organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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

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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 Rwp 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)[link], was first reported by Brianso (1978[Brianso, M.-C. (1978). Acta Cryst. B34, 679-680.]), hereafter referred to as form 1. Crystallization from ethanol yielded a second polymorph, which is reported here.

[Scheme 1]

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[link]).

The ion pairs in this new polymorph pack to form a hydrogen-bonded ladder parallel to the a axis (Fig. 2[link]). Each ladder consists of R43(10) (Etter, 1990[Etter, M. C. (1990). Acc. Chem. Res. 23, 120-126.]) hydrogen-bonded rings comprising four alternating ammonium and carboxyl­ate groups linked by N—H⋯O=C contacts (Table 1[link]). 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]
Figure 1
The asymmetric unit of (I)[link], with the atom-numbering scheme. Displacement spheres are shown at the 50% probability level (Bruker, 2000[Bruker (2000). SHELXTL. Version 6.10. Bruker AXS Inc., Madison, Wisconsin, USA.]). The dashed line indicates a hydrogen bond.
[Figure 2]
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]
Figure 3
Final observed (points), calculated (line) and difference [(yobsycalc)/σ(yobs)] 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[Shankland, K., David, W. I. F. & Sivia, D. S. (1997). J. Mater. Chem. 7, 569-572.]; 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

  • Mr = 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

  • Dx = 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

  • 2θmin = 6.0, 2θmax = 60.0°

  • Increment in 2θ = 0.017°

Refinement
  • Rp = 0.025

  • Rwp = 0.029

  • Rexp = 0.015

  • RB = 0.022

  • S = 2.03

  • Profile function: Fundamental parameters with axial divergence correction.

  • 161 parameters

  • Only H-atom coordinates refined

  • w = 1/σ(Yobs)2

  • (Δ/σ)max = 0.005

  • Preferred orientation correction: A spherical harmonics-based preferred orientation correction (Järvinen, 1993[Järvinen, M. (1993). J. Appl. Cryst. 26, 525-531.]) was applied with TOPAS (Coelho, 2003[Coelho, A. A. (2003). TOPAS User Manual. Version 3.1. Bruker AXS GmbH, Karlsruhe, Germany.]) during the Rietveld refinement

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA 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[Boultif, A. & Louër, D. (1991). J. Appl. Cryst. 24, 987-993.]] and the space group P212121 was assigned from volume considerations and a statistical consideration of the systematic absences (Markvardsen et al., 2001[Markvardsen, A. J., David, W. I. F., Johnson, J. C. & Shankland, K. (2001). Acta Cryst. A57, 47-54.]). The data set was background subtracted and truncated to 59.5° 2θ for Pawley fitting (Pawley, 1981[Pawley, G. S. (1981). J. Appl. Cryst. 14, 357-361.]; χ2Pawley = 6.10) and the structure solved using the simulated annealing (SA) global optimization procedure, described previously (David et al., 1998[David, W. I. F., Shankland, K. & Shankland, N. (1998). Chem. Commun. pp. 931-932.]), that is now implemented in the DASH computer program (David et al., 2001[David, W. I. F., Shankland, K., Cole, J., Maginn, S., Motherwell, W. D. S. & Taylor, R. (2001). DASH. Version 3.0 User Manual. Cambridge Crystallographic Data Centre, Cambridge, England.]). 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 χ2SA/χ2Pawley 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[Rietveld, H. M. (1969). J. Appl. Cryst. 2, 65-71.]) method as implemented in TOPAS (Coelho, 2003[Coelho, A. A. (2003). TOPAS User Manual. Version 3.1. Bruker AXS GmbH, Karlsruhe, Germany.]), with Rwp falling to 0.029 during the refinement. All atomic positions (including H atoms) for the structure of (I)[link] 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. Uiso 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[Järvinen, M. (1993). J. Appl. Cryst. 26, 525-531.]). 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[link].

