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The title compound {systematic name: catena-poly[lithium(I)-μ3-acetylsalicylato-hemi-μ2-aqua]}, {[Li(C9H7O4)]·0.5H2O}n, is the hemihydrate of the lithium salt of aspirin. The carboxylate groups and water molecules bridge between Li atoms to form a one-dimensional coordination chain composed of two distinct ring types. The water O atom lies on a twofold axis. Hydrogen bonding between water donors and carbonyl acceptors further links the coordination chains to form a sheet structure.
Supporting information
CCDC reference: 672399
The synthesis was carried out by reaction of Li2CO3 with acetysalicylic acid
(molar ratio 1:2) in water. The solution was left to evaporate. The first
crystals to appear were aspirin. These were removed and only then did crystals
of (I) form. IR (KBr, cm-1): 3429, 1745, 1728, 1614, 1590, 1561, 1400, 1232,
1195, 754. DSC (10 K per min) shows loss of the water molecule at 283 K.
Data collection: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); cell refinement: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); data reduction: DENZO (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).
catena-Poly[[lithium(I)-µ
3-acetylsalicylato] hemihydrate]
top
Crystal data top
[Li(C9H7O4)]·0.5H2O | F(000) = 808 |
Mr = 195.09 | Dx = 1.406 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -C 2yc | Cell parameters from 1779 reflections |
a = 26.262 (3) Å | θ = 1–25° |
b = 7.1677 (7) Å | µ = 0.11 mm−1 |
c = 10.3351 (8) Å | T = 123 K |
β = 108.687 (3)° | Block, colourless |
V = 1842.9 (3) Å3 | 0.2 × 0.1 × 0.05 mm |
Z = 8 | |
Data collection top
Nonius KappaCCD diffractometer | 1110 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.10 |
Graphite monochromator | θmax = 25.0°, θmin = 1.6° |
Phi and ω scans | h = −31→31 |
15207 measured reflections | k = −8→8 |
1624 independent reflections | l = −12→12 |
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)] = 0.040 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.095 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.02 | w = 1/[σ2(Fo2) + (0.0429P)2 + 0.6425P] where P = (Fo2 + 2Fc2)/3 |
1624 reflections | (Δ/σ)max = 0.001 |
137 parameters | Δρmax = 0.20 e Å−3 |
0 restraints | Δρmin = −0.19 e Å−3 |
Crystal data top
[Li(C9H7O4)]·0.5H2O | V = 1842.9 (3) Å3 |
Mr = 195.09 | Z = 8 |
Monoclinic, C2/c | Mo Kα radiation |
a = 26.262 (3) Å | µ = 0.11 mm−1 |
b = 7.1677 (7) Å | T = 123 K |
c = 10.3351 (8) Å | 0.2 × 0.1 × 0.05 mm |
β = 108.687 (3)° | |
Data collection top
Nonius KappaCCD diffractometer | 1110 reflections with I > 2σ(I) |
15207 measured reflections | Rint = 0.10 |
1624 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.040 | 0 restraints |
wR(F2) = 0.095 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.02 | Δρmax = 0.20 e Å−3 |
1624 reflections | Δρmin = −0.19 e Å−3 |
137 parameters | |
Special details top
Experimental. The water H-atom was found by difference synthesis and refined isotropically.
