High-pressure crystal structure of n-hexyl­amine

Kuleczka, B.; Sacharczuk, N.; Olejniczak, A.; Podsiadło, M.

doi:10.1107/S2053229625004504

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research papers

STRUCTURAL
CHEMISTRY

ISSN: 2053-2296

Volume 81| Part 6| June 2025| Pages 346-350

https://doi.org/10.1107/S2053229625004504

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High-pressure crystal structure of n-hexylamine

Bernadetta Kuleczka,^a Natalia Sacharczuk,^a Anna Olejniczak ^a and Marcin Podsiadło ^a ^*

^aFaculty of Chemistry, Adam Mickiewicz University, Uniwersytetu Poznańskiego 8, 61-614 Poznań, Poland
^*Correspondence e-mail: [email protected]

Edited by I. Oswald, University of Strathclyde, United Kingdom (Received 26 March 2025; accepted 20 May 2025; online 27 May 2025)

A primary amine, n-hexylamine (HA, C₆H₁₅N), has been studied at high pressure by single-crystal X-ray diffraction. The structure of this compound has been determined, at ambient temperature, from the freezing pressure up to 1.40 GPa. HA at high pressure crystallizes in the space group Pca2₁, which was already found at ambient pressure and low temperature. The compressibility of the N—H⋯N hydrogen bonds has been compared with that of the shortest C—H⋯N and H⋯H intermolecular distances, revealing that the H⋯H distances exhibit the highest degree of compressibility among them.

Keywords: hexylamine; crystal structure; N—H⋯N hydrogen bonds; aliphatic amines; in-situ crystallization; high pressure; compressibility.

CCDC references: 2434096; 2434097; 2434098

1. Introduction

N—H⋯N hydrogen bonds often compete with weaker C—H⋯N hydrogen bonds in crystals (Huang et al., 2013 ; Leigh et al., 2013 ; Podsiadło et al., 2017 ; Sacharczuk et al., 2023 ; Vega et al., 2005 ). The role of these interactions, as the main cohesion forces in crystals, has been well documented for biomolecules, self-organizing materials, pharmaceuticals and molecular switches (Desiraju & Steiner, 2001 ; Jeffrey & Saenger, 1994 ). The simplest aliphatic amines serve as model compounds for studying the nature of such interactions due to their molecular composition and the minimized effect of the molecular shape on dense packing.

Structural studies of the simplest n-aliphatic amines have been performed at low temperature and ambient pressure for methylamine (Atoji & Lipscomb, 1953 ), as well as for the series from ethylamine to n-decylamine (Maloney et al., 2014 ). These studies described the role of various types of intermolecular interactions in molecular association. N—H⋯N hydrogen bonds have been identified as the main cohesion force for the early primary amines; however, the role of dispersive interactions between alkyl chains was also emphasized (for the later compounds, the dispersion interactions dominate over hydrogen bonding). It was also found that dispersive interactions were particularly dominant in the regions between molecular layers linked by N—H⋯N hydrogen bonds (Maloney et al., 2014).

This study of n-hexylamine (HA; Scheme 1 and Fig. 1) extends our previous research on the simplest primary amines under high pressure. Recently, we have investigated the series from methylamine to n-pentylamine (Podsiadło et al., 2017; Sacharczuk et al., 2023). Only ethylamine crystallizes in the same phase under high pressure (phase II) as found at low temperature. In contrast, seven new polymorphs, different from the low-temperature ones, have been identified at high pressure for the remaining amines, i.e. one for methylamine (Podsiadło et al., 2017) and two each for propylamine, butylamine and pentylamine (Sacharczuk et al., 2023). In all these polymorphs, molecules interact through N—H⋯N hydrogen bonds. However, at high pressure, the role of C—H⋯N hydrogen bonds increases (Sacharczuk et al., 2023).

Figure 1
The molecular structures of HA at (a) 0.50 GPa, (b) 0.65 GPa and (c) 1.40 GPa (all at 295 K), showing the atomic labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.

In the present study, we have investigated HA at high pressure using single-crystal X-ray diffraction. The crystal structure has been determined previously at ambient pressure and low temperature only (Maloney et al., 2014). We have obtained and investigated single crystals of HA in a diamond-anvil cell (DAC) in the range between the freezing pressure at ambient temperature of 0.33 GPa up to 1.40 GPa.

2. Experimental

n-Hexylamine, HA (99%), from Sigma–Aldrich was crystallized in situ in a modified Merrill–Basset diamond-anvil cell (DAC; Bassett, 2009 ). The DAC was equipped with a 0.3 mm thick steel gasket with a hole of diameter 0.3 mm. At 295 K, HA froze at 0.33 GPa, in the form of a polycrystalline mass, filling the whole volume of the DAC chamber. A single crystal of HA was obtained under isothermal conditions. The polycrystalline mass was melted, except for one crystallite, by decreasing the pressure slowly. Then, again slowly, the pressure was increased allowing a single crystal of HA to grow and eventually fill the entire volume of the chamber (Fig. 2). Afterwards, the pressure was increased by ca 0.2 GPa to achieve a stable single crystal required for the X-ray diffraction measurement. Several attempts were made to grow a single crystal under isochoric conditions at pressures above 0.50 GPa; however, all were unsuccessful. The growing single crystals were very sensitive to temperature changes, and each time additional crystallites occurred, even with slow cooling. For this reason, single crystals at pressures of 0.65 and 1.40 GPa were obtained at room temperature by increasing the pressure in the chamber after performing the X-ray measurements at 0.50 and 0.65 GPa. The pressure was calibrated by the ruby fluorescence method (Mao et al., 1986 ; Piermarini et al., 1975 ) using a Photon Control spectrometer with an accuracy of 0.02 GPa. The calibrations were performed before and after each X-ray diffraction experiment. The progress of the growth of the HA single crystal is shown in Fig. 2 and Fig. S1 in the supporting information.

