Download citation
Download citation
link to html
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

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270107051104/gz3111sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270107051104/gz3111Isup2.hkl
Contains datablock I

CCDC reference: 672399

Comment top

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 CH···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.

Related literature top

For related literature, see: Allen (2002); Barneoud & Curet (1999); Bond et al. (2007); Grimvall & Wengelin (1967); Manojlovic & Speakman (1967); Ochsenbein et al. (2004); Stahl & Wermuth (2002); Viossat et al. (2003); Vishweshwar et al. (2005); Wilson (2002).

Experimental top

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.

Computing details top

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).

Figures top
[Figure 1] Fig. 1. The contents of the asymmetric unit, drawn with 50% probability displacement ellipsoids.
[Figure 2] Fig. 2. Part of the coordination chain that extends along the c direction. H atoms have been omitted for clarity. (Colour key inthe online version of the journal: Li light green, O red, C grey).
[Figure 3] Fig. 3. The packing viewed down the a axis, showing the hydrogen bonds (dashed bond) between the chains. Only H atoms of waters are shown for clarity.
catena-Poly[[lithium(I)-µ3-acetylsalicylato] hemihydrate] top
Crystal data top
[Li(C9H7O4)]·0.5H2OF(000) = 808
Mr = 195.09Dx = 1.406 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2ycCell parameters from 1779 reflections
a = 26.262 (3) Åθ = 1–25°
b = 7.1677 (7) ŵ = 0.11 mm1
c = 10.3351 (8) ÅT = 123 K
β = 108.687 (3)°Block, colourless
V = 1842.9 (3) Å30.2 × 0.1 × 0.05 mm
Z = 8
Data collection top
Nonius KappaCCD
diffractometer
1110 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.10
Graphite monochromatorθmax = 25.0°, θmin = 1.6°
Phi and ω scansh = 3131
15207 measured reflectionsk = 88
1624 independent reflectionsl = 1212
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.040Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.095H 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 parametersΔρmax = 0.20 e Å3
0 restraintsΔρmin = 0.19 e Å3
Crystal data top
[Li(C9H7O4)]·0.5H2OV = 1842.9 (3) Å3
Mr = 195.09Z = 8
Monoclinic, C2/cMo Kα radiation
a = 26.262 (3) ŵ = 0.11 mm1
b = 7.1677 (7) ÅT = 123 K
c = 10.3351 (8) Å0.2 × 0.1 × 0.05 mm
β = 108.687 (3)°
Data collection top
Nonius KappaCCD
diffractometer
1110 reflections with I > 2σ(I)
15207 measured reflectionsRint = 0.10
1624 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0400 restraints
wR(F2) = 0.095H atoms treated by a mixture of independent and constrained refinement
S = 1.02Δρmax = 0.20 e Å3
1624 reflectionsΔρmin = 0.19 e Å3
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
xyzUiso*/Ueq
Li10.02010 (13)0.0544 (5)0.8937 (3)0.0219 (8)
O10.07068 (5)0.0609 (2)0.81992 (13)0.0205 (4)
O20.04460 (5)0.07209 (19)0.59259 (13)0.0198 (4)
O30.15480 (5)0.2895 (2)0.94946 (12)0.0211 (4)
O40.08880 (6)0.4919 (2)0.84472 (15)0.0290 (4)
O1W0.00000.2690 (3)0.75000.0239 (5)
H1W0.0303 (10)0.344 (4)0.720 (3)0.083 (11)*
C10.07898 (8)0.0987 (3)0.70955 (19)0.0163 (5)
C20.13287 (8)0.1787 (3)0.71430 (19)0.0153 (5)
C30.14939 (8)0.1647 (3)0.5987 (2)0.0183 (5)
H30.12710.10170.52000.022*
C40.19762 (8)0.2409 (3)0.5971 (2)0.0218 (5)
H40.20780.23150.51710.026*
C50.23108 (8)0.3308 (3)0.7114 (2)0.0251 (5)
H50.26420.38250.71010.030*
C60.21580 (8)0.3448 (3)0.8274 (2)0.0221 (5)
H60.23860.40530.90660.027*
C70.16743 (8)0.2705 (3)0.82760 (19)0.0170 (5)
C80.11093 (9)0.3965 (3)0.9424 (2)0.0227 (5)
C90.09594 (10)0.3782 (3)1.0690 (2)0.0317 (6)
H9A0.07040.47681.07120.048*
H9B0.12820.38991.14900.048*