All other H-atoms were constrained to idealized geometry using riding models
with C—H = 0.95 Å and Uiso(H) = 1.2Ueq(C) for CH groups
and C—H = 0.98 Å and Uiso(H) = 1.5Ueq(C) for Me. |
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 | Uiso*/Ueq | |
Li1 | 0.02010 (13) | −0.0544 (5) | 0.8937 (3) | 0.0219 (8) | |
O1 | 0.07068 (5) | 0.0609 (2) | 0.81992 (13) | 0.0205 (4) | |
O2 | 0.04460 (5) | 0.07209 (19) | 0.59259 (13) | 0.0198 (4) | |
O3 | 0.15480 (5) | 0.2895 (2) | 0.94946 (12) | 0.0211 (4) | |
O4 | 0.08880 (6) | 0.4919 (2) | 0.84472 (15) | 0.0290 (4) | |
O1W | 0.0000 | −0.2690 (3) | 0.7500 | 0.0239 (5) | |
H1W | −0.0303 (10) | −0.344 (4) | 0.720 (3) | 0.083 (11)* | |
C1 | 0.07898 (8) | 0.0987 (3) | 0.70955 (19) | 0.0163 (5) | |
C2 | 0.13287 (8) | 0.1787 (3) | 0.71430 (19) | 0.0153 (5) | |
C3 | 0.14939 (8) | 0.1647 (3) | 0.5987 (2) | 0.0183 (5) | |
H3 | 0.1271 | 0.1017 | 0.5200 | 0.022* | |
C4 | 0.19762 (8) | 0.2409 (3) | 0.5971 (2) | 0.0218 (5) | |
H4 | 0.2078 | 0.2315 | 0.5171 | 0.026* | |
C5 | 0.23108 (8) | 0.3308 (3) | 0.7114 (2) | 0.0251 (5) | |
H5 | 0.2642 | 0.3825 | 0.7101 | 0.030* | |
C6 | 0.21580 (8) | 0.3448 (3) | 0.8274 (2) | 0.0221 (5) | |
H6 | 0.2386 | 0.4053 | 0.9066 | 0.027* | |
C7 | 0.16743 (8) | 0.2705 (3) | 0.82760 (19) | 0.0170 (5) | |
C8 | 0.11093 (9) | 0.3965 (3) | 0.9424 (2) | 0.0227 (5) | |
C9 | 0.09594 (10) | 0.3782 (3) | 1.0690 (2) | 0.0317 (6) | |
H9A | 0.0704 | 0.4768 | 1.0712 | 0.048* | |
H9B | 0.1282 | 0.3899 | 1.1490 | 0.048* | |
H9C | 0.0794 | 0.2560 | 1.0702 | 0.048* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Li1 | 0.0189 (19) | 0.029 (2) | 0.0178 (19) | −0.0011 (17) | 0.0060 (16) | 0.0022 (16) |
O1 | 0.0219 (8) | 0.0264 (9) | 0.0144 (8) | −0.0044 (7) | 0.0077 (6) | 0.0005 (6) |
O2 | 0.0174 (8) | 0.0271 (9) | 0.0143 (7) | −0.0038 (7) | 0.0040 (6) | −0.0045 (7) |
O3 | 0.0233 (9) | 0.0249 (9) | 0.0140 (8) | −0.0014 (7) | 0.0045 (7) | −0.0015 (6) |
O4 | 0.0358 (10) | 0.0274 (9) | 0.0260 (9) | 0.0063 (8) | 0.0131 (8) | 0.0046 (7) |
O1W | 0.0215 (14) | 0.0222 (13) | 0.0292 (13) | 0.000 | 0.0098 (11) | 0.000 |
C1 | 0.0176 (11) | 0.0155 (11) | 0.0153 (11) | 0.0012 (9) | 0.0045 (9) | −0.0017 (9) |
C2 | 0.0153 (11) | 0.0147 (11) | 0.0158 (11) | 0.0016 (9) | 0.0047 (9) | 0.0019 (9) |
C3 | 0.0185 (11) | 0.0193 (11) | 0.0169 (11) | −0.0001 (10) | 0.0052 (9) | 0.0012 (9) |
C4 | 0.0215 (13) | 0.0246 (13) | 0.0238 (12) | 0.0017 (10) | 0.0136 (10) | 0.0027 (10) |
C5 | 0.0159 (12) | 0.0262 (12) | 0.0347 (14) | −0.0032 (11) | 0.0104 (10) | 0.0011 (11) |
C6 | 0.0196 (12) | 0.0191 (12) | 0.0234 (12) | −0.0038 (10) | 0.0010 (10) | −0.0026 (10) |
C7 | 0.0196 (12) | 0.0172 (12) | 0.0152 (11) | 0.0021 (9) | 0.0069 (9) | 0.0023 (9) |
C8 | 0.0276 (13) | 0.0197 (12) | 0.0231 (12) | −0.0080 (11) | 0.0114 (11) | −0.0069 (10) |
C9 | 0.0450 (16) | 0.0298 (14) | 0.0257 (13) | −0.0093 (12) | 0.0189 (12) | −0.0064 (11) |
Geometric parameters (Å, º) top