Figure 2
Stages of the HA single-crystal growth inside the DAC chamber (polarized-light mode): (a) one crystal seed at 295 K and 0.33 GPa, (b)/(c) the single-crystal growth with increasing pressure and a simultaneous decrease in the volume of the high-pressure chamber, and (d) the single crystal filling the DAC chamber at 295 K and 0.50 GPa. The ruby chip, for pressure calibration, is located by the left edge of the DAC.

Rigaku Xcalibur EOS and Xcalibur ATLAS diffractometers were used for the high-pressure studies. The DAC was centred by the gasket-shadow method (Budzianowski & Katrusiak, 2004 ).

The room-temperature compressibility measurement was performed up to ca 2 GPa in a piston-and-cylinder apparatus (Baranowski & Moroz, 1982 ; Dziubek & Katrusiak, 2014 ) with an initial volume of ca 8.5 cm³.

2.1. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. The H atoms of the methylene and methyl groups were located based on the molecular geometry, with the C—H distances equal to 0.97 or 0.96 Å and their U_iso factors constrained to 1.2 or 1.5 times the U_eq value of their carrier. The H atoms of the amine (–NH₂) group were located based on the molecular geometry, assuming N—H distances equal to 0.90 Å, and their U_iso factors were constrained to 1.2 times the U_eq value of their carrier. The crystal data and refinement details are summarized in Tables 1 and 2, and Table S1 in the supporting information.

Table 1
Experimental details

For all determinations: C₆H₁₅N, M_r = 101.19, orthorhombic, Pca2₁, Z = 4. Experiments were carried out at 295 K with Mo Kα radiation. Absorption was corrected for by multi-scan methods (CrysAlis PRO; Rigaku OD, 2022 $[Rigaku OD (2022). CrysAlis PRO. Rigaku Oxford Diffraction Ltd, Yarnton, Oxfordshire, England.]$ ). Refinement was on 64 parameters with 1 restraint. H-atom parameters were constrained.

	HA at 0.50 GPa	HA at 0.65 GPa	HA at 1.40 GPa
Crystal data
a, b, c (Å)	6.9050 (9), 17.549 (7), 5.5212 (13)	6.8591 (9), 17.494 (5), 5.4892 (4)	6.7241 (19), 17.052 (13), 5.3367 (7)
V (Å³)	669.1 (3)	658.7 (2)	611.9 (5)
μ (mm⁻¹)	0.06	0.06	0.06
Crystal size (mm)	0.28 × 0.28 × 0.27	0.27 × 0.27 × 0.26	0.26 × 0.26 × 0.23

Data collection
Diffractometer	Rigaku Xcalibur Eos	Rigaku Xcalibur Atlas	Rigaku Xcalibur Atlas
T_min, T_max	0.573, 1.000	0.600, 1.000	0.447, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	4308, 832, 373	5447, 1085, 527	4114, 852, 401
R_int	0.071	0.063	0.068
(sin θ/λ)_max (Å⁻¹)	0.663	0.732	0.713

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.054, 0.118, 1.04	0.047, 0.131, 0.98	0.061, 0.194, 1.04
No. of reflections	832	1085	852
Δρ_max, Δρ_min (e Å⁻³)	0.09, −0.09	0.10, −0.10	0.17, −0.20
Absolute structure	Flack x determined using 128 quotients [(I⁺) − (I⁻)]/[(I⁺) + (I⁻)] (Parsons et al., 2013 )	Flack x determined using 181 quotients [(I⁺) − (I⁻)]/[(I⁺) + (I⁻)] (Parsons et al., 2013)	Flack x determined using 130 quotients [(I⁺) − (I⁻)]/[(I⁺) + (I⁻)] (Parsons et al., 2013)
Absolute structure parameter	−10.0 (10)	0.7 (10)	3.1 (10)
Computer programs: CrysAlis PRO (Rigaku OD, 2022 $[Rigaku OD (2022). CrysAlis PRO. Rigaku Oxford Diffraction Ltd, Yarnton, Oxfordshire, England.]$ ), SHELXT2018 (Sheldrick, 2015a ), SHELXL2018 (Sheldrick, 2015b ), Mercury (Macrae et al., 2020) and OLEX2 (Dolomanov et al., 2009 ).

