Powder study of (R)-1-phenyl­ethyl­ammonium (R)-2-phenyl­butyrate form 2

Fernandes, P.; Florence, A.; Shankland, K.; Karamertzanis, P.G.; Hulme, A.T.; Anandamanoharan, P.

doi:10.1107/S1600536806052652

organic compounds

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ISSN: 2056-9890

Volume 63| Part 1| January 2007| Pages o247-o249

https://doi.org/10.1107/S1600536806052652

Powder study of (R)-1-phenylethylammonium (R)-2-phenylbutyrate form 2

Philippe Fernandes,^a Alastair Florence,^a ^* Kenneth Shankland,^b Panagiotis G. Karamertzanis,^c Ashley T. Hulme ^c and Parathay Anandamanoharan ^d

^aSolid-State Research Group, Department of Pharmaceutical Sciences, University of Strathclyde, 27 Taylor Street, Glasgow G4 0NR, Scotland, ^bISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, England, ^cChristopher Ingold Laboratory, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, England, and ^dDepartment of Chemical Engineering, University College London, Torrington Place, London WC1E 7JE, England
^*Correspondence e-mail: alastair.florence@strath.ac.uk

(Received 1 November 2006; accepted 5 December 2006; online 13 December 2006)

The crystal structure of a new polymorph of the title compound, C₈H₁₂N⁺·C₁₀H₁₁O₂⁻, was solved by simulated annealing from laboratory X-ray powder diffraction data, collected at 295 K. Subsequent Rietveld refinement using data collected to 1.54 Å resolution yielded an R_wp of 0.029. The compound crystallized with one (R)-1-phenylethylammonium cation and one (R)-2-phenylbutyrate anion in the asymmetric unit.

Comment

The structure of the title compound, (I), was first reported by Brianso (1978 ), hereafter referred to as form 1. Crystallization from ethanol yielded a second polymorph, which is reported here.

The crystal structure of the new form (form 2) was solved by simulated annealing using laboratory capillary X-ray powder diffraction data. The compound crystallizes in the orthorhombic space group P2₁2₁2₁ with one (R)-1-phenylethylammonium cation and one (R)-2-phenylbutyrate anion in the asymmetric unit (Fig. 1).

The ion pairs in this new polymorph pack to form a hydrogen-bonded ladder parallel to the a axis (Fig. 2). Each ladder consists of R₄³(10) (Etter, 1990 ) hydrogen-bonded rings comprising four alternating ammonium and carboxylate groups linked by N—H⋯O=C contacts (Table 1). O1 forms a bifurcated hydrogen bond to H1NB and H1NC, while O2 forms just one hydrogen bond to H1NA. All strong hydrogen-bond donors and acceptors are satisfied.

Form 1 shows the same hydrogen-bonded ring motif, albeit with different packing of the ladders in the crystal structure. This arises because the orientation of the 2-phenylbutyrate ion with respect to the 1-phenylethylammonium ion is different. Also, the conformation of the terminal methyl group differs between the two forms – adopting a gauche conformation with respect to the carboxylate group in form 2, while in form 1 the groups are in an anti conformation.

Figure 1
The asymmetric unit of (I)

, with the atom-numbering scheme. Displacement spheres are shown at the 50% probability level (Bruker, 2000

). The dashed line indicates a hydrogen bond.

Figure 2
The hydrogen-bonded ladder motif observed in form 2. Atoms not directly involved in hydrogen-bond contacts have been omitted for clarity.

Figure 3
Final observed (points), calculated (line) and difference [(y_obs − y_calc)/σ(y_obs)] profiles for the Rietveld refinement of the title compound.

Experimental

(R)-2-phenylbutyric acid (Lancaster, 97% purity) and (R)-1-phenylethylammine (Alfa Aesar, 99+% purity) were used without further purification. The product was crystallized as a fine powder byevaporation of an ethanol solution with a starting ratio of 2:1 acid:base.

The sample was loaded into a 0.7 mm borosilicate glass capillary and rotated throughout the data collection to minimize preferred orientation effects. Data were collected using a variable count time (VCT) scheme in which the step time is increased with 2θ (Shankland et al., 1997 ; Hill & Madsen, 2002 $[Hill, R. J. & Madsen, I. C. (2002). Structure Determination from Powder Diffraction Data, edited by W. I. F. David, K. Shankland, L. B. McCusker & Ch. Baerlocher, pp. 114-116. Oxford: Oxford University Press.]$ ).

