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The structure of the hemihydrate of sodium phenoxy­acetate, Na+·C8H7O3-·0.5H2O, has been redetermined at low temperature (160 K). The structure consists of ribbons containing octahedral NaO6 units, and half of the Na2O2 squares within the ribbon are bridged by water mol­ecules which lie across twofold rotation axes in C2/c. The phenyl substituents lie on the outside of the ribbon.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270101013762/gd1176sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270101013762/gd1176Isup2.hkl
Contains datablock I

CCDC reference: 175070

Comment top

The structure of the title compound, (I), was first solved by X-ray photography (R = 0.096; Prout et al., 1971) and has now been redetermined at 160 K (R = 0.052) during an investigation of the impact of impurities on the crystallization of phenoxyacetic acid. The structure consists of a ribbon-like Na–O core, running parallel to the [001] direction, which is bridged above and below by water molecules. As in the acid salt (Evans et al., 2001), the phenyl groups form hydrocarbon layers on the outside of the Na–O ribbon. The ribbon consists of sodium ions surrounded by six O atoms in a distorted octahedral arrangement. The shortest Na···Na bridging distances [range 3.179 (2)–4.0384 (16) Å] are similar to those reported for other bridging systems (Albertsson, 1973).

Hydrates of other metal salts of phenoxyacetate have been determined. Some, like the sodium salt, are oligomeric, namely the lead (Archer et al., 1996; Mak et al., 1985) magnesium and cobalt salts (Smith et al., 1980), whereas the cadmium (Mak et al., 1985) and copper (Prout et al., 1968) derivatives contain discrete units.

Two structural features were identified in the CO2- group in the title compound. First, the distortion of the exo-C1 angles C15–C10–O1 and C11–C10–O1 [123.3 (2) and 116.4 (2)°, respectively], which deviate from the trigonal angle (120°). The distortion is caused by the steric requirements of the side chain and is found throughout the phenoxyalkanoic acid series (Kennard et al., 1982; Evans et al., 2001). Secondly, the C—O distances for both C2—O3 and C2—O2 are identical [1.251 (3) Å], and the former of the O3–C2–C3 and O2–C2–C3 angles [113.6 (2) and 119.0 (2) Å] deviates from the trigonal value. In disordered carboxylic acid groups (Leiserowitz, 1976), both bond lengths are also the same, but the O—C—C angles are both close to 120°. In the title compound, the similarity in C—O distances arises because the CO2- group is delocalized. However, the O2 and O3 atoms do not have similar environments, as O3 is involved in a hydrogen bond with water (see Table 2) and O2 is not. In contrast, O2 has many more contacts with sodium ions (see Table 1) as it is orientated into the NaO core.

Related literature top

For related literature, see: Albertsson et al. (1973); Archer et al. (1996); Evans et al. (2001); Kennard et al. (1982); Leiserowitz (1976); Mak et al. (1985); Prout et al. (1968, 1971); Smith et al. (1980).

Experimental top

A sample of powdered sodium hydrogen bis(phenoxyacetate) hydrate (Sigma–Aldrich) was dissolved in Edinburgh tap water and single crystals of sodium phenoxyacetate hemihydrate were obtained by slow evaporation of the aqueous solution.

Refinement top

The water H atoms were located in the difference map and their coordinates were freely refined, but their displacement parameters were treated as riding on oxygen (1.2Ueq of the bound atom). H atoms bonded to C atoms were treated as riding, with C—H distances in the range 0.95–0.99 Å.

