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2',4'-Difluoro-4-hydroxybiphenyl-3-carboxylic acid (diflunisal) hydrate, C13H8F2O3·H2O, forms a monoclinic crystal lattice with special channels parallel to the twofold screw axes along the b direction. These channels are occupied by disordered water molecules. The crystal lattice consists of dimers of diflunisal, in which two molecules are linked together by a pair of hydrogen bonds between their respective carboxyl groups.
Supporting information
CCDC reference: 165677
Key indicators
- Single-crystal X-ray study
- T = 298 K
- Mean (C-C) = 0.004 Å
- H-atom completeness 91%
- Disorder in main residue
- R factor = 0.050
- wR factor = 0.178
- Data-to-parameter ratio = 9.9
checkCIF results
No syntax errors found
ADDSYM reports no extra symmetry
Alert Level B:
PLAT_030 Alert B Refined Extinction parameter within range .... 1.90 Sigma
Alert Level C:
SHFSU_01 Alert C The absolute value of parameter shift to su ratio > 0.05
Absolute value of the parameter shift to su ratio given 0.072
Additional refinement cycles may be required.
PLAT_301 Alert C Main Residue Disorder ........................ 5.00 Perc.
PLAT_302 Alert C Anion/Solvent Disorder ....................... 50.00 Perc.
PLAT_722 Alert C Angle Calc 110.75, Rep 109.40, Dev. 1.35 Deg.
O1W -O2W -H12W 4.545 1.555 1.555
General Notes
FORMU_01 There is a discrepancy between the atom counts in the
_chemical_formula_sum and the formula from the _atom_site* data.
Atom count from _chemical_formula_sum:C13 H10 F2 O4
Atom count from the _atom_site data: C13 H9 F2 O4
CELLZ_01
From the CIF: _cell_formula_units_Z 8
From the CIF: _chemical_formula_sum C13 H10 F2 O4
TEST: Compare cell contents of formula and atom_site data
atom Z*formula cif sites diff
C 104.00 104.00 0.00
H 80.00 72.00 8.00
F 16.00 16.00 0.00
O 32.00 32.00 0.00
Difference between formula and atom_site contents detected.
WARNING: H atoms missing from atom site list. Is this intentional?
0 Alert Level A = Potentially serious problem
1 Alert Level B = Potential problem
4 Alert Level C = Please check
The solvate was grown by crystallization of a saturated solution of diflunisal
and acetone by vapour diffusion of H2O (Guillory, 1999). All programs used
in the solution (Sheldrick, 1997a), refinement (Sheldrick,
1997b) and display (Burnett & Johnson, 1996) of the structures are
included in the OSCAIL program package (McArdle, 1993).
Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: CAD-4 Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: OSCAIL (McArdle, 1993).
2',4'-Difluoro-4-hydroxybiphenyl-3-carboxylic acid hydrate
top
Crystal data top
