Benzyl­ammonium hexa­noate

Wood, M.H.; Clarke, S.M.

doi:10.1107/S1600536812039931

organic compounds

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ISSN: 2056-9890

Volume 68| Part 10| October 2012| Page o3004

https://doi.org/10.1107/S1600536812039931

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Benzylammonium hexanoate

Mary H. Wood ^a and Stuart M. Clarke ^a ^*

^aBP Institute and Department of Chemistry, University of Cambridge, Cambridge, England
^*Correspondence e-mail: stuart@bpi.cam.ac.uk

(Received 5 September 2012; accepted 20 September 2012; online 26 September 2012)

A binary mixture of benzylamine and hexanoic acid has been reacted to form the title salt, C₇H₁₀N⁺·C₆H₁₁O₂⁻. This crystal has a 1:1 stoichiometry of acid- and amine-derived species which contrasts with other related species which can have a number of other integer ratios of acid and amine components. The diffraction data indicate complete transfer of a proton from the acid to the amine to give the salt, comprising a cation and anion combination, with the formation of three hydrogen bonds around each ammonium group. This contrasts with other related species.

Related literature

For spectroscopic studies of acid–amine complexes, see: Karlsson et al. (2000 ); Paivarinta et al. (2000 ); Kohler et al. (1981 ); Smith et al. (2001 , 2002 ). For recent diffraction studies of acid–amine complexes, see: Jefferson et al. (2011 ); Sun et al. (2011 ).

Experimental

Crystal data

C₇H₁₀N⁺·C₆H₁₁O₂⁻
M_r = 223.31
Triclinic, $[P \overline 1]$
a = 5.7730 (3) Å
b = 7.7465 (4) Å
c = 15.1707 (8) Å
α = 98.318 (3)°
β = 90.638 (3)°
γ = 105.641 (2)°
V = 645.55 (6) Å³
Z = 2
Mo Kα radiation
μ = 0.08 mm⁻¹
T = 180 K
0.37 × 0.25 × 0.02 mm

Data collection

Nonius Kappa CCD diffractometer
Absorption correction: multi-scan (SORTAV; Blessing, 1995 ) T_min = 0.824, T_max = 1.000
9587 measured reflections
2915 independent reflections
1930 reflections with I > 2σ(I)
R_int = 0.060

Refinement

R[F² > 2σ(F²)] = 0.068
wR(F²) = 0.177
S = 1.04
2915 reflections
147 parameters
H-atom parameters constrained
Δρ_max = 0.59 e Å⁻³
Δρ_min = −0.33 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯O1	0.91	1.99	2.890 (3)	169
N1—H1B⋯O2ⁱ	0.91	1.81	2.705 (3)	169
N1—H1C⋯O1ⁱⁱ	0.91	1.88	2.769 (3)	164
C1—H1D⋯O2ⁱⁱⁱ	0.99	2.45	3.366 (3)	154
C7—H7⋯N1	0.95	2.58	2.902 (3)	100
C7—H7⋯O1ⁱⁱ	0.95	2.53	3.347 (3)	144
Symmetry codes: (i) -x, -y+1, -z; (ii) -x+1, -y+1, -z; (iii) x, y-1, z.

Data collection: COLLECT (Nonius, 1998 ); cell refinement: SCALEPACK (Otwinowski & Minor, 1997 ); data reduction: DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SIR92 (Altomare et al., 1994 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97.

Supporting information

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536812039931/mw2086sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536812039931/mw2086Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S1600536812039931/mw2086Isup3.cml

checkCIF report

Comment top

Several studies, mainly spectroscopy-based, have reported the existence of stable complexes formed between simple fatty acids and amines, both alkyl and aromatic-based e.g. (Karlsson et al., 2000). Numerous 1:1 acid:amine complexes have been identified; in addition, various examples of 2:1 and 3:1 adducts have been discovered, usually in an acid-rich environment (Sun et al., 2011; Kohler et al., 1981). Interestingly, no amine-rich complexes have yet been observed; indeed, it has been proposed that these would be highly unstable were they to form (Paivarinta et al., 2000), although there is a report of a diamine complex formed between methylamine and dnsa (3, 5-dinitrosalicyclic acid) due to deprotonation of the phenolic group in the acid (Smith et al., 2001; Smith et al., 2002).

