Hydrogen-bonding motifs and thermotropic polymorphism in redetermined halide salts of hexa­methyl­enediamine

The redetermined crystal structures of hexane-1,6-diammonium dichloride, C₆H₁₈N₂²⁺·2Cl^-, (I), hexane-1,6-diammonium dibromide, C₆H₁₈N₂²⁺·2Br^-, (II), and hexane-1,6-diammonium diiodide, C₆H₁₈N₂²⁺·2I^-, (III), are described, focusing on their hydrogen-bonding motifs. The chloride and bromide salts are isomorphous, with both demonstrating a small deviation from planarity [173.89 (10) and 173.0 (2)°, respectively] in the central C-C-C-C torsion angle of the hydro­carbon backbone. The chloride and bromide salts also show marked similarities in their hydrogen-bonding inter­actions, with subtle differences evident in the hydrogen-bond lengths reported. Bifurcated inter­actions are exhibited between the N-donor atoms and the halide acceptors in the chloride and bromide salts. The iodide salt is very different in mol­ecular structure, packing and inter­molecular inter­actions. The hydro­carbon chain of the iodide straddles an inversion centre and the ammonium groups on the diammonium cation of the iodide salt are offset from the planar hydro­carbon backbone by a torsion angle of 69.6 (4)°. All three salts exhibit thermotropic polymorphism, as is evident from differential scanning calorimetry analysis and variable-temperature powder X-ray diffraction studies.

S1. Comment

Applications and structure–property relationships of n-alkyl diammonium salts are of continued interest and form the basis of our investigations. Our research focuses specifically on these materials as they are precursor ligands in transition metal complexes that have applications in propellants, explosives and pyrotechnic compositions (Singh et al., 2006, 2005), and they have structure-directing properties in the synthesis of a number of nanoparticles (Chen et al., 2007; Takami et al., 2007).

The halide salts of hexamethylenediamine form the focus of this work. The structures of both the chloride salt, (I), and the bromide salt, (II), were initially determined almost 60 years ago (Binnie & Robertson, 1949a,b), and the chloride salt was redetermined 30 years ago (Borkakoti et al., 1978). Some hydrogen-bonding details were published in Borkakoti's paper and our work expands further on the motifs and networks visible in the chloride salt. No further work on the structure of the bromide has been published since 1949 and no discussion of the hydrogen-bonding patterns was presented by Binnie and Robertson. The structure of the iodide salt, (III), was initially determined 45 years ago (Han, 1963) and no further work has since been reported for this material. We present in this paper the redetermined structures of all three halide salts, (I)–(III), and compare their hydrogen-bonding networks, motifs and interactions.

Fig. 1 depicts the molecular structures of all three compounds. The chloride and bromide salts are isomorphous, and a non-standard unit cell (with a β angle less than 90°) was selected for the former so that the two salts would have compatible coordinates and so could be directly compared with each other. The asymmetric units of the chloride and bromide salts each consist of one hexane-1,6-diammonium cation and two halide anions. The diammonium cation chains deviate slightly from linearity, as can be seen from the torsion angles across C1—C2—C3—C4 (Tables 1 and 3). The iodide salt is markedly different from the other two halides in that its asymmetric unit consists of one-half of the hexane-1,6-diammonium cation and an iodide anion, with the hydrocarbon chain of the former straddling a crystallographic inversion centre. The ammonium groups of the iodide salt are offset from the linear hydrocarbon chain, as can be seen from the N1—C1—C2—C3 torsion angle (Table 5). All three structures are hydrogen-bonded three-dimensional lattices.

Figs. 2 and 3 depict the packing and the hydrogen-bonding motifs for both the chloride and bromide salts. Hydrogen-bond geometries for the chloride and bromide salts appear in Tables 2 and 4, respectively. There is evidence of bifurcated hydrogen-bonding interactions involving atoms H1E and H2D of the chloride salt (Table 2) and of the bromide salt (Table 4). Two of these contacts in both chloride and bromide salts (N1—H1E···Cl1, N2—H2D···Cl1, N1—H1C···Br1 and N2—H2D···Br1 [Please provide symmetry codes to enable unique identification of these contacts in the tables]) are almost out of the range of generally accepted hydrogen-bond distances and may be the consequences of stronger hydrogen-bonding interactions between the ammonium cation and the halide anion. The packing diagram and hydrogen-bonding motifs for the iodide salt can be seen in Fig. 4, which is clearly different from the chloride and bromide salts. Details of the hydrogen-bond geometry for the iodide salt are given in Table 6.

