Actinide-Silicon Multiradical Bonding: Infrared Spectra and Electronic Structures of the Si(μ-X)AnF3 (An = Th, U; X = H, F) Molecules
Actinide-Silicon Multiradical Bonding: Infrared Spectra and Electronic Structures of the Si(μ-X)AnF3 (An = Th, U; X = H, F) Molecules
复制标题
DOI：
10.1021/ja409527u
复制
发表时间：
2014-01-29
影响因子：
15
通讯作者：
Li, Jun
中科院分区：
文献类型：
--
作者：
Hu, Han-Shi;Wei, Fan;Li, Jun
我们报道了一系列Si(Mu-X)ANF(3)(An=Th，U；X=H，F)的单键和意想不到的多自由基特征，形成稀有的三线态硅烯。这些桥联分子是通过激光烧蚀的铀和钍原子与氟化硅反应在微观尺度上制备的，并通过Ar和Ne基质的红外光谱和相对论量子化学计算进行了鉴定。为了比较，对铀与CF4和CHF3的反应也进行了类似的霓基质实验。我们的密度泛函理论计算表明，在所有异构体中，具有U(IV)氧化态的Si-U单键物种Si(Mu-X)UF_3(X=H，F)和H或F的准无规桥配体是最稳定的，而天真预期的具有U(VI)氧化态的三键物种XSi=UF_3和具有U(V)氧化态的双键物种XSi中心点=(UF_3)-U中心点的能量明显较高。与XSiF3反应生成的类似的Th产物也更倾向于具有Si-Th单键和桥联H或F配体的Si(Mu-X)ThF3结构。用CCSD(T)和CASPT2方法进行的高水平从头算波函数理论计算证实，Si(Mu-X)UF3的基态为五重态，而Si(Mu-X)ThF3的基态为三重态，其中硅基上有两个未配对的电子。这些含硅分子作为XSiAnF(3)的最低能量异构体，代表了第一个具有不寻常的三重态硅烯和具有多自由基特性的单键的硅-榄系元素。它们与铀-碳类似物XCUF3形成了鲜明的对比，XCUF3形成了具有C-3v对称性的三键单重态基态。计算得到的Si(Mu-X)和F(3)络合物的振动频率与实验结果符合得很好。这些结果突出了3p和2p主族元素与榄系元素化学键的临界差异。这个。对于这些硅化合物，刘易斯电子对模型和八重态规则被打破。
We report a series of Si(mu-X)AnF(3) (An = Th, U; X = H, F) complexes with silicon-actinide(IV) single bonds and unexpected multiradical features that form rare triplet silylenes. These bridged molecules have been prepared in microscopic scale through reactions of laser-ablated uranium and thorium atoms with silicon fluorides and identified from infrared spectra in argon and neon matrixes and relativistic quantum chemical calculations. Similar neon matrix experiments for the reactions of uranium with CF4 and CHF3 were carried out for comparison. Our density functional theory calculations show that the Si-U single-bonded species Si(mu-X)UF3 (X = H, F) with U(IV) oxidation state and the quasi-agostic bridge ligand of H or F are most stable among all the isomers, whereas the naively anticipated triple-bonded species XSi=UF3 with U(VI) oxidation state and the double-bonded species XSi center dot=(UF3)-U-center dot with U(V) oxidation state lie markedly higher in energy. Similar thorium products from reactions with XSiF3 are also found to prefer the Si(mu-X)ThF3 structures with Si-Th single bonds and bridged H or F ligands. High level ab initio wave function theory calculations with the CCSD(T) and CASPT2 methods confirm that the ground states are quintet for Si(mu-X)UF3 and triplet for Si(mu-X)ThF3 with two unpaired electrons on the silylene group. These silicon-bearing molecules as the lowest-energy isomer of XSiAnF(3) represent the first silicon-actinide systems with unusual "triplet" silylenes and Si-An single bonds with multiradical character. They are in dramatic contrast to the uranium-carbon analogs, XC UF3, which form triple-bonded singlet ground states with C-3v symmetry. The calculated vibrational frequencies of the Si(mu-X)AnF(3) complexes agree well with experimental observations. These results accentuate the critical difference of chemical bonding of 3p- and 2p-row main-group elements with actinides. The. Lewis electron-pair model and the octet rule break down for these silicon compounds.