Extremely long C-C bonds in strained 1,1,2,2-tetraphenylcyclobutaarenes: 3,8-dichloro-1,1,2,2-tetraphenylcyclobuta-[b]naphthalene, C36H24Cl2, and 3,6,9,10-tetrachloro-4,5-dimethyl-1,1,2,2,7,7,8,8-octaphenyldicyclobuta[b,h]phenanthrene toluene solvate, C68H46Cl4..1.5C7H8

Cyclobutaarenes are highly strained compounds which exhibit unusual geometric features. Introduction of diphenyl substituents on the peripheral C atoms of the cyclobutene ring adds stereoelectronic effects and causes further distortion of the ring structure. The interatomic distances observed for the peripheral C-C bonds in the cyclobutene moiety of the two compounds are in the range 1.71-1.72 Å, among the longest of C_sp3-C_sp3 bonds previously reported for similar compounds. The core structure of the phenanthrodicyclobutene derivative is severely twisted due to non-bonding interactions between the chlorine substituents.