Rodríguez-Zavala J G, Guirado-López R A
Departamento de Ciencias Exactas y Tecnológicas, Centro Universitario de Los Lagos, Universidad de Guadalajara, Enrique Díaz de León S/N, 47460 Jalisco, México.
J Phys Chem A. 2006 Aug 3;110(30):9459-68. doi: 10.1021/jp061855m.
We have performed both semiempirical as well as ab initio density functional theory calculations in order to investigate the structural stability of highly hydroxylated C60(OH)32 fullerenes, so-called fullerenols. Interestingly, we have found that low-energy atomic configurations are obtained when the OH groups are covering the C60 in the form of small hydroxyl islands. The previous formation of OH molecular domains on the carbon surface, stabilized by hydrogen bonds between neighboring OH groups, defines the existence of C60(OH)32 fullerene structures with some elongated C-C bonds, closed electronic shells, and large highest occupied-lowest unoccupied molecular orbital energy gaps, with the latter two being well-known indicators of high chemical stability in these kind of carbon compounds. The calculated optical absorption spectra show that the location of the first single dipole-allowed excitation strongly depends on the precise distribution of the OH groups on the surface, a result that, combined with optical spectroscopy experiments, might provide an efficient way to identify the structure of these kinds of fullerene derivatives. We found that the presence of a few coadsorbed oxygen species on the fullerene surface leads in general to the existence of C60(OH)32O(x) (x = 1-4) compounds in which some of the C-C bonds just below the O impurities are replaced by C-O-C bridge bonds, leading to the formation of stable carbon-opened structures in agreement with the recent experimental work of Xing et al. (J. Phys. Chem. B 2004, 108, 11473). Actually, a more dramatic cage destruction is obtained when considering multiply charged C60(OH)32O(x)(+/-m) (m = 2, 4, 6) species (that can exist in both gas-phase and aqueous environments), where now sizable holes made of 9- and 10-membered rings can exist in the carbon network. We believe that our results are important if the controlled opening of carbon cages is needed and it should be taken into account also in several technological applications where the permanent encapsulation of atomic or molecular species in these types of fullerene derivatives is required.
为了研究高度羟基化的C60(OH)32富勒烯（即所谓的富勒醇）的结构稳定性，我们进行了半经验以及从头算密度泛函理论计算。有趣的是，我们发现当OH基团以小羟基岛的形式覆盖C60时，会得到低能量的原子构型。先前在碳表面形成的由相邻OH基团之间的氢键稳定的OH分子域，定义了具有一些伸长的C-C键、封闭电子壳层和大的最高占据-最低未占据分子轨道能隙的C60(OH)32富勒烯结构的存在，后两者是这类碳化合物中高化学稳定性的众所周知的指标。计算得到的光吸收光谱表明，第一个单偶极允许激发的位置强烈依赖于表面OH基团的精确分布，这一结果与光谱实验相结合，可能为识别这类富勒烯衍生物的结构提供一种有效的方法。我们发现富勒烯表面上一些共吸附的氧物种的存在通常会导致C60(OH)32O(x)（x = 1 - 4）化合物的存在，其中在O杂质正下方的一些C-C键被C-O-C桥键取代，从而导致形成与Xing等人最近的实验工作（《物理化学杂志B》2004年，108卷，11473页）一致的稳定的碳开孔结构。实际上，当考虑多电荷的C60(OH)32O(x)(+/-m)（m = 2, 4, 6）物种（其可存在于气相和水环境中）时，会得到更显著的笼破坏，此时碳网络中可存在由9元和10元环构成的相当大的孔洞。我们认为，如果需要可控地打开碳笼，我们的结果很重要，并且在需要将原子或分子物种永久封装在这类富勒烯衍生物中的若干技术应用中也应予以考虑。