Data collection: DIFFRAC plus XRD Commander (Kienle & Jacob, 2003[Kienle, M. & Jacob, M. (2003). DIFFRAC plus XRD Commander. Version 2.3. Bruker AXS GmbH, Karlsruhe, Germany.]); cell refinement: TOPAS (Coelho, 2003[Coelho, A. A. (2003). TOPAS User Manual. Version 3.1. Bruker AXS GmbH, Karlsruhe, Germany.]); data reduction: DASH (David et al., 2001[David, W. I. F., Shankland, K., Cole, J., Maginn, S., Motherwell, W. D. S. & Taylor, R. (2001). DASH. Version 3.0 User Manual. Cambridge Crystallographic Data Centre, Cambridge, England.]); program(s) used to solve structure: DASH; program(s) used to refine structure: TOPAS; molecular graphics: Mercury (Macrae et al., 2006[Macrae, C. F., Edgington, P. R., McCabe, P., Pidcock, E., Shields, G. P., Taylor, R., Towler, M. & van de Streek, J. (2006). J. Appl. Cryst. 39, 453-457.]) and SHELXTL (Bruker, 2000[Bruker (2000). SHELXTL. Version 6.10. Bruker AXS Inc., Madison, Wisconsin, USA.]); software used to prepare material for publication: enCIFer (Version 1.1; Allen et al., 2004[Allen, F. H., Johnson, O., Shields, G. P., Smith, B. R. & Towler, M. (2004). J. Appl. Cryst. 37, 335-338.]).

