固态C3O2的线性晶体结构揭示：碳氧化物与计算研究

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固态低氧化碳C3O2的结构是一个重要的研究课题，由Arkady Ellern、Thomas Drews和Konrad Seppelt*在柏林自由大学的化学研究所于2000年9月11日进行了一项深入探讨。该研究聚焦于这种化合物在固态下的结晶行为及其晶体结构特性。碳氧化物C3O2是从熔融状态中结晶出来的，这一过程揭示了其独特的物理性质。通过X射线结构测定，科学家们发现晶体中的基本结构单元，即不对称单元，包含了两个非晶格等效的分子。这些分子的尺寸分别为a=986.9(2) picometers (pm)，b=1206.0(2) pm，c=516.0(1) pm，对应的晶格空间群为Pnma。值得注意的是，这两个分子都是线性的，这意味着它们的原子排列遵循一条直线路径。然而，对振动幅度的仔细分析显示，尽管分子整体上呈现出线性结构，但在微观层面，存在一些系统的偏差。这可能暗示着C3O2的结构并非完全理想化的直线模式，而是可能存在一定程度的畸变或动态行为。这种细微的不规则性可能是由于电子分布、键合强度或者外部环境因素的影响。关键词“碳氧化物”、“三二氧化碳”、“晶体结构”和“从头计算”强调了这项研究的核心内容，即使用第一性原理的方法（从头计算）来揭示C3O2的晶体结构，这对于理解其物理和化学性质至关重要。此外，引入部分提到了研究的背景，即对固态碳氧化物结构的兴趣源于对这类化合物在实际应用中可能展现的独特性质的好奇，如催化剂活性、能量储存或转换等方面。这篇论文提供了关于固态C3O2的结构基础，对于理解和预测其在各种条件下的行为具有重要意义，为未来的理论和实验研究奠定了坚实的基础。

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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