The 1:1 acid:amine complexes are generally considered to derive their stablity from the complete transfer of a proton from the acid to the amine with subsequent cation-anion electrostatic interaction and strong hydrogen-bond formation. In 2:1 or high stoichiometry complexes, the hydrogen bond is considered to extend over the three (or more) species involved.

The 1:1 complex of hexanoic acid and benzylamine forms by reaction of the two species with complete proton transfer from the acid to the base. Each ammonium ion in this salt can now form three hydrogen bonds, one of which is shown in Fig. 1 and all three in Fig. 2. This work follows from similar findings reported by (Jefferson et al., 2011) who report the structure of a 1:1 complex of octanoic acid and decylamine using the same experimental method of preparation. This work differs from the previous study concerning complex formation with an aromatic amine, rather than an alkyl amine reported previously. In general, few examples of such single-crystal data exist for such complexes, due mainly to the difficulty of growing suitable crystals. The molecular arrangement of the alkyl and aromatic groups is also somewhat surprising. One might have imagined the aromatic rings interacting strongly together and 'stacking' separately from the alkyl chains of the hexanoic acid. However, they appear to be arranged adjacent to each other in the 1:1 crystal, with the planes of the aromatic ring and the alkyl chain backbone essentially parallel, Fig. 2.

Related literature top

For spectroscopic studies of acid–amine complexes, see: Karlsson et al. (2000); Paivarinta et al. (2000); Kohler et al. (1981); Smith et al. (2001, 2002). For recent diffraction studies of acid–amine complexes, see: Jefferson et al. (2011); Sun et al. (2011).

Experimental top

Hexanoic acid and benzylamine, with purities of 99.5% and 99.7% respectively as determined by titration and GC, were purchased from Sigma Aldrich and used without further purification. The crystals were grown by pipetting a small volume (approximately 1 ml) of each into two small vials, and leaving both within a larger vial over a number of weeks all under an inert atmosphere of nitrogen. After this period numerous crystals were observed, with particularly abundant growth on a polypropylene surface that had been left therein as a nucleating surface. The inert atmosphere was employed to minimize reaction of the amine with atmospheric CO₂, which can make such complexation studies difficult (Sun et al. 2011).

Elemental analysis gave values of 69.85%, 6.22%, 9.42% and 14.52% for carbon, nitrogen, hydrogen and oxygen respectively. For a 1:1 complex these values are expected to be 69.92%, 6.27%, 9.48% and 14.32%, in excellent agreement. The 1:1 stoichiometry also agrees with the crystal structure determination given here. The experimental sample temperature 180 K represents a compromise of several factors. It is selected as the temperature which is cold enough to get improved thermal factors but not so cold that the crystals fracture and it is a temperature at which the cryostream can run efficiently for an extended period.

Structure description top

For spectroscopic studies of acid–amine complexes, see: Karlsson et al. (2000); Paivarinta et al. (2000); Kohler et al. (1981); Smith et al. (2001, 2002). For recent diffraction studies of acid–amine complexes, see: Jefferson et al. (2011); Sun et al. (2011).

Computing details top

Data collection: COLLECT (Nonius, 1998); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top

	Fig. 1. Perspective view of the asymmetric unit showing one of the three N—H···O hydrogen bonds
	Fig. 2. Illustration of the packing. Hydrogen bonds are shown by dashed lines.

Benzylammonium hexanoate top

Crystal data top

C₇H₁₀N⁺·C₆H₁₁O₂⁻	Z = 2
M_r = 223.31	F(000) = 244
Triclinic, P1	D_x = 1.149 Mg m⁻³
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 5.7730 (3) Å	Cell parameters from 18567 reflections
b = 7.7465 (4) Å	θ = 1.0–27.5°
c = 15.1707 (8) Å	µ = 0.08 mm⁻¹
α = 98.318 (3)°	T = 180 K
β = 90.638 (3)°	Block, colourless
γ = 105.641 (2)°	0.37 × 0.25 × 0.02 mm
V = 645.55 (6) Å³

