化学 1985

C₆₀：巴克明斯特富勒烯

克罗托、希思、奥布莱恩、柯尔与斯莫利

六十个碳原子折成一只中空的足球——纯碳的第三种形态，宽约一纳米。

Choose your version

In depth · the introduction

拿一束激光去照普通的铅笔石墨，碳会做出一件没人料到的事：六十个原子啪地扣成一只中空的球，形状恰如一只足球。

核心想法

人们一直以为纯碳只有两种形态：石墨（柔软、灰色、层层堆叠的薄片）和金刚石（坚硬、透明、刚性的晶格）。1985 年，第三种冒了出来——一个恰好由六十个碳原子组成的分子，排布在一只极小的中空球面上。它的花纹正是足球的花纹：二十块六边形的拼片，加十二块五边形的，每个角上都是一个碳原子。它宽约一纳米——大约是一根头发丝直径的十万分之一。

它是如何诞生的

来自萨塞克斯的化学家哈里·克罗托，对垂死的恒星所造出的长碳分子很好奇。他听说得州莱斯大学的理查德·斯莫利有一台机器，能把任何固体轰成蒸气，再看原子会拼成什么。1985 年 9 月的十一天里，克罗托、斯莫利、罗伯特·柯尔，加上两位研究生——詹姆斯·希思与肖恩·奥布莱恩——气化石墨，一次次看到同一个顽固的信号：六十个碳的团簇。

为什么是六十，又为什么这么稳？一天深夜，他们用纸剪出五边形和六边形，拼着想把一只球合拢。克罗托想起了建筑师巴克明斯特·富勒的网格穹顶——足球的形状一下子对上了号。他们把这个分子命名为「巴克明斯特富勒烯」；不久大家就只叫它「巴克球」。

它为何重要

它揭示了碳的一整套全新化学。如果六十个原子能合成一只笼子，那么七十个也能，长长的管子也能——于是有了碳纳米管，最终有了如今贯穿现代电子学与材料科学的单层石墨烯。一种再熟悉不过的元素，铅笔和煤烟的材料，竟藏着无人想象过的建筑。这一发现摘得了 1996 年诺贝尔化学奖。

一个可以想象的画面

试着把一张全是六边形孔的平整铁丝网，服服帖帖地裹到一只球上。你做不到；它要么摊平，要么皱起。要让它弯曲并合拢，你得塞进几个五边形的孔。足球用恰好十二个五边形掺在六边形之间解决了这个问题，C₆₀ 也是如此。正是那十二个五边形，把平整的碳片弯成了一只闭合的笼子。

它的位置

一个世纪以前，凯库勒把碳画进了苯那个扁平的六元环（kekule-1865）；巴克球则把这些环卷进了第三个维度。它立于纳米碳家族——巴克球、碳纳米管、石墨烯——的源头，自那以后一直塑造着材料科学；而它的起点，恰如其分地，是一个关于群星之间化学的问题。

The original document

Original source text

H. W. Kroto, J. R. Heath, S. C. O’Brien, R. F. Curl & R. E. Smalley · Nature 318 (1985): 162–163

The work began as astrochemistry, not materials science. Kroto wanted to know how long carbon chains form in the atmospheres of red-giant stars, and Smalley at Rice had built a machine that could vaporize almost anything with a pulsed laser and freeze the vapour into clusters in a jet of helium. They turned it on graphite.

During experiments aimed at understanding the mechanisms by which long-chain carbon molecules are formed in interstellar space and circumstellar shells, graphite has been vaporized by laser irradiation, producing a remarkably stable cluster consisting of 60 carbon atoms.

In the time-of-flight mass spectrum, the peak at 720 atomic mass units — exactly 60 carbons — stood up far above its neighbours and grew more dominant the longer the hot carbon was left to anneal in helium. A flat sheet of graphite has reactive edges; only a closed surface has none. The authors reasoned to the one shape that closes 60 equivalent carbons with no dangling bonds.

Concerning the question of what kind of 60-carbon atom structure might give rise to a superstable species, we suggest a truncated icosahedron, a polygon with 60 vertices and 32 faces, 12 of which are pentagonal and 20 hexagonal. This object is commonly encountered as the football shown in Fig. 1.

The C60 molecule which results when a carbon atom is placed at each vertex of this structure has all valences satisfied by two single bonds and one double bond, has many resonance structures, and appears to be aromatic.

[ … ]

They named the cage after the architect Buckminster Fuller, whose geodesic domes — pentagons set among hexagons — had given Kroto the clue to its shape; and they cheerfully apologized for the mouthful.

We are disturbed at the number of letters and syllables in the rather fanciful but highly appropriate name we have chosen in the title to refer to this C60 species.

Rice Quantum Institute, Houston, Texas · Nature, 14 November 1985