Crystal Structure of 2-(4-Hydroxy-3-Methoxyphenyl)-6- (4-Hydroxy-3-Methoxystyryl)-1-Methyl-2, 3-Dihydropyridine-4 (1H)-One by X-Ray Powder Diffraction

Problem statement: The studied dihydropyridone was synthesized for th e first time via the microwave assisted reaction of curcumin and methylamine and it is important to support the mechanism by the crystal structure. Approach: The crystal structure of the title compound was determined using high resolution x-ray diffract ion. PowderSolve program was used to solve the structure while the refinement was done in mate ri l studio Reflex module. Results: The findings obtained with high-resolution x-ray powder diffraction and molecular location methods based on simulated annealing algorithm after Rietve ld r finement showed that the monoclinic unit cell was a = 13.4925 Å, b = 12.8162 Å, c = 11.5231 Å, α = 90.000°, β = 99.0401°, γ = 90.000°; cell volume = 1967.85 Å 3 and space group P 21/a with 4 molecules in a unit cell. Conclusion/Recommendations: Powder diffractometry could be a powerful tool for determining crystal structures for organic molecules.

The compound is yellow powder and difficult to crystallize. Powder x-ray diffraction is the method of choice for characterizing the structures if solids are not available as suitable single crystals. Over past decade, Structure Determination from Powder Diffraction (SDPD) has matured into a technique that is widely and successfully used in the context of organic, inorganic and organometallic compounds (David and Shankland, 2008;Bail, 2005).

MATERIALS AND METHODS
The compound was synthesized according to previously described procedure (Elias et al., 2008).
High resolution x-ray powder diffraction data was collected on an MXPI8A-HF (MAC science, Japan) diffractometer with Cu-Kα (1.540593 Å) radiation at room temperature. The tube voltage and the tube current were 50 kV and 200 MA respectively. The 2Ө scan range was from 3 to 80° with a step size of 0.02° and counting time of 3 sec per step. The powder diffraction pattern was auto indexed using Treor 90 with Powder X software (Dong, 1999). PowdeSolve software (Engel et al., 1999) was used to solve the structure using simulated annealing method. The refinement was done in material studio Reflex module.

RESULTS
The crystallographic details are summarized in Table 1.
The final positional parameters are listed in Table 2. Figure 2 shows a plot of the refined diffraction pattern. The agreement factors were R wp = 13.04% and R p = 9.97%.
The representation of the crystal system with four molecules in the unit cell is shown in Fig. 3.  The overall shape of the molecule is illustrated in Fig. 4.
Torsion angels, bond lengths and bond angels are gathered in Table 3-5 respectively.

DISCUSSION
The molecule is twisted about the bond C14-C20, the value of the torsion angle C15-C14-C20-C25 is -108.2°. The phenyl rings are essentially planar (Table 3).
Meanwhile the double bonds C12-C17 and C10-C11 (1.365 and 1.366 Å respectively) become longer compared to the C=C bond in ethylene which is 1.334-1.339 Å (Choi, 1997). The bond length of C12-C17 is comparable to the value of the corresponding bond in 1, 3-cyclohexendione in its crystalline enol form measured by inelastic incoherent neutron scattering spectra (Hudson et al., 2004), which is 1.361 Å. To less degree of agreement (but of reasonable similarity) are other bonds on this compound corresponding to the bonds C14-C15, C15-C16, C16-C17 and C16-O18 which are 1.448, 1.531, 1.532 and 1.241 Å respectively. The torsion angels between geminal protons H39 and H40 and the proton H38 are 40.1 and -81.9°. This supports the assignment of the two peaks that appear in 1 H NMR spectrum of the studied compound which appear as two doublets of doublets at 2.42 ppm (J = 16 and 4 Hz) and at 2.84 ppm (J = 16 and 7 Hz) (Elias et al., 2008). The distortion of the pyridone ring forces the protons H39 and H40 to adopt two different torsion angles with the O18 atom. The observed values of these torsion angles are -82.1 and 30.3° respectively. The measured angels are gathered in Table 5.

CONCLUSION
The study demonstrates that structure determining from powder diffractometry could be a powerful tool for determining crystal structures for organic molecules.