Beautiful photo of Chern's C60@60 at the Columbia Secondary School

The superbuckyball, C60@C60, made by Chern is now on exhibition at the Columbia Secondary School, New York. This is for an event called MoSAIC—Mathematics of Science, Art, Industry, Culture—the festival, an offshoot of the annual Bridges Organization international conference dedicated to the connections between art and mathematics.

There is a nice photo of this C60@C60 in the Columbia Spectator.

Short summary of zome-type superbuckyball part IV: Tori and miscellaneous

Lastly, we will address some other examples of this method of constructing graphitic structures from C60s. We will start with planar tori. All of the zometool models of these tori reported here are composed of entirely blue struts.

Threefold torus⊗C60 with g=1: C216 (C3v)

Fourfold torus⊗C60 with g=0: C224 (C2h)

As noted parenthetically, the rotational symmetry of this structure is actually twofold only.

Fivefold torus⊗C60 with g=0: C280 (C5v)

Sixfold torus⊗C60 with g=0: C336 (D3v)

Hyper cube⊗C60 with g=(0,3,1): C1536 (Th)

Perhaps this hypercube should be also classified as polyhedron in the previous post, since it IS a regular polyhedron in 4D. As can be seen, there are three different kinds of struts (two blues with different lengths and one yellow) in this structure. It is thus more difficult to find a reasonable set of g parameters that suits all of their intricate geometric relations. The CNTs in the outer layer are bent to accommodate this incommensurability. I have to point out that, in graph theory, 4D hypercube cannot be represented by a planar graph. This fact leads to considerable difficulty, if not impossible, in constructing corresponding graphitic structures with out previous approach of using the inner part of TCNTs. However, with the zome-type construction scheme this is nothing different than other graphically simpler structures.

Dodecahedron with V-shape edges⊗C80 with g=1: C4960 (Ih)

Note that one has to at least use C80 (or larger Ih-symmetric fullerenes) instead of C60 for the nodes, since the yellow struts joining at the same node are nearest neighbors to each other. Total fifty C80s were used, twenty for the (inner) dodecahedron and thirty for the (outer) edges. If I make it to the Bridges this year in Enschede, I'll bring a beaded molecule of this model with me.

Last but not least, how can I not play with trefoil knot?

Trefoil knot⊗C60 with g=(0,1,3): C912 (D3)

Unfortunately, so far I have not thought of any general scheme to construct arbitrary torus knots, as trefoil knot is only the simplest nontrivial case of them. In principle as long as the structure (or the space curve as for knots) can be constructed with zometool, there is also graphitic analogs of it and presumably beaded molecules as well. This concludes this series of posts. I'm currently working on a beaded molecule of C60⊗C60 with g=1 posted previously. I'm about half way there and I might talk about some specific beading strategies of this kind of structures later on.

Short summary of zome-type superbuckyball part III: Polyhedra

In this post I will present some other polyhedra built with the same principle. As you might know that the C20 and the C60 discussed in the previous post are exactly regular dodecahedron and the truncated icosahedron (an Archimedean polyhedron).

Cube⊗C60 with g=1: C624

I'd like to note that the symmetry of this structure belongs to the Th point group, although it looks as if it's got a higher symmetry of octahedral group. This is so because of the fact that locally there is only C2 rotational symmetries along each of the joining tubes. And there is no C4 rotational symmetry, not only in this structure but also in all other structures constructed with the golden ratio field where zometool is based on.

Icosahedron⊗C60 with g=2: C1560

I've posted a closely related high-genus structure quite some time ago using a different algorithm. There I treated the construction of high-genus fullerenes by replacing the faces of the underlying polyhedra by some carefully truncated inner part of a toroidal CNT. As suggested by Bih-Yaw that the current scheme of constructing superfullerenes is one another aspect of high-genus fullerene. Previously we are "puncturing holes" along the radial direction and connecting an inner fullerene with an outer one. Here we break and connect fullerenes in the lateral directions. Although topologically they are identical, as you can see the actual shapes of the resulting super-structures are quite different.

For your convenience I repost the structure here for comparison:

The construction of (regular) tetrahedron and octahedron requires the use of green struts. For now I have not come up with the corresponding strategy for green strut yet. We will move on to other polyhedra in the rest of this post.