Examination of the packing diagram of the chloride salt in Fig. 2 shows, at first glance, six different hydrogen-bonding ring motifs (top of Fig. 2, within the solid circle). All hydrogen-bonding motifs are described using graph-set notation (Bernstein, 2002). There is one seven-membered ring (on the left within the solid circle) involving three diammonium cations and three chloride anions, with graph-set notation R³₄(19), one six-membered ring (centre of the solid circle) involving two diammonium cations and two chloride anions, R²₄(22), and another seven-membered ring (on the right within the solid circle) involving three diammonium cations and three chloride anions, R³₄(19). The remaining three motifs appear to be an overlaid square, and diamond-shaped rings and multiple triangular rings, that when viewed slightly offset from the a axis and magnified (bottom left of Fig. 2) are actually interactions that link the packing sheets together. Further magnification of one diammonium cation clearly shows the eight individual hydrogen-bonding contacts (bottom right of Fig. 2) and demonstrates the bifurcation mentioned above.

An identical pattern exists for the bromide salt in Fig. 3 that shows, at first glance, six different hydrogen-bonding ring motifs (top of Fig. 3, within the solid circle). The same three ring motifs (two seven-membered rings and one six-membered ring) that are described for the chloride salt also exist in the bromide salt. The remaining three motifs (overlaid square and diamond-shaped rings plus multiple triangular rings), when also viewed slightly offset from the a axis and magnified (bottom left of Fig. 3), are actually the interactions that link the packing sheets together. As with the chloride salt, further magnification of one diammonium cation clearly shows the eight individual hydrogen-bonding contacts (bottom right of Fig. 3).

Fig. 4 shows the packing diagram and hydrogen-bonding interactions for the iodide salt. A view of the packing down the a axis shows, at first glance, two different hydrogen-bonding ring motifs (top left of Fig. 4, within the solid circle). There is one large ten-membered ring involving four diammonium cations and four iodide anions, graph-set motif R⁴₆(30). The remaining motif is triangular and, when viewed slightly offset from the a axis and magnified (bottom left of Fig. 4) these are the interactions that link the packing layers together. A view of the packing down the c axis (top right of Fig. 4) reveals further six-membered ring motifs that are shaped as elongated hexagons with the graph-set R²₄(22). The individual hydrogen-bonding contacts that link the layers are shown as a magnified view at the bottom right of Fig. 4, where the three hydrogen-bonding contacts in the asymmetric unit of the iodide salt are clearly evident.

The thermal properties of these salts were investigated by differential scanning calorimetry (DSC) and hot-stage microscopy. Fig. 5 shows the DSC scans for all three halide salts. The chloride shows two endothermic events, while the bromide and iodide each show one. Hot-stage microscopy showed that the first endothermic event exhibits a change in morphology of the crystals, while the second, seen only in the chloride salt, is a sublimation at 493 K. Based on these observations, we decided to carry out variable-temperature powder diffraction (VT-PXRD) studies to establish if the changes in crystal morphologies are thermotropic phase changes. The VT-PXRD results for the chloride, bromide and iodide salts are shown in Figs. 6, 7, and 8, respectively. Each figure shows a powder pattern of the starting material at 303 K (top), a powder pattern of the material after the phase change at the respective high-temperature value (middle) and a powder pattern of the material on cooling back down to the starting temperature of 303 K (bottom). The results allow us to conclude that the endothermic events evident from the DSC data are in fact thermotropic phase changes. It is evident from the powder data that the chloride and bromide exhibit irreversible phase changes, which was also confirmed by the hot-stage microscopy. The iodide, however, exhibits a reversible phase change, as the two powder patterns at 303 K are identical. Further investigation is required in order to characterize the different phases.

Related literature

For related literature, see: Bernstein (2002); Binnie & Robertson (1949a, 1949b); Borkakoti et al. (1978); Chen et al. (2007); Han (1963); Singh et al. (2005, 2006); Takami et al. (2007).