Supporting information


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+·C10H11O2F(000) = 616.0
Mr = 285.37Dx = 1.104 Mg m3
Orthorhombic, P212121Cu Kα1 radiation, λ = 1.54056 Å
Hall symbol: P 2ac 2abµ = 0.56 mm1
a = 6.0620 (1) ÅT = 295 K
b = 16.7794 (3) ÅParticle morphology: needles
c = 16.8881 (4) Åwhite
V = 1717.80 (6) Å3cylinder, 12 × 0.7 mm
Z = 4Specimen 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 D8Scan method: step
Primary focussing, Ge 111 monochromator2θmin = 6.0°, 2θmax = 60.0°, 2θstep = 0.017°
Specimen mounting: 0.7 mm borosilicate capillary
Refinement top
Least-squares matrix: selected elements only101 restraints
Rp = 0.0251 constraint
Rwp = 0.029Only H-atom coordinates refined
Rexp = 0.015Weighting scheme based on measured s.u.'s 1/σ(Yobs)2
RBragg = 0.022(Δ/σ)max = 0.005
3176 data pointsBackground 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
xyzUiso*/Ueq
O10.0508 (4)0.71000 (16)0.0862 (3)0.0421 (7)*
O20.3485 (5)0.64160 (14)0.1193 (3)0.0421 (7)*
C10.14750 (17)0.65000 (8)0.11781 (10)0.0421 (7)*
C20.00199 (18)0.58450 (6)0.14941 (8)0.0421 (7)*
C30.10549 (19)0.54720 (8)0.22291 (6)0.0421 (7)*
C40.13261 (15)0.60880 (5)0.28920 (5)0.0421 (7)*
C50.0445 (2)0.52320 (9)0.08661 (10)0.0421 (7)*
C60.1146 (2)0.46661 (10)0.06781 (8)0.0421 (7)*
C70.07689 (19)0.41050 (8)0.00882 (15)0.0421 (7)*
C80.1161 (3)0.41261 (12)0.03600 (16)0.0421 (7)*
C90.2746 (2)0.46912 (13)0.01690 (18)0.0421 (7)*
C100.2409 (2)0.52330 (8)0.04430 (9)0.0421 (7)*
N10.62344 (14)0.76268 (5)0.07509 (5)0.0421 (7)*
C110.78013 (14)0.89484 (5)0.10073 (6)0.0421 (7)*
C120.58697 (19)0.83985 (7)0.11586 (7)0.0421 (7)*
C130.54484 (18)0.82600 (11)0.20304 (8)0.0421 (7)*
C140.70957 (17)0.79300 (11)0.25178 (6)0.0421 (7)*
C150.66760 (18)0.78130 (10)0.33136 (6)0.0421 (7)*
C160.46837 (18)0.80664 (12)0.36380 (6)0.0421 (7)*
C170.30689 (18)0.83888 (11)0.31627 (6)0.0421 (7)*
C180.34622 (17)0.84983 (10)0.23623 (7)0.0421 (7)*
H20.1337 (9)0.6075 (3)0.1667 (3)0.0760*
H3A0.0084 (7)0.5056 (3)0.2389 (3)0.0760*
H3B0.2445 (10)0.5257 (3)0.2071 (3)0.0760*
H4A0.0122 (8)0.6269 (3)0.3047 (3)0.0760*
H4B0.2255 (8)0.6525 (3)0.2712 (3)0.0760*
H4C0.1912 (9)0.5830 (3)0.3361 (3)0.0760*
H60.2528 (8)0.4653 (3)0.0942 (3)0.0760*
H70.1872 (7)0.3724 (2)0.0051 (3)0.0760*
H80.1355 (9)0.3764 (3)0.0787 (3)0.0760*
H90.4167 (8)0.4686 (2)0.0417 (3)0.0760*
H100.3532 (8)0.5609 (3)0.0570 (3)0.0760*
H1NA0.4916 (9)0.7307 (3)0.0781 (3)0.0760*
H1NB0.7429 (10)0.7305 (3)0.0970 (3)0.0760*
H1NC0.6548 (12)0.7730 (3)0.0206 (3)0.0760*
H11A0.7480 (8)0.9464 (3)0.1241 (3)0.0760*
H11B0.9131 (9)0.8714 (3)0.1224 (3)0.0760*
H11C0.7980 (7)0.9015 (3)0.0449 (3)0.0760*
H120.4565 (9)0.8623 (3)0.0938 (3)0.0760*
H140.8497 (10)0.7792 (3)0.2291 (3)0.0760*
H150.7892 (12)0.7620 (3)0.3634 (3)0.0760*
H160.4371 (11)0.7971 (3)0.4182 (3)0.0760*
H170.1700 (9)0.8569 (3)0.3396 (3)0.0760*
H180.2294 (9)0.8672 (3)0.2010 (3)0.0760*
Geometric parameters (Å, º) top
O1—C11.282 (3)C6—H60.949 (5)
O2—C11.227 (3)C7—H70.955 (4)
N1—C121.4831 (14)C8—H80.950 (6)
N1—H1NC0.956 (5)C9—H90.958 (5)
N1—H1NA0.964 (5)C10—H100.953 (5)
N1—H1NB0.976 (6)C11—C121.5125 (14)