Table 2
Selected crystal data of HA at 0.1 MPa/150 K and 0.50, 0.65 and 1.40 GPa (all at 295 K)

	C₆H₁₅N^a	C₆H₁₅N^b	C₆H₁₅N^b	C₆H₁₅N^b
p (GPa)	0.0001	0.50 (2)	0.65 (2)	1.40 (2)
T (K)	150	295 (2)	295 (2)	295 (2)
Crystal system	Orthorhombic	Orthorhombic	Orthorhombic	Orthorhombic
Space group	Pca2₁	Pca2₁	Pca2₁	Pca2₁
a (Å)	6.9725 (3)	6.9050 (9)	6.8591 (9)	6.7241 (19)
b (Å)	17.7977 (6)	17.549 (7)	17.494 (5)	17.052 (13)
c (Å)	5.6105 (2)	5.5212 (13)	5.4892 (4)	5.3367 (7)
V (Å³)	696.23 (5)	669.1 (3)	658.7 (2)	611.9 (5)
Z, Z′	4, 1	4, 1	4, 1	4, 1
D_x (g cm⁻³)	0.965	1.005	1.020	1.098
R₁ [F² > 2σ(F²)]	0.0418	0.0544	0.0472	0.0612
R₁ (all data)	-	0.1726	0.1434	0.1624
References: (a) Maloney et al. (2014); (b) this work.

3. Results and discussion

The single crystal of HA was obtained at the lowest possible pressure of 0.50 GPa (ca 0.2 GPa above the freezing pressure) to ensure the stability of the crystal during the X-ray diffraction data collection experiment. Two additional measurements were performed on this crystal compressed under isothermal conditions to 0.65 GPa and then to 1.40 GPa. The pressure of 1.40 GPa was the highest, at which the compressive stress on the crystal did not significantly affect the quality of the diffraction data. Above 1.40 GPa, the HA single crystal cracked due to mechanical stress. The crystals obtained under high pressure are denser than those crystallized at ambient pressure and low temperature (Table 2). All the unit-cell parameters of the investigated HA crystals decrease with increasing pressure, leading to the more dense structures. The molecular volume of HA as a function of pressure has been plotted in Fig. 3.

Figure 3
The molecular volume of HA at room temperature as a function of pressure measured in the piston-and-cylinder press (blue circles). The volumes measured at high pressure (red triangles) and low temperature (green square; Maloney et al., 2014

) by single-crystal X-ray diffraction have been indicated. The freezing pressure (f.p.) of 0.33 GPa is marked with a vertical dashed line.

The compression of the molecular volume of HA measured at 295 K in a piston-and-cylinder press (Baranowski & Moroz, 1982; Dziubek & Katrusiak, 2014) changes abruptly by 2.6% on freezing the liquid at 0.33 GPa (Fig. 3). After freezing, the solid HA is initially strongly compressed until about 0.80 GPa; thereafter, the compression decreases monotonically, and at 1.96 GPa, the volume reaches about 65% of the liquid at 0.1 MPa and 80% of the solid at 0.33 GPa. The molecular volume determined using the piston-and-cylinder press is consistent with that obtained by single-crystal X-ray diffraction (Fig. 3).

HA at 0.1 MPa/150 K crystallizes in the noncentrosymmetric space group Pca2₁, adopting a layered arrangement with infinite N—H⋯N hydrogen-bonded chains running within the layers (Maloney et al., 2014). These N—H⋯N hydrogen-bonded chains can be described by the symbol C₁¹(2) according to the graph-set notation of hydrogen bonds (Etter et al., 1990 ). Within the chains, each N atom acts as a donor and an acceptor of an H atom. These chains are retained at high pressure when HA crystallizes in the same phase at 0.33 GPa/295 K (Fig. 4). This structure remains stable up to at least a pressure of 1.40 GPa.

Figure 4
Structures of HA at low-temperature (Maloney et al., 2014

) and high-pressure conditions: (a) 0.1 MPa/150 K and (b) 1.40 GPa/295 K. Four hydrogen bonds (N—H⋯N) and one short intermolecular H⋯H distance at the end of the carbon chains are marked with dashed lines (distances are indicated). The intermolecular space accessible to a probe with a radius of 0.7 Å and a grid spacing of 0.1 Å (Macrae et al., 2020

) is indicated in yellow.

N—H⋯N hydrogen bonds play a major role in the cohesion force in HA crystals at ambient pressure/low temperature and within the investigated pressure range at room temperature. These interactions at ambient pressure/low temperature are characterized by intermolecular H⋯N distances shorter by ca 0.45 Å (Maloney et al., 2014) than the sum of the van der Waals radii of H and N atoms of 2.75 Å (Bondi, 1964 ) (Figs. 4 and 5). At 0.50 GPa, these distances are 2.229 (6) Å, and they are even shorter at 1.40 GPa, i.e. 2.168 (5) Å (Figs. 4 and 5, and Table 3).

Table 3
Hydrogen-bond geometry (Å, °)

N1—H1⋯N1ⁱ	0.50 GPa	0.65 GPa	1.40 GPa
N1—H1	0.900 (7)	0.900 (4)	0.900 (7)
H1⋯N1ⁱ	2.229 (6)	2.230 (3)	2.168 (5)
N1⋯N1ⁱ	3.116 (7)	3.115 (4)	3.050 (8)
N1—H1⋯N1ⁱ	168.2 (2)	167.44 (13)	166.4 (2)
Symmetry code: (i) −x + 1, −y, z − $[{1\over 2}]$ .

Figure 5
Intermolecular H⋯N and H⋯H distances (Å) observed in HA structures plotted as a function of pressure. The two shortest distances for each type are presented: blue circles represent the N—H⋯N and blue squares depict the C—H⋯N hydrogen–acceptor (H⋯A) distances, while red triangles represent intermolecular H⋯H distances. Blue and red horizontal lines show the sum of the van der Waals radii of H and N of 2.75 Å, and of two H atoms of 2.40 Å (Bondi, 1964

). The estimated standard deviations are smaller than the plotted symbols.

