Azetidine, pyrrolidine and hexa­methyl­eneimine at 170 K

The crystal structures of the cyclic amines azetidine (C₃H₇N), pyrrolidine (C₄H₉N) and hexa­methyl­eneimine (homopiperidine, C₆H₁₃N), of the series (CH₂)_nNH, with n = 3, 4 and 6, respectively, have been determined at 170 K, following in situ crystallization from the melt. These structures provide crystallographic data to complete the homologous series of cyclic amines (CH₂)_nNH, for n = 2–6. Azetidine and pyrrolidine contain chains propagating along 2₁ screw axes, in which the mol­ecules are linked by co-operative N—H...N hydrogen bonds. Azetidine has two mol­ecules in its asymmetric unit, while pyrrolidine has only one. Hexamethyl­ene­imine contains tetra­meric hydrogen-bonded rings formed about crystallographic inversion centres, with two mol­ecules in its asymmetric unit. The observation of crystallographically distinct mol­ecules in the hydrogen-bonded chains of azetidine and cyclic hydrogen-bonded motifs in hexa­methyl­eneimine is consistent with expecta­tions derived from comparison with monoalcohols forming chains or rings by co-operative O—H...O hydrogen bonds. The next member of the cyclic amine series, hepta­methyl­eneimine, forms a cubic plastic phase on cooling from the melt.

S1. Comment

Contemporary developments in instrumentation and techniques for in situ crystallization have greatly simplified the task of obtaining diffraction data for low-melting materials (Boese & Nussbaumer, 1994; Davies & Bond, 2001). This manuscript describes single-crystal X-ray structures for the cyclic amines azetidine, (I), pyrrolidine, (II), and hexamethyleneimine (homopiperidine), (III), all of which are liquid under ambient conditions. Together with the previously reported structures of aziridine (Mitzel et al., 1997) and piperazine (Parkin et al., 2004), these structures provide crystallographic data to complete the homologous series of cyclic amines, (CH₂)_nNH, for n = 2–6.

In each structure of the series, molecules are linked by cooperative N—H···N hydrogen bonds with comparable geometric characteristics (Tables 1–3). Aziridine (n = 2), azetidine (n = 3; Fig. 1), pyrollidine (n = 4; Fig. 2) and piperazine (n = 5) all form one-dimensional hydrogen-bonded chains. In these last two structures, the chains propagate along 2₁ screw axes in space group P2₁/c, with one molecule in the asymmetric unit (Fig. 3). In azetidine, the chains also propagate along 2₁ screw axes in P2₁/c, but with two crystallographically distinct molecules in each chain (Fig. 4). Thus, every second molecule along the chain is related by the 2₁ screw operation, and every fourth molecule is related by translation along b. Aziridine crystallizes in space group P1 with three crystallographically distinct molecules in each hydrogen-bonded chain. The chain conformation has approximate 3₁ screw symmetry (Fig. 5), with every third molecule related by translation along b. In hexamethyleneimine (Fig. 6), the molecules form tetrameric rings with a closed cycle of cooperative N—H···N hydrogen bonds. The rings are formed about crystallographic inversion centres in space group P2₁/n, with two of the four molecules of the tetramer being crystallographically distinct (Fig. 7).

The N—H···N hydrogen-bond motifs in the cyclic amines are reminiscent of those observed frequently in monoalcohols. For example, hydrogen-bonded chains exist in both the ambient pressure (Jönsson, 1976) and high-pressure (Allan & Clark, 1999) polymorphs of ethanol, while the more bulky 3-ethyl-3-pentanol forms cyclic tetramers (Bond, 2006). The NH group resembles the OH group in that it can act simultaneously as a hydrogen-bond donor (albeit a worse one than OH; Steiner, 2002) and as an acceptor. Thus, extended chains and closed rings are expected motifs in both cases. For the monoalcohols, Brock & Duncan (1994) noted that the occurrence of structures with more than one crystallographically distinct molecule is anomalously high on account of frequent conflicts between the spatial requirements of O—H···O hydrogen bonds and the overall contraints of molecular close packing, i.e. that molecules are most often arranged about inversion centres, 2₁ screw axes or glide planes. Formation of extended O—H···O hydrogen-bonded chains in the monoalcohols requires that the O atoms are brought within ca 2.7–2.9 Å of each other. In the cyclic amines, the corresponding N···N distance is slightly longer (ca 3.1–3.2 Å). Within these contraints, O—H···O or N—H···N hydrogen-bonded chains might be compatible with molecular packing about 2₁ screw axes or glide planes, for example as in pyrrolidine and piperazine. In other cases, however, such compatibility may not be assured, and the chain motifs are therefore much more likely [compared with structures in the Cambridge Structural Database (Allen, 2002) as a whole] to be formed either with more than one crystallographically disinct molecule, as in azetidine, or around screw or roto-inversion axes of order 3, 4 or 6, as approximated by aziridine. For more bulky molecules, cyclic motifs offer a further alternative. These are commonly tetrameric and may be formed in tetragonal space groups (e.g. 2-phenyladamantan-2-ol; Singelenberg & van Eijck, 1987) or about inversion centres with two crystallographically distinct molecules, as in hexamethyleneimine and 3-ethyl-3-pentanol (Bond, 2006). It has been observed that the packing arrangements of bulky alcohols can be made to resemble those of smaller alcohols on application of increased pressure. For example, the crystal structures of 2-chlorophenol and 4-fluorophenol at ambient pressure contain hydrogen-bonded chains propagating along 3₂ and 3 axes, respectively, while at high pressure both contain chains along 2₁ axes (Oswald et al., 2005).