Crystal data

C₈H₁₂N⁺·C₁₀H₁₁O₂⁻
M_r = 285.37
Orthorhombic, P 2₁ 2₁ 2₁
a = 6.0620 (1) Å
b = 16.7794 (3) Å
c = 16.8881 (4) Å
V = 1717.80 (6) Å³
Z = 4
D_x = 1.104 Mg m⁻³
Cu Kα₁ radiation
Wavelength of incident radiation: 1.54056 Å
μ = 0.56 mm⁻¹
T = 295 K
Specimen shape: cylinder
12 × 0.7 × 0.7 mm
Specimen prepared at 380 K
Particle morphology: needle, white

Data collection

Bruker AXS D8 Advance diffractometer
Specimen mounting: 0.7 mm borosilicate capillary
Specimen mounted in transmission mode
Scan method: step
Absorption correction: none
2θ_min = 6.0, 2θ_max = 60.0°
Increment in 2θ = 0.017°

Refinement

R_p = 0.025
R_wp = 0.029
R_exp = 0.015
R_B = 0.022
S = 2.03
Profile function: Fundamental parameters with axial divergence correction.
161 parameters
Only H-atom coordinates refined
w = 1/σ(Y_obs)²
(Δ/σ)_max = 0.005
Preferred orientation correction: A spherical harmonics-based preferred orientation correction (Järvinen, 1993 ) was applied with TOPAS (Coelho, 2003 ) during the Rietveld refinement

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1NA⋯O2	0.964 (5)	1.863 (6)	2.732 (3)	148.5 (5)
N1—H1NB⋯O1ⁱ	0.976 (6)	1.907 (7)	2.744 (3)	142.2 (5)
N1—H1NC⋯O1ⁱⁱ	0.956 (5)	1.932 (7)	2.797 (5)	149.4 (6)
C10—H10⋯O2ⁱⁱⁱ	0.953 (5)	2.492 (6)	3.426 (3)	166.8 (4)
Symmetry codes: (i) x+1, y, z; (ii) $[x+{\script{1\over 2}}, -y+{\script{3\over 2}}, -z]$ ; (iii) x-1, y, z.

The diffraction pattern indexed to a monoclinic cell [M(19) = 30.7, F(19) = 63.0; DICVOL91; Boultif & Louër, 1991 ] and the space group P2₁2₁2₁ was assigned from volume considerations and a statistical consideration of the systematic absences (Markvardsen et al., 2001 ). The data set was background subtracted and truncated to 59.5° 2θ for Pawley fitting (Pawley, 1981 ; χ²_Pawley = 6.10) and the structure solved using the simulated annealing (SA) global optimization procedure, described previously (David et al., 1998 ), that is now implemented in the DASH computer program (David et al., 2001 ). The SA structure solution used 311 reflections and involved the optimization of two fragments totaling 14 degrees of freedom (six positional and orientational for each fragment present in the asymmetric unit plus a torsion angle for each fragment). All degrees of freedom were assigned random values at the start of the simulated annealing. The best SA solution had a favourable χ²_SA/χ²_Pawley ratio of 3.41 and a chemically reasonable packing arrangement, with no significant misfit to the diffraction data.

The solved structure was then refined against the data in the range 6–59.7° 2θ using a restrained Rietveld (1969 ) method as implemented in TOPAS (Coelho, 2003), with R_wp falling to 0.029 during the refinement. All atomic positions (including H atoms) for the structure of (I) were refined, subject to a series of restraints on bond lengths, bond angles and planarity. The refined C—H distances were 0.949 (5)–0.973 (5) Å. U_iso values for H atoms were constrained to equal 0.076 Å².

The restraints were set such that bonds and angles did not deviate more than 0.01 Å and 0.8°, respectively, from their initial values during the refinement. Atoms C16, C15, C14, C13, C18, C17, H16, H15, H14, H18 and H17 (phenylethylammonium) and atoms C5, C6, C7, C8, C9, C10, H6, H7, H8, H9 and H10 (phenylbutyrate) were restrained to lie in respective planar groups. A spherical harmonics (fourth order) correction of intensities for preferred orientation was applied in the final refinement (Järvinen, 1993). The refined final spherical harmonics coefficients were consistent with mild preferred orientation effects in the sample. The observed and calculated diffraction patterns for the refined crystal structure are shown in Fig. 3.