It is characteristic that the second shortest intermolecular H⋯N distances from the N—H⋯N hydrogen bonding are approximately 0.6 Å longer than the shortest. Within the investigated pressure range, these distances remain longer than the sum of the van der Waals radii (Fig. 5). Such a property was observed for the first time in the high-pressure structures of the simplest primary amines (Podsiadło et al., 2017; Sacharczuk et al., 2023). Furthermore, even in the HA structure at 1.40 GPa, no intermolecular H⋯N distances from C—H⋯N hydrogen bonds shorter than the sum of the van der Waals radii are observed. HA is therefore the first primary n-amine in the series from methyl- to hexylamine where, at high pressure, only single N—H⋯N hydrogen-bonded chains are observed. The C—H⋯N hydrogen bonds are not formed at all and no phase transition, that would allow molecular rearrangement and the formation of C—H⋯N interactions, occurred (Podsiadło et al., 2017; Sacharczuk et al., 2023). In the series from methyl- to pentylamine, high pressure does not affect the main cohesive force (N—H⋯N hydrogen bonds); however, intermolecular C—H⋯N interactions are observed in the high-pressure polymorphs (Podsiadło et al., 2017; Sacharczuk et al., 2023).

In the HA crystals, only at a pressure of 1.40 GPa do the shortest intermolecular H⋯H distances, at the end of the carbon chains, become shorter than the sum of the van der Waals radii of two H atoms of 2.4 Å (Bondi, 1964) (Figs. 4 and 5, and Fig. S2 in the supporting information). It is characteristic that, with increasing pressure, these shortest intermolecular H⋯H distances are more compressible than the main N—H⋯N contacts (Figs. 4 and 5). This is related to the voids observed in the crystals between the ends of the carbon chains (Fig. 4).

In the series from methyl- to hexylamine, HA forms the least dense crystals in the structures determined just above their freezing pressure. The crystal density of methylamine determined at 3.65 GPa is 1.165 g cm⁻³ (Podsiadło et al., 2017), ethylamine at 1.40 GPa is 1.046 g cm⁻³ (Sacharczuk et al., 2023), propylamine at 2.25 GPa is 1.109 g cm⁻³ (Sacharczuk et al., 2023), butylamine at 1.45 GPa is 1.059 g cm⁻³ (Sacharczuk et al., 2023) and pentylamine at 1.05 GPa is 1.049 g cm⁻³ (Sacharczuk et al., 2023). The crystal density of HA, determined within this study, at 0.50 GPa is 1.005 g cm⁻³. This correlates with the void volumes in the structures mentioned above, which, in the series from methyl- to hexylamine, are 0, 7.15, 7.86, 12.94, 13.65 and 38.45 Å³, respectively (the intermolecular space accessible to a probe with a radius of 0.6 Å and a grid spacing of 0.1 Å; the parameters used in the calculations differ from those used in Fig. 4, ensuring distinguishable void volumes across the entire series; Macrae et al., 2020 ).

4. Conclusions

The high-pressure crystal structure of HA is isostructural with the phase determined at low temperature at 0.1 MPa (Maloney et al., 2014). This represents the first example among the series of the simplest aliphatic amines where the crystal symmetry remains unchanged between low-temperature and high-pressure conditions. The space group symmetry of Pca2₁ remains stable within the investigated pressure range. Similar to other aliphatic n-amines, the main cohesion force in the HA crystals involves the N—H⋯N hydrogen-bonded chains. However, no additional intermolecular distances shorter than the sum of the van der Waals radii are observed. This is unique within the high-pressure studies of the methyl- to pentylamine series, where high pressure enhances the role of intermolecular C—H⋯N interactions. Only at 1.40 GPa does the first intermolecular H⋯H distance become shorter than the sum of the van der Waals radii of two H atoms. The compressibility of this distance exceeds that of the intermolecular N—H⋯N hydrogen bonds. This effect results from the voids surrounding the methyl groups at the ends of the carbon chains. The HA crystal obtained just above the freezing pressure is the least dense structure among the high-pressure structures determined in the methyl- to hexylamine series.

Supporting information

CCDC references: 2434096; 2434097; 2434098

Crystal structure: contains datablocks hexylamine_0_50GPa, hexylamine_0_65GPa, hexylamine_1_40GPa, global. DOI: https://doi.org/10.1107/S2053229625004504/vp3043sup1.cif

Structure factors: contains datablock hexylamine_0_50GPa. DOI: https://doi.org/10.1107/S2053229625004504/vp3043hexylamine_0_50GPasup2.hkl

Structure factors: contains datablock hexylamine_0_65GPa. DOI: https://doi.org/10.1107/S2053229625004504/vp3043hexylamine_0_65GPasup3.hkl

Structure factors: contains datablock hexylamine_1_40GPa. DOI: https://doi.org/10.1107/S2053229625004504/vp3043hexylamine_1_40GPasup4.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2053229625004504/vp3043hexylamine_0_50GPasup5.cml

Additional figures and table. DOI: https://doi.org/10.1107/S2053229625004504/vp3043sup6.pdf

