11—C12—H12B	111.8 (7)
C9—C8—H8B	112.5 (8)	H12A—C12—H12B	109.0 (10)
H8A—C8—H8B	108.7 (10)
C5—N1—N2—N3	0.27 (11)	C5—C6—N7—C8	−173.00 (6)
N1—N2—N3—N4	−0.50 (11)	C12—N7—C8—C9	56.12 (9)
N2—N3—N4—C5	0.51 (10)	C6—N7—C8—C9	−178.94 (7)
N3—N4—C5—N1	−0.35 (10)	N7—C8—C9—C10	−55.01 (11)
N3—N4—C5—C6	−179.44 (8)	C8—C9—C10—C11	54.36 (13)
N2—N1—C5—N4	0.06 (11)	C9—C10—C11—C12	−55.55 (13)
N2—N1—C5—C6	179.18 (8)	C8—N7—C12—C11	−56.86 (10)
N4—C5—C6—N7	−74.86 (10)	C6—N7—C12—C11	−179.73 (7)
N1—C5—C6—N7	106.15 (9)	C10—C11—C12—N7	57.06 (12)
C5—C6—N7—C12	−48.92 (9)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N7—H7···N4^i	0.943 (14)	1.874 (14)	2.8007 (11)	166.9 (11)
C9—H9B···N3^i	0.975 (14)	2.608 (13)	3.4067 (15)	139.3 (10)
C6—H6A···N2^ii	0.979 (13)	2.482 (13)	3.4555 (13)	172.9 (10)
C12—H12B···N3^iii	0.975 (12)	2.579 (12)	3.4801 (14)	153.7 (9)
C8—H8A···N1^iv	1.004 (13)	2.602 (13)	3.5345 (13)	154.5 (9)

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