Piperazine Functionalization of C 70 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 as12 {N(CH2 CH2 )2 N}2 C70 with addends on opposite poles of the C70 cage and a structure with C2v symmetry. In12 {I2 N(CH2 CH2 )2 N}2 C70 , individual12 {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.