Computing details top

n-Hexylamine (hexylamine_0_50GPa) top

Crystal data top

C₆H₁₅N	D_x = 1.005 Mg m⁻³
M_r = 101.19	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pca2₁	Cell parameters from 598 reflections
a = 6.9050 (9) Å	θ = 3.8–17.7°
b = 17.549 (7) Å	µ = 0.06 mm⁻¹
c = 5.5212 (13) Å	T = 295 K
V = 669.1 (3) Å³	Disc, colourless
Z = 4	0.28 × 0.28 × 0.27 mm
F(000) = 232

Data collection top

Rigaku Xcalibur Eos diffractometer	373 reflections with I > 2σ(I)
Detector resolution: 16.2413 pixels mm^-1	R_int = 0.071
φ– and ω–scans	θ_max = 28.1°, θ_min = 3.2°
Absorption correction: multi-scan (CrysAlis PRO; Rigaku OD, 2022)	h = −9→9
T_min = 0.573, T_max = 1.000	k = −16→16
4308 measured reflections	l = −6→6
832 independent reflections

Refinement top

Refinement on F²	Hydrogen site location: mixed
Least-squares matrix: full	H-atom parameters constrained
R[F² > 2σ(F²)] = 0.054	w = 1/[σ²(F_o²) + (0.0376P)²] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.118	(Δ/σ)_max < 0.001
S = 1.04	Δρ_max = 0.09 e Å⁻³
832 reflections	Δρ_min = −0.09 e Å⁻³
64 parameters	Absolute structure: Flack x determined using 128 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
1 restraint	Absolute structure parameter: −10.0 (10)
Primary atom site location: dual

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Rigaku Xcalibur EOS and Xcalibur ATLAS diffractometers were used for the high-pressure studies. The X-ray wavelength used in all experiments was 0.71073 Å. The DAC was centred by the gasket-shadow method (Budzianowski & Katrusiak, 2004). The CrysAlis PRO program suite was used for data collection, determination of the UB matrices and data reductions. All data were accounted for the Lorentz, polarization and absorption effects. OLEX2 (Dolomanov et al., 2009), SHELXT (Sheldrick, 2015a) and SHELXL (Sheldrick, 2015b) were used to solve the structures by direct methods, and then to the full-matrix least-squares refinement.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
N1	0.5556 (7)	0.0349 (4)	0.9147 (10)	0.0687 (19)
H2	0.682796	0.038908	0.947803	0.082*
H1	0.539765	0.010808	0.772063	0.082*
C1	0.4704 (8)	0.1102 (6)	0.9009 (13)	0.063 (3)
H12	0.488877	0.134938	1.056331	0.076*
H11	0.332065	0.104265	0.877298	0.076*
C2	0.5449 (8)	0.1627 (6)	0.7081 (12)	0.055 (3)
H22	0.683900	0.167532	0.728087	0.066*
H21	0.522184	0.138989	0.551947	0.066*
C3	0.4591 (6)	0.2410 (7)	0.7031 (12)	0.062 (3)
H32	0.480115	0.264728	0.859597	0.075*
H31	0.320307	0.236485	0.679769	0.075*
C4	0.5394 (8)	0.2926 (5)	0.5096 (13)	0.061 (3)
H42	0.678221	0.297005	0.532398	0.074*
H41	0.517725	0.269072	0.352958	0.074*
C5	0.4533 (8)	0.3714 (5)	0.5061 (12)	0.070 (3)
H52	0.470541	0.394238	0.664685	0.084*
H51	0.315124	0.367130	0.477184	0.084*
C6	0.5390 (8)	0.4243 (5)	0.3177 (16)	0.088 (3)
H63	0.476617	0.473119	0.327290	0.132*
H62	0.675190	0.430265	0.347089	0.132*
H61	0.519522	0.403112	0.159285	0.132*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.073 (3)	0.079 (7)	0.055 (5)	0.004 (3)	0.001 (4)	0.003 (3)
C1	0.059 (3)	0.076 (10)	0.054 (7)	−0.003 (5)	0.000 (5)	0.003 (5)
C2	0.053 (3)	0.055 (11)	0.057 (7)	−0.001 (5)	−0.007 (5)	−0.002 (5)
C3	0.048 (3)	0.085 (12)	0.054 (7)	0.005 (5)	0.001 (5)	−0.004 (5)
C4	0.056 (3)	0.078 (11)	0.051 (7)	−0.002 (4)	−0.002 (5)	0.004 (4)
C5	0.071 (4)	0.082 (10)	0.057 (7)	−0.004 (5)	0.001 (5)	0.005 (5)
C6	0.088 (4)	0.099 (12)	0.076 (9)	0.008 (5)	−0.005 (6)	0.012 (5)

Geometric parameters (Å, º) top

N1—H2	0.9000	C3—C4	1.507 (8)
N1—H1	0.9001	C4—H42	0.9700
N1—C1	1.449 (9)	C4—H41	0.9700
C1—H12	0.9700	C4—C5	1.506 (8)
C1—H11	0.9700	C5—H52	0.9700
C1—C2	1.498 (10)	C5—H51	0.9700
C2—H22	0.9700	C5—C6	1.515 (11)
C2—H21	0.9700	C6—H63	0.9600
C2—C3	1.497 (12)	C6—H62	0.9600
C3—H32	0.9700	C6—H61	0.9600
C3—H31	0.9700

