organic compounds
Pamoic acid determined from powder diffraction data
aUniversity Chemical Laboratory, Lensfield Road, Cambridge CB2 1EW, England, and bCambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, England
*Correspondence e-mail: jb442@cam.ac.uk
The title compound [systematic name: 4,4′-methylenebis(3-hydroxy-2-naphthoic acid)], C23H16O6, has one half-molecule in the The molecular twofold rotational axis about the central C atom is preserved on crystallization. A chain formed by R22(8) hydrogen bonds runs along the c axis and an intramolecular O—H⋯O=C—OH hydrogen bond is also formed. The was solved by simulated annealing from laboratory X-ray powder diffraction data, with data collected at room temperature. of this model led to a final Rwp value of 0.0391 at 1.39 Å resolution.
Comment
The title compound, (I), is used in the pharmaceutical industry as a counter-ion to obtain long-acting formulations of certain basic drugs (Jorgensen, 1998), and is also of fundamental interest because of the possibility of extensive hydrogen bonding in the solid state. Attempts have been made to grow single crystals of pamoic acid for (Blackburn et al., 1996, Haynes et al., 2005) but these have proved unsuccessful; thus we have employed X-ray powder diffraction to solve and refine the which is reported here for the first time.
The compound crystallizes in the C2/c with one half-molecule of pamoic acid in the (Fig. 1). A twofold rotation axis passes through C1. The –OH and –CO2H groups lie in the plane of the attached ring.
A corrugated chain of molecules running along the c axis is formed by intermolecular R22(8) hydrogen bonds (Fig. 2a). The hydrogen bonds themselves are oriented at approximately 45° to the chain propagation vector (Fig. 2b). Other than hydrogen bonding, the only short intermolecular contact (less than the sum of the van der Waals radii) is an aromatic C—H⋯π interaction (symmetry code: ½ − x, ½ + y, − z) between H10 and C10 of 2.684 (8) Å, which can be compared with the van der Waals distance of 2.9 Å. Of 48362 short aromatic–aromatic C—H⋯π contacts in the Cambridge Structural Database (CSD; Version 5.26 of November 2005; Allen, 2002), only 624 (1.3%) are as short or shorter; the median is 2.837 Å. The bis-pyridinium salt of pamoic acid (CSD refcode TABMAK; Blackburn et al., 1996) exhibits a similar C—H⋯π distance of 2.646 Å, although between a different pair of atoms. This type of contact may therefore play a role in stabilizing the observed crystal structures in pamoic acid derivatives; however, further work will be necessary to confirm this.
Experimental
Pamoic acid (97%+) was obtained from Sigma and used without further purification. No impurities were detected by X-ray powder diffraction. The sample was lightly ground and loaded into a 0.7 mm-diameter Lindemann glass capillary. Data were collected in Debye–Scherrer geometry employing Co Kα1 radiation.
Crystal data
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Data collection
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Refinement
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As noted in _pd_proc_ls_special_details, the
was characterised by a relatively shallow minimum with respect to the lattice parameters and which were refined for the final cycle to generate s.u.'s..Two powder diffraction patterns were collected. Initially a pattern was collected using a Philips Xpert diffractometer operating in Bragg–Brentano mode with a flat-plate sample. No monochromation or collimation was employed. A full pattern was collected in under five minutes; this was used to solve the
Subsequent attempts to use this pattern in a Rietveld analysis were not successful owing to difficulties in modelling the diffraction peak shapes from the high-intensity operation mode. Thus a second pattern was collected for approximately 24 h using a monochromatic Stoe Stadi-P instrument operating in Debye–Scherrer geometry with the sample contained in a glass capillary. The resulting pattern proved suitable for a full Rietveld analysis.The initial X-ray powder diffraction pattern was used for DASH (David et al., 2004). The powder pattern was truncated to 45.3° 2θ (Cu Kα), corresponding to a real-space resolution of 2.0 Å. The background was subtracted with a Bayesian high-pass filter (David & Sivia, 2001). Peak positions for indexing were obtained by fitting with an asymmetry-corrected Voigt function, followed by indexing with the program DICVOL (Boultif & Louer, 1991). Pawley was used to extract integrated intensities and their correlations, from which the was determined using Bayesian statistical analysis (Markvardsen et al., 2001). Possible space groups were Cc or C2/c, the latter implying that the molecule sits on a special position; both space groups were tried. Simulated annealing was used to solve the from the powder pattern in The starting molecular geometry was taken from entry TABMAK (Blackburn et al., 1996) from the CSD. When choosing Cc as the the consists of a full pamoic acid molecule, which then has four independent flexible torsions, one for each of the two carboxylic acid groups and two across the central C atom. All these four torsion angles were left fully flexible during the simulated annealing, which, combined with three translational and three rotational gives a total of ten When choosing C2/c as the the pamoic acid molecule is constrained by symmetry to sit on a twofold rotation axis through the central C atom, C1. Suitable constraints for atom C1 were therefore included in the simulated annealing runs for that namely fixing its x coordinate at 1/2, fixing its z coordinate at 3/4 and setting its occupancy to 0.5 to account for site multiplicity. Imposing these constraints reduces the number of from ten to five. The background subtraction, indexing, Pawley space-group determination and simulated annealing algorithms used are as implemented in the program DASH. With the default settings for the simulated annealing, ten simulated annealing runs for each of both space groups readily yielded ten identical crystal structures. The two space groups Cc and C2/c gave identical crystal structures with comparable figures of merit, indicating that the higher-symmetry was the correct one, and was carried out in C2/c only. Suitable constraints were imposed on bond lengths, angles and planar groups, including bonds to H atoms. The CH and CH2 C—H distances were constrained to be 0.93 and 0.97 Å respectively, with C—C and C—O contraints taken from CSD entry TABMAK (Blackburn et al., 1996). The (Fig. 3), using the GSAS software suite (Larson & Von Dreele, 2000), converged readily to yield acceptable figures of merit (χ2 = 1.425, Rp = 0.0298 and Rwp = 0.0392) and a chemically reasonable structural model. An overall isotropic displacement parameter was employed to model the entire molecule. Standard deviations are taken from the program employed and represent statistical uncertainties rather than estimates of the absolute error, which are likely to be considerably greater.