C13H8F2O3·H2O | F(000) = 1024 |
Mr = 268.21 | Dx = 1.417 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71069 Å |
a = 34.650 (2) Å | Cell parameters from 25 reflections |
b = 3.730 (2) Å | θ = 12–16° |
c = 20.760 (2) Å | µ = 0.12 mm−1 |
β = 110.47 (6)° | T = 298 K |
V = 2513.7 (14) Å3 | Needle, white |
Z = 8 | 0.30 × 0.20 × 0.15 mm |
Data collection top
Enraf-Nonius CAD-4 diffractometer | Rint = 0.014 |
Radiation source: fine-focus sealed tube | θmax = 25.0°, θmin = 1.3° |
Graphite monochromator | h = −1→40 |
ω–2θ scans | k = 0→4 |
2306 measured reflections | l = −24→23 |
2221 independent reflections | 3 standard reflections every 120 min |
1127 reflections with I > 2σ(I) | intensity decay: 1% |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.050 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.178 | w = 1/[σ2(Fo2) + (0.1388P)2] where P = (Fo2 + 2Fc2)/3 |
S = 0.83 | (Δ/σ)max = 0.072 |
2221 reflections | Δρmax = 0.26 e Å−3 |
225 parameters | Δρmin = −0.16 e Å−3 |
12 restraints | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0019 (10) |
Crystal data top
C13H8F2O3·H2O | V = 2513.7 (14) Å3 |
Mr = 268.21 | Z = 8 |
Monoclinic, C2/c | Mo Kα radiation |
a = 34.650 (2) Å | µ = 0.12 mm−1 |
b = 3.730 (2) Å | T = 298 K |
c = 20.760 (2) Å | 0.30 × 0.20 × 0.15 mm |
β = 110.47 (6)° | |
Data collection top
Enraf-Nonius CAD-4 diffractometer | Rint = 0.014 |
2306 measured reflections | 3 standard reflections every 120 min |
2221 independent reflections | intensity decay: 1% |
1127 reflections with I > 2σ(I) | |
Refinement top
R[F2 > 2σ(F2)] = 0.050 | 12 restraints |
wR(F2) = 0.178 | H atoms treated by a mixture of independent and constrained refinement |
S = 0.83 | Δρmax = 0.26 e Å−3 |
2221 reflections | Δρmin = −0.16 e Å−3 |
225 parameters | |
Special details top
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 | Occ. (<1) |
O2 | 0.21016 (6) | 0.4183 (7) | 0.51319 (10) | 0.0799 (7) | |
O1 | 0.14124 (7) | 0.6837 (7) | 0.51807 (10) | 0.0803 (7) | |
F1 | 0.04258 (6) | 0.7662 (6) | 0.01551 (9) | 0.1004 (8) | |
O3 | 0.21697 (6) | 0.3433 (6) | 0.41116 (10) | 0.0744 (7) | |
F22 | 0.14811 (9) | 0.9780 (9) | 0.22339 (15) | 0.0729 (9) | 0.50 |
F21 | 0.02001 (9) | 0.4863 (9) | 0.21767 (16) | 0.0710 (9) | 0.50 |
O1W | 0.2503 (14) | 0.30 (2) | 0.2028 (17) | 0.61 (4) | 0.35 |
H11W | 0.2347 | 0.1304 | 0.1861 | 0.22 (7)* | 0.50 |
H21W | 0.2221 | 0.4924 | 0.1899 | 0.10 (2)* | 0.50 |
O2W | 0.2684 (12) | 0.03 (2) | 0.284 (2) | 0.81 (6) | 0.65 |
H12W | 0.2842 | −0.0501 | 0.2660 | 0.21 (6)* | 0.50 |
H22W | 0.2717 | 0.2020 | 0.3112 | 0.14 (4)* | 0.50 |
H2O | 0.2441 (11) | 0.247 (9) | 0.4415 (16) | 0.090 (10)* | |