H2—N1—H1	109.5	C4—C3—H31	108.6
C1—N1—H2	109.6	C3—C4—H42	108.6
C1—N1—H1	109.4	C3—C4—H41	108.6
N1—C1—H12	108.0	H42—C4—H41	107.6
N1—C1—H11	108.0	C5—C4—C3	114.6 (7)
N1—C1—C2	117.3 (7)	C5—C4—H42	108.6
H12—C1—H11	107.2	C5—C4—H41	108.6
C2—C1—H12	108.0	C4—C5—H52	108.6
C2—C1—H11	108.0	C4—C5—H51	108.6
C1—C2—H22	108.2	C4—C5—C6	114.7 (6)
C1—C2—H21	108.2	H52—C5—H51	107.6
H22—C2—H21	107.4	C6—C5—H52	108.6
C3—C2—C1	116.2 (7)	C6—C5—H51	108.6
C3—C2—H22	108.2	C5—C6—H63	109.5
C3—C2—H21	108.2	C5—C6—H62	109.5
C2—C3—H32	108.6	C5—C6—H61	109.5
C2—C3—H31	108.6	H63—C6—H62	109.5
C2—C3—C4	114.8 (6)	H63—C6—H61	109.5
H32—C3—H31	107.5	H62—C6—H61	109.5
C4—C3—H32	108.6

N1—C1—C2—C3	−178.1 (6)	C2—C3—C4—C5	−179.7 (6)
C1—C2—C3—C4	179.1 (6)	C3—C4—C5—C6	177.9 (6)

n-Hexylamine (hexylamine_0_65GPa) top

Crystal data top

C₆H₁₅N	D_x = 1.020 Mg m⁻³
M_r = 101.19	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pca2₁	Cell parameters from 1173 reflections
a = 6.8591 (9) Å	θ = 3.2–23.5°
b = 17.494 (5) Å	µ = 0.06 mm⁻¹
c = 5.4892 (4) Å	T = 295 K
V = 658.7 (2) Å³	Disc, colourless
Z = 4	0.27 × 0.27 × 0.26 mm
F(000) = 232

Data collection top

Rigaku Xcalibur Atlas diffractometer	527 reflections with I > 2σ(I)
Detector resolution: 10.5384 pixels mm^-1	R_int = 0.063
φ– and ω–scans	θ_max = 31.4°, θ_min = 3.2°
Absorption correction: multi-scan (CrysAlis PRO; Rigaku OD, 2022)	h = −8→8
T_min = 0.600, T_max = 1.000	k = −15→15
5447 measured reflections	l = −7→7
1085 independent reflections

Refinement top

Refinement on F²	Hydrogen site location: mixed
Least-squares matrix: full	H-atom parameters constrained
R[F² > 2σ(F²)] = 0.047	w = 1/[σ²(F_o²) + (0.0573P)²] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.131	(Δ/σ)_max < 0.001
S = 0.98	Δρ_max = 0.10 e Å⁻³
1085 reflections	Δρ_min = −0.10 e Å⁻³
64 parameters	Absolute structure: Flack x determined using 181 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
1 restraint	Absolute structure parameter: 0.7 (10)
Primary atom site location: dual

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
N1	0.5563 (5)	0.0358 (3)	0.9205 (5)	0.0550 (14)
H2	0.684017	0.040646	0.954979	0.066*
H1	0.542127	0.011566	0.777019	0.066*
C1	0.4676 (5)	0.1112 (3)	0.9056 (6)	0.0464 (17)
H12	0.484199	0.136515	1.061406	0.056*
H11	0.328753	0.104832	0.879059	0.056*
C2	0.5472 (5)	0.1630 (3)	0.7083 (6)	0.0442 (17)
H22	0.686689	0.168369	0.731413	0.053*
H21	0.526551	0.138715	0.551522	0.053*
C3	0.4575 (5)	0.2410 (4)	0.7023 (7)	0.0497 (17)
H32	0.475565	0.264744	0.860355	0.060*
H31	0.318406	0.235580	0.675689	0.060*
C4	0.5404 (5)	0.2940 (3)	0.5071 (7)	0.0464 (15)
H42	0.679673	0.299029	0.533055	0.056*
H41	0.521480	0.270362	0.349076	0.056*
C5	0.4517 (5)	0.3729 (4)	0.5013 (6)	0.0539 (16)
H51	0.312578	0.368251	0.473613	0.065*
H52	0.470200	0.396829	0.659017	0.065*
C6	0.5376 (5)	0.4237 (3)	0.3078 (9)	0.0695 (17)
H63	0.475481	0.472863	0.313277	0.104*
H62	0.674870	0.429650	0.336080	0.104*
H61	0.517151	0.401053	0.150563	0.104*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.065 (3)	0.055 (5)	0.0453 (17)	0.0000 (18)	−0.004 (2)	0.004 (2)
C1	0.051 (3)	0.045 (7)	0.043 (2)	−0.003 (2)	0.001 (3)	−0.003 (3)
C2	0.046 (3)	0.049 (7)	0.0372 (19)	0.001 (2)	0.000 (2)	0.001 (2)
C3	0.040 (3)	0.065 (7)	0.044 (2)	0.000 (2)	0.000 (3)	0.002 (2)
C4	0.043 (3)	0.055 (6)	0.041 (2)	−0.002 (2)	−0.003 (3)	0.000 (2)
C5	0.054 (3)	0.059 (6)	0.048 (2)	−0.002 (2)	0.004 (3)	0.001 (2)
C6	0.072 (3)	0.077 (6)	0.060 (3)	0.004 (2)	0.001 (3)	0.008 (3)