S2. Experimental

For the preparation of (I), concentrated hydrochloric acid (HCl, 2 ml, 63.6 mmol; Merck) was added to 1,6-diaminohexane (0.50 g, 4.30 mmol; Aldrich) in a sample vial. For the preparation of (II), concentrated hydrobromic acid (HBr, 2 ml, 37.07 mmol; Merck) was added to 1,6-diaminohexane (0.50 g, 4.30 mmol; Aldrich) in a sample vial. For the preparation of (III), concentrated hydriodic acid (HI, 2 ml, 26.58 mmol; Merck) was added to 1,6-diaminohexane (0.50 g, 4.30 mmol; Aldrich) in a sample vial. The three individual sample mixtures were refluxed at 363 K for 2 h. The three solutions were cooled to room temperature at 2 K h^-1 and colourless crystals of hexane-1,6-diammonium dichloride, (I), hexane-1,6-diammonium dibromide, (II), and hexane-1,6-diammonium diiodide, (III), were formed. Suitable crystals of each salt were selected for study by single-crystal X-ray diffraction. The polycrystalline powders used for the variable-temperature powder diffraction studies were obtained by hand-milling each salt using an agate mortar and pestle.

The powder patterns for the three halide salts were collected on a PANalytical XPert Pro powder diffractometer (Cu Kα) fitted with an Anton Paar HTK1200 variable-temperature oven with an alumina sample cup. The powder patterns were collected at selected temperatures within the angular range 5° < 2θ < 60°.

S3. Refinement

H atoms were positioned geometrically and refined in the riding-model approximation, with C—H = 0.97 and N—H = 0.89 Å, and with U_iso(H) = 1.2U_eq(C) or 1.5U_eq(N). For (III), the highest peak of 1.34 e Å^-3 in the final difference map lies 0.75 Å from atom I1.

Computing details

For all compounds, data collection: SMART-NT (Bruker, 1999); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001) and Mercury (Macrae et al., 2006); software used to prepare material for publication: PLATON (Spek, 2003) and publCIF (Westrip, 2008).

Figures

	Fig. 1. The molecular structures of (I) (left), (II) (centre) and (III) (right), showing the atomic numbering schemes. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry code: (i) 1 - x, -y, 2 - z.]
	Fig. 2. A packing diagram for (I), viewed down the a axis, showing the hydrogen-bonding network and motifs (top). A magnified view of the ring motifs (slightly offset from the a axis) is shown at the bottom left; selected cation chains have been truncated for clarity. A close-up view of the individual hydrogen-bonding contacts is shown at the bottom right.
	Fig. 3. A packing diagram for (II), viewed down the a axis, showing the hydrogen-bonding network and motifs (top). A magnified view of the ring motifs (slightly offset from the a axis) is shown at the bottom left; selected cation chains have been truncated for clarity. A close-up view of the individual hydrogen-bonding contacts is shown at the bottom right.
	Fig. 4. A packing diagram for (III), viewed down the a axis (top left) and down the c axis (top right), showing the hydrogen-bonding network and motifs. A magnified view of the ten-membered ring motif (slightly offset from the a axis) is shown at the bottom left. A close-up view of the asymmetric unit of (III) is given at the bottom right and shows the individual hydrogen-bonding contacts.
	Fig. 5. DSC traces of the three halide salts.
	Fig. 6. Comparative powder diffraction patterns of the chloride salt. The pattern at the top is of the material at the starting temperature of 303 K. The pattern in the middle is of the salt at 453 K after undergoing the phase change. The pattern at the bottom is of the salt after it has been cooled down to the starting temperature.
	Fig. 7. Comparative powder diffraction patterns of the bromide salt. The pattern at the top is of the material at the starting temperature of 303 K. The pattern in the middle is of the salt at 403 K after undergoing the phase change. The pattern at the bottom is of the salt after it has been cooled down to the starting temperature.
	Fig. 8. Comparative powder diffraction patterns of the iodide salt. The pattern at the top is of the material at the starting temperature of 303 K. The pattern in the middle is of the salt at 343 K after undergoing the phase change. The pattern at the bottom is of the salt after it has been cooled down to the starting temperature.

