单、双核钌羰基化合物Ru(CO)_n(n=5,4,3)和Ru_2(CO)_n(n=9,8)的理论研究

Theoretical study on homoleptic mononuclear and binuclear ruthenium carbonyls Ru(CO)_n(n=5,4,3) and Ru_2(CO)_n(n=9,8)

采用两种密度泛函方法对中性单核Ru(CO)n(n=5,4,3)和双核Ru2(CO)n(n=9,8)化合物进行理论计算,优化出16个稳定异构体.研究发现,和Os(CO)5类似,Ru(CO)5存在两个能量接近的最低异构体.Ru(CO)4的能量最低异构体为C2v对称性的单态构型.Ru(CO)3能量最低异构体为Cs对称性的单态构型.Ru2(CO)9的两个能量接近的最低异构体分别含有单个桥羰基和3个桥羰基.双核不饱和Ru2(CO)8的能量最低异构体为含有两个桥羰基的单态C2构型.通过比较M2(CO)n(M=Fe,Ru,Os;n=9,8)的能量最低构型,发现Fe和Ru倾向于形成含有多个桥配位羰基的构型,而Os则更倾向于形成不含桥配位羰基的构型.对离解能的研究表明,和失去一个羰基生成Ru2(CO)8相比,Ru2(CO)9更容易离解为Ru(CO)5和Ru(CO)4.

Homoleptic mononuclear and binuclear ruthenium carbonyls Ru（CO）n （n = 5, 4, 3） and Ru2（CO）n （n = 9,8） have been investigated using density functional theory. Sixteen isomers are obtained. For Ru（CO）5, the lowest-energy structure is the singlet D3h trigonal bipyramid. Similar to Os（CO）5, the distorted square pyramid isomer with C2v symmetry lies -7 kJ·mol^-1 higher in energy. For the unsaturated mononuclear ruthenium carbonyls Ru（CO）4 and Ru（CO）3, a singlet structure with C2v symmetry and a Cs bent T-shaped structure are the lowest-energy structures, respectively. The global minimum for the Ru2（CO）9 is a singly bridged （CO）4Ru（fl-CO）Ru（CO）4 structure. A triply bridged Ru2（CO）6（μ-CO）3 structure analogous to the known Fe2（CO）9 structure is predicted to lie very close in energy to the global minimum. For Ru2（CO）8, the doubly bridged C2 structure is predicted to be the global minimum. For the lowest-energy structures of M2（CO）n （M = Fe, Ru, Os, n = 9,8）, it is found that both iron and ruthenium are favored to form structures containing more bridging carbonyl groups, while osmium prefers to have structures with less bridging carbonyl groups. The study of dissociation energy shows that the dissociation of Ru2（CO）9 into the mononuclear fragments Ru（CO）5 ＋ Ru（CO）4 is a less energetically demanding process than the dissociation of one carbonyl group from Ru2（CO）9 to give Ru2（CO）8.