H1O | 0.1735 (17) | 0.594 (18) | 0.545 (3) | 0.20 (2)* | |
H12 | 0.0012 (9) | 0.565 (8) | 0.0892 (14) | 0.078 (8)* | |
H6 | 0.0475 (9) | 0.933 (8) | 0.3163 (13) | 0.070 (8)* | |
H2 | 0.1563 (7) | 0.512 (7) | 0.3167 (12) | 0.054 (7)* | |
H10 | 0.1109 (9) | 0.940 (8) | 0.0936 (14) | 0.072 (8)* | |
H5 | 0.0757 (8) | 0.897 (8) | 0.4393 (14) | 0.073 (8)* | |
C1 | 0.10061 (7) | 0.7280 (6) | 0.30416 (13) | 0.0523 (7) | |
C2 | 0.13952 (8) | 0.6003 (7) | 0.34099 (13) | 0.0531 (7) | |
C3 | 0.15455 (7) | 0.5818 (7) | 0.41225 (13) | 0.0544 (7) | |
C4 | 0.12911 (8) | 0.6963 (7) | 0.44856 (14) | 0.0583 (7) | |
C5 | 0.09024 (8) | 0.8234 (8) | 0.41219 (15) | 0.0603 (7) | |
C6 | 0.07633 (8) | 0.8403 (7) | 0.34188 (14) | 0.0570 (7) | |
C7 | 0.19583 (8) | 0.4423 (8) | 0.44992 (14) | 0.0604 (7) | |
C8 | 0.08514 (8) | 0.7419 (6) | 0.22797 (13) | 0.0523 (7) | |
C9 | 0.10952 (8) | 0.8607 (8) | 0.19111 (14) | 0.0594 (7) | |
C10 | 0.09597 (9) | 0.8707 (9) | 0.12048 (15) | 0.0675 (8) | |
C11 | 0.05671 (10) | 0.7592 (8) | 0.08547 (14) | 0.0697 (8) | |
C12 | 0.03057 (9) | 0.6409 (9) | 0.11752 (15) | 0.0668 (8) | |
C13 | 0.04560 (8) | 0.6320 (8) | 0.18820 (13) | 0.0581 (7) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
O2 | 0.0695 (13) | 0.1062 (18) | 0.0642 (13) | 0.0226 (13) | 0.0238 (10) | 0.0031 (12) |
O1 | 0.0802 (14) | 0.1068 (17) | 0.0590 (12) | 0.0176 (13) | 0.0309 (10) | −0.0026 (11) |
F1 | 0.1103 (15) | 0.1289 (19) | 0.0616 (11) | −0.0115 (13) | 0.0294 (10) | 0.0072 (10) |
O3 | 0.0604 (12) | 0.0973 (16) | 0.0683 (13) | 0.0203 (12) | 0.0259 (10) | 0.0016 (11) |
F22 | 0.0619 (18) | 0.090 (2) | 0.0715 (19) | −0.0175 (17) | 0.0293 (15) | 0.0015 (18) |
F21 | 0.0579 (16) | 0.084 (2) | 0.0758 (18) | −0.0040 (16) | 0.0291 (15) | −0.0006 (17) |
O1W | 0.91 (8) | 0.72 (8) | 0.41 (4) | 0.44 (7) | 0.49 (5) | 0.22 (4) |
O2W | 0.74 (7) | 1.09 (12) | 0.86 (9) | −0.04 (7) | 0.60 (7) | 0.19 (7) |
C1 | 0.0554 (15) | 0.0419 (15) | 0.0622 (16) | 0.0010 (11) | 0.0238 (12) | −0.0001 (11) |
C2 | 0.0585 (16) | 0.0454 (15) | 0.0621 (16) | 0.0026 (12) | 0.0293 (13) | −0.0006 (12) |
C3 | 0.0551 (15) | 0.0474 (15) | 0.0644 (16) | 0.0018 (12) | 0.0256 (12) | −0.0015 (12) |
C4 | 0.0614 (16) | 0.0546 (16) | 0.0633 (17) | 0.0024 (13) | 0.0273 (13) | −0.0041 (13) |
C5 | 0.0620 (17) | 0.0585 (17) | 0.0689 (18) | 0.0033 (14) | 0.0335 (15) | −0.0042 (14) |
C6 | 0.0537 (15) | 0.0495 (15) | 0.0713 (18) | 0.0052 (14) | 0.0262 (13) | 0.0004 (14) |
C7 | 0.0591 (15) | 0.0597 (17) | 0.0657 (18) | 0.0031 (14) | 0.0261 (14) | 0.0002 (13) |
C8 | 0.0555 (15) | 0.0408 (15) | 0.0638 (16) | 0.0029 (11) | 0.0249 (12) | 0.0002 (11) |