Data collection top

Nonius Kappa CCD diffractometer	1930 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.060
Thin slice ω and φ scans	θ_max = 27.5°, θ_min = 3.6°
Absorption correction: multi-scan (SORTAV; Blessing, 1995)	h = −7→7
T_min = 0.824, T_max = 1.000	k = −10→10
9587 measured reflections	l = −19→19
2915 independent reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.068	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.177	H-atom parameters constrained
S = 1.04	w = 1/[σ²(F_o²) + (0.0564P)² + 0.4841P] where P = (F_o² + 2F_c²)/3
2915 reflections	(Δ/σ)_max < 0.001
147 parameters	Δρ_max = 0.59 e Å⁻³
0 restraints	Δρ_min = −0.33 e Å⁻³

Crystal data top

C₇H₁₀N⁺·C₆H₁₁O₂⁻	γ = 105.641 (2)°
M_r = 223.31	V = 645.55 (6) Å³
Triclinic, P1	Z = 2
a = 5.7730 (3) Å	Mo Kα radiation
b = 7.7465 (4) Å	µ = 0.08 mm⁻¹
c = 15.1707 (8) Å	T = 180 K
α = 98.318 (3)°	0.37 × 0.25 × 0.02 mm
β = 90.638 (3)°

Data collection top

Nonius Kappa CCD diffractometer	2915 independent reflections
Absorption correction: multi-scan (SORTAV; Blessing, 1995)	1930 reflections with I > 2σ(I)
T_min = 0.824, T_max = 1.000	R_int = 0.060
9587 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.068	0 restraints
wR(F²) = 0.177	H-atom parameters constrained
S = 1.04	Δρ_max = 0.59 e Å⁻³
2915 reflections	Δρ_min = −0.33 e Å⁻³
147 parameters

Special details top

Experimental. The data is moderately weak at high angle (66% observed), a fact reflected in the rather large K value in the analysis of variance.

Absorption correction: multi-scan from symmetry-related measurements Sortav (Blessing, 1995)