The crystal structure of azetidine was used as a target in the third blind test of crystal structure prediction (CSP2004) organized by the Cambridge Crystallographic Data Centre (Day et al., 2005). The two crystallographically distinct molecules provided difficulty in this exercise, and the correct structure was not present amongst the first three predictions of any of the participants. It was noted that the structure at 170 K appears to be a saddle point on the potential energy surface, with a low barrier for transformation to a postulated lower-symmetry structure in space group P1 with four molecules in the asymmetric unit.

Related literature

For related literature, see: Allan & Clark (1999); Allen (2002); Boese & Nussbaumer (1994); Bond (2006); Brock & Duncan (1994); Bruker (2003); Davies & Bond (2001); Day et al. (2005); Görbitz (1999); Jönsson (1976); Mitzel et al. (1997); Oswald et al. (2005); Parkin et al. (2004); Singelenberg & van Eijck (1987); Steiner (2002).

S2. Experimental

Single crystals of pyrrolidine and hexamethyleneimine were grown in 0.3 mm diameter glass capillaries at a temperature just below the melting point of the sample, using the manual zone-refinement technique described by Davies & Bond (2001). The diffraction patterns were indexed at a temperature just below the melting point from a series of images collected by rotation about the capillary axis, with the capillary remaining in the horizontal position in which the crystal was grown. Moving the capillary away from horizontal at this delicate stage resulted in loss of the crystal, while subsequent cooling (to 170 K) for data collection caused growth of multiple crystals. The orientation matrix established for the initial single crystal was retained and used throughout the data collection and integration, and any possible overlap with diffraction patterns from other crystal components was ignored. For both compounds, this strategy provided acceptable R_int values, although the relatively high R values for refinement of hexamethyleneimine are likely to be attributable largely to more significant overlap in its diffraction pattern. Since there were clearly contributions from many crystals, however, the approximations associated with ignoring overlap completely were preferred to the approximations associated with integration on the basis of numerous partially overlapping components. It was not possible to grow suitable crystals of azetidine using the manual technique and crystallization was therefore achieved from a sample mounted in a 0.66 mm diameter capillary held at 170 K, using the laser-assisted zone-refinement technique of Boese & Nussbaumer (1994). Again, the diffraction pattern contained contributions from more than one crystal, but a single crystal could be indexed using the program GEMINI (Bruker, 2003) and integration on the basis of this single component provided good results. In all cases, the exact size of the crystal used for data collection is uncertain, and it is probable that the length along the capillary axis exceeds the size of the X-ray beam. This seems to have little influence on the final refined parameters (Görbitz, 1999). Following data collection at 170 K, further cooling of the crystals caused deterioration of the peak shapes for all three compounds, to the extent that no further useful data could be obtained. Attempts were made to crystallize the next member of the series, heptamethyleneimine, but this forms a plastic phase on cooling from the melt. The diffraction pattern could be indexed on the basis of a cubic lattice with dimension 11.647 (3) Å, but it was not possible to establish any definite structural model.

S3. Refinement

H atoms bound to C atoms were positioned geometrically and allowed to ride during refinement, with C—H = 0.99 Å and U_iso(H) = 1.2U_eq(C). H atoms of the NH groups were located in difference Fourier maps and refined with isotropic displacement parameters. For azetidine and pyrrolidine, no restraints were required. For hexamethyleneimine, the two N—H distances were restrained to a common refined value with standard uncertainty 0.01 Å. Atoms C4, C5, C11 and C12 in hexamethyleneimine were modelled as disordered, each as two components with site occupancy factor 0.5. The C—C bonds in this region (12 in total) were restrained to a common refined value with standard uncertainty 0.01 Å.