Small Rhombicosidodecahedron⊗C60 with g=1: C5040

This Archimedean solid is of special interest since the ball of zometool is exactly it. The squares, the equilateral triangles, and the regular pentagons correspond directly to C2, C3, and C5 rotational axes, respectively. The existence of this superfullerene guarantees the possibility of building hierarchy of Sierpinski superbuckyballs. In other words, this superbuckyball can serve as nodes of a "supersuperbuckyball", with the connecting strut automatically defined. Although we are likely to stop at the current (second) level because of physical limitations, either using beads, zometool, or even just computer simulations.

Rhombic triacontahedron⊗C60 with g=1: C3120

You need red struts only for this structure.

Five compound cubes⊗C60 with g=(0,1): C6000

You need blue struts with two different lengths for this structure, which is the reason why the g factor is a two component vector here. Note that at each level the length of the strut (measured from the center of the ball at one end to the center of the other) is inflated by a factor of golden ratio. Thus, comparing to other superfullerenes introduced previously, there is additional strain energy related to the commensurability of the lengths of CNTs. It is always an approximation to use a CNT of certain length to replace the struts of a zometool model. It is also interesting to note that, comparing to the zometool model, this particular superbuckyball makes clear reference to the encompassing dodecahedron. In this perspective it is not surprising that the structure has Ih symmetry.

Dual of C80⊗C60 with g=2: C5880

This structure is obtained by inflating each of the equilateral triangles of a regular icosahedron to four equilateral triangles. An equivalent way of saying this is "inflation with Goldberg vector (2,0)".

In addition to the above mentioned, Dr. George Hart has summarized some of the polyhedra construtable with zometool here. In principle they can all be realized, at least on computers or with beads and threads, by this methodology. And there is going to be one last post in this series to cover those that are not classifiable into categories discussed so far.

Short summary of zome-type superbuckyball part II: Superfullerenes

We will move on to our main and original goal of devising this technique: constructing superfullerenes. Readers familiar with zometool would know that C60 can be built with solely blue struts (two fold rotation axes). So here it is.

C60⊗C60 with g=0: C3240

I've borrowed the notation of Kronecker product (⊗) since these two mathematical operations are in some sense similar: each entry (atom) of the matrix (fullerene) before the ⊗ sign is "expanded" into the second matrix times the original entry (the spatial location of that atom). The meaning of g will become clear once you see an example of g=1 as shown below.

C60⊗C60 with g=1: C4680

It is obvious that g indicates the length of the struts (straight CNTs). In the first case the length is essentially zero, so pairs of heptagons "merge" into octagons at the interface. For clarity the rotatable models of four connected superatoms of the above two superbuckyballs are presented below as well. Since all of these superatoms are identical and can be related through mirror symmetries, readers of interest can start with them to build your own models.

For convenience I also show the rotatable models for the superbuckyball proposed and its beaded model constructed by Bih-Yaw in the previous posts.

C60⊗C60 with g=0: C2700

C60⊗C60 with g=1: C4500

Upon close inspection, notice that there is still local threefold symmetry at each of the node in this case. While on the contrary, there are only mirror symmetries in the zome-type superbuckyball. This asymmetry leads to the fact that there is almost no strain when constructing the beaded model of these structures, or even the actual microscopic realization. This is not an issue concerning the 1D structures in the previous post, since they are all simply connected and there is no such thing as commensurability among multiple struts that join at the same node. However, the above two superstructures seem to be pretty stable and beadable, which surprise me a lot in this regard. According to Bih-Yaw, the tension of the five-member rings and the stress in the six-member rings magically balance each other. This is not so for the dodecahedron case, where tension is built everywhere in the model without being compensated by stress.

Having demonstrated the above mentioned, there is nothing so different in constructing other types of superfullerenes. Below I listed a few that I have done coding with.

C20⊗C60 with g=1: C1560

Although I have not tried to build this one with beads yet, I believe that it is quite doable in the sense of stability as mentioned above.

C80⊗C60 with g=1: C6720

C180⊗C60 with g=1: C15480

I'd like to point out in the last two cases you need red struts as well as blue ones. It can be shown that all (n,n) or (n,0) type icosahedral fullerenes are constructable from zometool (with blue and red struts). For now I just manually find out what are the atoms needing to be deleted/connected, well, in an efficient way. I hope one day I can come up with a general automatic routine that does all these for me, which should be taking account of different orbits in a symmetry group. C180 (a (3,0) Ih fullerene) is the largest one I've ever played with.