Data collection: DIFFRAC plus XRD Commander (Kienle & Jacob, 2003 ); cell refinement: TOPAS (Coelho, 2003); data reduction: DASH (David et al., 2001); program(s) used to solve structure: DASH; program(s) used to refine structure: TOPAS; molecular graphics: Mercury (Macrae et al., 2006 ) and SHELXTL (Bruker, 2000 ); software used to prepare material for publication: enCIFer (Version 1.1; Allen et al., 2004 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S1600536806052652/ci2215sup1.cif

Rietveld powder data: contains datablock I. DOI: https://doi.org/10.1107/S1600536806052652/ci2215Isup2.rtv

Computing details top

Data collection: DIFFRAC plus XRD Commander (Kienle & Jacob, 2003); cell refinement: TOPAS (Coelho, 2003); data reduction: DASH (David et al., 2001); program(s) used to solve structure: DASH; program(s) used to refine structure: TOPAS; molecular graphics: Mercury (Macrae et al., 2006) and SHELXTL (Bruker, 2000); software used to prepare material for publication: enCIFer (Version 1.1; Allen et al., 2004).

(R)-1-phenylethylammonium (R)-2-phenylbutyrate top

Crystal data top

C₈H₁₂N⁺·C₁₀H₁₁O₂⁻	F(000) = 616.0
M_r = 285.37	D_x = 1.104 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Cu Kα₁ radiation, λ = 1.54056 Å
Hall symbol: P 2ac 2ab	µ = 0.56 mm⁻¹
a = 6.0620 (1) Å	T = 295 K
b = 16.7794 (3) Å	Particle morphology: needles
c = 16.8881 (4) Å	white
V = 1717.80 (6) Å³	cylinder, 12 × 0.7 mm
Z = 4	Specimen preparation: Prepared at 380 K

Data collection top

Bruker AXS D8 Advance diffractometer	Data collection mode: transmission
Radiation source: sealed X-ray tube, Bruker-AXS D8	Scan method: step
Primary focussing, Ge 111 monochromator	2θ_min = 6.0°, 2θ_max = 60.0°, 2θ_step = 0.017°
Specimen mounting: 0.7 mm borosilicate capillary

Refinement top

Least-squares matrix: selected elements only	101 restraints
R_p = 0.025	1 constraint
R_wp = 0.029	Only H-atom coordinates refined
R_exp = 0.015	Weighting scheme based on measured s.u.'s 1/σ(Y_obs)²
R_Bragg = 0.022	(Δ/σ)_max = 0.005
3176 data points	Background function: Chebyshev polynomial
Profile function: Fundamental parameters with axial divergence correction.	Preferred orientation correction: A spherical harmonics-based preferred orientation correction (Järvinen, 1993) was applied with TOPAS (Coelho, 2003) during the Rietveld refinement.
161 parameters

Special details top

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

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

	x	y	z	U_iso*/U_eq
O1	0.0508 (4)	0.71000 (16)	0.0862 (3)	0.0421 (7)*
O2	0.3485 (5)	0.64160 (14)	0.1193 (3)	0.0421 (7)*
C1	0.14750 (17)	0.65000 (8)	0.11781 (10)	0.0421 (7)*
C2	0.00199 (18)	0.58450 (6)	0.14941 (8)	0.0421 (7)*
C3	0.10549 (19)	0.54720 (8)	0.22291 (6)	0.0421 (7)*
C4	0.13261 (15)	0.60880 (5)	0.28920 (5)	0.0421 (7)*
C5	−0.0445 (2)	0.52320 (9)	0.08661 (10)	0.0421 (7)*
C6	0.1146 (2)	0.46661 (10)	0.06781 (8)	0.0421 (7)*
C7	0.07689 (19)	0.41050 (8)	0.00882 (15)	0.0421 (7)*
C8	−0.1161 (3)	0.41261 (12)	−0.03600 (16)	0.0421 (7)*
C9	−0.2746 (2)	0.46912 (13)	−0.01690 (18)	0.0421 (7)*
C10	−0.2409 (2)	0.52330 (8)	0.04430 (9)	0.0421 (7)*
N1	0.62344 (14)	0.76268 (5)	0.07509 (5)	0.0421 (7)*
C11	0.78013 (14)	0.89484 (5)	0.10073 (6)	0.0421 (7)*
C12	0.58697 (19)	0.83985 (7)	0.11586 (7)	0.0421 (7)*
C13	0.54484 (18)	0.82600 (11)	0.20304 (8)	0.0421 (7)*
C14	0.70957 (17)	0.79300 (11)	0.25178 (6)	0.0421 (7)*
C15	0.66760 (18)	0.78130 (10)	0.33136 (6)	0.0421 (7)*
C16	0.46837 (18)	0.80664 (12)	0.36380 (6)	0.0421 (7)*
C17	0.30689 (18)	0.83888 (11)	0.31627 (6)	0.0421 (7)*
C18	0.34622 (17)	0.84983 (10)	0.23623 (7)	0.0421 (7)*
H2	−0.1337 (9)	0.6075 (3)	0.1667 (3)	0.0760*
H3A	0.0084 (7)	0.5056 (3)	0.2389 (3)	0.0760*
H3B	0.2445 (10)	0.5257 (3)	0.2071 (3)	0.0760*
H4A	−0.0122 (8)	0.6269 (3)	0.3047 (3)	0.0760*
H4B	0.2255 (8)	0.6525 (3)	0.2712 (3)	0.0760*
H4C	0.1912 (9)	0.5830 (3)	0.3361 (3)	0.0760*
H6	0.2528 (8)	0.4653 (3)	0.0942 (3)	0.0760*
H7	0.1872 (7)	0.3724 (2)	−0.0051 (3)	0.0760*
H8	−0.1355 (9)	0.3764 (3)	−0.0787 (3)	0.0760*
H9	−0.4167 (8)	0.4686 (2)	−0.0417 (3)	0.0760*
H10	−0.3532 (8)	0.5609 (3)	0.0570 (3)	0.0760*
H1NA	0.4916 (9)	0.7307 (3)	0.0781 (3)	0.0760*
H1NB	0.7429 (10)	0.7305 (3)	0.0970 (3)	0.0760*
H1NC	0.6548 (12)	0.7730 (3)	0.0206 (3)	0.0760*
H11A	0.7480 (8)	0.9464 (3)	0.1241 (3)	0.0760*
H11B	0.9131 (9)	0.8714 (3)	0.1224 (3)	0.0760*
H11C	0.7980 (7)	0.9015 (3)	0.0449 (3)	0.0760*
H12	0.4565 (9)	0.8623 (3)	0.0938 (3)	0.0760*
H14	0.8497 (10)	0.7792 (3)	0.2291 (3)	0.0760*
H15	0.7892 (12)	0.7620 (3)	0.3634 (3)	0.0760*
H16	0.4371 (11)	0.7971 (3)	0.4182 (3)	0.0760*
H17	0.1700 (9)	0.8569 (3)	0.3396 (3)	0.0760*
H18	0.2294 (9)	0.8672 (3)	0.2010 (3)	0.0760*

