化學 1985

C₆₀：巴克明斯特富勒烯

克羅托、希思、奧布萊恩、柯爾與斯莫利

六十個碳原子摺成一隻中空的足球——純碳的第三種形態，寬約一奈米。

Choose your version

In depth · the introduction

拿一束雷射去照普通的鉛筆石墨，碳會做出一件沒人料到的事：六十個原子啪地扣成一隻中空的球，形狀恰如一隻足球。

核心想法

人們一直以為純碳只有兩種形態：石墨（柔軟、灰色、層層堆疊的薄片）和鑽石（堅硬、透明、剛性的晶格）。1985 年，第三種冒了出來——一個恰好由六十個碳原子組成的分子，排佈在一隻極小的中空球面上。它的花紋正是足球的花紋：二十塊六邊形的拼片，加十二塊五邊形的，每個角上都是一個碳原子。它寬約一奈米——大約是一根頭髮絲直徑的十萬分之一。

它是如何誕生的

來自薩塞克斯的化學家哈里·克羅托，對垂死的恆星所造出的長碳分子很好奇。他聽說德州萊斯大學的理查德·斯莫利有一台機器，能把任何固體轟成蒸氣，再看原子會拼成什麼。1985 年 9 月的十一天裡，克羅托、斯莫利、羅伯特·柯爾，加上兩位研究生——詹姆斯·希思與肖恩·奧布萊恩——氣化石墨，一次次看到同一個頑固的信號：六十個碳的團簇。

為什麼是六十，又為什麼這麼穩？一天深夜，他們用紙剪出五邊形和六邊形，拼著想把一隻球合攏。克羅托想起了建築師巴克明斯特·富勒的網格穹頂——足球的形狀一下子對上了號。他們把這個分子命名為「巴克明斯特富勒烯」；不久大家就只叫它「巴克球」。

它為何重要

它揭示了碳的一整套全新化學。如果六十個原子能合成一隻籠子，那麼七十個也能，長長的管子也能——於是有了碳奈米管，最終有了如今貫穿現代電子學與材料科學的單層石墨烯。一種再熟悉不過的元素，鉛筆和煤煙的材料，竟藏著無人想像過的建築。這一發現摘得了 1996 年諾貝爾化學獎。

一個可以想像的畫面

試著把一張全是六邊形孔的平整鐵絲網，服服貼貼地裹到一隻球上。你做不到；它要麼攤平，要麼皺起。要讓它彎曲並合攏，你得塞進幾個五邊形的孔。足球用恰好十二個五邊形摻在六邊形之間解決了這個問題，C₆₀ 也是如此。正是那十二個五邊形，把平整的碳片彎成了一隻閉合的籠子。

它的位置

一個世紀以前，凱庫勒把碳畫進了苯那個扁平的六元環（kekule-1865）；巴克球則把這些環捲進了第三個維度。它立於奈米碳家族——巴克球、碳奈米管、石墨烯——的源頭，自那以後一直塑造著材料科學；而它的起點，恰如其分地，是一個關於群星之間化學的問題。

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