I plan to talk about other types of regular polyhedra in the next post.

Short summary of zome-type superbuckyball part I: 1D Linear and Helical C60 Polymers

Recently I've been playing with all kinds of these superbuckyballs, based on the methodology of replacing balls and struts of zometool by Ih-symmetric fullerenes and straight CNTs. Taking C60 for example, blue struts correspond to removing two atoms next to some particular C2 rotation axes. And the connecting CNTs are of chiral vector (4,0). On the other hand, yellow and red struts correspond to C3 and C5 rotation axes, respectively. In addition, due to the property of the golden field, the algebraic field of zometool, superstructures using yellow or red struts only have the possibility of being polymers of C60. This means that the number of atoms is a multiple of 60, i.e. no atoms needed to be deleted or added when constructing the superbuckyball.

Here I will briefly summarize some of the cases I've done coding with. Hopefully I'd soon come up with a short paper ready to submit to the Bridges 2013 on this topic.

First let us start with the trivial C60 dimers. As mentioned, structures with red or yellow struts cases have the atom-preserving property. The C120 isomers corresponding to joining two C60s along their fivefold and threefold axes are shown below. I should mention that they were also discussed in Diudea and Nagy's book . In particular for the C3-joined case there are two possibilities of local atomic connectivity.

C3-fused C120, case 1 (with octagons and pentagons at the interface)

C3-fused C120, case 2 (with heptagons at the interface)

C5-fused C120

For the case of blue struts (twofold rotation axes)

C2-fused C116

C2-fused C132

Some of them were already made previously by us, see here for example. But we did not realize back then this particular connection with zometool. To my knowledge, there has not been any experimental characterization of such dimers. Synthetic chemists do make C60 dimers but those are of partial sp3 characteristics, i.e. some interfacial atoms have four neighbors instead of three. Please refer to Diudea and Nagy's book for further details if you are interested.

One can come up with the one dimensional C60 chains without too much effort by enforcing periodic boundary condition. So the structure repeats itself indefinitely along the direction of polymerization. See for example below.

Also, it is one step away from constructing the 2D analog of this kind of structure.

A little bit more sophisticated extension of the above scheme is to consider helical screw symmetry. A (discrete) helical curve is defined by the angle between adjacent unit cells and the dihedral angle between next-nearest neighbors. I recommend readers of interest to play with the awesome virtual zome program vZome developed by Scott Vorthmann. You have to write Scott an email for the license of the full version of vZome. Anyway, here are some examples of helical C60 polymers.

C3-fused fourfold C60 helix

C5-fused fivefold C60 helix

Notice that if you are looking along the axes of the helices, the C60s that are four/five unit cells away lie exactly on top of each other. Curiously, this result is actually symmetry-determined, since I've tested with the relaxation scheme that does not require such symmetry. In other words, even if I optimize the geometries with full degrees of freedom of a general helix, the screw angles will still be 2*pi/4 or 2*pi/5 in the above cases.

New superbuckyball for math art exhibition of JMM 2013

I made a new superbuckyball for the Mathart exhibition of Joint Mathematical Meeting JMM held in San Diego this few days. The original one made by students of TFGS is too big (~60cm wide) to bring to the US. The new one is made by 8mm beads and is about 40cm wide.

One more picture of super buckyball

Super Buckyball as a Molecular Sculpture

I have written an article about super buckyball, Super buckyball as a molecular sculpture - its structure and the construction method (分子雕塑─超級珠璣碳球的結構與製作), in Chinese recently. I guess it will appear in the next issue of CHEMISTRY (The Chinese Chemical Society, Taipei) (化學季刊), a local chemistry journal in Taiwan. I tried to describe the construction method of the super buckyball in details in this paper. Also, in the reference 1 of this paper, I commented on how this paper was inspired by the Horibe's works, particularly, the idea of fusing many C60s into structured super fullerenes, which is the way I understand many of his beautiful models. I wrote it in Chinese because I hope local high-school students in Taiwan can read the paper more easily and reconstruct the model as a school activity.