Geometric parameters (Å, º) top

O1—C1	1.282 (3)	C6—H6	0.949 (5)
O2—C1	1.227 (3)	C7—H7	0.955 (4)
N1—C12	1.4831 (14)	C8—H8	0.950 (6)
N1—H1NC	0.956 (5)	C9—H9	0.958 (5)
N1—H1NA	0.964 (5)	C10—H10	0.953 (5)
N1—H1NB	0.976 (6)	C11—C12	1.5125 (14)
C1—C2	1.5069 (17)	C12—C13	1.5123 (18)
C2—C3	1.5252 (17)	C13—C18	1.3870 (17)
C2—C5	1.504 (2)	C13—C14	1.4076 (18)
C3—C4	1.5326 (14)	C14—C15	1.3818 (15)
C5—C6	1.390 (2)	C15—C16	1.3927 (17)
C5—C10	1.3885 (19)	C16—C17	1.3767 (17)
C6—C7	1.390 (3)	C17—C18	1.3848 (16)
C7—C8	1.394 (3)	C11—H11A	0.971 (5)
C8—C9	1.388 (3)	C11—H11B	0.969 (5)
C9—C10	1.392 (3)	C11—H11C	0.956 (5)
C2—H2	0.954 (5)	C12—H12	0.952 (5)
C3—H3B	0.955 (6)	C14—H14	0.960 (6)
C3—H3A	0.952 (5)	C15—H15	0.970 (7)
C4—H4A	0.965 (5)	C16—H16	0.952 (5)
C4—H4B	0.973 (5)	C17—H17	0.967 (5)
C4—H4C	0.970 (5)	C18—H18	0.970 (5)

