Solid state structural relation and binary melting phase diagram of (S-) and racemic 2-(2-nitro-1-phenylethyl)-1,3-diphenyl-propane-1,3-dione

• Fractional crystallization has provided both (S)-1 and (R,S)-1 solid compounds.
• Crystal structure of (S)-1 has been solved by single crystal X-ray diffraction.
• Powder XRD pattern of (R,S)-1 could be indexed in space group Pbca.
• Differences in the FTIR spectra reflect those of in secondary interactions.
• Binary melting phase diagram of the two crystals has been constructed based on DSC.

Both the S enantiomer and the racemic (RS) forms of 2-(2-nitro-1-phenylethyl)-1,3-diphenyl-propane-1,3-dione (1) have been obtained from the same reaction media by fractional crystallization from toluene. First, the racemic compound, (R,S)-1, was precipitated (mp. 159.7 °C), then, from the filtrate, (S)-1 (mp. 135.6 °C) was crystallized. The absolute configuration (S) and crystal structure of (S)-1 has been solved by single crystal X-ray diffraction (R = 0.0377). (S)-1 crystallizes in the orthorhombic crystal system (space group P212121 (19), a = 10.6377(2) Å, b = 11.4348(2) Å, c = 31.3543(6) Å, Z = 8, Z′ = 2). Powder XRD pattern of the racemic crystal (R,S)-1 could be indexed in the orthorhombic space group Pbca (61) (a = 22.18(7) Å, b = 17.08(3) Å, c = 9.96(3) Å, Z = 8, Z′ = 1). Differences in secondary bonding interactions and crystal stability of both (S)-1 and (R,S)-1 were evaluated on the basis of their FTIR spectra, melting points, and enthalpies of fusion. The expected eutectic-type binary melting phase diagram of (S)-1 and (R,S)-1 crystals has been constructed based on differential scanning calorimetric (DSC) measurements and calculation of the liquidus curves according to the combination of the simplified Schröder–van Laar and Prigogine–Defay equations.