H9C0.07940.25601.07020.048*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Li10.0189 (19)0.029 (2)0.0178 (19)0.0011 (17)0.0060 (16)0.0022 (16)
O10.0219 (8)0.0264 (9)0.0144 (8)0.0044 (7)0.0077 (6)0.0005 (6)
O20.0174 (8)0.0271 (9)0.0143 (7)0.0038 (7)0.0040 (6)0.0045 (7)
O30.0233 (9)0.0249 (9)0.0140 (8)0.0014 (7)0.0045 (7)0.0015 (6)
O40.0358 (10)0.0274 (9)0.0260 (9)0.0063 (8)0.0131 (8)0.0046 (7)
O1W0.0215 (14)0.0222 (13)0.0292 (13)0.0000.0098 (11)0.000
C10.0176 (11)0.0155 (11)0.0153 (11)0.0012 (9)0.0045 (9)0.0017 (9)
C20.0153 (11)0.0147 (11)0.0158 (11)0.0016 (9)0.0047 (9)0.0019 (9)
C30.0185 (11)0.0193 (11)0.0169 (11)0.0001 (10)0.0052 (9)0.0012 (9)
C40.0215 (13)0.0246 (13)0.0238 (12)0.0017 (10)0.0136 (10)0.0027 (10)
C50.0159 (12)0.0262 (12)0.0347 (14)0.0032 (11)0.0104 (10)0.0011 (11)
C60.0196 (12)0.0191 (12)0.0234 (12)0.0038 (10)0.0010 (10)0.0026 (10)
C70.0196 (12)0.0172 (12)0.0152 (11)0.0021 (9)0.0069 (9)0.0023 (9)
C80.0276 (13)0.0197 (12)0.0231 (12)0.0080 (11)0.0114 (11)0.0069 (10)
C90.0450 (16)0.0298 (14)0.0257 (13)0.0093 (12)0.0189 (12)0.0064 (11)
Geometric parameters (Å, º) top
Li1—O11.918 (3)C1—Li1ii2.708 (4)
Li1—O2i1.952 (3)C2—C71.396 (3)
Li1—O2ii1.971 (4)C2—C31.399 (3)
Li1—O1W2.085 (4)C3—C41.384 (3)
Li1—Li1ii2.815 (6)C3—H30.9500
Li1—Li1iii2.836 (6)C4—C51.384 (3)
O1—C11.258 (2)C4—H40.9500
O2—C11.270 (2)C5—C61.385 (3)
O2—Li1iv1.952 (3)C5—H50.9500
O2—Li1ii1.971 (4)C6—C71.378 (3)
O3—C81.367 (3)C6—H60.9500
O3—C71.408 (2)C8—C91.488 (3)
O4—C81.204 (2)C9—H9A0.9800
O1W—Li1ii2.085 (4)C9—H9B0.9800
O1W—H1W0.92 (3)C9—H9C0.9800
C1—C21.513 (3)
O1—Li1—O2i114.21 (18)O1—C1—C2118.97 (18)
O1—Li1—O2ii123.60 (19)O2—C1—C2117.39 (16)
O2i—Li1—O2ii87.40 (14)C7—C2—C3117.00 (18)
O1—Li1—O1W94.85 (14)C7—C2—C1123.79 (16)
O2i—Li1—O1W128.69 (19)C3—C2—C1119.20 (17)
O2ii—Li1—O1W111.30 (16)C4—C3—C2121.13 (19)
O1—Li1—C1ii111.68 (15)C4—C3—H3119.4
O2i—Li1—C1ii113.08 (15)C2—C3—H3119.4
O2ii—Li1—C1ii25.87 (7)C5—C4—C3120.47 (19)
O1W—Li1—C1ii91.51 (13)C5—C4—H4119.8
O1—Li1—Li1ii69.77 (13)C3—C4—H4119.8
O2i—Li1—Li1ii175.47 (16)C4—C5—C6119.4 (2)
O2ii—Li1—Li1ii92.03 (16)C4—C5—H5120.3
O1W—Li1—Li1ii47.54 (10)C6—C5—H5120.3
C1ii—Li1—Li1ii66.18 (12)C7—C6—C5119.78 (19)
O1—Li1—Li1iii131.8 (2)C7—C6—H6120.1
O2i—Li1—Li1iii43.97 (10)C5—C6—H6120.1
O2ii—Li1—Li1iii43.43 (10)C6—C7—C2122.20 (17)
O1W—Li1—Li1iii133.1 (2)C6—C7—O3116.47 (18)
C1ii—Li1—Li1iii69.17 (14)C2—C7—O3121.32 (17)
Li1ii—Li1—Li1iii135.3 (2)O4—C8—O3122.40 (18)
C1—O1—Li1142.83 (16)O4—C8—C9126.5 (2)
C1—O2—Li1iv154.97 (16)O3—C8—C9111.10 (19)
C1—O2—Li1ii111.52 (15)C8—C9—H9A109.5
Li1iv—O2—Li1ii92.60 (14)C8—C9—H9B109.5
C8—O3—C7116.28 (15)H9A—C9—H9B109.5
Li1—O1W—Li1ii84.9 (2)C8—C9—H9C109.5
Li1—O1W—H1W131.2 (18)H9A—C9—H9C109.5
Li1ii—O1W—H1W101.2 (18)H9B—C9—H9C109.5
O1—C1—O2123.64 (18)
O2i—Li1—O1—C1174.2 (2)O2—C1—C2—C7158.46 (19)
O2ii—Li1—O1—C181.9 (3)O1—C1—C2—C3159.22 (18)
O1W—Li1—O1—C137.7 (3)O2—C1—C2—C320.2 (3)
Li1ii—Li1—O1—C13.4 (2)C7—C2—C3—C40.8 (3)
Li1iii—Li1—O1—C1136.8 (3)C1—C2—C3—C4177.99 (19)
O1—Li1—O1W—Li1ii56.77 (10)C2—C3—C4—C51.0 (3)
O2i—Li1—O1W—Li1ii176.7 (3)C3—C4—C5—C60.3 (3)
O2ii—Li1—O1W—Li1ii72.22 (15)C4—C5—C6—C70.5 (3)
C1ii—Li1—O1W—Li1ii55.14 (9)C5—C6—C7—C20.7 (3)
Li1iii—Li1—O1W—Li1ii117.6 (3)C5—C6—C7—O3179.72 (17)
Li1—O1—C1—O26.7 (4)C3—C2—C7—C60.0 (3)
Li1—O1—C1—C2172.7 (2)C1—C2—C7—C6178.75 (19)
Li1—O1—C1—Li1ii3.4 (2)C3—C2—C7—O3179.05 (17)
Li1iv—O2—C1—O1168.5 (3)C1—C2—C7—O32.2 (3)
Li1ii—O2—C1—O14.9 (3)C8—O3—C7—C6115.7 (2)
Li1iv—O2—C1—C210.9 (5)C8—O3—C7—C265.3 (2)
Li1ii—O2—C1—C2174.55 (17)C7—O3—C8—O410.6 (3)
Li1iv—O2—C1—Li1ii163.6 (4)C7—O3—C8—C9169.76 (16)
O1—C1—C2—C722.1 (3)
Symmetry codes: (i) x, y, z+1/2; (ii) x, y, z+3/2; (iii) x, y, z+2; (iv) x, y, z1/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1W—H1W···O4v0.92 (3)1.88 (3)2.806 (2)176 (3)
Symmetry code: (v) x, y1, z+3/2.