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 (Å²) top

	x	y	z	U_iso*/U_eq
N1	0.2211 (3)	0.3348 (3)	0.04302 (13)	0.0433 (5)
H1A	0.2402	0.4524	0.0359	0.052*
H1B	0.0980	0.2617	0.0056	0.052*
H1C	0.3594	0.3036	0.0301	0.052*
O1	0.3458 (3)	0.7110 (2)	0.01788 (10)	0.0369 (4)
O2	0.1113 (3)	0.8658 (2)	0.08527 (12)	0.0499 (5)
C1	0.1663 (4)	0.3134 (4)	0.13431 (15)	0.0435 (6)
H1D	0.1370	0.1838	0.1402	0.052*
H1E	0.0153	0.3472	0.1473	0.052*
C2	0.3600 (4)	0.4245 (3)	0.20347 (14)	0.0330 (5)
C3	0.3043 (4)	0.4336 (3)	0.29247 (16)	0.0406 (6)
H3	0.1468	0.3744	0.3079	0.049*
C4	0.4766 (5)	0.5283 (4)	0.35889 (16)	0.0477 (7)
H4	0.4366	0.5337	0.4196	0.057*
C5	0.7059 (5)	0.6149 (4)	0.33769 (17)	0.0476 (7)
H5	0.8237	0.6795	0.3836	0.057*
C6	0.7630 (4)	0.6073 (3)	0.24995 (17)	0.0403 (6)
H6	0.9204	0.6679	0.2350	0.048*
C7	0.5917 (4)	0.5113 (3)	0.18271 (15)	0.0353 (5)
H7	0.6335	0.5052	0.1222	0.042*
C8	0.3117 (4)	0.8349 (3)	0.07608 (14)	0.0295 (5)
C9	0.5207 (4)	0.9530 (3)	0.13816 (14)	0.0317 (5)
H9A	0.5665	1.0766	0.1220	0.038*
H9B	0.6610	0.9029	0.1296	0.038*
C10	0.4613 (4)	0.9650 (3)	0.23628 (14)	0.0318 (5)
H10A	0.3210	1.0151	0.2450	0.038*
H10B	0.4160	0.8416	0.2527	0.038*
C11	0.6721 (4)	1.0840 (3)	0.29756 (14)	0.0335 (5)
H11A	0.7103	1.2091	0.2834	0.040*
H11B	0.8151	1.0385	0.2856	0.040*
C12	0.6235 (4)	1.0890 (3)	0.39634 (15)	0.0410 (6)
H12A	0.4842	1.1386	0.4088	0.049*
H12B	0.5800	0.9635	0.4102	0.049*
C13	0.8384 (5)	1.2031 (4)	0.45713 (16)	0.0548 (7)
H13A	0.7975	1.2008	0.5195	0.082*
H13B	0.8795	1.3285	0.4451	0.082*
H13C	0.9765	1.1536	0.4459	0.082*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.0280 (10)	0.0569 (13)	0.0401 (11)	0.0120 (9)	−0.0066 (8)	−0.0083 (10)
O1	0.0315 (8)	0.0390 (9)	0.0364 (9)	0.0099 (7)	−0.0016 (7)	−0.0069 (7)
O2	0.0281 (9)	0.0604 (11)	0.0541 (11)	0.0168 (8)	−0.0111 (7)	−0.0223 (9)
C1	0.0300 (12)	0.0537 (15)	0.0380 (13)	0.0004 (11)	0.0007 (10)	−0.0003 (11)
C2	0.0305 (11)	0.0324 (12)	0.0336 (12)	0.0080 (9)	−0.0025 (9)	−0.0011 (9)
C3	0.0390 (13)	0.0409 (13)	0.0392 (13)	0.0082 (10)	0.0040 (10)	0.0030 (10)
C4	0.0592 (17)	0.0549 (16)	0.0300 (12)	0.0199 (13)	−0.0033 (12)	0.0019 (11)
C5	0.0488 (16)	0.0467 (15)	0.0431 (14)	0.0134 (12)	−0.0185 (12)	−0.0063 (11)
C6	0.0310 (12)	0.0369 (13)	0.0487 (14)	0.0056 (10)	−0.0071 (10)	0.0006 (11)
C7	0.0300 (12)	0.0365 (12)	0.0365 (12)	0.0067 (9)	−0.0026 (9)	0.0014 (10)
C8	0.0260 (11)	0.0302 (11)	0.0297 (11)	0.0048 (9)	−0.0014 (8)	0.0024 (9)
C9	0.0249 (11)	0.0343 (12)	0.0323 (11)	0.0050 (9)	−0.0017 (9)	−0.0003 (9)
C10	0.0268 (11)	0.0329 (12)	0.0324 (11)	0.0046 (9)	−0.0017 (9)	0.0009 (9)
C11	0.0301 (11)	0.0341 (12)	0.0318 (11)	0.0035 (9)	−0.0029 (9)	0.0013 (9)
C12	0.0392 (13)	0.0440 (14)	0.0332 (12)	0.0027 (11)	−0.0027 (10)	0.0016 (10)
C13	0.0500 (16)	0.0684 (19)	0.0341 (13)	0.0016 (14)	−0.0057 (12)	−0.0016 (13)

Geometric parameters (Å, º) top

N1—C1	1.447 (3)	C6—H6	0.9500
N1—H1A	0.9100	C7—H7	0.9500
N1—H1B	0.9100	C8—C9	1.520 (3)
N1—H1C	0.9100	C9—C10	1.527 (3)
O1—C8	1.265 (3)	C9—H9A	0.9900
O2—C8	1.248 (3)	C9—H9B	0.9900
C1—C2	1.511 (3)	C10—C11	1.522 (3)
C1—H1D	0.9900	C10—H10A	0.9900
C1—H1E	0.9900	C10—H10B	0.9900
C2—C3	1.388 (3)	C11—C12	1.525 (3)
C2—C7	1.388 (3)	C11—H11A	0.9900
C3—C4	1.383 (3)	C11—H11B	0.9900
C3—H3	0.9500	C12—C13	1.522 (3)
C4—C5	1.378 (4)	C12—H12A	0.9900
C4—H4	0.9500	C12—H12B	0.9900
C5—C6	1.372 (4)	C13—H13A	0.9800
C5—H5	0.9500	C13—H13B	0.9800
C6—C7	1.390 (3)	C13—H13C	0.9800