(I) Hexane-1,6-diammonium dichloride

Crystal data

C6H18N2^2+·2Cl^−	F(000) = 408
Mr = 189.12	Dx = 1.231 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 7105 reflections
a = 4.6042 (1) Å	θ = 2.6–28.3°
b = 14.1570 (3) Å	µ = 0.58 mm^−1
c = 15.6614 (4) Å	T = 295 K
β = 89.327 (1)°	Block, colourless
V = 1020.77 (4) Å^3	0.48 × 0.20 × 0.18 mm
Z = 4

Data collection

Bruker SMART CCD diffractometer	2540 independent reflections
Radiation source: sealed tube	2195 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.021
ϕ and ω scans	θmax = 28.3°, θmin = 1.9°
Absorption correction: multi-scan (APEX2 AXScale; Bruker, 2008)	h = −6→5
Tmin = 0.769, Tmax = 0.903	k = −18→14
10699 measured reflections	l = −20→20

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)] = 0.026	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.075	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0381P)^2 + 0.2526P] where P = (Fo^2 + 2Fc^2)/3
2540 reflections	(Δ/σ)max < 0.001
93 parameters	Δρmax = 0.37 e Å^−3
0 restraints	Δρmin = −0.25 e Å^−3
0 constraints

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	0.4217 (2)	0.30716 (8)	0.47640 (8)	0.0348 (2)
H1A	0.2900	0.2794	0.4355	0.042*
H1B	0.3058	0.3351	0.5220	0.042*
C2	0.6136 (3)	0.23043 (8)	0.51306 (8)	0.0350 (3)
H2A	0.7542	0.2591	0.5507	0.042*
H2B	0.7198	0.2000	0.4668	0.042*
C3	0.4414 (3)	0.15602 (8)	0.56252 (8)	0.0363 (3)
H3A	0.3344	0.1864	0.6087	0.044*
H3B	0.3019	0.1268	0.5248	0.044*
C4	0.6367 (3)	0.08023 (8)	0.59923 (7)	0.0353 (2)
H4A	0.7894	0.1106	0.6314	0.042*
H4B	0.7282	0.0461	0.5524	0.042*
C5	0.4812 (3)	0.00937 (9)	0.65728 (8)	0.0363 (3)
H5A	0.3806	0.0426	0.7030	0.044*
H5B	0.3385	−0.0255	0.6248	0.044*
C6	0.6998 (3)	−0.05814 (9)	0.69430 (8)	0.0399 (3)
H6A	0.7939	−0.0922	0.6479	0.048*
H6B	0.8479	−0.0219	0.7233	0.048*
N1	0.5963 (2)	0.38203 (6)	0.43368 (6)	0.0356 (2)
H1C	0.7170	0.4077	0.4711	0.053*
H1D	0.4784	0.4264	0.4136	0.053*
H1E	0.6982	0.3569	0.3907	0.053*
N2	0.5737 (2)	−0.12784 (7)	0.75545 (6)	0.0385 (2)
H2C	0.4937	−0.0974	0.7995	0.058*
H2D	0.7134	−0.1659	0.7740	0.058*
H2E	0.4387	−0.1619	0.7294	0.058*
Cl1	0.12529 (6)	−0.04025 (2)	0.889257 (17)	0.03620 (10)
Cl2	0.92317 (7)	0.22584 (2)	0.78350 (2)	0.04679 (11)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0320 (6)	0.0317 (6)	0.0408 (6)	0.0009 (5)	−0.0004 (4)	0.0031 (5)
C2	0.0330 (6)	0.0292 (6)	0.0428 (6)	0.0004 (4)	0.0011 (5)	0.0047 (5)
C3	0.0341 (6)	0.0336 (6)	0.0411 (6)	−0.0019 (5)	0.0016 (5)	0.0052 (5)
C4	0.0341 (6)	0.0332 (6)	0.0387 (6)	−0.0027 (5)	0.0010 (5)	0.0053 (5)
C5	0.0330 (6)	0.0363 (6)	0.0397 (6)	−0.0017 (5)	0.0015 (5)	0.0066 (5)
C6	0.0341 (6)	0.0445 (7)	0.0412 (6)	−0.0009 (5)	0.0035 (5)	0.0131 (5)
N1	0.0404 (5)	0.0275 (5)	0.0389 (5)	0.0053 (4)	0.0012 (4)	0.0031 (4)
N2	0.0390 (5)	0.0377 (5)	0.0387 (5)	0.0048 (4)	0.0059 (4)	0.0085 (4)
Cl1	0.03770 (16)	0.03604 (16)	0.03484 (15)	−0.00033 (11)	0.00045 (11)	−0.00302 (10)
Cl2	0.04648 (19)	0.04294 (19)	0.05082 (19)	−0.00607 (13)	0.00529 (14)	0.00756 (13)

Geometric parameters (Å, º)

