Crystal structure, ab initio calculations and fingerprint plots of a new polymorph of N′,N″,N″′-triphenylbiuret

A new polymorph of N′,N″,N″′-triphenylbiuret, C20H17N3O2 (form II), has been synthesized and the structure has been solved by X-ray diffraction. The crystals are monoclinic, space group P21/c, with a = 7.6966 (3) Å, b = 12.5490 (4) Å, c = 18.5996 (6) Å, β = 107.632(2)°, Mr = 331.37, V = 1712.04 (10) Å3, Z = 4 and R = 0.0454. The hydrogen bonding of this polymorph is considerably different from that of the previously known structure. The molecules are linked in infinite chains, via C–H⋯O hydrogen bonds and there is also an intramolecular N–H⋯O hydrogen bond.The intermolecular interactions present in this polymorph, and on the previously reported polymorph, were analysed by means of the fingerprint plots derived from the Hirshfeld surfaces. The fingerprint plots evidenced the different packing modes of the two structures.Quantum–mechanical ab initio calculations for the free molecule were performed using the Hartree–Fock and DFT/B3LYP methods with the 6-31G(d,p) basis set of wave functions. The solid-state conformations compared with those obtained theoretically from DFT calculations for the isolated molecules show significant differences.Some difficulties of using quantum–mechanical calculations for the determination of relative conformational energies are also discussed.

► Structure of new polymorph of N′,N′′,N′′′-triphenylbiuret.
► Packing modes of the two known polymorphs analysed with fingerprint plots.
► Ab initio calculations show effect of crystal packing on molecular conformations.
► Relative conformational energies calculated with several different methods.