C3O2固体形态：碳氧化物晶体结构揭秘

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本文是一篇发表于2000年的学术论文，标题为"固体状态下碳三氧化物C3O2的结构"，作者为Arkady Ellern、Thomas Drews和Konrad Seppelt，他们来自德国柏林自由大学化学研究所。研究者们通过熔融结晶的方式获得了碳三氧化物的晶体，并进行了深入的X射线结构分析。文章的核心内容集中在对C3O2晶体结构的详细描述上。在晶体的对称单元中，发现了两种非晶格等效的分子，这表明其结构具有一定的复杂性。晶体参数为：a轴长度为986.9(2)皮米（pm），b轴长度为1206.0(2) pm，c轴长度为516.0(1) pm，空间群为Pnma，这是一个常见的斜方晶系。这两个分子都是线性的，但通过对振动幅度的细致观察，研究人员发现存在系统性的偏离线性的特征。作者们引入部分讨论了这项研究的重要性，指出碳三氧化物，即二氧化碳的三原子版本，其结构特性对于理解其物理性质和化学反应性能至关重要。通过实验结晶和理论计算相结合的方法，他们揭示了这种化合物在固态下的精确结构模型，这对于材料科学、催化作用以及环境化学等领域具有实际应用价值。特别是对于那些依赖于C3O2分子结构特性的研究，如潜在的催化剂设计或反应机理探讨，这项工作提供了宝贵的基础数据。这篇论文不仅报道了C3O2在固态下的晶体结构参数，还揭示了其非传统线性结构的细节，为进一步探索碳氧化物家族的性质提供了重要的实验证据。对于从事材料科学和化学领域的研究人员来说，这是一项不可或缺的研究成果。

The Structure of Carbon Suboxide, C

, in the Solid State

Arkady Ellern, Thomas Drews and Konrad Seppelt*

Berlin, Institut fuÈ r Chemie der Freien UniversitaÈt

Received September 11th, 2000.

Abstract. Carbon suboxide, C

, is crystallized from the

melt. According to the X-ray structure determination the

crystal contains two non-crystallographically equivalent mo-

lecules in the asymmetric unit: a = 986.9(2), b = 1206.0(2),

c = 516.0(1) pm, space group Pnma. Both molecules are

linear. A close inspection of the vibrational amplitudes indi-

cates some systematic deviations from linearity.

Keywords: Carbon oxide; Tricarbon dioxide; Crystal struc-

ture; Ab initio calculations

Die Struktur des OCCCO im festen Zustand

Inhaltsu

bersicht. Kohlenstoffsuboxid, C

, wurde aus der

Schmelze auskristallisiert. Die Kristallstruktur ist aus zwei

kristallographisch verschiedenen MolekuÈ len aufgebaut. a =

986.9(2), b = 1206.0(2), c = 516.0(1) pm, Raumgruppe Pnma.

Beide MolekuÈ le sind linear. Eine genaue Analyse der Schwin-

gungsellipsoide deutet auf systematische Abweichungen von

der LinearitaÈt hin.

Introduction

From the viewpoint of conventional bonding models,

carbon suboxide, OCCCO, should be a totally linear

molecule. The first question about this arose in 1953

from observations of fine structures in the infrared

spectrum [1]. Today the molecule is best described as

quasilinear [2]. The combined results of i.r. data [3±7]

and electron diffraction measurements [8, 9] agree

that the barrier towards bending at the central carbon

atom is 30.56 cm

±1

(= 0.37 kJ mol

±1

) [6] and with this

only a few cm

±1

above the vibrational ground state. It

is this same order of magnitude of bending barrier

and vibrational state that makes it impossible to de-

cide between linear (no bending barrier) and non line-

ar (high bending barrier) [10]. Other molecules with

similar behaviour are the fulminates X-CNO [11]. Pre-

vious ab initio calculations have predicted, indepen-

dently of basis sets and methods employed, a linear

geometry [12, 13] see also Table 1.

Our approach has been the determination of the

structure in the solid state. Of course it can be antici-

pated that even weak intermolecular interactions will

be strong enough to influence the CCC bond angle

due to its extremely flat potential.

There are precedents for such investigations. The

heterocumulene (C

)

P=C=P(C

)

is found to be

non linear in the crystal, and two crystallographically

different molecules in the unit cell exhibit strongly dif-

ferent P±C±P angles, of 143.8(6) and 130.1(6) [14].

The other example that can be cited here is that of

C±CºSF

. There exist two crystal phases that differ

not only in the packing of the molecules, but also in

the C±C±S angles of 171.4 and 162.9° [15, 16].

Results

We prepared C

according to the historic method

of dehydrating malonic acid with P

that has been

used already by O. Diels [17]. The yield is very moder-

ate, but the product can easily be purified by vacuum

distillation. Crystal growth has been performed out of

the liquid slightly below the melting point of ±112.5 °C

in situ directly on the diffractometer. The result of the

single crystal structure determination is laid down in

Tables 2, and 3, and Fig. 1±3.

The packing of the molecule is simple: The mole-

cules lie almost perfectly oriented in the ac plane of

the orthorhombic lattice, in layers at y = 0, 0.25, 0.5,

0.75. Each layer has a herringbone pattern, see Fig. 1.

Layers at y = 0.25 and 0.75 are made up by mole-

cule I, layers at y = 0 and 0.5 by molecule II. All atoms

of molecule I lie on a crystallographic mirror plane.

The central atom C2 of molecule II is positioned on a

inversion center. These special positions generate cer-

tain constraints on the geometry and on the vibra-

tional parameters, if no disorder is present.

Both molecules appear completely linear, the lar-

gest deviation from linearity is 1.7(1)° at the central

carbon atom of molecule I. The CC and CO bond

lengths are somewhat shorter than in the gas phase

(electron diffraction), see Table 3. This may well be a

vibrational shrinkage effect, see below.

Z. Anorg. Allg. Chem. 2001, 627, 73±76 Ó WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001 0044±2313/01/62773±76 $ 17.50+.50/0 73

* Prof. Dr. K. Seppelt,

Institut fuÈ r Chemie der FU Berlin,

Fabeckstraûe 34±36,

D-14195 Berlin,

Fax: Int.code +(30) 83 85 42 89

e-mail: seppelt@chemie.fu-berlin.de

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