Computing details

Data collection: SMART (Bruker, 1997) for (I); APEX2 (Bruker, 2004) for (II), (III). For all compounds, cell refinement: SAINT (Bruker, 2003); data reduction: SAINT (Bruker, 2003). Program(s) used to solve structure: SIR92 (Altomare et al., 1994) for (I); SHELXTL (Sheldrick, 2008) for (II), (III). For all compounds, program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. The two molecules in the asymmetric unit of azetidine, (I), with displacement ellipsoids drawn at the 50% probability level, except for H atoms bound to C atoms, which are shown as small spheres of arbitrary radii.
	Fig. 2. The molecular structure of pyrrolidine, (II), with displacement ellipsoids drawn at the 50% probability level, except for H atoms bound to C atoms,which are shown as small spheres of arbitrary radii.
	Fig. 3. A view of pyrrolidine along the c axis, showing two chains linked by cooperative N—H···N hydrogen bonds (dashed lines) propagating along 21 screw axes parallel to the baxis . H atoms bound to C atoms have been omitted. [Symmetry code: (i) -x, -1/2 + y, 1/2 - z.]
	Fig. 4. A view of azetidine along the c axis, showing one chain linked by cooperative N—H···N hydrogen bonds (dashed lines) propagating along a 21 screw axis parallel to the b axis. The two crystallographically distinct molecules and their symmetry equivalents are distinguished by their shading. H atoms bound to C atoms have been omitted. [Symmetry codes: (i) 1 - x, -1/2 + y, 1/2 - z; (ii) 1 - x, 1/2 + y, 1/2 - z.]
	Fig. 5. Perpendicular views of the hydrogen-bonded chains in aziridine (Mitzel et al., 1997), showing the approximate 31 screw symmetry. The three crystallographically distinct molecules and their symmetry equivalents are distinguished by their shading. H atoms bound to C atoms have been omitted.
	Fig. 6. The two molecules in the asymmetric unit of hexamethyleneimine, (III), with displacement ellipsoids drawn at the 50% probability level, except for H atoms bound to C atoms, which are shown as small spheres of arbitrary radii.
	Fig. 7. The unit-cell contents of hexamethyleneimine, showing tetramers linked by cooperative N—H···N hydrogen bonds (dashed lines). The two crystallographically distinct molecules and their symmetry equivalents are distinguished by their shading. H atoms bound to C atoms have been omitted.

(I) azetidine

Crystal data

C3H7N	F(000) = 256
Mr = 57.10	Dx = 1.007 Mg m^−3
Monoclinic, P21/c	Melting point: 190 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 9.507 (3) Å	Cell parameters from 1395 reflections
b = 9.122 (3) Å	θ = 2–25°
c = 9.790 (3) Å	µ = 0.06 mm^−1
β = 117.469 (4)°	T = 170 K
V = 753.3 (4) Å^3	Cylinder, colourless
Z = 8	1.00 × 0.33 (radius) mm

Data collection

Bruker SMART APEX CCD area-detector diffractometer	1782 independent reflections
Radiation source: fine-focus sealed tube	1144 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.035
ϕ and ω scans	θmax = 28.3°, θmin = 2.4°
Absorption correction: multi-scan (SADABS; Bruker, 2003)	h = −10→12
Tmin = 0.688, Tmax = 0.960	k = −11→12
4439 measured reflections	l = −12→12

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)] = 0.056	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.162	w = 1/[σ^2(Fo^2) + (0.067P)^2 + 0.1013P] where P = (Fo^2 + 2Fc^2)/3
S = 1.04	(Δ/σ)max < 0.001
1782 reflections	Δρmax = 0.18 e Å^−3
83 parameters	Δρmin = −0.18 e Å^−3
0 restraints	Extinction correction: SHELXTL (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.044 (9)

Special details

Experimental. Crystal grown in situ at 170 K using the laser-assisted zone-refinment technique of Boese (Boese & Nussbaumer, 1994).

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	0.33607 (17)	0.80512 (15)	0.10290 (15)	0.0489 (4)
H1	0.412 (2)	0.851 (2)	0.178 (2)	0.058 (5)*
C2	0.3048 (2)	0.8502 (2)	−0.05269 (18)	0.0568 (5)
H2A	0.3360	0.7761	−0.1075	0.068*
H2B	0.3484	0.9478	−0.0565	0.068*
C3	0.1294 (2)	0.8517 (3)	−0.1004 (2)	0.0685 (6)
H3A	0.0726	0.7613	−0.1532	0.082*
H3B	0.0733	0.9406	−0.1574	0.082*
C4	0.1775 (2)	0.8558 (2)	0.07009 (19)	0.0642 (5)
H4A	0.1761	0.9554	0.1096	0.077*
H4B	0.1185	0.7858	0.1018	0.077*
N5	0.37687 (16)	0.46573 (16)	0.13886 (14)	0.0490 (4)
H5	0.368 (2)	0.559 (2)	0.1393 (19)	0.058 (5)*
C6	0.3319 (2)	0.4012 (2)	−0.01410 (19)	0.0609 (5)
H6A	0.4233	0.3699	−0.0295	0.073*
H6B	0.2576	0.4624	−0.1010	0.073*
C7	0.2523 (2)	0.2769 (2)	0.0269 (2)	0.0645 (5)
H7A	0.3201	0.1894	0.0706	0.077*
H7B	0.1464	0.2498	−0.0560	0.077*
C8	0.2492 (2)	0.3812 (2)	0.1461 (2)	0.0630 (5)
H8A	0.1485	0.4361	0.1102	0.076*
H8B	0.2798	0.3352	0.2475	0.076*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0523 (8)	0.0475 (8)	0.0399 (7)	−0.0018 (6)	0.0153 (6)	0.0022 (6)
C2	0.0585 (11)	0.0710 (12)	0.0423 (9)	0.0021 (8)	0.0246 (8)	−0.0016 (8)
C3	0.0559 (11)	0.0975 (15)	0.0452 (10)	0.0039 (10)	0.0174 (8)	0.0017 (9)
C4	0.0572 (11)	0.0907 (15)	0.0483 (10)	−0.0012 (9)	0.0276 (8)	0.0050 (9)
N5	0.0570 (8)	0.0415 (8)	0.0417 (7)	−0.0025 (6)	0.0171 (6)	0.0009 (5)
C6	0.0651 (11)	0.0696 (13)	0.0527 (10)	−0.0087 (9)	0.0312 (8)	−0.0084 (8)
C7	0.0629 (12)	0.0650 (12)	0.0625 (11)	−0.0167 (9)	0.0262 (9)	−0.0164 (9)
C8	0.0774 (13)	0.0644 (12)	0.0561 (10)	−0.0119 (9)	0.0384 (9)	−0.0041 (8)