分子雕塑 ⎯ 超級珠璣碳球的結構與製作

金必耀

臺灣大學 化學系

摘要:串珠是最適合用來建構各種芙類分子模型的材料,珠子代表芙類分子中的碳碳鍵,珠子的硬殼作 用正好模擬微觀芙類分子內的化學鍵作用。本文將介紹以模組化方式,讓許多對基本串珠模型建構有一 定認識的人,親手一起協同製作大型的超級芙類分子模型,非常適合作為中學化學與立體幾何教育的活 動,所製作的巨型模型不僅是一個為微觀分子模型,更可以說是一件具有科學含意的雕塑藝術品。

Super Buckyball as a Molecular Sculpture − Its Structure and the Construction Method

Bih-Yaw Jin

Department of Chemistry, Center of Theoretical Sciences and Center for Quantum Science and Engineering, National Taiwan University, Taipei 10617, Taiwan

ABSTRACT

Mathematical beading can be exploited to construct faithful physical model of any fullerene. The hard sphere interactions among different beads effectively mimic the ligand close packing of carbon-carbon bonds in fullerenes. Here we show a simple modular approach for students to build complicated graphitic structures together. Particularly, we describe in details the structure of the so-called super buckyball, which consists of sixty fused buckyballs, and our hands-on experience in making its bead model by the students of the Taipei First Girls High School collaboratively.

Coalescence of two or more C60s

Previously, I constructed many large graphitic structures by fusing C60 along a particular 5-fold axis. But in addition to the 5-fold axes, one can also fuse two C60s along a particular 3-fold axis to get different kind of fused structures. One can easily see that the topological charges of necks in these two structures are the same, i.e. (-1)x6=0x3+(-2)*3=-6. The total topological charges are, of course, equal to 18x1+(-6)=12. However the relative arrangement for the two C60s are different, staggered for the pure-heptagon neck, while eclipsed for the hexagon-octagon neck. In fact, Diudea and Nagy have already done a lot on this possibility. Read the book for more information.

The following two pictures show two possible ways of coalescence: the neck of the first one consists of a ring of octagons and hexagons alternatively; the second one is a ring of six heptagons, instead.

In principle, one can create a one-dimensional tube by coalescence of many C60s repeatedly.

Super Buckyball

Mr. Hwang took this picture of my group the next day after I had the workshop last month.

One more super carbon tetrahedron

I made another super carbon tetrahedron (超級碳正四面體) consisting of four fused C60s with 8mm beads. Unlike the previous one, the two neighbored C60s are connected by a ring of hexagons.

Bucky doghouse

The north hemisphere of the super Buckyball might be used as a Bucky doghouse. I tested it with my niece's brown poodle dog last weekend. But apparently he didn't like to be put inside it. It is still too small for him.

Super Buckyball (超級珠璣碳球)

After about ten days of hard working, we finally created this fabulous super Buckyball. I have to thank the alumni association of the Taipei First Girls High School (TFGH), especially the classes 1981, 1971, and 1961, who kindly sponsor this project and donate this super Buckyball to the TFGH as a gift from their 30-, 40-, and 50-years joint reunion.
Of course, the crucial collaborative effort of students (mainly from classes 2She (二射) and 2Yue (二樂)) and teachers of the TFGH makes this super Buckyball possible in about two weeks.

Explaining the weaving path to students:

Students working hard:

Super Buckyball (超級珠璣碳球)

The first super Buckyball, C₄₅₀₀, was created by students (class 3Gong 三恭) from the Taipei First Girls High School (TFGH) 北一女中 today. Each unit in this beautiful bead model is a punctured C60 with three holes surrounded by a neck of five heptagons. It took them exactly one week to construct it. The diameter of this small super Buckyball (made of 6750 6mm beads) is about 40 cm already. They might still need to clean all the loose ends up later next week.

In addition to this small super Buckyball, I am still working with teachers and some other students from the TFGH on a bigger super Buckyball made of 12mm beads. Hopefully, we can have the whole structure done early next week. Since the total weight of this model is going to be eight times of this small super Buckyball, so we need to be very careful about the rigidity of each units and necks connecting them. I name these kinds of bead models as "超級珠璣碳球" in Chinese which means literally "the super bead carbon ball".