Computing details top

Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: SHELXTL (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound viewed down the b axis. The unit cell is superimposed, one-fifth of the original size. Displacement ellipsoids are shown at the 60% probability level. [Symmetry codes: (A) 1 - x, -y, -z; (B) 1 - x, y, 0.5 - z; (C) x, -y, z - 0.5; (D) x, y, z - 1.]
Sodium phenoxyacetate hemihydrate top
Crystal data top
Na+·C8H7O3·0.5H2OF(000) = 760
Mr = 183.13Dx = 1.530 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
a = 34.149 (11) ÅCell parameters from 32 reflections
b = 7.654 (3) Åθ = 5.3–12.3°
c = 6.144 (2) ŵ = 0.16 mm1
β = 98.02 (3)°T = 160 K
V = 1590.2 (10) Å3Needle, colourless
Z = 80.74 × 0.26 × 0.05 mm
Data collection top
Bruker P4
diffractometer
1127 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.069
Graphite monochromatorθmax = 25.0°, θmin = 2.4°
ω scansh = 401
Absorption correction: ψ scan
(North et al., 1968)
k = 91
Tmin = 0.719, Tmax = 0.792l = 77
1719 measured reflections3 standard reflections every 97 reflections
1400 independent reflections intensity decay: none
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)] = 0.052Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.139H atoms treated by a mixture of independent and constrained refinement
S = 1.04 w = 1/[σ2(Fo2) + (0.0816P)2 + 1.4634P]
where P = (Fo2 + 2Fc2)/3
1400 reflections(Δ/σ)max < 0.001
117 parametersΔρmax = 0.36 e Å3
0 restraintsΔρmin = 0.49 e Å3
Crystal data top
Na+·C8H7O3·0.5H2OV = 1590.2 (10) Å3
Mr = 183.13Z = 8
Monoclinic, C2/cMo Kα radiation
a = 34.149 (11) ŵ = 0.16 mm1
b = 7.654 (3) ÅT = 160 K
c = 6.144 (2) Å0.74 × 0.26 × 0.05 mm
β = 98.02 (3)°
Data collection top
Bruker P4
diffractometer
1127 reflections with I > 2σ(I)
Absorption correction: ψ scan
(North et al., 1968)
Rint = 0.069
Tmin = 0.719, Tmax = 0.7923 standard reflections every 97 reflections
1719 measured reflections intensity decay: none
1400 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0520 restraints
wR(F2) = 0.139H atoms treated by a mixture of independent and constrained refinement
S = 1.04Δρmax = 0.36 e Å3
1400 reflectionsΔρmin = 0.49 e Å3
117 parameters
Special details top

