Xie Yaoming, King R Bruce, Schaefer Henry F
Center for Computational Chemistry and Department of Chemistry, University of Georgia, Athens, GA 30602, USA.
Spectrochim Acta A Mol Biomol Spectrosc. 2005 May;61(7):1693-9. doi: 10.1016/j.saa.2004.12.039.
The homoleptic cobalt carbonyls Co4(CO)12 and Co6(CO)16 are characterized by their equilibrium geometries, thermochemistry, and vibrational frequencies using density functional theory (DFT) methods with the B3LYP, BLYP, and BP86 functionals. The B3LYP predicted CoCo distances are 2.51 and 2.47 A for the C3v and Td structures, respectively, of Co4(CO)12. The global minimum for Co4(CO)12 has C3v symmetry with three bridging and nine terminal carbonyls. The 2.51 and 2.52 A CoCo distances suggest the single bond required for an 18-electron configuration for the metal atoms. This structure is close to an experimentally realized structure. A more symmetrical Co4(CO)12 structure with Td symmetry, analogous to that observed in the valence isoelectronic Ir4(CO)12 molecule, lies approximately 28 kcal/mol higher in energy and exhibits a small imaginary vibrational frequency ( approximately 40i). It has a slightly shorter CoCo distance of 2.47 A. Both Co4(CO)12 structures satisfy the 18-electron rule. The Co6(CO)16 structure has Td symmetry and satisfies the Wade-Mingos rules for an octahedral cluster. The nu(CO) carbonyl frequencies for both Co4(CO)12 and Co6(CO)16 computed with the BP86 functional are closer to the experimental values than those computed with the B3LYP and BLYP functionals. The structure of Co6(CO)16 is not known experimentally, but the BP86 functional predicts 2.56 A (CoCo), 1.77 and 2.02 A (CoC), and 1.66 and 1.20 A (CO) for the bond distances.
使用密度泛函理论（DFT）方法，结合B3LYP、BLYP和BP86泛函，对同核羰基钴Co4(CO)12和Co6(CO)16的平衡几何结构、热化学性质和振动频率进行了表征。B3LYP预测，对于Co4(CO)12的C3v和Td结构，Co-Co距离分别为2.51 Å和2.47 Å。Co4(CO)12的全局最小值具有C3v对称性，有三个桥连羰基和九个端基羰基。2.51 Å和2.52 Å的Co-Co距离表明金属原子的18电子构型所需的单键。该结构与实验实现的结构相近。具有Td对称性的更对称的Co4(CO)12结构，类似于在价电子等电子体Ir4(CO)12分子中观察到的结构，能量约高28 kcal/mol，并且表现出小的虚振动频率（约40i）。它的Co-Co距离稍短，为2.47 Å。两种Co4(CO)12结构都满足18电子规则。Co6(CO)16结构具有Td对称性，并且满足八面体簇的Wade-Mingos规则。用BP86泛函计算的Co4(CO)12和Co6(CO)16的ν(CO)羰基频率比用B3LYP和BLYP泛函计算的更接近实验值。Co6(CO)16的结构在实验上尚不清楚，但BP86泛函预测键长为2.56 Å（Co-Co）、1.77 Å和2.02 Å（Co-C）以及1.66 Å和1.20 Å（C-O）。