Geometric parameters (Å, º)

N1—C4	1.464 (2)	N5—C8	1.467 (2)
N1—C2	1.470 (2)	N5—C6	1.477 (2)
N1—H1	0.87 (2)	N5—H5	0.86 (2)
C2—C3	1.510 (3)	C6—C7	1.516 (3)
C2—H2A	0.99	C6—H6A	0.99
C2—H2B	0.99	C6—H6B	0.99
C3—C4	1.513 (2)	C7—C8	1.517 (2)
C3—H3A	0.99	C7—H7A	0.99
C3—H3B	0.99	C7—H7B	0.99
C4—H4A	0.99	C8—H8A	0.99
C4—H4B	0.99	C8—H8B	0.99
C4—N1—C2	89.34 (12)	C8—N5—C6	88.87 (12)
C4—N1—H1	114.0 (12)	C8—N5—H5	115.9 (12)
C2—N1—H1	116.1 (12)	C6—N5—H5	114.7 (11)
N1—C2—C3	89.39 (12)	N5—C6—C7	88.64 (13)
N1—C2—H2A	113.7	N5—C6—H6A	113.9
C3—C2—H2A	113.7	C7—C6—H6A	113.9
N1—C2—H2B	113.7	N5—C6—H6B	113.9
C3—C2—H2B	113.7	C7—C6—H6B	113.9
H2A—C2—H2B	111.0	H6A—C6—H6B	111.1
C2—C3—C4	85.99 (13)	C6—C7—C8	85.61 (14)
C2—C3—H3A	114.3	C6—C7—H7A	114.4
C4—C3—H3A	114.3	C8—C7—H7A	114.4
C2—C3—H3B	114.3	C6—C7—H7B	114.4
C4—C3—H3B	114.3	C8—C7—H7B	114.4
H3A—C3—H3B	111.5	H7A—C7—H7B	111.5
N1—C4—C3	89.50 (13)	N5—C8—C7	88.98 (12)
N1—C4—H4A	113.7	N5—C8—H8A	113.8
C3—C4—H4A	113.7	C7—C8—H8A	113.8
N1—C4—H4B	113.7	N5—C8—H8B	113.8
C3—C4—H4B	113.7	C7—C8—H8B	113.8
H4A—C4—H4B	111.0	H8A—C8—H8B	111.0
C4—N1—C2—C3	−18.32 (15)	C8—N5—C6—C7	−21.33 (15)
N1—C2—C3—C4	17.74 (15)	N5—C6—C7—C8	20.66 (14)
C2—N1—C4—C3	18.28 (15)	C6—N5—C8—C7	21.33 (15)
C2—C3—C4—N1	−17.81 (15)	C6—C7—C8—N5	−20.80 (14)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N5—H5···N1	0.86 (2)	2.27 (2)	3.120 (2)	171.5 (15)
N1—H1···N5^i	0.87 (2)	2.24 (2)	3.102 (2)	174.4 (16)

Symmetry code: (i) −x+1, y+1/2, −z+1/2.