H1NA—N1—H1NB	106.7 (5)	C8—C7—H7	118.1 (3)
H1NA—N1—H1NC	108.5 (5)	C9—C8—H8	121.8 (4)
H1NB—N1—H1NC	108.5 (5)	C7—C8—H8	120.0 (4)
C12—N1—H1NC	108.6 (3)	C10—C9—H9	117.6 (3)
C12—N1—H1NA	109.8 (3)	C8—C9—H9	121.0 (3)
C12—N1—H1NB	114.7 (3)	C5—C10—H10	119.9 (3)
O2—C1—C2	119.36 (18)	C9—C10—H10	119.7 (3)
O1—C1—O2	123.6 (2)	C11—C12—C13	112.89 (10)
O1—C1—C2	116.92 (14)	N1—C12—C13	110.06 (11)
C1—C2—C3	110.29 (10)	N1—C12—C11	109.80 (9)
C3—C2—C5	111.74 (10)	C12—C13—C14	120.66 (10)
C1—C2—C5	111.02 (12)	C12—C13—C18	119.72 (11)
C2—C3—C4	111.22 (10)	C14—C13—C18	119.53 (12)
C6—C5—C10	118.57 (14)	C13—C14—C15	119.61 (11)
C2—C5—C6	119.88 (12)	C14—C15—C16	119.93 (11)
C2—C5—C10	121.51 (12)	C15—C16—C17	120.48 (10)
C5—C6—C7	120.82 (12)	C16—C17—C18	119.92 (10)
C6—C7—C8	120.68 (14)	C13—C18—C17	120.38 (12)
C7—C8—C9	118.2 (2)	C12—C11—H11A	108.6 (3)
C8—C9—C10	121.15 (17)	C12—C11—H11B	109.4 (3)
C5—C10—C9	120.48 (13)	C12—C11—H11C	109.0 (3)
C5—C2—H2	109.3 (3)	H11A—C11—H11B	112.0 (4)
C1—C2—H2	108.5 (3)	H11A—C11—H11C	108.6 (4)
C3—C2—H2	105.8 (3)	H11B—C11—H11C	109.0 (4)
C2—C3—H3A	106.1 (3)	N1—C12—H12	106.7 (3)
C2—C3—H3B	106.9 (3)	C11—C12—H12	109.6 (3)
C4—C3—H3A	110.7 (3)	C13—C12—H12	107.6 (3)
C4—C3—H3B	111.4 (3)	C13—C14—H14	119.3 (3)
H3A—C3—H3B	110.4 (4)	C15—C14—H14	121.1 (3)
H4A—C4—H4B	112.0 (4)	C14—C15—H15	116.8 (4)
H4A—C4—H4C	104.6 (4)	C16—C15—H15	122.8 (4)
C3—C4—H4C	109.6 (3)	C15—C16—H16	120.1 (4)
C3—C4—H4A	108.2 (3)	C17—C16—H16	119.2 (4)
C3—C4—H4B	110.0 (3)	C16—C17—H17	119.7 (3)
H4B—C4—H4C	112.3 (4)	C18—C17—H17	120.3 (3)
C7—C6—H6	117.8 (3)	C13—C18—H18	118.2 (3)
C5—C6—H6	121.4 (3)	C17—C18—H18	120.9 (3)
C6—C7—H7	121.0 (3)

O1—C1—C2—C5	89.7 (3)	C7—C8—C9—C10	1.2 (3)
O2—C1—C2—C3	38.2 (3)	C8—C9—C10—C5	1.5 (3)
O2—C1—C2—C5	−86.2 (3)	N1—C12—C13—C14	64.12 (18)
C1—C2—C3—C4	61.18 (12)	N1—C12—C13—C18	−119.26 (15)
C5—C2—C3—C4	−174.82 (9)	C11—C12—C13—C14	−58.95 (19)
C1—C2—C5—C6	78.06 (16)	C11—C12—C13—C18	117.68 (14)
C1—C2—C5—C10	−99.50 (15)	C12—C13—C14—C15	179.65 (15)
C3—C2—C5—C6	−45.52 (17)	C18—C13—C14—C15	3.0 (3)
C3—C2—C5—C10	136.93 (14)	C12—C13—C18—C17	−178.80 (14)
C2—C5—C6—C7	−178.62 (15)	C14—C13—C18—C17	−2.1 (3)
C10—C5—C6—C7	−1.0 (2)	C13—C14—C15—C16	−4.0 (3)
C2—C5—C10—C9	175.95 (16)	C14—C15—C16—C17	4.0 (3)
C6—C5—C10—C9	−1.6 (2)	C15—C16—C17—C18	−3.1 (3)
C5—C6—C7—C8	3.8 (3)	C16—C17—C18—C13	2.2 (3)
C6—C7—C8—C9	−3.8 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1NA···O2	0.964 (5)	1.863 (6)	2.732 (3)	148.5 (5)
N1—H1NB···O1ⁱ	0.976 (6)	1.907 (7)	2.744 (3)	142.2 (5)
N1—H1NC···O1ⁱⁱ	0.956 (5)	1.932 (7)	2.797 (5)	149.4 (6)
C10—H10···O2ⁱⁱⁱ	0.953 (5)	2.492 (6)	3.426 (3)	166.8 (4)

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

Acknowledgements

We thank the Basic Technology programme of the UK Research Councils for funding under the project Control and Prediction of the Organic Solid State (https://www.cposs.org.uk).

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