C1—N1	1.4849 (14)	C5—C6	1.5087 (17)
C1—C2	1.5173 (16)	C5—H5A	0.9700
C1—H1A	0.9700	C5—H5B	0.9700
C1—H1B	0.9700	C6—N2	1.4880 (14)
C2—C3	1.5244 (15)	C6—H6A	0.9700
C2—H2A	0.9700	C6—H6B	0.9700
C2—H2B	0.9700	N1—H1C	0.8900
C3—C4	1.5174 (16)	N1—H1D	0.8900
C3—H3A	0.9700	N1—H1E	0.8900
C3—H3B	0.9700	N2—H2C	0.8900
C4—C5	1.5265 (15)	N2—H2D	0.8900
C4—H4A	0.9700	N2—H2E	0.8900
C4—H4B	0.9700
N1—C1—C2	111.52 (9)	C6—C5—C4	109.57 (10)
N1—C1—H1A	109.3	C6—C5—H5A	109.8
C2—C1—H1A	109.3	C4—C5—H5A	109.8
N1—C1—H1B	109.3	C6—C5—H5B	109.8
C2—C1—H1B	109.3	C4—C5—H5B	109.8
H1A—C1—H1B	108.0	H5A—C5—H5B	108.2
C1—C2—C3	112.67 (10)	N2—C6—C5	114.24 (10)
C1—C2—H2A	109.1	N2—C6—H6A	108.7
C3—C2—H2A	109.1	C5—C6—H6A	108.7
C1—C2—H2B	109.1	N2—C6—H6B	108.7
C3—C2—H2B	109.1	C5—C6—H6B	108.7
H2A—C2—H2B	107.8	H6A—C6—H6B	107.6
C4—C3—C2	111.98 (10)	C1—N1—H1C	109.5
C4—C3—H3A	109.2	C1—N1—H1D	109.5
C2—C3—H3A	109.2	H1C—N1—H1D	109.5
C4—C3—H3B	109.2	C1—N1—H1E	109.5
C2—C3—H3B	109.2	H1C—N1—H1E	109.5
H3A—C3—H3B	107.9	H1D—N1—H1E	109.5
C3—C4—C5	114.48 (10)	C6—N2—H2C	109.5
C3—C4—H4A	108.6	C6—N2—H2D	109.5
C5—C4—H4A	108.6	H2C—N2—H2D	109.5
C3—C4—H4B	108.6	C6—N2—H2E	109.5
C5—C4—H4B	108.6	H2C—N2—H2E	109.5
H4A—C4—H4B	107.6	H2D—N2—H2E	109.5
N1—C1—C2—C3	176.12 (10)	C3—C4—C5—C6	−176.27 (11)
C1—C2—C3—C4	−179.62 (10)	C4—C5—C6—N2	177.22 (10)
C2—C3—C4—C5	173.90 (10)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1C···Cl1^i	0.89	2.43	3.2599 (11)	156
N1—H1C···Cl1^ii	0.89	2.94	3.3754 (10)	112
N1—H1D···Cl1^iii	0.89	2.32	3.2000 (10)	168
N1—H1E···Cl2^iii	0.89	2.29	3.1695 (10)	172
N2—H2C···Cl1	0.89	2.33	3.1765 (10)	158
N2—H2D···Cl2^iv	0.89	2.43	3.1616 (10)	139
N2—H2D···Cl1^v	0.89	3.18	3.5361 (11)	107
N2—H2E···Cl2^vi	0.89	2.31	3.1511 (11)	157

Symmetry codes: (i) −x+1, y+1/2, −z+3/2; (ii) x+1, −y+1/2, z−1/2; (iii) x, −y+1/2, z−1/2; (iv) −x+2, y−1/2, −z+3/2; (v) x+1, y, z; (vi) −x+1, y−1/2, −z+3/2.

(II) Hexane-1,6-diammonium dibromide

Crystal data

C6H18N2^2+·2Br^−	F(000) = 552
Mr = 278.04	Dx = 1.671 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 9920 reflections
a = 4.7044 (1) Å	θ = 2.5–28.0°
b = 14.4462 (3) Å	µ = 7.28 mm^−1
c = 16.2582 (4) Å	T = 295 K
β = 90.115 (1)°	Rectangular, colourless
V = 1104.92 (4) Å^3	0.44 × 0.26 × 0.10 mm
Z = 4