Geometric parameters (Å, º) top

N1—H2	0.9000	C3—C4	1.528 (6)
N1—H1	0.9000	C4—H42	0.9700
N1—C1	1.454 (6)	C4—H41	0.9700
C1—H12	0.9700	C4—C5	1.508 (6)
C1—H11	0.9700	C5—H51	0.9700
C1—C2	1.514 (6)	C5—H52	0.9700
C2—H22	0.9700	C5—C6	1.505 (6)
C2—H21	0.9700	C6—H63	0.9600
C2—C3	1.496 (6)	C6—H62	0.9600
C3—H32	0.9700	C6—H61	0.9600
C3—H31	0.9700

H2—N1—H1	109.5	C4—C3—H31	108.6
C1—N1—H2	109.5	C3—C4—H42	108.5
C1—N1—H1	109.4	C3—C4—H41	108.5
N1—C1—H12	108.4	H42—C4—H41	107.5
N1—C1—H11	108.4	C5—C4—C3	114.9 (4)
N1—C1—C2	115.6 (3)	C5—C4—H42	108.5
H12—C1—H11	107.4	C5—C4—H41	108.5
C2—C1—H12	108.4	C4—C5—H51	108.9
C2—C1—H11	108.4	C4—C5—H52	108.9
C1—C2—H22	108.7	H51—C5—H52	107.7
C1—C2—H21	108.7	C6—C5—C4	113.4 (4)
H22—C2—H21	107.6	C6—C5—H51	108.9
C3—C2—C1	114.4 (4)	C6—C5—H52	108.9
C3—C2—H22	108.7	C5—C6—H63	109.5
C3—C2—H21	108.7	C5—C6—H62	109.5
C2—C3—H32	108.6	C5—C6—H61	109.5
C2—C3—H31	108.6	H63—C6—H62	109.5
C2—C3—C4	114.6 (3)	H63—C6—H61	109.5
H32—C3—H31	107.6	H62—C6—H61	109.5
C4—C3—H32	108.6

N1—C1—C2—C3	−178.2 (4)	C2—C3—C4—C5	−179.6 (4)
C1—C2—C3—C4	178.7 (3)	C3—C4—C5—C6	179.7 (3)

n-Hexylamine (hexylamine_1_40GPa) top

Crystal data top

C₆H₁₅N	D_x = 1.098 Mg m⁻³
M_r = 101.19	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pca2₁	Cell parameters from 794 reflections
a = 6.7241 (19) Å	θ = 3.8–23.7°
b = 17.052 (13) Å	µ = 0.06 mm⁻¹
c = 5.3367 (7) Å	T = 295 K
V = 611.9 (5) Å³	Disc, colourless
Z = 4	0.26 × 0.26 × 0.23 mm
F(000) = 232

Data collection top

Rigaku Xcalibur Atlas diffractometer	401 reflections with I > 2σ(I)
Detector resolution: 10.5384 pixels mm^-1	R_int = 0.068
φ– and ω–scans	θ_max = 30.4°, θ_min = 3.3°
Absorption correction: multi-scan (CrysAlis PRO; Rigaku OD, 2022)	h = −8→8
T_min = 0.447, T_max = 1.000	k = −14→13
4114 measured reflections	l = −7→7
852 independent reflections

Refinement top

Refinement on F²	Hydrogen site location: mixed
Least-squares matrix: full	H-atom parameters constrained
R[F² > 2σ(F²)] = 0.061	w = 1/[σ²(F_o²) + (0.0896P)²] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.194	(Δ/σ)_max < 0.001
S = 1.04	Δρ_max = 0.17 e Å⁻³
852 reflections	Δρ_min = −0.19 e Å⁻³
64 parameters	Absolute structure: Flack x determined using 130 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
1 restraint	Absolute structure parameter: 3.1 (10)
Primary atom site location: dual

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
N1	0.5636 (8)	0.0353 (5)	0.9407 (9)	0.058 (2)
H2	0.694796	0.041899	0.966999	0.069*
H1	0.544766	0.009549	0.795479	0.069*
C1	0.4647 (9)	0.1130 (6)	0.9275 (12)	0.053 (3)
H12	0.484791	0.140747	1.084208	0.063*
H11	0.322777	0.105681	0.904622	0.063*
C2	0.5466 (9)	0.1622 (6)	0.7122 (11)	0.050 (3)
H22	0.689124	0.168003	0.733140	0.060*
H21	0.523657	0.134733	0.555654	0.060*
C3	0.4542 (8)	0.2414 (6)	0.6972 (12)	0.056 (3)
H32	0.470772	0.267628	0.857227	0.067*
H31	0.312710	0.235476	0.667628	0.067*
C4	0.5425 (9)	0.2932 (6)	0.4908 (10)	0.047 (3)
H42	0.684285	0.298718	0.519215	0.057*
H41	0.524514	0.267358	0.330484	0.057*
C5	0.4508 (9)	0.3733 (6)	0.4782 (11)	0.063 (3)
H52	0.467165	0.398929	0.639147	0.075*
H51	0.309275	0.367858	0.447405	0.075*
C6	0.5408 (8)	0.4251 (5)	0.2748 (12)	0.069 (3)
H63	0.476291	0.475376	0.275976	0.103*
H62	0.680310	0.431891	0.306105	0.103*
H61	0.522333	0.400803	0.114258	0.103*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.067 (4)	0.064 (9)	0.042 (3)	−0.002 (3)	−0.009 (3)	0.005 (3)
C1	0.059 (5)	0.048 (13)	0.051 (4)	0.002 (4)	−0.002 (4)	0.004 (4)
C2	0.048 (5)	0.064 (12)	0.038 (3)	0.002 (4)	−0.004 (4)	0.002 (4)
C3	0.043 (5)	0.084 (12)	0.041 (3)	−0.007 (4)	0.005 (4)	−0.005 (4)
C4	0.052 (5)	0.055 (11)	0.035 (3)	0.000 (4)	−0.003 (4)	0.006 (4)
C5	0.057 (6)	0.082 (13)	0.049 (4)	−0.002 (4)	0.006 (4)	−0.004 (5)
C6	0.068 (5)	0.095 (12)	0.043 (4)	0.006 (4)	0.006 (5)	0.008 (4)