with the programData collection: WinXPow (Stoe & Cie, 1999); cell GSAS (Larson & Von Dreele, 2000); program(s) used to solve structure: DASH (David et al., 2004); program(s) used to refine structure: GSAS; molecular graphics: PLATON (Spek, 2003).
Supporting information
https://doi.org/10.1107/S1600536806005812/cv6632sup1.cif
contains datablocks global, I. DOI:Rietveld powder data: contains datablock I. DOI: https://doi.org/10.1107/S1600536806005812/cv6632Isup2.rtv
Data collection: Stoe Software (Stoe & Cie, 2002); cell
GSAS (Larson & Von Dreele, 2000); program(s) used to solve structure: DASH (David et al., 2004); program(s) used to refine structure: GSAS; molecular graphics: PLATON (Spek, 2003).C23H16O6 | Z = 4 |
Mr = 388.37 | F(000) = 808.0 |
Monoclinic, C2/c | Dx = 1.499 Mg m−3 |
Hall symbol: -C 2yc | Co Kα1 radiation, λ = 1.78892 Å |
a = 19.7348 (7) Å | µ = 2.19 mm−1 |
b = 4.78768 (12) Å | T = 298 K |
c = 19.2544 (4) Å | yellow |
β = 108.9622 (17)° | cylinder, 12 × 0.7 mm |
V = 1720.5 (1) Å3 | Specimen preparation: Prepared at 298 K |
Stoe linear PSD diffractometer | Data collection mode: transmission |
Radiation source: sealed X-ray tube, Stoe STADI-P | Scan method: step |
Primary focussing, Ge 111 monochromator | 2θmin = 2.0°, 2θmax = 79.99°, 2θstep = 0.01° |
Specimen mounting: 0.7 mm Lindemann glass capillary |
Refinement on Inet | 98 parameters |
Least-squares matrix: selected elements only | 82 restraints |
Rp = 0.030 | H-atom parameters constrained |
Rwp = 0.039 | Weighting scheme based on measured s.u.'s 1/σ(Yobs)2 |
Rexp = 0.035 | (Δ/σ)max = 1.61 |
R(F2) = 0.07174 | Background function: Chebyshev polynomial |
7199 data points | Preferred orientation correction: none |
Profile function: pseudo_Voigt (Thompson et al., 1987) with the asymmetry correction (Finger et al., 1994) |
Refinement. CW Profile function number 3 with 19 terms Pseudovoigt profile coefficients as parameterized in P. Thompson, D·E. Cox & J·B. Hastings (1987). J. Appl. Cryst.,20,79–83. Asymmetry correction of L·W. Finger, D·E. Cox & A. P. Jephcoat (1994). J. Appl. Cryst.,27,892–900. #1(GU) = 77.113 #2(GV) = 62.885 #3(GW) = 0.872 #4(GP) = 0.000 #5(LX) = 4.481 #6(LY) = 0.000 #7(S/L) = 0.0130 #8(H/L) = 0.0430 #9(trns) = 0.00 #10(shft)= 0.0000 #11(stec)= 0.00 #12(ptec)= 0.00 #13(sfec)= 0.00 #14(L11) = 0.000 #15(L22) = 0.000 #16(L33) = 0.000 #17(L12) = 0.000 #18(L13) = 0.000 #19(L23) = 0.000 Peak tails are ignored where the intensity is below 0.0010 times the peak |
x | y | z | Uiso*/Ueq | ||
C1 | 0.5 | 0.4911 (9) | 0.75 | 0.1191 (10)* | |
H1 | 0.52716 | 0.6087 | 0.72753 | 0.1191 (10)* | |
C2 | 0.44887 (7) | 0.3128 (8) | 0.69098 (14) | 0.1191 (10)* | |
C3 | 0.47616 (10) | 0.1354 (10) | 0.6498 (3) | 0.1191 (10)* | |
C4 | 0.42915 (11) | −0.0317 (10) | 0.5937 (2) | 0.1191 (10)* | |