Experimental details

Crystal data
Chemical formula[Li(C9H7O4)]·0.5H2O
Mr195.09
Crystal system, space groupMonoclinic, C2/c
Temperature (K)123
a, b, c (Å)26.262 (3), 7.1677 (7), 10.3351 (8)
β (°) 108.687 (3)
V3)1842.9 (3)
Z8
Radiation typeMo Kα
µ (mm1)0.11
Crystal size (mm)0.2 × 0.1 × 0.05
Data collection
DiffractometerNonius KappaCCD
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
15207, 1624, 1110
Rint0.10
(sin θ/λ)max1)0.596
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.040, 0.095, 1.02
No. of reflections1624
No. of parameters137
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.20, 0.19

Computer programs: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998), DENZO (Otwinowski & Minor, 1997), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEPII (Johnson, 1976).

Selected geometric parameters (Å, º) top
Li1—O11.918 (3)Li1—O2ii1.971 (4)
Li1—O2i1.952 (3)Li1—O1W2.085 (4)
O1—Li1—O2i114.21 (18)O1—Li1—O1W94.85 (14)
O1—Li1—O2ii123.60 (19)O2i—Li1—O1W128.69 (19)
O2i—Li1—O2ii87.40 (14)O2ii—Li1—O1W111.30 (16)
O2—C1—C2—C320.2 (3)
Symmetry codes: (i) x, y, z+1/2; (ii) x, y, z+3/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1W—H1W···O4iii0.92 (3)1.88 (3)2.806 (2)176 (3)
Symmetry code: (iii) x, y1, z+3/2.
 

Follow Acta Cryst. C
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds