H2-Binding by Neutral and Multiply Charged Titaniums: Hydrogen Storage Capacity of Titanium Mono- and Dications

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• 作者：Han Myoung Lee ; Dong Young Kim ; Chaeho Pak ; N. Jiten Singh ; Kwang S. Kim
• 刊名：Journal of Chemical Theory and Computation
• 出版年：2011
• 出版时间：April 12, 2011
• 年：2011
• 卷：7
• 期：4
• 页码：969-978
• 全文大小：962K
• 年卷期：v.7,no.4(April 12, 2011)
• ISSN：1549-9626

文摘

Given that transition metal鈭抙ydrogen systems have been studied as a predecessor for hydrogen storage materials, we have investigated the neutral and multiply charged titanium鈭扝₂ systems (Ti鈭扝₂, Ti⁺鈭扝₂, Ti²⁺鈭扝₂, Ti³⁺鈭扝₂, and Ti⁴⁺鈭扝₂) using density functional theory (DFT) and high-level ab initio calculations, including coupled cluster theory with single, double, and perturbatively triple excitations [CCSD(T)]. These systems show different types of hydrogenation depending on their charged state. The neutral Ti鈭扝₂ system shows dihydride structure with covalent interaction where the Ti鈭扝 distance is 1.76 脜, while H₂ is dissociated into two neigboring hydride ions by withdrawing electrons from Ti. The charged Ti⁺鈭扝₂, Ti²⁺鈭扝₂, and Ti³⁺鈭扝₂ systems show dihydrogen structures with noncovalent interaction, where the Ti⁺鈭扝, Ti²⁺鈭扝, and Ti³⁺鈭扝 distances are 2.00, 2.14, and 2.12 脜, respectively. The main binding energies in these systems arise from the hydrogen polarizability driven interaction by the positive charge of Tiⁿ⁺ (n = 1鈭?). Among Tiⁿ⁺鈭扝₂ (n = 1鈭?) the Ti⁺鈭扝₂ has the shortest distance against our common expectation, while Ti²⁺鈭扝₂ has the longest distance. The Ti⁺鈭扝₂ distance is the shortest because of the d鈭捪? molecular orbital (MO) interaction which is not present in Ti²⁺鈭扝₂ and Ti³⁺鈭扝₂. The Ti⁴⁺ ion does not bind H₂. In this regard, we have investigated the maximal hydrogen binding capacity by Ti complexes. The coordination of titanium mono- and dications complexed with dihydrogen (H₂) [Ti⁺(H₂)_n and Ti²⁺(H₂)_m] is studied along with their structures, binding energies, electronic properties, and spectra. The titanium monocations of the quartet ground state have up to the hexacoordinaton, while titanium dications of the triplet ground state have up to the octacoordination at very low temperatures. At room temperature, the monocations favor penta- to hexacoordination, while the dications favor hexacoordination. This information would be useful for the design of hydrogen storage devices of Ti complexes, such as Ti-decorated/dispersed polymer鈭抔raphene hybrid materials.