Experimental. Collimator size 1.5 mm

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
Na10.46847 (3)0.17124 (13)0.03367 (15)0.0158 (3)
O10.40157 (5)0.2474 (2)0.1427 (3)0.0191 (5)
O20.46095 (5)0.1196 (2)0.4207 (3)0.0176 (4)
O30.44708 (5)0.2918 (3)0.6954 (3)0.0193 (5)
O40.50000.4255 (4)0.25000.0225 (6)
H40.5200 (9)0.492 (5)0.247 (5)0.027*
C20.44134 (7)0.2340 (3)0.5031 (4)0.0142 (5)
C30.40562 (7)0.3153 (3)0.3616 (4)0.0165 (6)
H3A0.38140.28960.42730.020*
H3B0.40890.44370.35780.020*
C100.36439 (7)0.2537 (3)0.0232 (4)0.0149 (5)
C110.35837 (8)0.1527 (3)0.1669 (4)0.0192 (6)
H11A0.37960.08770.21160.023*
C120.32123 (8)0.1475 (4)0.2904 (4)0.0239 (6)
H12A0.31710.07840.41990.029*
C130.29003 (8)0.2417 (4)0.2277 (4)0.0244 (6)
H13A0.26450.23520.31150.029*
C140.29651 (8)0.3456 (4)0.0413 (4)0.0225 (6)
H14A0.27530.41180.00140.027*
C150.33357 (8)0.3539 (4)0.0838 (4)0.0194 (6)
H15A0.33790.42730.20950.023*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Na10.0206 (6)0.0161 (6)0.0109 (5)0.0006 (4)0.0027 (4)0.0010 (4)
O10.0202 (9)0.0267 (10)0.0107 (9)0.0048 (8)0.0037 (7)0.0033 (8)
O20.0210 (9)0.0157 (9)0.0170 (9)0.0031 (7)0.0062 (7)0.0026 (7)
O30.0238 (10)0.0225 (10)0.0114 (9)0.0012 (8)0.0016 (7)0.0004 (7)
O40.0324 (15)0.0138 (14)0.0232 (14)0.0000.0107 (12)0.000
C20.0162 (12)0.0127 (12)0.0147 (12)0.0044 (10)0.0060 (10)0.0021 (10)
C30.0211 (13)0.0178 (13)0.0114 (12)0.0019 (10)0.0047 (10)0.0009 (10)
C100.0186 (12)0.0150 (12)0.0115 (12)0.0019 (10)0.0035 (9)0.0036 (10)
C110.0261 (14)0.0184 (13)0.0142 (12)0.0009 (11)0.0067 (10)0.0002 (11)
C120.0325 (15)0.0264 (15)0.0128 (13)0.0080 (12)0.0029 (11)0.0013 (11)
C130.0206 (13)0.0323 (16)0.0194 (14)0.0057 (12)0.0003 (11)0.0037 (12)
C140.0214 (13)0.0254 (15)0.0218 (14)0.0026 (11)0.0067 (11)0.0036 (12)
C150.0228 (13)0.0215 (14)0.0139 (12)0.0012 (11)0.0033 (10)0.0002 (11)
Geometric parameters (Å, º) top
Na1—O3i2.298 (2)C2—C31.528 (3)
Na1—O2ii2.335 (2)C3—H3A0.9900
Na1—O2iii2.420 (2)C3—H3B0.9900
Na1—O22.459 (2)C10—C111.392 (4)
Na1—O42.513 (2)C10—C151.394 (4)
Na1—O12.537 (2)C11—C121.385 (4)
Na1—Na1iii3.179 (2)C11—H11A0.9500
Na1—Na1iv3.454 (2)C12—C131.385 (4)
Na1—Na1ii4.0384 (16)C12—H12A0.9500
O1—C101.376 (3)C13—C141.387 (4)
O1—C31.431 (3)C13—H13A0.9500
O2—C21.251 (3)C14—C151.388 (4)
O3—C21.251 (3)C14—H14A0.9500
O4—H40.85 (3)C15—H15A0.9500
O3i—Na1—O2ii96.08 (7)O3—C2—O2127.4 (2)
O3i—Na1—O2iii110.87 (7)O3—C2—C3113.6 (2)
O2ii—Na1—O2iii86.86 (7)O2—C2—C3119.0 (2)
O3i—Na1—O2151.19 (7)O1—C3—C2110.6 (2)
O2ii—Na1—O296.45 (6)O1—C3—H3A109.5
O2iii—Na1—O295.65 (7)C2—C3—H3A109.5
O3i—Na1—O4103.07 (7)O1—C3—H3B109.5
O2ii—Na1—O4156.46 (7)C2—C3—H3B109.5
O2iii—Na1—O473.67 (6)H3A—C3—H3B108.1
O2—Na1—O473.01 (6)O1—C10—C11116.4 (2)
O3i—Na1—O187.83 (7)O1—C10—C15123.5 (2)
O2ii—Na1—O1103.40 (7)C11—C10—C15120.1 (2)
O2iii—Na1—O1157.84 (7)C12—C11—C10119.5 (2)
O2—Na1—O164.04 (6)C12—C11—H11A120.3
O4—Na1—O191.01 (6)C10—C11—H11A120.3
C10—O1—C3116.72 (18)C11—C12—C13121.0 (3)
C10—O1—Na1131.72 (14)C11—C12—H12A119.5
C3—O1—Na1111.06 (14)C13—C12—H12A119.5
C2—O2—Na1v126.13 (15)C12—C13—C14119.2 (3)
C2—O2—Na1iii114.81 (16)C12—C13—H13A120.4
Na1v—O2—Na1iii93.14 (7)C14—C13—H13A120.4
C2—O2—Na1114.37 (15)C13—C14—C15120.8 (3)
Na1v—O2—Na1114.75 (8)C13—C14—H14A119.6
Na1iii—O2—Na181.32 (7)C15—C14—H14A119.6
C2—O3—Na1vi134.45 (17)C14—C15—C10119.4 (2)
Na1—O4—Na1iii78.48 (10)C14—C15—H15A120.3
Na1—O4—H4137 (2)C10—C15—H15A120.3
Na1iii—O4—H4101 (2)
O3i—Na1—O1—C1033.2 (2)O4—Na1—O2—Na1iii52.29 (5)
O2ii—Na1—O1—C1062.6 (2)O1—Na1—O2—Na1iii152.04 (7)
O2iii—Na1—O1—C10178.4 (2)Na1iv—Na1—O2—Na1iii61.42 (7)
O2—Na1—O1—C10153.3 (2)Na1ii—Na1—O2—Na1iii104.16 (5)
O4—Na1—O1—C10136.2 (2)Na1v—Na1—O2—Na1iii89.47 (8)
Na1iii—Na1—O1—C10175.07 (19)O3i—Na1—O4—Na1iii159.36 (7)
Na1iv—Na1—O1—C1086.3 (2)O2ii—Na1—O4—Na1iii15.73 (13)
Na1ii—Na1—O1—C1029.5 (2)O2iii—Na1—O4—Na1iii51.12 (5)
Na1v—Na1—O1—C10125.5 (2)O2—Na1—O4—Na1iii50.23 (5)
O3i—Na1—O1—C3138.19 (16)O1—Na1—O4—Na1iii112.64 (6)
O2ii—Na1—O1—C3126.07 (16)Na1iv—Na1—O4—Na1iii41.18 (4)
O2iii—Na1—O1—C310.2 (3)Na1ii—Na1—O4—Na1iii92.96 (10)
O2—Na1—O1—C335.36 (15)Na1v—Na1—O4—Na1iii31.05 (3)
O4—Na1—O1—C335.15 (16)Na1vi—O3—C2—O235.7 (4)
Na1iii—Na1—O1—C313.59 (16)Na1vi—O3—C2—C3143.41 (18)
Na1iv—Na1—O1—C3102.40 (18)Na1v—O2—C2—O362.3 (3)
Na1ii—Na1—O1—C3159.13 (14)Na1iii—O2—C2—O352.0 (3)
Na1v—Na1—O1—C363.18 (15)Na1—O2—C2—O3143.5 (2)
O3i—Na1—O2—C225.2 (3)Na1v—O2—C2—C3116.7 (2)
O2ii—Na1—O2—C2140.46 (14)Na1iii—O2—C2—C3128.97 (19)
O2iii—Na1—O2—C2132.08 (16)Na1—O2—C2—C337.4 (3)
O4—Na1—O2—C261.08 (16)C10—O1—C3—C2156.0 (2)
O1—Na1—O2—C238.66 (16)Na1—O1—C3—C231.3 (2)
Na1iii—Na1—O2—C2113.38 (18)O3—C2—C3—O1178.2 (2)
Na1iv—Na1—O2—C2174.80 (16)O2—C2—C3—O12.6 (3)
Na1ii—Na1—O2—C2142.46 (15)C3—O1—C10—C11165.4 (2)
Na1v—Na1—O2—C2157.2 (2)Na1—O1—C10—C1123.6 (3)
O3i—Na1—O2—Na1v131.95 (14)C3—O1—C10—C1514.5 (3)
O2ii—Na1—O2—Na1v16.70 (13)Na1—O1—C10—C15156.49 (19)
O2iii—Na1—O2—Na1v70.77 (9)O1—C10—C11—C12177.5 (2)
O4—Na1—O2—Na1v141.76 (9)C15—C10—C11—C122.4 (4)
O1—Na1—O2—Na1v118.50 (10)C10—C11—C12—C130.1 (4)
Na1iii—Na1—O2—Na1v89.47 (8)C11—C12—C13—C141.5 (4)
Na1iv—Na1—O2—Na1v28.04 (10)C12—C13—C14—C150.9 (4)
Na1ii—Na1—O2—Na1v14.70 (11)C13—C14—C15—C101.3 (4)
O3i—Na1—O2—Na1iii138.58 (13)O1—C10—C15—C14176.9 (2)
O2ii—Na1—O2—Na1iii106.17 (7)C11—C10—C15—C143.0 (4)
O2iii—Na1—O2—Na1iii18.70 (9)
Symmetry codes: (i) x, y, z1; (ii) x, y, z1/2; (iii) x+1, y, z+1/2; (iv) x+1, y, z; (v) x, y, z+1/2; (vi) x, y, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O4—H4···O3vii0.85 (3)2.00 (3)2.809 (3)157 (3)
Symmetry code: (vii) x+1, y+1, z+1.