C1—C21.5069 (17)C12—C131.5123 (18)
C2—C31.5252 (17)C13—C181.3870 (17)
C2—C51.504 (2)C13—C141.4076 (18)
C3—C41.5326 (14)C14—C151.3818 (15)
C5—C61.390 (2)C15—C161.3927 (17)
C5—C101.3885 (19)C16—C171.3767 (17)
C6—C71.390 (3)C17—C181.3848 (16)
C7—C81.394 (3)C11—H11A0.971 (5)
C8—C91.388 (3)C11—H11B0.969 (5)
C9—C101.392 (3)C11—H11C0.956 (5)
C2—H20.954 (5)C12—H120.952 (5)
C3—H3B0.955 (6)C14—H140.960 (6)
C3—H3A0.952 (5)C15—H150.970 (7)
C4—H4A0.965 (5)C16—H160.952 (5)
C4—H4B0.973 (5)C17—H170.967 (5)
C4—H4C0.970 (5)C18—H180.970 (5)
H1NA—N1—H1NB106.7 (5)C8—C7—H7118.1 (3)
H1NA—N1—H1NC108.5 (5)C9—C8—H8121.8 (4)
H1NB—N1—H1NC108.5 (5)C7—C8—H8120.0 (4)
C12—N1—H1NC108.6 (3)C10—C9—H9117.6 (3)
C12—N1—H1NA109.8 (3)C8—C9—H9121.0 (3)
C12—N1—H1NB114.7 (3)C5—C10—H10119.9 (3)
O2—C1—C2119.36 (18)C9—C10—H10119.7 (3)
O1—C1—O2123.6 (2)C11—C12—C13112.89 (10)
O1—C1—C2116.92 (14)N1—C12—C13110.06 (11)
C1—C2—C3110.29 (10)N1—C12—C11109.80 (9)
C3—C2—C5111.74 (10)C12—C13—C14120.66 (10)
C1—C2—C5111.02 (12)C12—C13—C18119.72 (11)
C2—C3—C4111.22 (10)C14—C13—C18119.53 (12)
C6—C5—C10118.57 (14)C13—C14—C15119.61 (11)
C2—C5—C6119.88 (12)C14—C15—C16119.93 (11)
C2—C5—C10121.51 (12)C15—C16—C17120.48 (10)
C5—C6—C7120.82 (12)C16—C17—C18119.92 (10)
C6—C7—C8120.68 (14)C13—C18—C17120.38 (12)
C7—C8—C9118.2 (2)C12—C11—H11A108.6 (3)
C8—C9—C10121.15 (17)C12—C11—H11B109.4 (3)
C5—C10—C9120.48 (13)C12—C11—H11C109.0 (3)
C5—C2—H2109.3 (3)H11A—C11—H11B112.0 (4)
C1—C2—H2108.5 (3)H11A—C11—H11C108.6 (4)
C3—C2—H2105.8 (3)H11B—C11—H11C109.0 (4)
C2—C3—H3A106.1 (3)N1—C12—H12106.7 (3)
C2—C3—H3B106.9 (3)C11—C12—H12109.6 (3)
C4—C3—H3A110.7 (3)C13—C12—H12107.6 (3)
C4—C3—H3B111.4 (3)C13—C14—H14119.3 (3)
H3A—C3—H3B110.4 (4)C15—C14—H14121.1 (3)
H4A—C4—H4B112.0 (4)C14—C15—H15116.8 (4)
H4A—C4—H4C104.6 (4)C16—C15—H15122.8 (4)
C3—C4—H4C109.6 (3)C15—C16—H16120.1 (4)
C3—C4—H4A108.2 (3)C17—C16—H16119.2 (4)
C3—C4—H4B110.0 (3)C16—C17—H17119.7 (3)
H4B—C4—H4C112.3 (4)C18—C17—H17120.3 (3)
C7—C6—H6117.8 (3)C13—C18—H18118.2 (3)
C5—C6—H6121.4 (3)C17—C18—H18120.9 (3)
C6—C7—H7121.0 (3)
O1—C1—C2—C589.7 (3)C7—C8—C9—C101.2 (3)
O2—C1—C2—C338.2 (3)C8—C9—C10—C51.5 (3)
O2—C1—C2—C586.2 (3)N1—C12—C13—C1464.12 (18)
C1—C2—C3—C461.18 (12)N1—C12—C13—C18119.26 (15)
C5—C2—C3—C4174.82 (9)C11—C12—C13—C1458.95 (19)
C1—C2—C5—C678.06 (16)C11—C12—C13—C18117.68 (14)
C1—C2—C5—C1099.50 (15)C12—C13—C14—C15179.65 (15)
C3—C2—C5—C645.52 (17)C18—C13—C14—C153.0 (3)
C3—C2—C5—C10136.93 (14)C12—C13—C18—C17178.80 (14)
C2—C5—C6—C7178.62 (15)C14—C13—C18—C172.1 (3)
C10—C5—C6—C71.0 (2)C13—C14—C15—C164.0 (3)
C2—C5—C10—C9175.95 (16)C14—C15—C16—C174.0 (3)
C6—C5—C10—C91.6 (2)C15—C16—C17—C183.1 (3)
C5—C6—C7—C83.8 (3)C16—C17—C18—C132.2 (3)
C6—C7—C8—C93.8 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1NA···O20.964 (5)1.863 (6)2.732 (3)148.5 (5)
N1—H1NB···O1i0.976 (6)1.907 (7)2.744 (3)142.2 (5)
N1—H1NC···O1ii0.956 (5)1.932 (7)2.797 (5)149.4 (6)
C10—H10···O2iii0.953 (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) x1, 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).

References

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