Supra­molecular networks in (9-fluoro-4H-chromeno[4,3-c]isoxazol-3-yl)methanol and its 9-chloro analogue at 100 K

The title compounds, (9-fluoro-4H-chromeno[4,3-c]isoxazol-3-yl)methanol, C₁₁H₈FNO₃, (I), and (9-chloro-4H-chromeno[4,3-c]isoxazol-3-yl)methanol, C₁₁H₈ClNO₃, (II), crystallize in the ortho­rhom­bic space group Pbca with Z′ = 1 and the triclinic space group P with Z′ = 6, respectively. The simple replacement of F by Cl in the main mol­ecular scaffold of (I) and (II) results in significant differences in the inter­molecular inter­action patterns and a corresponding change in the point-group symmetry from D_2h to C_i = S₂. These striking differences are manifested through the presence of C—H...F and the absence of O—H...O and C—H...O inter­actions in (I), and the absence of C—H...Cl and the presence of O—H...O and C—H...O inter­actions in (II). However, the geometry of the synthons formed by the O—H...N and O—H...X (X = F or Cl) inter­actions observed in the constitution of the supra­molecular networks of both (I) and (II) remains similar. Also, C—H...O inter­actions are not preferred in the presence of F in (I), while they are much preferred in the presence of Cl in (II).

Supra­molecular sheets in (4H-chromeno[4,3-c]isoxazol-3-yl)methanol and its hydrated 8-methyl-substituted analogue at 100 K

The title compounds, (4H-chromeno[4,3-c]isoxazol-3-yl)metha­nol, C₁₁H₉NO₃, (I), and (8-methyl-4H-chromeno[4,3-c]isoxazol-3-yl)methanol monohydrate, C₁₂H₁₁NO₃·H₂O, (II), crystallize in the monoclinic space groups P2₁/c and C2/c, respectively. The simple addition of a methyl substituent in (II) results in a change in the structure type and substantially alters the inter­molecular inter­action patterns, while retaining the point-group symmetry 2/m. Compound (II) crystallizes as a hydrate and the resulting hydrogen-bonding inter­actions involving the water mol­ecule are the cause of differences in the hydrogen-bonded supra­molecular motifs present in (I) and (II). The water mol­ecule in (II) is disordered over two positions having very similar orientations, with occupancies of 0.571 (18) and 0.429 (18), although the pattern of hydrogen-bonding inter­actions for the two disordered water mol­ecules remains essentially the same. In both compounds, the primary donor hy­droxy group adopts a trans conformation with respect to the isoxazole O atom, with a torsion angle of 170.65 (8)° for (I) and 179.56 (10)° for (II), the small difference being due to differences in the hydrogen-bonding environment of the hy­droxy group. In (I), mol­ecules are linked through two independent O-H...N and C-H...O hydrogen bonds and form sheets of centrosymmetric R₄⁴(18) and R₄⁴(14) rings extending parallel to the (100) plane. The supra­molecular motifs in (II) generate two-dimensional sheets parallel to the (100) plane through a combination of O-H...X (X = N, O) and C-H...O hydrogen bonds, leading to water-assisted noncentrosymmetric R₂²(8) and R₆⁶(20) motifs. The present work is an example of how the simple replacement of a substituent in the main mol­ecular scaffold may transform the structure type, paving the way for a variety of supra­molecular motifs and consequently altering the complexity of the inter­molecular inter­action patterns.