(II) pyrrolidine

Crystal data

C4H9N	F(000) = 160
Mr = 71.12	Dx = 1.042 Mg m^−3
Monoclinic, P21/c	Melting point: 210 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 8.6753 (8) Å	Cell parameters from 2626 reflections
b = 5.2078 (5) Å	θ = 2.5–26.1°
c = 10.7108 (10) Å	µ = 0.06 mm^−1
β = 110.451 (3)°	T = 170 K
V = 453.41 (7) Å^3	Cylinder, colourless
Z = 4	0.35 × 0.15 (radius) mm

Data collection

Bruker Nonius X8 APEXII CCD area-detector diffractometer	900 independent reflections
Radiation source: fine-focus sealed tube	760 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.026
thin–slice ω and ϕ scans	θmax = 26.1°, θmin = 4.0°
Absorption correction: multi-scan (SADABS; Bruker, 2003)	h = −10→10
Tmin = 0.853, Tmax = 0.977	k = −6→6
5429 measured reflections	l = −13→13

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)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.110	H atoms treated by a mixture of independent and constrained refinement
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0456P)^2 + 0.1266P] where P = (Fo^2 + 2Fc^2)/3
900 reflections	(Δ/σ)max < 0.001
50 parameters	Δρmax = 0.16 e Å^−3
0 restraints	Δρmin = −0.13 e Å^−3

Special details

Experimental. Xtal grown in situ at ca 203 K in 0.3 mm capillary. The crystal length was not estimated, but it probably exceeded the width of the collimator. There were certainly several crystals present at 170 K. One crystal could be indexed very close to the melting point then only this one was considered at the lower temperature. Indexing at 170 K was not possible.

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	0.10684 (13)	0.5232 (2)	0.30411 (12)	0.0402 (3)
H1	0.038 (2)	0.411 (3)	0.2626 (17)	0.054 (5)*
C2	0.18779 (17)	0.4308 (3)	0.43977 (13)	0.0422 (4)
H2A	0.1061	0.3551	0.4745	0.051*
H2B	0.2441	0.5741	0.4989	0.051*
C3	0.31260 (16)	0.2278 (3)	0.43463 (13)	0.0423 (4)
H3A	0.4145	0.2400	0.5138	0.051*
H3B	0.2663	0.0529	0.4305	0.051*
C4	0.34677 (18)	0.2893 (3)	0.30783 (15)	0.0463 (4)
H4A	0.3177	0.1419	0.2455	0.056*
H4B	0.4643	0.3318	0.3284	0.056*
C5	0.23822 (19)	0.5199 (3)	0.24830 (14)	0.0465 (4)
H5A	0.3032	0.6804	0.2713	0.056*
H5B	0.1914	0.5048	0.1500	0.056*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0346 (6)	0.0328 (6)	0.0469 (7)	0.0027 (5)	0.0062 (5)	0.0002 (5)
C2	0.0442 (8)	0.0433 (8)	0.0425 (8)	0.0096 (6)	0.0192 (6)	0.0010 (6)
C3	0.0429 (7)	0.0417 (8)	0.0406 (7)	0.0109 (6)	0.0124 (6)	0.0015 (6)
C4	0.0483 (8)	0.0421 (8)	0.0554 (9)	0.0047 (6)	0.0269 (7)	−0.0024 (6)
C5	0.0644 (9)	0.0331 (7)	0.0477 (8)	−0.0005 (6)	0.0270 (7)	0.0012 (6)

Geometric parameters (Å, º)

N1—C2	1.4570 (17)	C3—H3A	0.99
N1—C5	1.4604 (18)	C3—H3B	0.99
N1—H1	0.84 (2)	C4—C5	1.522 (2)
C2—C3	1.5281 (17)	C4—H4A	0.99
C2—H2A	0.99	C4—H4B	0.99
C2—H2B	0.99	C5—H5A	0.99
C3—C4	1.5220 (19)	C5—H5B	0.99
C2—N1—C5	103.38 (10)	H3A—C3—H3B	108.9
C2—N1—H1	107.6 (12)	C3—C4—C5	104.77 (11)
C5—N1—H1	106.5 (11)	C3—C4—H4A	110.8
N1—C2—C3	107.05 (10)	C5—C4—H4A	110.8
N1—C2—H2A	110.3	C3—C4—H4B	110.8
C3—C2—H2A	110.3	C5—C4—H4B	110.8
N1—C2—H2B	110.3	H4A—C4—H4B	108.9
C3—C2—H2B	110.3	N1—C5—C4	107.14 (11)
H2A—C2—H2B	108.6	N1—C5—H5A	110.3
C4—C3—C2	104.36 (11)	C4—C5—H5A	110.3
C4—C3—H3A	110.9	N1—C5—H5B	110.3
C2—C3—H3A	110.9	C4—C5—H5B	110.3
C4—C3—H3B	110.9	H5A—C5—H5B	108.5
C2—C3—H3B	110.9
C5—N1—C2—C3	−35.77 (14)	C2—N1—C5—C4	35.32 (14)
N1—C2—C3—C4	22.47 (15)	C3—C4—C5—N1	−21.25 (15)
C2—C3—C4—C5	−0.69 (15)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···N1^i	0.84 (2)	2.35 (2)	3.1716 (13)	163.7 (15)

Symmetry code: (i) −x, y−1/2, −z+1/2.