(I found many pictures at TFGS's website. http://web.fg.tp.edu.tw/~chemistry/blog/?page_id=2&nggpage=8, 2012/9/1)

Super carbon tetrahedron

We can make a super carbon tetrahedron (超級碳正四面體) with four C60 building blocks that have three holes drilled on the three pentagons surrounding the same hexagon. Of course, four equal CNTs with suitable length are required to connect these four punctured C60s. Here, in addition to heptagons (blue), one also creates three octagons (purple) and one nonagon (red) on the C60 at each vertex. Of course, this structure was created by Mr. Horibe first.

Building blocks:

Corresponding Schlegel diagram and weaving path for creating a single vertex (punctured C60):

Super regular triangle

If the holes on C60 are located at two neighbored pentagons, the angle created between the necks at these two positions is very close to 60 degrees. So one can use three such units to make a triangle consisting of three C60s at position of vertices connected by three CNT (carbon nanotube) struts. This kind of construction scheme seems be proposed by Mr. Horibe first.

Since there are many different ways to puncture holes on a C60 or other Goldberg polyhedra, we can then use different lengths of CNTs to connect them to get complicated 2D or 3D structures. When resulting structures are cage-like, I will call them super fullerenes (超級芙類分子). Here I have a super carbon triangle （超級碳三角, 注意不是鐵三角） and the previous dodecahedron consisting of 20 C60s should be a super dodecahedron （超級十二面體）.

Two holes in a C60

There are three distinct ways to drill two holes in a C60, which can be specified by the smallest number of non-disrupted hexagons between two pentagons:
a. The shortest separation between two pentagons we can drill is one hexagon.

b. The next one is two pentagons separated by two hexagons.
c.The third one is two holes located at antipodal position.

We can see in the case (a) two octagons are created at the position of original hexagon. In addition to this octagon, there are eight other heptagons surrounding these two holes. Using this Shlegel diagram, one can easily figure out the resulting connectivity diagram when holes are introduced in the original C60.

"Super" dodecahedron consisting of 20 punctured C60s

This is the final bead model of a dodecahedron by connecting 20 C60s with three holes described in previous post. The C60 units in this structure is distorted quite significantly.

Building blocks for the type-II high-genus fullerenes

The building block of type-II high-genus fullerenes can be chosen to be an arbitrary Goldberg polyhedron. Puncturing three holes along three carefully chosen pentagons can create a basic unit with three coordination (or a trivalent unit).
I use C60 and its Schlegel diagram to illustrate how to puncture a hole on an arbitrary pentagon.

1. Schlegel diagram of C60

2. C60 with a hole punctured on a pentagon: one pentagon and five hexagons are replaced by five heptagons.

In principle, one can connect two this kind of unit with one hole to create a fused C120 with dumbbel-shape.

3. Of course, if we like, we can puncture two holes on a C60. There are three possible ways. Here I only show the situation with two pentagons separated by two hexagons. The resulting structure will contain two holes connected (or separated) by two heptagons.

There are two other different ways to puncture second hole. If the second pentagon separated from the first one by one CC bond are punctured, the resulting structure will have an octagon. The third situation is that the second pentagon is located at the antipodal position. I will talk about these situations later.

4. Punctured C60 with three holes:

It is easy to see that there are five heptagons and five more bonds are introduced around each hole. So one needs 105 beads for creating a single unit.

5. Here are two possible weaving path. I usually used the first path though. a. non-spiral path

b. spiral path

6. I am working on a project with teachers and students of the Taipei First Girls High School (北一女). We are going to make a giant buckyball consisting of sixty units of punctured C60s. Here are a few basic units I made:

105 12mm faceted beads are used for each unit.

Comments on type-II high-genus fullerenes

It is of interest to compare the bead model of a dodecahedron fused by 20 C60 in the previous post to high-genus fullerenes we discussed before. In fact, one can also view that bead model as a high-genus fullerene with genus=11, which is obtained by substracting one from the number of faces in a dodecahedron. The most important difference between these two types of high-genus fullerenes is the orientations of the TCNT necks relative the surface of the polyhedron. In the original high-genus fullerenes, which I will call the type-I high-genus fullerene from now on, the orientations of the TCNT necks are along the normal of the polyhedron. Here in the type-II high-genus fullerene, the orientations of the TCNT necks, which are created by fusing two neighbored C60, are lying on the surface of polyhedron (dodecahedron here) and along the directions of its edges.