Chemistry Letters, Vol.43, No.1, 86-88, 2014
Expandability of Ultralong C-C Bonds: Largely Different C-1-C-2 Bond Lengths Determined by Low-temperature X-ray Structural Analyses on Pseudopolymorphs of 1,1-Bis(4-fluorophenyl)-2,2-bis(4-methoxyphenyl)pyracene
Low-temperature X-ray analyses on several pseudopolymorphs (solvate crystals) revealed that the C-1-C-2 bond length of the highly congested title molecule can adopt quite different values [1.700(6)-1.739(6)angstrom]. Such an unusual observation indicates that the ultralong covalent bond is endowed with "expandability," thus the prestrained bond can be elongated or shortened very easily accompanied by only a minute change in energy, which can be compensated by intermolecular perturbation in the crystal.