Data collection

Bruker SMART CCD diffractometer	2753 independent reflections
Radiation source: sealed tube	2364 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.042
ϕ and ω scans	θmax = 28.3°, θmin = 1.9°
Absorption correction: multi-scan (APEX2 AXScale; Bruker, 2008)	h = −6→6
Tmin = 0.117, Tmax = 0.483	k = −19→19
19693 measured reflections	l = −21→21

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)] = 0.025	H-atom parameters constrained
wR(F^2) = 0.060	w = 1/[σ^2(Fo^2) + (0.023P)^2 + 0.7117P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max = 0.002
2753 reflections	Δρmax = 0.84 e Å^−3
94 parameters	Δρmin = −0.65 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*^=kFc[1+0.001xFc^2^λ^3^/sin(2θ)]^-1/4^
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0151 (6)

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 F^2^ against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F^2^, conventional R-factors R are based on F, with F set to zero for negative F^2^. The threshold expression of F^2^ > σ(F^2^) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F^2^ 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	0.4145 (5)	0.30294 (17)	0.47953 (15)	0.0406 (5)
H1A	0.2816	0.2758	0.4408	0.049*
H1B	0.3058	0.3303	0.5239	0.049*
C2	0.6059 (5)	0.22767 (16)	0.51396 (15)	0.0394 (5)
H2A	0.7481	0.2557	0.5494	0.047*
H2B	0.7042	0.1974	0.4690	0.047*
C3	0.4408 (5)	0.15551 (17)	0.56270 (16)	0.0428 (5)
H3A	0.3418	0.1858	0.6076	0.051*
H3B	0.2994	0.1272	0.5272	0.051*
C4	0.6327 (5)	0.08106 (17)	0.59718 (15)	0.0421 (5)
H4A	0.7880	0.1104	0.6266	0.051*
H4B	0.7140	0.0465	0.5518	0.051*
C5	0.4852 (5)	0.01335 (17)	0.65505 (16)	0.0431 (5)
H5A	0.3924	0.0472	0.6990	0.052*
H5B	0.3413	−0.0211	0.6251	0.052*
C6	0.7001 (5)	−0.05245 (19)	0.69073 (16)	0.0476 (6)
H6A	0.7850	−0.0876	0.6463	0.057*
H6B	0.8501	−0.0168	0.7168	0.057*
N1	0.5814 (4)	0.37625 (13)	0.43757 (12)	0.0408 (4)
H1C	0.6968	0.4034	0.4737	0.061*
H1D	0.4635	0.4182	0.4165	0.061*
H1E	0.6839	0.3511	0.3974	0.061*
N2	0.5816 (4)	−0.11829 (14)	0.75204 (12)	0.0411 (4)
H2C	0.5006	−0.0868	0.7928	0.062*
H2D	0.7209	−0.1533	0.7722	0.062*
H2E	0.4523	−0.1542	0.7279	0.062*
Br1	0.10941 (5)	−0.040380 (16)	0.887786 (14)	0.03875 (9)
Br2	0.92032 (6)	0.226290 (19)	0.784156 (17)	0.05109 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0363 (11)	0.0383 (12)	0.0472 (13)	0.0026 (9)	0.0007 (9)	0.0023 (10)
C2	0.0380 (11)	0.0320 (12)	0.0482 (13)	0.0016 (9)	0.0024 (10)	0.0050 (10)
C3	0.0400 (12)	0.0402 (13)	0.0482 (13)	−0.0016 (10)	0.0022 (10)	0.0057 (10)
C4	0.0404 (12)	0.0401 (13)	0.0459 (13)	−0.0036 (10)	0.0022 (10)	0.0071 (10)
C5	0.0400 (12)	0.0404 (13)	0.0489 (13)	−0.0024 (10)	0.0021 (10)	0.0085 (10)
C6	0.0395 (12)	0.0556 (16)	0.0476 (14)	−0.0023 (11)	0.0040 (10)	0.0164 (12)
N1	0.0474 (11)	0.0317 (10)	0.0435 (11)	0.0071 (8)	0.0012 (9)	0.0028 (8)
N2	0.0410 (10)	0.0410 (11)	0.0413 (10)	0.0025 (8)	0.0054 (8)	0.0082 (9)
Br1	0.04040 (13)	0.03815 (14)	0.03770 (13)	−0.00208 (9)	0.00054 (9)	−0.00454 (9)
Br2	0.05037 (16)	0.04514 (16)	0.05778 (17)	−0.00364 (11)	0.00645 (12)	0.01089 (11)

