Decafluorocyclohex-1-ene at 4.2 K – crystal structure and theoretical analysis of weak interactions

Abstract

The crystal structure of 1,2,3,3,4,4,5,5,6,6-decafluorocyclohex-1-ene (decafluorocyclohex-1-ene, C6F10) was solved in direct space from neutron powder diffraction data previously collected at 4.2 K [Pawley, G. S. (1981). J. Appl. Cryst. 14, 357-361] and refined by energy minimization in the solid state. To optimize the positions of the 64 atoms in the monoclinic computational cell the PBESOL and hybrid PBE0 functionals were used. The crystal structure of the title compound, which is liquid at room temperature, is built of antiparallel pairs of molecules assembled into molecular columns stacked along the a axis. Dominating the crystal-building forces are weak intermolecular dispersion interactions. Bonding conditions in the structure were analysed by theoretical molecular calculations of representative next-neighbor molecular dimers carried out using dispersion-corrected density functional theory (DFT) functionals and the SCS-MP2 wavefunction method. The largest interaction energy is of the order of ∼ 21 kJ mol(-1), above the interaction energy of a benzene dimer (11.3 kJ mol(-1)) and close to that of a water dimer (20.9 kJ mol(-1)). The interaction energy for the second most stable dimer can be compared with either that of a benzene dimer or of a C-H...π hydrogen bond. The remaining five weakly interacting dimers (∼ 4.2-8.4 kJ mol(-1)) can be characterized as having stronger interactions than those of methane dimers (-2.2 kJ mol(-1)), but weaker than those of benzene molecule pairs or weak C-H...C interactions for instance.