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.