Geometric parameters (Å, º)

C1—N1	1.485 (3)	C5—C6	1.503 (3)
C1—C2	1.518 (3)	C5—H5A	0.9700
C1—H1A	0.9700	C5—H5B	0.9700
C1—H1B	0.9700	C6—N2	1.487 (3)
C2—C3	1.523 (3)	C6—H6A	0.9700
C2—H2A	0.9700	C6—H6B	0.9700
C2—H2B	0.9700	N1—H1C	0.8900
C3—C4	1.511 (3)	N1—H1D	0.8900
C3—H3A	0.9700	N1—H1E	0.8900
C3—H3B	0.9700	N2—H2C	0.8900
C4—C5	1.525 (3)	N2—H2D	0.8900
C4—H4A	0.9700	N2—H2E	0.8900
C4—H4B	0.9700
N1—C1—C2	111.50 (19)	C6—C5—C4	109.7 (2)
N1—C1—H1A	109.3	C6—C5—H5A	109.7
C2—C1—H1A	109.3	C4—C5—H5A	109.7
N1—C1—H1B	109.3	C6—C5—H5B	109.7
C2—C1—H1B	109.3	C4—C5—H5B	109.7
H1A—C1—H1B	108.0	H5A—C5—H5B	108.2
C1—C2—C3	112.28 (19)	N2—C6—C5	114.2 (2)
C1—C2—H2A	109.1	N2—C6—H6A	108.7
C3—C2—H2A	109.1	C5—C6—H6A	108.7
C1—C2—H2B	109.1	N2—C6—H6B	108.7
C3—C2—H2B	109.1	C5—C6—H6B	108.7
H2A—C2—H2B	107.9	H6A—C6—H6B	107.6
C4—C3—C2	112.0 (2)	C1—N1—H1C	109.5
C4—C3—H3A	109.2	C1—N1—H1D	109.5
C2—C3—H3A	109.2	H1C—N1—H1D	109.5
C4—C3—H3B	109.2	C1—N1—H1E	109.5
C2—C3—H3B	109.2	H1C—N1—H1E	109.5
H3A—C3—H3B	107.9	H1D—N1—H1E	109.5
C3—C4—C5	114.4 (2)	C6—N2—H2C	109.5
C3—C4—H4A	108.7	C6—N2—H2D	109.5
C5—C4—H4A	108.7	H2C—N2—H2D	109.5
C3—C4—H4B	108.7	C6—N2—H2E	109.5
C5—C4—H4B	108.7	H2C—N2—H2E	109.5
H4A—C4—H4B	107.6	H2D—N2—H2E	109.5
N1—C1—C2—C3	175.8 (2)	C3—C4—C5—C6	−175.4 (2)
C1—C2—C3—C4	−179.7 (2)	C4—C5—C6—N2	176.6 (2)
C2—C3—C4—C5	173.0 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1C···Br1^i	0.89	2.56	3.408 (2)	159
N1—H1C···Br1^ii	0.89	3.11	3.529 (2)	111
N1—H1D···Br1^iii	0.89	2.47	3.3466 (19)	168
N1—H1E···Br2^iii	0.89	2.43	3.313 (2)	174
N2—H2C···Br1	0.89	2.50	3.330 (2)	156
N2—H2D···Br2^iv	0.89	2.59	3.299 (2)	137
N2—H2D···Br1^v	0.89	3.09	3.505 (2)	111
N2—H2E···Br2^vi	0.89	2.47	3.310 (2)	158

Symmetry codes: (i) −x+1, y+1/2, −z+3/2; (ii) x+1, −y+1/2, z−1/2; (iii) x, −y+1/2, z−1/2; (iv) −x+2, y−1/2, −z+3/2; (v) x+1, y, z; (vi) −x+1, y−1/2, −z+3/2.