C9 | 0.0631 (16) | 0.0510 (15) | 0.0678 (17) | −0.0015 (13) | 0.0277 (13) | 0.0009 (13) |
C10 | 0.0754 (19) | 0.0673 (19) | 0.0697 (19) | −0.0049 (16) | 0.0376 (16) | 0.0022 (16) |
C11 | 0.085 (2) | 0.070 (2) | 0.0562 (17) | 0.0017 (16) | 0.0264 (15) | 0.0061 (14) |
C12 | 0.0597 (17) | 0.0722 (19) | 0.0656 (18) | 0.0014 (15) | 0.0182 (14) | 0.0003 (15) |
C13 | 0.0538 (15) | 0.0548 (16) | 0.0717 (18) | 0.0005 (13) | 0.0293 (13) | 0.0023 (13) |
Geometric parameters (Å, º) top
O2—C7 | 1.234 (3) | C2—C3 | 1.388 (4) |
O1—C4 | 1.355 (3) | C2—H2 | 0.95 (2) |
O1—H1O | 1.11 (6) | C3—C4 | 1.411 (3) |
F1—C11 | 1.361 (3) | C3—C7 | 1.465 (4) |
O3—C7 | 1.316 (3) | C4—C5 | 1.378 (4) |
O3—H2O | 1.00 (3) | C5—C6 | 1.369 (4) |
F22—C9 | 1.343 (4) | C5—H5 | 0.92 (3) |
F21—C13 | 1.355 (4) | C6—H6 | 1.02 (3) |
O1W—O2Wi | 1.18 (4) | C8—C13 | 1.391 (4) |
O1W—H11W | 0.8200 | C8—C9 | 1.395 (4) |
O1W—H21W | 1.1686 | C9—C10 | 1.375 (4) |
O2W—O1Wii | 1.18 (4) | C10—C11 | 1.364 (4) |
O2W—H12W | 0.8200 | C10—H10 | 0.92 (3) |
O2W—H22W | 0.8297 | C11—C12 | 1.371 (4) |
C1—C2 | 1.381 (4) | C12—C13 | 1.375 (4) |
C1—C6 | 1.399 (3) | C12—H12 | 1.02 (3) |
C1—C8 | 1.483 (4) | | |
| | | |
C4—O1—H1O | 116 (3) | C5—C6—H6 | 119.2 (14) |
C7—O3—H2O | 108.5 (17) | C1—C6—H6 | 119.0 (15) |
O2Wi—O1W—H11W | 109.6 | O2—C7—O3 | 121.8 (3) |
O2Wi—O1W—H21W | 27.1 | O2—C7—C3 | 123.2 (2) |
H11W—O1W—H21W | 90.3 | O3—C7—C3 | 114.9 (2) |
O1Wii—O2W—H12W | 109.4 | C13—C8—C9 | 115.3 (2) |
O1Wii—O2W—H22W | 110.9 | C13—C8—C1 | 122.4 (2) |
H12W—O2W—H22W | 130.2 | C9—C8—C1 | 122.3 (2) |
C2—C1—C6 | 117.1 (2) | F22—C9—C10 | 115.6 (3) |
C2—C1—C8 | 121.4 (2) | F22—C9—C8 | 121.2 (3) |
C6—C1—C8 | 121.5 (2) | C10—C9—C8 | 123.2 (3) |
C1—C2—C3 | 122.5 (2) | C11—C10—C9 | 117.7 (3) |
C1—C2—H2 | 118.9 (14) | C11—C10—H10 | 115.5 (17) |
C3—C2—H2 | 118.5 (14) | C9—C10—H10 | 126.8 (18) |
C2—C3—C4 | 118.9 (2) | F1—C11—C10 | 118.8 (3) |
C2—C3—C7 | 121.3 (2) | F1—C11—C12 | 118.2 (3) |
C4—C3—C7 | 119.9 (2) | C10—C11—C12 | 123.0 (3) |
O1—C4—C5 | 118.4 (2) | C11—C12—C13 | 117.3 (3) |
O1—C4—C3 | 122.6 (2) | C11—C12—H12 | 120.3 (16) |
C5—C4—C3 | 119.0 (3) | C13—C12—H12 | 122.4 (16) |
C6—C5—C4 | 120.8 (3) | F21—C13—C12 | 115.4 (3) |
C6—C5—H5 | 125.1 (17) | F21—C13—C8 | 121.0 (3) |
C4—C5—H5 | 114.1 (17) | C12—C13—C8 | 123.6 (2) |
C5—C6—C1 | 121.8 (3) | | |
| | | |
C6—C1—C2—C3 | 0.0 (4) | C2—C1—C8—C9 | −43.2 (3) |
C8—C1—C2—C3 | −179.5 (2) | C6—C1—C8—C9 | 137.4 (3) |
C1—C2—C3—C4 | 0.3 (4) | C13—C8—C9—F22 | 179.2 (3) |
C1—C2—C3—C7 | 179.5 (2) | C1—C8—C9—F22 | −1.9 (4) |
C2—C3—C4—O1 | 179.3 (3) | C13—C8—C9—C10 | 0.1 (4) |
C7—C3—C4—O1 | 0.1 (4) | C1—C8—C9—C10 | 179.0 (3) |