(III) hexamethyleneimine

Crystal data

C6H13N	F(000) = 448
Mr = 99.17	Dx = 0.998 Mg m^−3
Monoclinic, P21/n	Melting point: 236 K
Hall symbol: -P 2yn	Mo Kα radiation, λ = 0.71073 Å
a = 11.0201 (14) Å	Cell parameters from 6154 reflections
b = 10.3027 (13) Å	θ = 2.6–23.2°
c = 12.7322 (15) Å	µ = 0.06 mm^−1
β = 114.110 (5)°	T = 170 K
V = 1319.5 (3) Å^3	Cylinder, colourless
Z = 8	0.35 × 0.15 (radius) mm

Data collection

Bruker Nonius X8 APEXII CCD area-detector diffractometer	2509 independent reflections
Radiation source: fine-focus sealed tube	1824 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.051
thin–slice ω and ϕ scans	θmax = 25.9°, θmin = 3.7°
Absorption correction: multi-scan (SADABS; Bruker, 2003)	h = −12→13
Tmin = 0.688, Tmax = 0.981	k = −12→12
16092 measured reflections	l = −14→15

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)] = 0.083	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.269	H atoms treated by a mixture of independent and constrained refinement
S = 1.12	w = 1/[σ^2(Fo^2) + (0.1254P)^2 + 0.8949P] where P = (Fo^2 + 2Fc^2)/3
2509 reflections	(Δ/σ)max < 0.001
173 parameters	Δρmax = 0.29 e Å^−3
14 restraints	Δρmin = −0.22 e Å^−3

Special details

Experimental. Xtal grown in situ in 0.3 mm capillary at ca 230 K. The crystal length was not estimated, but it probably exceeded the width of the collimator. There were certainly several crystals present at 170 K. One crystal could be indexed very close to the melting point then only this one was considered at the lower temperature. The multi-scan correction is accounting for effects other than absoprtion by the crystal, including absoption by the capillary and the probable presence of overlapping reflections from other crystals present.

