Fullerenes

I  worked for several years in a group, in Kitazawa Laboratory of The University of Tokyo,  in the field of fullerene chemistry and physics.  The other people working in this field were : Hidekazu Shimotani (Ph. D. student), Mitsuhiro Iwaya (M. Sc. student), Jiang Wang (M. Sc. student), Seitaro Ito (M. Sc. student), M. Suetsuna ( M.Sc. student), M. Haba (undergraduate student)

Former members that I worked with are: Lixin Xiao, S. Tanibayashi, Kentaro Nakahara and we enjoyed collaborating with several other groups from Japan, USA and Europe.

The topics of interest are the design, synthesis and characterization of fullerene polymers, carbon allotropes and directly connected fullerene dimers.  Some new attempts are  now made on synthesizing fullerene based ligands for transitional metal complexes, endohedral fullerenes and CVD growth of carbon nanotubes.  These works are much based on theoretical calculations and a part of  them are shown in here.  The optimized structures shown hereafter were obtained from ab initio calculations.  Usually we use HF/6-31G but in some cases (for instance C121) higher quality data were obtained (B3LYP/6-31G* or B3PW91/6-31G**).  These are obtained with Gaussian 98 on several workstations in our group.

Carbon allotropes

It is now widely accepted that fullerenes are the third (and somehow unexpected) form of carbon.  If you don’t know yet what are the fullerenes, take a look at the most known member of this family, the Buckminsterfullerene or “the soccer ball”, C60 (this is a VRML file, you’ll need a vrml viewer).

Related to fullerenes, we have been interested and succeded in the synthesis of all-carbon dimers such as C122 and C121.  One interesting point is to know how the fullerene cages  (actually the pi-electrons on them) are interacting together in dimeric and polymeric structures.  Here is picture of the structure of C122 (cyclo-propylidene derivative) and also an STM image of this fullerene dimer. The image was acquired with an UHV-STM at 66K.

Another interesting dimer is C121 (actually there are three possible structures for C121, the same applies to C122 dimer).  We have isolated two isomers of C121, see the optimized structure for a C121 dimer having D2d symmetry

Other derivatives

See the four possible structures for C122H4 (these four structures were initially considered possible based on 13C-NMR experiments): A, B, C, D; the correct structure is B (pdb files).  This structure was determined by isotopically marked experiments, 2D-NMR and supported by ab-initio calculations.  You can download the manuscript on this topic in the Vitae section.

It seems that the fullerene cages in C122H4 are interacting (according to e-chem measurements, performed by Ana Bettencourt Dias from Syracuse and Alan Balch from University of California-Davis), see the HOMO and LUMO plots of C122H4.

Fulleroids

Known as fulleroids (or homofullerenes, according to others) are systems in which the number of the pi-electrons on the cage remains the same after chemical functionalization.  This can be seen as an insertion of a group R onto the fullerene cage.  The famous example is C60CH2 which can exist in two forms known as 6-6 and 6-5.  By 6-6 and 6-5 it is denoted a connection made at  the junction between two hexagons and at the junction between one hexagon and one pentagon, respectively.  The isomer -6 is a methanofullerene while the 6-5 is a fulleroid or homofullerene.  An interesting  point is which fulleroid is more stable among the two possible, when the attached groups are different.  For instance, let’s take C60CHBr.  There are three possible isomers: one methanofullerene and two  fulleroids: A, B and C.  The B and C differ by the position of the bromine relative to the fullerene cage.  Among these isomers, the theoretical calculations showed that A is the most stable of them. However, it was quite surprising that  there is a significant difference in the stabilities of B and C.  The compound A was recently synthesized by us and we found interesting electronic effects around the cyclopropane cage. 

-more data to come,..someday