Experimental details

Crystal data
Chemical formulaNa+·C8H7O3·0.5H2O
Mr183.13
Crystal system, space groupMonoclinic, C2/c
Temperature (K)160
a, b, c (Å)34.149 (11), 7.654 (3), 6.144 (2)
β (°) 98.02 (3)
V3)1590.2 (10)
Z8
Radiation typeMo Kα
µ (mm1)0.16
Crystal size (mm)0.74 × 0.26 × 0.05
Data collection
DiffractometerBruker P4
diffractometer
Absorption correctionψ scan
(North et al., 1968)
Tmin, Tmax0.719, 0.792
No. of measured, independent and
observed [I > 2σ(I)] reflections
1719, 1400, 1127
Rint0.069
(sin θ/λ)max1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.052, 0.139, 1.04
No. of reflections1400
No. of parameters117
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.36, 0.49

Computer programs: XSCANS (Siemens, 1996), XSCANS, SHELXTL (Bruker, 1999), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXTL.

Selected geometric parameters (Å, º) top
Na1—O3i2.298 (2)Na1—Na1iv3.454 (2)
Na1—O2ii2.335 (2)Na1—Na1ii4.0384 (16)
Na1—O2iii2.420 (2)O1—C101.376 (3)
Na1—O22.459 (2)O1—C31.431 (3)
Na1—O42.513 (2)O2—C21.251 (3)
Na1—O12.537 (2)O3—C21.251 (3)
Na1—Na1iii3.179 (2)
O3i—Na1—O2ii96.08 (7)O2iii—Na1—O473.67 (6)
O3i—Na1—O2iii110.87 (7)O2—Na1—O473.01 (6)
O2ii—Na1—O2iii86.86 (7)O3i—Na1—O187.83 (7)
O3i—Na1—O2151.19 (7)O2ii—Na1—O1103.40 (7)
O2ii—Na1—O296.45 (6)O2iii—Na1—O1157.84 (7)
O2iii—Na1—O295.65 (7)O2—Na1—O164.04 (6)
O3i—Na1—O4103.07 (7)O4—Na1—O191.01 (6)
O2ii—Na1—O4156.46 (7)
Symmetry codes: (i) x, y, z1; (ii) x, y, z1/2; (iii) x+1, y, z+1/2; (iv) x+1, y, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O4—H4···O3v0.85 (3)2.00 (3)2.809 (3)157 (3)
Symmetry code: (v) x+1, y+1, z+1.
 

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