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)
N1	0.3562 (2)	0.5819 (2)	0.0683 (2)	0.0424 (6)
H1	0.350 (3)	0.515 (3)	0.021 (2)	0.042 (7)*
C2	0.3410 (3)	0.5335 (3)	0.1691 (3)	0.0523 (8)
H2A	0.3781	0.4447	0.1858	0.063*
H2B	0.2450	0.5277	0.1516	0.063*
C3	0.4084 (3)	0.6168 (3)	0.2764 (3)	0.0608 (9)
H3A	0.3579	0.6070	0.3248	0.073*	0.50
H3B	0.4984	0.5811	0.3205	0.073*	0.50
H3C	0.3987	0.5743	0.3423	0.073*	0.50
H3D	0.5045	0.6232	0.2944	0.073*	0.50
C4	0.4224 (6)	0.7613 (6)	0.2587 (5)	0.0504 (17)	0.50
H4A	0.4961	0.7737	0.2343	0.060*	0.50
H4B	0.4472	0.8061	0.3334	0.060*	0.50
C5	0.2980 (6)	0.8258 (7)	0.1704 (5)	0.0523 (18)	0.50
H5A	0.2187	0.7862	0.1754	0.063*	0.50
H5B	0.2990	0.9190	0.1897	0.063*	0.50
C6	0.2860 (4)	0.8138 (3)	0.0489 (3)	0.0644 (9)
H6A	0.3703	0.8416	0.0456	0.077*	0.50
H6B	0.2145	0.8720	−0.0016	0.077*	0.50
H6C	0.3306	0.8566	0.0047	0.077*	0.50
H6D	0.2002	0.8589	0.0293	0.077*	0.50
C4A	0.3495 (9)	0.7523 (6)	0.2608 (6)	0.0672 (19)	0.50
H4C	0.2528	0.7439	0.2390	0.081*	0.50
H4D	0.3880	0.7970	0.3362	0.081*	0.50
C5A	0.3693 (10)	0.8377 (7)	0.1738 (6)	0.069 (2)	0.50
H5C	0.3542	0.9285	0.1909	0.082*	0.50
H5D	0.4637	0.8308	0.1859	0.082*	0.50
C7	0.2550 (3)	0.6757 (3)	0.0052 (3)	0.0602 (9)
H7A	0.1702	0.6491	0.0083	0.072*
H7B	0.2418	0.6738	−0.0765	0.072*
N8	0.6496 (2)	0.6463 (2)	0.09841 (19)	0.0433 (6)
H8	0.567 (3)	0.630 (3)	0.093 (3)	0.065 (10)*
C9	0.7372 (3)	0.6199 (4)	0.2172 (3)	0.0678 (10)
H9A	0.7017	0.5446	0.2440	0.081*
H9B	0.7358	0.6956	0.2645	0.081*
C10	0.8784 (3)	0.5921 (4)	0.2377 (3)	0.0741 (11)
H10A	0.8896	0.4966	0.2406	0.089*	0.50
H10B	0.9357	0.6258	0.3150	0.089*	0.50
H10C	0.9284	0.5685	0.3196	0.089*	0.50
H10D	0.8803	0.5162	0.1906	0.089*	0.50
C11	0.9331 (8)	0.6453 (9)	0.1524 (10)	0.084 (3)	0.50
H11A	1.0312	0.6383	0.1910	0.101*	0.50
H11B	0.9040	0.5844	0.0866	0.101*	0.50
C12	0.9033 (8)	0.7784 (9)	0.1027 (9)	0.080 (3)	0.50
H12A	0.9231	0.8414	0.1663	0.095*	0.50
H12B	0.9636	0.7978	0.0646	0.095*	0.50
C13	0.7655 (4)	0.7984 (4)	0.0191 (4)	0.0742 (11)
H13A	0.7478	0.7388	−0.0465	0.089*	0.50
H13B	0.7574	0.8882	−0.0109	0.089*	0.50
H13C	0.7892	0.8917	0.0265	0.089*	0.50
H13D	0.7277	0.7767	−0.0639	0.089*	0.50
C11A	0.9460 (7)	0.7015 (8)	0.2099 (6)	0.064 (2)	0.50
H11C	1.0430	0.6852	0.2425	0.076*	0.50
H11D	0.9303	0.7820	0.2450	0.076*	0.50
C12A	0.8942 (7)	0.7187 (10)	0.0800 (6)	0.063 (2)	0.50
H12C	0.8792	0.6312	0.0447	0.075*	0.50
H12D	0.9653	0.7602	0.0632	0.075*	0.50
C14	0.6593 (4)	0.7779 (3)	0.0635 (4)	0.0691 (10)
H14A	0.6775	0.8361	0.1301	0.083*
H14B	0.5724	0.8034	0.0027	0.083*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0375 (12)	0.0423 (12)	0.0466 (13)	−0.0031 (9)	0.0162 (10)	−0.0095 (10)
C2	0.0548 (17)	0.0472 (16)	0.0523 (17)	−0.0039 (13)	0.0193 (13)	0.0000 (13)
C3	0.0609 (19)	0.072 (2)	0.0455 (17)	−0.0014 (16)	0.0176 (14)	−0.0017 (15)
C4	0.035 (3)	0.065 (4)	0.051 (4)	−0.015 (3)	0.017 (3)	−0.029 (3)
C5	0.037 (3)	0.045 (4)	0.076 (5)	−0.008 (3)	0.024 (3)	−0.024 (3)
C6	0.068 (2)	0.0451 (17)	0.070 (2)	0.0068 (14)	0.0182 (17)	0.0013 (15)
C4A	0.065 (5)	0.079 (5)	0.057 (4)	−0.008 (4)	0.024 (4)	−0.027 (4)
C5A	0.085 (6)	0.043 (4)	0.081 (6)	−0.018 (4)	0.038 (5)	−0.019 (3)
C7	0.0635 (19)	0.0502 (18)	0.0505 (18)	0.0010 (14)	0.0064 (15)	−0.0010 (13)
N8	0.0340 (12)	0.0463 (13)	0.0486 (13)	−0.0034 (9)	0.0158 (10)	−0.0062 (10)
C9	0.0589 (19)	0.093 (3)	0.0486 (18)	0.0053 (18)	0.0188 (15)	−0.0027 (17)
C10	0.0470 (18)	0.092 (3)	0.063 (2)	0.0029 (17)	0.0019 (16)	0.0085 (19)
C11	0.038 (4)	0.085 (6)	0.124 (9)	−0.006 (4)	0.029 (5)	0.007 (6)
C12	0.057 (5)	0.085 (7)	0.092 (7)	−0.048 (5)	0.026 (5)	−0.024 (5)
C13	0.077 (2)	0.058 (2)	0.095 (3)	−0.0026 (17)	0.043 (2)	0.0181 (18)
C11A	0.035 (3)	0.072 (5)	0.062 (4)	−0.017 (3)	−0.003 (3)	−0.014 (4)
C12A	0.035 (4)	0.088 (7)	0.062 (5)	−0.028 (4)	0.017 (3)	−0.003 (5)
C14	0.063 (2)	0.0527 (18)	0.094 (3)	0.0112 (16)	0.0354 (19)	0.0114 (18)

Geometric parameters (Å, º)