C1—N1—H1A	109.5	O1—C8—C9	119.66 (18)
C1—N1—H1B	109.5	C8—C9—C10	112.88 (17)
H1A—N1—H1B	109.5	C8—C9—H9A	109.0
C1—N1—H1C	109.5	C10—C9—H9A	109.0
H1A—N1—H1C	109.5	C8—C9—H9B	109.0
H1B—N1—H1C	109.5	C10—C9—H9B	109.0
N1—C1—C2	114.89 (19)	H9A—C9—H9B	107.8
N1—C1—H1D	108.5	C11—C10—C9	112.24 (18)
C2—C1—H1D	108.5	C11—C10—H10A	109.2
N1—C1—H1E	108.5	C9—C10—H10A	109.2
C2—C1—H1E	108.5	C11—C10—H10B	109.2
H1D—C1—H1E	107.5	C9—C10—H10B	109.2
C3—C2—C7	118.7 (2)	H10A—C10—H10B	107.9
C3—C2—C1	117.8 (2)	C10—C11—C12	113.42 (18)
C7—C2—C1	123.4 (2)	C10—C11—H11A	108.9
C4—C3—C2	120.4 (2)	C12—C11—H11A	108.9
C4—C3—H3	119.8	C10—C11—H11B	108.9
C2—C3—H3	119.8	C12—C11—H11B	108.9
C5—C4—C3	120.5 (2)	H11A—C11—H11B	107.7
C5—C4—H4	119.7	C13—C12—C11	113.0 (2)
C3—C4—H4	119.7	C13—C12—H12A	109.0
C6—C5—C4	119.6 (2)	C11—C12—H12A	109.0
C6—C5—H5	120.2	C13—C12—H12B	109.0
C4—C5—H5	120.2	C11—C12—H12B	109.0
C5—C6—C7	120.3 (2)	H12A—C12—H12B	107.8
C5—C6—H6	119.8	C12—C13—H13A	109.5
C7—C6—H6	119.8	C12—C13—H13B	109.5
C2—C7—C6	120.4 (2)	H13A—C13—H13B	109.5
C2—C7—H7	119.8	C12—C13—H13C	109.5
C6—C7—H7	119.8	H13A—C13—H13C	109.5
O2—C8—O1	122.74 (19)	H13B—C13—H13C	109.5
O2—C8—C9	117.60 (19)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1	0.91	1.99	2.890 (3)	169
N1—H1B···O2ⁱ	0.91	1.81	2.705 (3)	169
N1—H1C···O1ⁱⁱ	0.91	1.88	2.769 (3)	164
C1—H1D···O2ⁱⁱⁱ	0.99	2.45	3.366 (3)	154
C7—H7···N1	0.95	2.58	2.902 (3)	100
C7—H7···O1ⁱⁱ	0.95	2.53	3.347 (3)	144

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

Experimental details

Crystal data
Chemical formula	C₇H₁₀N⁺·C₆H₁₁O₂⁻
M_r	223.31
Crystal system, space group	Triclinic, P1
Temperature (K)	180
a, b, c (Å)	5.7730 (3), 7.7465 (4), 15.1707 (8)
α, β, γ (°)	98.318 (3), 90.638 (3), 105.641 (2)
V (Å³)	645.55 (6)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	0.08
Crystal size (mm)	0.37 × 0.25 × 0.02

Data collection
Diffractometer	Nonius Kappa CCD
Absorption correction	Multi-scan (SORTAV; Blessing, 1995)
T_min, T_max	0.824, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	9587, 2915, 1930
R_int	0.060
(sin θ/λ)_max (Å⁻¹)	0.649

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.068, 0.177, 1.04
No. of reflections	2915
No. of parameters	147
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.59, −0.33

Computer programs: COLLECT (Nonius, 1998), DENZO and SCALEPACK (Otwinowski & Minor, 1997), SIR92 (Altomare et al., 1994), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1	0.91	1.99	2.890 (3)	169
N1—H1B···O2ⁱ	0.91	1.81	2.705 (3)	169
N1—H1C···O1ⁱⁱ	0.91	1.88	2.769 (3)	164
C1—H1D···O2ⁱⁱⁱ	0.99	2.45	3.366 (3)	154
C7—H7···N1	0.95	2.58	2.902 (3)	100
C7—H7···O1ⁱⁱ	0.95	2.53	3.347 (3)	144

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

Acknowledgements

The authors thank the Department of Chemistry, the BP Institute and the Oppenheimer Trust for financial and technical assistance, and Dr J. E. Davies for collecting and analysing the X-ray data. Thanks are also due to Professor Mague for help improving the clarity of the figures.

References

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