C2—C3—C4—C5 | −0.2 (4) | F22—C9—C10—C11 | −179.0 (3) |
C7—C3—C4—C5 | −179.4 (3) | C8—C9—C10—C11 | 0.2 (5) |
O1—C4—C5—C6 | −179.7 (3) | C9—C10—C11—F1 | −179.9 (3) |
C3—C4—C5—C6 | −0.2 (4) | C9—C10—C11—C12 | 0.3 (5) |
C4—C5—C6—C1 | 0.5 (4) | F1—C11—C12—C13 | 179.3 (3) |
C2—C1—C6—C5 | −0.3 (4) | C10—C11—C12—C13 | −1.0 (5) |
C8—C1—C6—C5 | 179.1 (2) | C11—C12—C13—F21 | −174.8 (3) |
C2—C3—C7—O2 | −179.3 (3) | C11—C12—C13—C8 | 1.2 (5) |
C4—C3—C7—O2 | −0.1 (4) | C9—C8—C13—F21 | 175.1 (3) |
C2—C3—C7—O3 | 0.9 (4) | C1—C8—C13—F21 | −3.9 (4) |
C4—C3—C7—O3 | −180.0 (2) | C9—C8—C13—C12 | −0.8 (4) |
C2—C1—C8—C13 | 135.7 (3) | C1—C8—C13—C12 | −179.7 (3) |
C6—C1—C8—C13 | −43.7 (3) | | |
Symmetry codes: (i) −x+1/2, y+1/2, −z+1/2; (ii) −x+1/2, y−1/2, −z+1/2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H2O···O2iii | 1.00 (4) | 1.65 (4) | 2.650 (3) | 176 (4) |
O1—H1O···O2 | 1.11 (6) | 1.75 (6) | 2.620 (4) | 131 (4) |
Symmetry code: (iii) −x+1/2, −y+1/2, −z+1. |
Experimental details
Crystal data |
Chemical formula | C13H8F2O3·H2O |
Mr | 268.21 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 298 |
a, b, c (Å) | 34.650 (2), 3.730 (2), 20.760 (2) |
β (°) | 110.47 (6) |
V (Å3) | 2513.7 (14) |
Z | 8 |
Radiation type | Mo Kα |
µ (mm−1) | 0.12 |
Crystal size (mm) | 0.30 × 0.20 × 0.15 |
|
Data collection |
Diffractometer | Enraf-Nonius CAD-4 diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 2306, 2221, 1127 |
Rint | 0.014 |
(sin θ/λ)max (Å−1) | 0.595 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.050, 0.178, 0.83 |
No. of reflections | 2221 |
No. of parameters | 225 |
No. of restraints | 12 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.26, −0.16 |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H2O···O2i | 1.00 (4) | 1.65 (4) | 2.650 (3) | 176 (4) |
O1—H1O···O2 | 1.11 (6) | 1.75 (6) | 2.620 (4) | 131 (4) |
Symmetry code: (i) −x+1/2, −y+1/2, −z+1. |
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Diflunisal is a difluorphenyl derivative of acetyl salicylic acid (aspirin), which is used therapeutically as an anti-inflammatory drug similar to aspirin. The structure of unsolvated diflunisal was described earlier (Kim & Park, 1996). However, this new investigation displays properties of clathrate materials and includes in the crystal lattice solvent molecules. Here, the structure of its hydrate, (I), is reported. The investigated structure is characterized as a packing of the diflunisal dimers, which is obtained by energetic equivalent hydrogen bonds between two adjacent molecules (Table 1). Probably, atom O2 takes part in forming not only the intermolecular bonds but also the intramolecular ones O1—H10···O2.