N1—C7	1.446 (4)	N8—C14	1.444 (4)
N1—C2	1.449 (4)	N8—C9	1.449 (4)
N1—H1	0.90 (2)	N8—H8	0.90 (3)
C2—C3	1.524 (4)	C9—C10	1.498 (5)
C2—H2A	0.99	C9—H9A	0.99
C2—H2B	0.99	C9—H9B	0.99
C3—C4	1.523 (6)	C10—C11	1.542 (8)
C3—H3A	0.99	C10—H10A	0.99
C3—H3B	0.99	C10—H10B	0.99
C4—C5	1.525 (7)	C11—C12	1.490 (8)
C4—H4A	0.99	C11—H11A	0.99
C4—H4B	0.99	C11—H11B	0.99
C5—C6	1.503 (7)	C12—C13	1.470 (8)
C5—H5A	0.99	C12—H12A	0.99
C5—H5B	0.99	C12—H12B	0.99
C6—C7	1.515 (4)	C13—C14	1.509 (5)
C6—H6A	0.99	C13—H13A	0.99
C6—H6B	0.99	C13—H13B	0.99
C4A—C5A	1.498 (8)	C11A—C12A	1.524 (8)
C4A—H4C	0.99	C11A—H11C	0.99
C4A—H4D	0.99	C11A—H11D	0.99
C5A—H5C	0.99	C12A—H12C	0.99
C5A—H5D	0.99	C12A—H12D	0.99
C7—H7A	0.99	C14—H14A	0.99
C7—H7B	0.99	C14—H14B	0.99
C7—N1—C2	112.3 (2)	C14—N8—C9	113.3 (3)
C7—N1—H1	107.9 (18)	C14—N8—H8	110 (2)
C2—N1—H1	109.0 (18)	C9—N8—H8	106 (2)
N1—C2—C3	114.2 (2)	N8—C9—C10	114.8 (3)
N1—C2—H2A	108.7	N8—C9—H9A	108.6
C3—C2—H2A	108.7	C10—C9—H9A	108.6
N1—C2—H2B	108.7	N8—C9—H9B	108.6
C3—C2—H2B	108.7	C10—C9—H9B	108.6
H2A—C2—H2B	107.6	H9A—C9—H9B	107.5
C4—C3—C2	117.4 (3)	C9—C10—C11	119.1 (4)
C4—C3—H3A	108.0	C9—C10—H10A	107.5
C2—C3—H3A	108.0	C11—C10—H10A	107.5
C4—C3—H3B	108.0	C9—C10—H10B	107.5
C2—C3—H3B	108.0	C11—C10—H10B	107.5
H3A—C3—H3B	107.2	H10A—C10—H10B	107.0
C3—C4—C5	114.8 (5)	C12—C11—C10	123.0 (8)
C3—C4—H4A	108.6	C12—C11—H11A	106.6
C5—C4—H4A	108.6	C10—C11—H11A	106.6
C3—C4—H4B	108.6	C12—C11—H11B	106.6
C5—C4—H4B	108.6	C10—C11—H11B	106.6
H4A—C4—H4B	107.5	H11A—C11—H11B	106.5
C6—C5—C4	113.4 (5)	C13—C12—C11	114.8 (6)
C6—C5—H5A	108.9	C13—C12—H12A	108.6
C4—C5—H5A	108.9	C11—C12—H12A	108.6
C6—C5—H5B	108.9	C13—C12—H12B	108.6
C4—C5—H5B	108.9	C11—C12—H12B	108.6
H5A—C5—H5B	107.7	H12A—C12—H12B	107.5
C5—C6—C7	111.6 (4)	C12—C13—C14	116.0 (6)
C5—C6—H6A	109.3	C12—C13—H13A	108.3
C7—C6—H6A	109.3	C14—C13—H13A	108.3
C5—C6—H6B	109.3	C12—C13—H13B	108.3
C7—C6—H6B	109.3	C14—C13—H13B	108.3
H6A—C6—H6B	108.0	H13A—C13—H13B	107.4
C5A—C4A—H4C	108.1	C12A—C11A—H11C	109.6
C5A—C4A—H4D	108.1	C12A—C11A—H11D	109.6
H4C—C4A—H4D	107.3	H11C—C11A—H11D	108.1
C4A—C5A—H5C	107.7	C11A—C12A—H12C	107.9
C4A—C5A—H5D	107.7	C11A—C12A—H12D	107.9
H5C—C5A—H5D	107.1	H12C—C12A—H12D	107.2
N1—C7—C6	114.6 (3)	N8—C14—C13	114.4 (3)
N1—C7—H7A	108.6	N8—C14—H14A	108.7
C6—C7—H7A	108.6	C13—C14—H14A	108.7
N1—C7—H7B	108.6	N8—C14—H14B	108.7
C6—C7—H7B	108.6	C13—C14—H14B	108.7
H7A—C7—H7B	107.6	H14A—C14—H14B	107.6
C7—N1—C2—C3	−86.5 (3)	C14—N8—C9—C10	−80.7 (4)
N1—C2—C3—C4	28.7 (5)	N8—C9—C10—C11	24.7 (7)
C2—C3—C4—C5	44.9 (6)	C9—C10—C11—C12	41.5 (11)
C3—C4—C5—C6	−85.3 (7)	C10—C11—C12—C13	−70.5 (14)
C4—C5—C6—C7	70.5 (6)	C11—C12—C13—C14	60.4 (11)
C2—N1—C7—C6	85.2 (3)	C9—N8—C14—C13	87.7 (4)
C5—C6—C7—N1	−62.3 (4)	C12—C13—C14—N8	−64.6 (6)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N8—H8···N1	0.90 (3)	2.27 (3)	3.167 (3)	176 (3)
N1—H1···N8^i	0.90 (2)	2.25 (3)	3.150 (3)	175 (2)

Symmetry code: (i) −x+1, −y+1, −z.