Piperazine Functionalization of C₇₀ for Incorporation into Supramolecular Assemblies

The photochemical reaction of piperazine with C₇₀ produces a mono-adduct (N(CH₂ CH₂ )₂ NC₇₀ ) in high yield (67 %) along with three bis-adducts. These piperazine adducts can combine with various Lewis acids to form crystalline supramolecular aggregates suitable for X-ray diffraction. The structure of the mono-adduct was determined from examination of the adduct I₂ N(CH₂ CH₂ )₂ NI₂ C₇₀ that was formed by reaction of N(CH₂ CH₂ )₂ NC₇₀ with I₂ . Crystals of polymeric {Rh₂ (O₂ CCF₃ )₄ N(CH₂ CH₂ )₂ NC₇₀ }_n ⋅nC₆ H₆ that formed from reaction of the mono-adduct with Rh₂ (O₂ CCF₃ )₄ contain a sinusoidal strand of alternating molecules of N(CH₂ CH₂ )₂ NC₇₀ and Rh₂ (O₂ CCF₃ )₄ connected through Rh-N bonds. Silver nitrate reacts with N(CH₂ CH₂ )₂ NC₇₀ to form black crystals of {(Ag(NO₃ ))₄ (N(CH₂ CH₂ )₂ NC₇₀ )₄ }_n ⋅7nCH₂ Cl₂ that contain parallel, nearly linear chains of alternating (N(CH₂ CH₂ )₂ NC₇₀ molecules and silver ions. Four of these {Ag(NO₃ )N(CH₂ CH₂ )₂ NC₇₀ }_n chains adopt a structure that resembles a columnar micelle with the ionic silver nitrate portion in the center and the nearly non-polar C₇₀ cages encircling that core. Of the three bis-adducts, one was definitively identified through crystallization in the presence of I₂ as ¹² {N(CH₂ CH₂ )₂ N}₂ C₇₀ with addends on opposite poles of the C₇₀ cage and a structure with C_2v symmetry. In ¹² {I₂ N(CH₂ CH₂ )₂ N}₂ C₇₀ , individual ¹² {I₂ N(CH₂ CH₂ )₂ N}₂ C₇₀ units are further connected by secondary I2⋅⋅⋅N2 interactions to form chains that occur in layers within the crystal. Halogen bond formation between a Lewis base such as a tertiary amine and I₂ is suggested as a method to produce ordered crystals with complex supramolecular structures from substances that are otherwise difficult to crystallize.