(III) Hexane-1,6-diammonium diiodide

Crystal data

C6H18N2^2+·2I^−	F(000) = 348
Mr = 372.02	Dx = 2.014 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 4034 reflections
a = 4.8884 (1) Å	θ = 2.6–28.4°
b = 12.8756 (4) Å	µ = 5.08 mm^−1
c = 9.7488 (3) Å	T = 295 K
β = 90.423 (2)°	Rectangular, colourless
V = 613.58 (3) Å^3	0.48 × 0.18 × 0.18 mm
Z = 2

Data collection

Bruker SMART CCD diffractometer	1551 independent reflections
Radiation source: sealed tube	1452 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.028
ϕ and ω scans	θmax = 28.5°, θmin = 2.6°
Absorption correction: integration (XPREP; Bruker, 2008)	h = −6→6
Tmin = 0.194, Tmax = 0.462	k = −16→17
5135 measured reflections	l = −13→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)] = 0.024	H-atom parameters constrained
wR(F^2) = 0.060	w = 1/[σ^2(Fo^2) + (0.0229P)^2 + 0.6405P] where P = (Fo^2 + 2Fc^2)/3
S = 1.09	(Δ/σ)max = 0.001
1551 reflections	Δρmax = 1.24 e Å^−3
48 parameters	Δρmin = −0.51 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.197 (4)

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 F^2^ against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F^2^, conventional R-factors R are based on F, with F set to zero for negative F^2^. The threshold expression of F^2^ > σ(F^2^) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F^2^ 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	−0.0321 (8)	0.0608 (3)	0.6821 (3)	0.0520 (8)
H1A	0.0757	0.0423	0.6025	0.062*
H1B	−0.2126	0.0306	0.6704	0.062*
C2	0.1010 (8)	0.0158 (3)	0.8091 (4)	0.0505 (7)
H2A	0.2714	0.0523	0.8263	0.061*
H2B	0.1454	−0.0564	0.7917	0.061*
C3	−0.0725 (7)	0.0216 (3)	0.9368 (3)	0.0487 (7)
H3A	−0.2404	−0.0169	0.9215	0.058*
H3B	−0.1212	0.0935	0.9536	0.058*
N1	−0.0576 (6)	0.1762 (2)	0.6895 (3)	0.0438 (6)
H1C	−0.1704	0.1932	0.7571	0.066*
H1D	−0.1238	0.2002	0.6103	0.066*
H1E	0.1063	0.2040	0.7055	0.066*
I1	0.45332 (4)	0.296919 (16)	0.91589 (2)	0.04509 (13)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.071 (2)	0.0499 (18)	0.0348 (15)	−0.0074 (15)	−0.0029 (14)	−0.0038 (13)
C2	0.0589 (19)	0.0463 (16)	0.0463 (17)	0.0110 (14)	0.0059 (14)	0.0016 (13)
C3	0.0476 (17)	0.0559 (18)	0.0426 (16)	0.0112 (13)	0.0016 (13)	0.0094 (14)
N1	0.0466 (14)	0.0497 (13)	0.0350 (13)	0.0017 (11)	−0.0043 (10)	0.0036 (11)
I1	0.03897 (16)	0.05445 (18)	0.04178 (16)	0.00382 (7)	−0.00353 (8)	−0.01024 (7)

Geometric parameters (Å, º)

C1—N1	1.494 (4)	C3—C3^i	1.522 (6)
C1—C2	1.510 (5)	C3—H3A	0.9700
C1—H1A	0.9700	C3—H3B	0.9700
C1—H1B	0.9700	N1—H1C	0.8900
C2—C3	1.513 (5)	N1—H1D	0.8900
C2—H2A	0.9700	N1—H1E	0.8900
C2—H2B	0.9700
N1—C1—C2	112.2 (3)	C2—C3—C3^i	112.8 (3)
N1—C1—H1A	109.2	C2—C3—H3A	109.0
C2—C1—H1A	109.2	C3^i—C3—H3A	109.0
N1—C1—H1B	109.2	C2—C3—H3B	109.0
C2—C1—H1B	109.2	C3^i—C3—H3B	109.0
H1A—C1—H1B	107.9	H3A—C3—H3B	107.8
C1—C2—C3	114.5 (3)	C1—N1—H1C	109.5
C1—C2—H2A	108.6	C1—N1—H1D	109.5
C3—C2—H2A	108.6	H1C—N1—H1D	109.5
C1—C2—H2B	108.6	C1—N1—H1E	109.5
C3—C2—H2B	108.6	H1C—N1—H1E	109.5
H2A—C2—H2B	107.6	H1D—N1—H1E	109.5
N1—C1—C2—C3	69.6 (4)	C1—C2—C3—C3^i	−178.3 (4)

Symmetry code: (i) −x, −y, −z+2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1C···I1^ii	0.89	2.76	3.617 (3)	163
N1—H1D···I1^iii	0.89	2.79	3.586 (3)	149
N1—H1E···I1	0.89	2.91	3.666 (3)	144

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