Geometric parameters (Å, º) top

N1—H2	0.9000	C3—C4	1.532 (11)
N1—H1	0.8998	C4—H42	0.9700
N1—C1	1.485 (12)	C4—H41	0.9700
C1—H12	0.9700	C4—C5	1.499 (11)
C1—H11	0.9700	C5—H52	0.9700
C1—C2	1.526 (11)	C5—H51	0.9700
C2—H22	0.9700	C5—C6	1.525 (10)
C2—H21	0.9700	C6—H63	0.9600
C2—C3	1.489 (11)	C6—H62	0.9600
C3—H32	0.9700	C6—H61	0.9600
C3—H31	0.9700

H2—N1—H1	109.5	C4—C3—H31	108.8
C1—N1—H2	109.5	C3—C4—H42	108.9
C1—N1—H1	109.3	C3—C4—H41	108.9
N1—C1—H12	109.4	H42—C4—H41	107.7
N1—C1—H11	109.4	C5—C4—C3	113.4 (6)
N1—C1—C2	111.4 (6)	C5—C4—H42	108.9
H12—C1—H11	108.0	C5—C4—H41	108.9
C2—C1—H12	109.4	C4—C5—H52	108.9
C2—C1—H11	109.4	C4—C5—H51	108.9
C1—C2—H22	109.0	C4—C5—C6	113.4 (6)
C1—C2—H21	109.0	H52—C5—H51	107.7
H22—C2—H21	107.8	C6—C5—H52	108.9
C3—C2—C1	112.9 (6)	C6—C5—H51	108.9
C3—C2—H22	109.0	C5—C6—H63	109.5
C3—C2—H21	109.0	C5—C6—H62	109.5
C2—C3—H32	108.8	C5—C6—H61	109.5
C2—C3—H31	108.8	H63—C6—H62	109.5
C2—C3—C4	113.6 (5)	H63—C6—H61	109.5
H32—C3—H31	107.7	H62—C6—H61	109.5
C4—C3—H32	108.8

N1—C1—C2—C3	−178.5 (7)	C2—C3—C4—C5	−179.3 (7)
C1—C2—C3—C4	176.9 (6)	C3—C4—C5—C6	179.2 (5)

Selected crystal data of HA at 0.1 MPa/150 K and 0.50, 0.65 and 1.40 GPa (all at 295 K) top

	C₆H₁₅N^a	C₆H₁₅N^b	C₆H₁₅N^b	C₆H₁₅N^b
p (GPa)	0.0001	0.50 (2)	0.65 (2)	1.40 (2)
T (K)	150	295 (2)	295 (2)	295 (2)
Crystal system	Orthorhombic	Orthorhombic	Orthorhombic	Orthorhombic
Space group	Pca2₁	Pca2₁	Pca2₁	Pca2₁
a (Å)	6.9725 (3)	6.9050 (9)	6.8591 (9)	6.7241 (19)
b (Å)	17.7977 (6)	17.549 (7)	17.494 (5)	17.052 (13)
c (Å)	5.6105 (2)	5.5212 (13)	5.4892 (4)	5.3367 (7)
V (Å³)	696.23 (5)	669.1 (3)	658.7 (2)	611.9 (5)
Z, Z?	4, 1	4, 1	4, 1	4, 1
D_x (g?cm^-3)	0.965	1.005	1.020	1.098
R₁ [F² > 2σ(F²)]	0.0418	0.0544	0.0472	0.0612
R₁ (all data)	-	0.1726	0.1434	0.1624

References: (a) Maloney et al. (2014); (b) this work.

Hydrogen-bond geometry (Å, °) top

N1—H1···N1ⁱ	0.50 GPa	0.65 GPa	1.40 GPa
N1—H1	0.900 (7)	0.900 (4)	0.900 (7)
H1···N1	2.229 (6)	2.230 (3)	2.168 (5)
N1···N1	3.116 (7)	3.115 (4)	3.050 (8)
N1—H1···N1	168.2 (2)	167.44 (13)	166.4 (2)

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

Funding information

Funding for this research was provided by: National Science Centre (grant No. 2020/37/B/ST4/00982).

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