6-[(2E)-3,7-Dimethylocta-2,6-dien-1-yl]-5,7-dihydroxy-8-(2-methylbutanoyl)-4-phenyl-2H-chromen-2-one–6-[(2E)-3,7-dimethylocta-2,6-dien-1-yl]-5,7-dihydroxy-8-(3-methylbutanoyl)-4-phenyl-2H-chromen-2-one (1/1) from Mesua elegans 1

The title co-crystal, C30H34O5·C30H34O5, comprises a 1:1 mixture of two mostly superimposed molecules with the same chemical formula that differ in the nature of the substituent (2-methylbutanoyl or 3-methylbutanoyl) bound at the exocyclic ketone. The lactone ring is close to planar (r.m.s. deviation = 0.058 Å) and the phenyl ring is twisted out of this plane [dihedral angle = 60.08 (9)°]. The geranyl substituent is almost normal to benzene ring to which it is connected [C—C—Car—Car (ar = aromatic) torsion angle = −87.8 (2)°]. Intramolecular O—H⋯O and O—H⋯π interactions are formed. In the crystal, supramolecular chains are formed along the a axis owing to C—H⋯O contacts, with the lactone carbonyl atom accepting two such bonds.

The title co-crystal, C 30 H 34 O 5 ÁC 30 H 34 O 5 , comprises a 1:1 mixture of two mostly superimposed molecules with the same chemical formula that differ in the nature of the substituent (2-methylbutanoyl or 3-methylbutanoyl) bound at the exocyclic ketone. The lactone ring is close to planar (r.m.s. deviation = 0.058 Å ) and the phenyl ring is twisted out of this plane [dihedral angle = 60.08 (9) ]. The geranyl substituent is almost normal to benzene ring to which it is connected [C-C-C ar -C ar (ar = aromatic) torsion angle = À87.8 (2) ]. Intramolecular O-HÁ Á ÁO and O-HÁ Á Á interactions are formed. In the crystal, supramolecular chains are formed along the a axis owing to C-HÁ Á ÁO contacts, with the lactone carbonyl atom accepting two such bonds.   Table 1 Hydrogen-bond geometry (Å , ).
The molecular components of the co-crystal (I) are shown in Figs 1 and 2. The r.m.s. deviation for the fitted atoms of the lactone ring = 0.058 Å with maximum deviations of 0.043 (2) Å for the C3 atoms and -0.058 (2) Å for the C4 atom.
The phenyl ring is twisted out of this plane, forming a dihedral angle of 60.08 (9)°. The excocyclic carbonyl atom is coplanar with the benzene ring to which it is connected with the C7-C8-C26-O5 torsion angle being 2.2 (10)°; the equivalent torsion angle for the molecule with the 3-methylbutanoyl is 9.9 (9)°. The co-planarity is readily accounted for in terms of intramolecular O-H···O hydrogen bonds. The geranyl group projects almost normal to the plane through the benzene ring with the C5-C6-C16-C17 torsion angle being -87.8 (2)°. The second hydroxyl group forms an intramolecular O-H···π interaction with the phenyl ring, Table 1.
In the crystal, the lactone-carbonyl atom participates in two C-H···O interactions, Table 1, to link molecules into a supramolecular chain along the a axis, Fig. 3.

Experimental
Dried ground bark (1.5 kg) of Mesua elegans (Clusiaceae), collected from Sungai Badak Forest Reserve, Sintok, Kedah, Malaysia, was extracted with hexane (3 × 4 L, 48 h) at room temperature. The hexane was evaporated to give a yellow gum (120 g). A portion of the extract (10 g) was subjected to column chromatography over silica gel (230-400 mesh) and eluted with hexane:ethyl acetate (from 9.5 to 0) and ethyl acetate:methanol (5:5) to give six fractions. The first fraction was subjected to further silica gel chromatography and eluted with hexane:ethyl acetate (from 9.7 to 9.4) to produce two other sub-fractions. The co-crystal was obtained from the second sub-fraction and recrystallized from its methanol solution as colourless prisms.

Refinement
Carbon-bound H-atoms were placed in calculated positions [C-H = 0.95 to 1.00 Å, U iso (H) = 1.2 to 1.5U eq (C)] and were included in the refinement in the riding model approximation. The hydroxy H-atoms were located in a difference Fourier map, and were refined with a distance restraint of O-H = 0.84±0.01 Å; their U iso values were refined.
The crystal is a co-crystal of two molecules having an identical chemical composition. One has an 2-methylbutanoyl substituent in the fused-ring whereas the other has the isomeric 3-methylbutanoyl substituent. As the occupancy refined to a nearly 1:1 ratio, the occupancy of each substituent was set as exactly 0.5.