The conformation state of a diflunisal molecule may be characterized as follows: the phenyl planes are tilted round the C1—C8 bond by a dihedral angle of 43.9 (1)°. Similar values of angles have been reported for π-stacking interactions in nucleic acids (Langlet et al., 1981; Rein, 1978; Claverie, 1978). For comparison, the planes of benzene molecules in an orthorhombic crystal, which are situated 5.81 Å apart, form a dihedral angle of 29° (Bacon at al., 1964). It should be noted that theoretical analysis of the structure of benzene clusters (Sun & Bernstein, 1996) derives dihedral angles between planes of benzene molecules corresponding to approximately 40°, where the molecules are packed in a herring-bone fashion.
In diflunisal, the hydroxyl group is tilted against the phenyl group: the torsion angle C3—C4—O1—H1O is 3(3)°. The geometry of carboxyl group slightly differs from a planar arrangement [torsion angle O2—C7—O3—H2O is 2(2)°] and is approximately coplanar with the phenyl fragment [torsion angle O3—C7—C3—C2 is 0.7 (4)°]. The F atoms in positions 2'- and 6'- are disordered. This means that the peaks found for F21 and F22 are a combination of a half-hydrogen peak with a half-fluorine peak even though the bond lengths found for the C—F bonds are normal. This may be explained by the fact that fluorine is a much heavier element compared to hydrogen (19:1), so the influence of hydrogen on the C—F bond will be negligible. The phenyl groups of neighbouring parallel molecules are stacked face-to-face and shifted by Rshift = 1.6 Å. The distance between these planes of the phenyl rings is Rb = 3.73 Å. These parameters are in good agreement with the values for the local energetic minimum calculated for benzene dimers: Rshift* = 1.6 Å and Rb* = 3.85 Å (Hobza at al., 1993, 1994), and the relative orientation and packing of phenyl rings in diflunisal follow in general the rules of packing of benzene dimers. Out of four energetic minima calculated for benzene arrangement (parallel staggered PS; parallel displaced, PD; herring-bone, H; T-shape, T), in the present case, two such local energetic minima are realised (PD and H).
The characteristic (specific) property of the crystal lattice of diflunisal is the existence of channels along the twofold screw axes and parallel to the b direction. The geometry of these channels allows accommodation of solvent molecules of appropriate sizes. In the present case, the channels are filled by water molecules, which are situated in a disordered state. It should be noted the investigated solvate is stable at room conditions. In order to check the stoichiometry of the solvate DSC and TG measurements were carried out at various heating rates (v = 1–20 K min-1). The heat effect occurring during desolvation at v = 10 K min-1 and temperature interval from 353 to 383 K is 16 J mol-1. The average mass losses achieved 7.1% and it corresponded to a stoichiometry of diflunisal:water as 1:1. This result is in a good agreement with the X-ray experiment. Considering the possible orientations of the water molecule in the two sites, a calculation has been carried out by using the HYDROGEN program (Nardelli, 1999). These results lead to conclude that the water molecules in the channels form hydrogen bonds between themselves. However, these molecules (guests) are located at relatively long distances from host(diflunisal)-molecules and do not take part in specific host–guest interactions.