Li1—O1 | 1.918 (3) | C1—Li1ii | 2.708 (4) |
Li1—O2i | 1.952 (3) | C2—C7 | 1.396 (3) |
Li1—O2ii | 1.971 (4) | C2—C3 | 1.399 (3) |
Li1—O1W | 2.085 (4) | C3—C4 | 1.384 (3) |
Li1—Li1ii | 2.815 (6) | C3—H3 | 0.9500 |
Li1—Li1iii | 2.836 (6) | C4—C5 | 1.384 (3) |
O1—C1 | 1.258 (2) | C4—H4 | 0.9500 |
O2—C1 | 1.270 (2) | C5—C6 | 1.385 (3) |
O2—Li1iv | 1.952 (3) | C5—H5 | 0.9500 |
O2—Li1ii | 1.971 (4) | C6—C7 | 1.378 (3) |
O3—C8 | 1.367 (3) | C6—H6 | 0.9500 |
O3—C7 | 1.408 (2) | C8—C9 | 1.488 (3) |
O4—C8 | 1.204 (2) | C9—H9A | 0.9800 |
O1W—Li1ii | 2.085 (4) | C9—H9B | 0.9800 |
O1W—H1W | 0.92 (3) | C9—H9C | 0.9800 |
C1—C2 | 1.513 (3) | | |
| | | |
O1—Li1—O2i | 114.21 (18) | O1—C1—C2 | 118.97 (18) |
O1—Li1—O2ii | 123.60 (19) | O2—C1—C2 | 117.39 (16) |
O2i—Li1—O2ii | 87.40 (14) | C7—C2—C3 | 117.00 (18) |
O1—Li1—O1W | 94.85 (14) | C7—C2—C1 | 123.79 (16) |
O2i—Li1—O1W | 128.69 (19) | C3—C2—C1 | 119.20 (17) |
O2ii—Li1—O1W | 111.30 (16) | C4—C3—C2 | 121.13 (19) |
O1—Li1—C1ii | 111.68 (15) | C4—C3—H3 | 119.4 |
O2i—Li1—C1ii | 113.08 (15) | C2—C3—H3 | 119.4 |
O2ii—Li1—C1ii | 25.87 (7) | C5—C4—C3 | 120.47 (19) |
O1W—Li1—C1ii | 91.51 (13) | C5—C4—H4 | 119.8 |
O1—Li1—Li1ii | 69.77 (13) | C3—C4—H4 | 119.8 |
O2i—Li1—Li1ii | 175.47 (16) | C4—C5—C6 | 119.4 (2) |
O2ii—Li1—Li1ii | 92.03 (16) | C4—C5—H5 | 120.3 |
O1W—Li1—Li1ii | 47.54 (10) | C6—C5—H5 | 120.3 |
C1ii—Li1—Li1ii | 66.18 (12) | C7—C6—C5 | 119.78 (19) |
O1—Li1—Li1iii | 131.8 (2) | C7—C6—H6 | 120.1 |
O2i—Li1—Li1iii | 43.97 (10) | C5—C6—H6 | 120.1 |
O2ii—Li1—Li1iii | 43.43 (10) | C6—C7—C2 | 122.20 (17) |
O1W—Li1—Li1iii | 133.1 (2) | C6—C7—O3 | 116.47 (18) |
C1ii—Li1—Li1iii | 69.17 (14) | C2—C7—O3 | 121.32 (17) |
Li1ii—Li1—Li1iii | 135.3 (2) | O4—C8—O3 | 122.40 (18) |
C1—O1—Li1 | 142.83 (16) | O4—C8—C9 | 126.5 (2) |
C1—O2—Li1iv | 154.97 (16) | O3—C8—C9 | 111.10 (19) |
C1—O2—Li1ii | 111.52 (15) | C8—C9—H9A | 109.5 |
Li1iv—O2—Li1ii | 92.60 (14) | C8—C9—H9B | 109.5 |
C8—O3—C7 | 116.28 (15) | H9A—C9—H9B | 109.5 |
Li1—O1W—Li1ii | 84.9 (2) | C8—C9—H9C | 109.5 |
Li1—O1W—H1W | 131.2 (18) | H9A—C9—H9C | 109.5 |
Li1ii—O1W—H1W | 101.2 (18) | H9B—C9—H9C | 109.5 |
O1—C1—O2 | 123.64 (18) | | |
| | | |
O2i—Li1—O1—C1 | 174.2 (2) | O2—C1—C2—C7 | 158.46 (19) |
O2ii—Li1—O1—C1 | −81.9 (3) | O1—C1—C2—C3 | 159.22 (18) |
O1W—Li1—O1—C1 | 37.7 (3) | O2—C1—C2—C3 | −20.2 (3) |
Li1ii—Li1—O1—C1 | −3.4 (2) | C7—C2—C3—C4 | −0.8 (3) |
Li1iii—Li1—O1—C1 | −136.8 (3) | C1—C2—C3—C4 | 177.99 (19) |
O1—Li1—O1W—Li1ii | −56.77 (10) | C2—C3—C4—C5 | 1.0 (3) |
O2i—Li1—O1W—Li1ii | 176.7 (3) | C3—C4—C5—C6 | −0.3 (3) |
O2ii—Li1—O1W—Li1ii | 72.22 (15) | C4—C5—C6—C7 | −0.5 (3) |
C1ii—Li1—O1W—Li1ii | 55.14 (9) | C5—C6—C7—C2 | 0.7 (3) |
Li1iii—Li1—O1W—Li1ii | 117.6 (3) | C5—C6—C7—O3 | 179.72 (17) |
Li1—O1—C1—O2 | 6.7 (4) | C3—C2—C7—C6 | 0.0 (3) |
Li1—O1—C1—C2 | −172.7 (2) | C1—C2—C7—C6 | −178.75 (19) |
Li1—O1—C1—Li1ii | 3.4 (2) | C3—C2—C7—O3 | −179.05 (17) |
Li1iv—O2—C1—O1 | −168.5 (3) | C1—C2—C7—O3 | 2.2 (3) |
Li1ii—O2—C1—O1 | −4.9 (3) | C8—O3—C7—C6 | 115.7 (2) |
Li1iv—O2—C1—C2 | 10.9 (5) | C8—O3—C7—C2 | −65.3 (2) |
Li1ii—O2—C1—C2 | 174.55 (17) | C7—O3—C8—O4 | −10.6 (3) |
Li1iv—O2—C1—Li1ii | −163.6 (4) | C7—O3—C8—C9 | 169.76 (16) |
O1—C1—C2—C7 | −22.1 (3) | | |
Symmetry codes: (i) x, −y, z+1/2; (ii) −x, y, −z+3/2; (iii) −x, −y, −z+2; (iv) x, −y, z−1/2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O1W—H1W···O4v | 0.92 (3) | 1.88 (3) | 2.806 (2) | 176 (3) |
Symmetry code: (v) −x, y−1, −z+3/2. |
Experimental details
Crystal data |
Chemical formula | [Li(C9H7O4)]·0.5H2O |
Mr | 195.09 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 123 |
a, b, c (Å) | 26.262 (3), 7.1677 (7), 10.3351 (8) |
β (°) | 108.687 (3) |
V (Å3) | 1842.9 (3) |
Z | 8 |
Radiation type | Mo Kα |
µ (mm−1) | 0.11 |
Crystal size (mm) | 0.2 × 0.1 × 0.05 |
|
Data collection |
Diffractometer | Nonius KappaCCD diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 15207, 1624, 1110 |
Rint | 0.10 |
(sin θ/λ)max (Å−1) | 0.596 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.040, 0.095, 1.02 |
No. of reflections | 1624 |
No. of parameters | 137 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.20, −0.19 |
Selected geometric parameters (Å, º) topLi1—O1 | 1.918 (3) | Li1—O2ii | 1.971 (4) |
Li1—O2i | 1.952 (3) | Li1—O1W | 2.085 (4) |
| | | |
O1—Li1—O2i | 114.21 (18) | O1—Li1—O1W | 94.85 (14) |
O1—Li1—O2ii | 123.60 (19) | O2i—Li1—O1W | 128.69 (19) |
O2i—Li1—O2ii | 87.40 (14) | O2ii—Li1—O1W | 111.30 (16) |
| | | |
O2—C1—C2—C3 | −20.2 (3) | | |
Symmetry codes: (i) x, −y, z+1/2; (ii) −x, y, −z+3/2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O1W—H1W···O4iii | 0.92 (3) | 1.88 (3) | 2.806 (2) | 176 (3) |
Symmetry code: (iii) −x, y−1, −z+3/2. |
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Apsirin (acetylsalicylic acid) and its salts are widely used pharmaceutically for their analgesic, antipyretic and anti-inflammatory properties. Aspirin itself is only sparingly soluble in water and so its salt forms may be used to combat this and hence improve its bioavailability (Stahl & Wermuth, 2002; Barneoud & Curet, 1999). The most common counter-ions for pharmaceutical acids are sodium, potassium and calcium. Despite this fact, no structures of akaline metal salts of aspirin are known. This is not owing to lack of interest, as highlighted by the recent debate on the structures of aspirin (Bond et al., 2007) and the reported formation and characterization of calcium aspirinate by Ochsenbein et al. (2004). As well as difficulties with chemical instability, Ochsenbein and co-workers encountered problems with rapid phase changes. Indeed the Ca salt was described as a furtive form, isolated only by microscopic examination of an evaporating droplet. Other relevant structural work on aspirin salts includes the isomorphic KH (Manojlovic & Speakman, 1967) and RbH (Grimvall & Wengelin, 1967) salts. The structures of numerous transition metal complexes of aspirin are also known [see Viossat et al. (2003) for a typical example]. As part of a study into structure/property correlations of s-block metal benzoate salts, we attempted the preparation of crystals of the alkaline metal salts of aspirin. We report here the structure of the hemihydrate of the lithium salt, (I).
The asymmetric unit of (I) is composed of one lithium cation, one acetylsalicylate anion and half a water molecule (Fig. 1), the O atom of which lies on a twofold axis. The Li1 coordination has a distorted tetrahedral geometry [angular range 87.40 (14)–128.69 (19)°]. Of the carboxylate O atoms, atom O1 makes only one contact with Li and this is shorter than those formed by the bridging O2 atom (Table 1). The Li1 to bridging water distance is longer again, perhaps reflecting the neutral nature of atom O1W. All bond lengths lie within the normal ranges found for similar bonds in the Cambridge Structural Database (CSD; Version 5.28 of May 2007; Allen, 2002). The ester group does not directly interact with the Li atom.
The interactions between Li and O atoms combine to form a one-dimensional coordination polymer propagating along the crystallographic c direction. This chain is composed of two different ring types, viz. four-membered (O2/Li1/O2/Li1) and six-membered (O1/Li1/O1W/Li1/O2/C1) (Fig. 2). Ten Li benzoate hydrate structures were found in a CSD search, and although one-dimensional chains were common, none had the same motif of alternating rings as (I). An alternative description of the larger ring is that it consists of a water molecule bridging over an eight-atom ring formed from two Li carboxylate groups in an [LiOCO]2 arrangement, reminiscent of the classic hydrogen-bonded carboxylic acid dimer with Li replacing H. The two reported structures of aspirin have such dimeric arrangements in common (Wilson, 2002; Vishweshwar et al., 2005; Bond et al., 2007). The aspirin structures differ from one another in the detail of the C—H···O(carbonyl) interactions formed by the ester group. The presence of water in (I) replaces the weak C—H donors, and here the coordination chains link to each other through hydrogen bonding between the water molecule and atom O4 of the ester group, forming an R22(18) motif (see Table 2). This forms linkages in the b-axis direction (Fig. 3) to give an overall two-dimensional sheet structure with layers parallel to the bc plane. The sheets with their polar bonding modes are separated by a double hydrophobic layer formed by aromatic rings. The carboxylate group has lost its coplanarity with the aromatic ring [dihedral angle between plane of aromatic ring and CO2 plane is 20.9 (2)°]. A similar twist is seen in the calcium aspirinate structure (Ochsenbein et al., 2004) and other salt forms and differs from the strict planarity found in aspirin itself.