C5 | 0.45887 (14) | −0.2268 (11) | 0.5504 (3) | 0.1191 (10)* | |
C6 | 0.35639 (12) | 0.0016 (10) | 0.5744 (2) | 0.1191 (10)* | |
H6 | 0.32608 | −0.1053 | 0.5367 | 0.1191 (10)* | |
C7 | 0.32741 (10) | 0.1893 (9) | 0.6134 (2) | 0.1191 (10)* | |
C8 | 0.25262 (11) | 0.2114 (10) | 0.5963 (2) | 0.1191 (10)* | |
H8 | 0.22249 | 0.1056 | 0.5582 | 0.1191 (10)* | |
C9 | 0.22445 (14) | 0.3951 (11) | 0.6325 (3) | 0.1191 (10)* | |
H9 | 0.17496 | 0.4089 | 0.6205 | 0.1191 (10)* | |
C10 | 0.26911 (15) | 0.5591 (10) | 0.6896 (3) | 0.1191 (10)* | |
H10 | 0.24890 | 0.6825 | 0.7146 | 0.1191 (10)* | |
C11 | 0.34234 (13) | 0.5319 (8) | 0.7105 (2) | 0.1191 (10)* | |
H11 | 0.37152 | 0.6486 | 0.7466 | 0.1191 (10)* | |
C12 | 0.37302 (8) | 0.3591 (8) | 0.6683 (2) | 0.1191 (10)* | |
O1 | 0.54800 (13) | 0.1241 (11) | 0.6627 (3) | 0.1191 (10)* | |
H1A | 0.5579 | −0.024 | 0.6387 | 0.1191 (10)* | |
O2 | 0.41729 (19) | −0.3766 (9) | 0.5024 (3) | 0.1191 (10)* | |
H2A | 0.4407 | −0.479 | 0.4852 | 0.1191 (10)* | |
O3 | 0.5278 (2) | −0.2538 (10) | 0.5663 (3) | 0.1191 (10)* |
C1—H1 | 0.97 | C7—C8 | 1.4078 (12) |
C1—H1i | 0.97 | C7—C12 | 1.4035 (11) |
C2—C3 | 1.3845 (11) | C8—H8 | 0.93 |
C2—C12 | 1.4337 (11) | C8—C9 | 1.3494 (12) |
C3—C4 | 1.4201 (11) | C9—H9 | 0.93 |
C3—O1 | 1.3587 (12) | C9—C10 | 1.4046 (12) |
C4—C5 | 1.4930 (12) | C10—H10 | 0.93 |
C4—C6 | 1.3707 (12) | C10—C11 | 1.3744 (12) |
C5—O2 | 1.244 (4) | C11—H11 | 0.93 |
C5—O3 | 1.299 (4) | C11—C12 | 1.4253 (12) |
C6—H6 | 0.93 | O1—H1A | 0.90 |
C6—C7 | 1.4063 (11) | O2—H2A | 0.82 |
H1—C1—H1i | 109 | C7—C8—H8 | 120 |
C3—C2—C12 | 118.84 (8) | C7—C8—C9 | 120.28 (12) |
C2—C3—C4 | 120.13 (14) | H8—C8—C9 | 120 |
C2—C3—O1 | 119.80 (11) | C8—C9—H9 | 120 |
C4—C3—O1 | 120.07 (13) | C8—C9—C10 | 120.66 (14) |
C3—C4—C5 | 119.97 (15) | H9—C9—C10 | 120 |
C3—C4—C6 | 120.54 (9) | C9—C10—H10 | 120 |
C5—C4—C6 | 119.25 (9) | C9—C10—C11 | 120.60 (11) |
C4—C5—O2 | 119.4 (2) | H10—C10—C11 | 120 |
C4—C5—O3 | 120.09 (12) | C10—C11—H11 | 120 |
O2—C5—O3 | 120.31 (14) | C10—C11—C12 | 119.26 (10) |
C4—C6—H6 | 120 | H11—C11—C12 | 120 |
C4—C6—C7 | 120.12 (9) | C2—C12—C7 | 119.36 (9) |
H6—C6—C7 | 120 | C2—C12—C11 | 120.75 (9) |
C6—C7—C8 | 119.99 (10) | C7—C12—C11 | 118.57 (14) |
C6—C7—C12 | 119.98 (13) | C3—O1—H1A | 109 |
C8—C7—C12 | 120.01 (9) | C5—O2—H2A | 109 |
Symmetry code: (i) −x+1, y, −z+3/2. |
D—H···A | D—H | H···A | D···A | D—H···A |
O2—H2A···O3ii | 0.82 | 1.85 | 2.643 (4) | 166 |
O1—H1A···O3 | 0.90 | 1.72 | 2.529 (4) | 147 |
Symmetry code: (ii) −x+1, −y−1, −z+1. |
Acknowledgements
DH, WJ and WDSM thank the Pfizer Institute for Pharmaceutical Materials Science for funding. JB thanks Jesus College, Cambridge, for the award of a Junior Research Fellowship.
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