Crystal structures and hydrogen bonding in the morpholinium salts of four phenoxyacetic acid analogues

The anhydrous morpholinium salts of phenoxyacetic acid, (4-fluorophenoxy)acetic acid and the isomeric (3,5-dichlorophenoxy)acetic acid and (2,4-dichlorophenoxy)acetic acid, provide three similar examples of one-dimensional hydrogen-bonded chain polymers and one of a cyclic hydrogen-bonded heterotetramer.


Figure 3
The atom-numbering scheme and the molecular conformation of the morpholinium cation (B) and the 3,5-D anion (A) in (III), with displacement ellipsoids drawn at the 40% probability level. The cationanion hydrogen bonds are shown as dashed lines.

Figure 4
The atom-numbering scheme and the molecular conformation of the morpholinium cation (B) and the 2,4-D anion (A) in (IV), with displacement ellipsoids drawn at the 40% probability level. The cationanion hydrogen bonds are shown as dashed lines.

Figure 6
The one-dimensional hydrogen-bonded polymeric structure of (II) extending along a. For symmetry codes, see Table 2.

Figure 7
The one-dimensional hydrogen-bonded polymeric structure of (III) extending along a. For symmetry codes, see Table 3 Figure 8 The cyclic hydrogen-bonded heterotetramer structure of (IV). For symmetry codes, see Table 4.
Only weak inter-unit C-HÁ Á ÁO interactions to carboxyl or phenoxy O-atom acceptors are present in (IV) ( Table 4), while nointeractions are found in any of the structures.

Synthesis and crystallization
The title compounds (I)-(IV) were prepared by the dropwise addition of morpholine at room temperature to solutions of phenoxyacetic acid (150 mg), (4-fluorophenoxy)acetic (170 mg), (2,4-dichlorophenoxy)acetic acid or (2,4-dichlorophenoxy)acetic acid (220 mg), respectively, in 15 ml of ethanol. Room-temperature evaporation of the solutions gave either colourless plates of (III) or needles of (IV) from which specimens were cleaved for the X-ray analyses. For (I) and (II), the same preparative procedure was employed using phenoxyacetic acid or (4-fluorophenoxy)acetic acid but the final oils which resulted after solvent evaporation were redissolved in ethanol, finally giving thin colourless fragile plates of compounds (I) and (II) from which specimens were cleaved for the X-ray analyses.

(I) Tetrahydro-2H-1,4-oxazin-4-ium phenoxyacetate
Crystal data Hall symbol: -P 1 a = 5.7079 (5) Å b = 9.7735 (9) Å c = 11.3586 (10) Å α = 78.277 (7)°β = 86.171 (7)°γ = 77.512 (7)  Hydrogen site location: inferred from neighbouring sites H atoms treated by a mixture of independent and constrained refinement where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.16 e Å −3 Δρ min = −0.17 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

(III) Tetrahydro-2H-1,4-oxazin-4-ium (3,5-dichlorophenoxy)acetate
Crystal data C 4 H 10 NO + ·C 8 H 5 Cl 2 O 3 − M r = 308.15 Triclinic, P1 Hall symbol: -P 1 a = 5.1733 (4) Å b = 11.3751 (10) Å c = 11.7808 (10) Å α = 86.904 (7)°β = 85.106 (7) Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.