Accounting for the Differences in the Structures and Relative Energies of the Highly Homoatomic np-np
详细信息 查看全文
- 作者：Scott Brownridge ; Margaret-Jane Crawford ; Hongbin Du ; Richard D. Harcourt ; Carsten Knapp ; Risto S. Laitinen ; Jack Passmore ; J. Mikko Rautiainen ; Reijo J. Suontamo ; Jussi Valkonen
- 刊名：Inorganic Chemistry
- 出版年：2007
- 出版时间：February 5, 2007
- 年：2007
- 卷：46
- 期：3
- 页码：681 - 699
- 全文大小：951K
- 年卷期：v.46,no.3(February 5, 2007)
- ISSN：1520-510X
文摘
The bonding in the highly homoatomic np
-np (n 
3)-bonded S2I42+ (three 
+ two bonds), the Se-I -bondedSe2I42+ (four + one bonds), and their higher-energy isomers have been studied using modern DFT and abinitio calculations and theoretical analysis methods: atoms in molecules (AIM), molecular orbital (MO), naturalbond orbital (NBO), and valence bond (VB) analyses, giving their relative energies, theoretical bond orders, andatomic charges. The aim of this work was to seek theory-based answers to four main questions: (1) Are thepreviously proposed simple *-* bonding models valid for S2I42+ and Se2I42+? (2) What accounts for the differencein the structures of S2I42+ and Se2I42+? (3) Why are the classically bonded isolobal P2I4 and As2I4 structures notadopted? (4) Is the high experimentally observed S-S bond order supported by theoretical bond orders, and howdoes it relate to high bond orders between other heavier main group elements? The AIM analysis confirmed thehigh bond orders and established that the weak bonds observed in S2I42+ and Se2I42+ are real and the bonding inthese cations is covalent in nature. The full MO analysis confirmed that S2I42+ contains three and two bonds,that the positive charge is essentially equally distributed over all atoms, that the bonding between S2 and two I2+units in S2I42+ is best described by two mutually perpendicular 4c2e *-* bonds, and that in Se2I42+, two SeI2+moieties are joined by a 6c2e *-* bond, both in agreement with previously suggested models. The VB treatmentprovided a complementary approach to MO analysis and provided insight how the formation of the weak bondsaffects the other bonds. The NBO analysis and the calculated AIM charges showed that the minimization of theelectrostatic repulsion between EI2+ units (E = S, Se) and the delocalization of the positive charge are the mainfactors that explain why the nonclassical structures are favored for S2I42+ and Se2I42+. The difference in the structuresof S2I42+ and Se2I42+ is related to the high strength of the S-S bond compared to the weak S-I bond and theadditional stabilization from increased delocalization of positive charge in the structure of S2I42+ compared to thestructure of Se2I42+. The investigation of the E2X42+ series (E = S, Se, Te; X = Cl, Br, I) revealed that only S2I42+adopts the highly np-np (n 3)-bonded structure, while all other dications favor the -bonded Se2I42+ structure.Theoretical bond order calculations for S2I42+ confirm the previously presented experimentally based bond ordersfor S-S (2.1-2.3) and I-I (1.3-1.5) bonds. The S-S bond is determined to have the highest reported S-S bondorder in an isolated compound and has a bond order that is either similar to or slightly less than the Si-Si bondorder in the proposed triply bonded [(Me3Si)2CH]2(iPr)SiSi
SiSi(iPr)[CH(SiMe3)2]2 depending on the definition ofbond orders used.
-np (n 3)-bonded S2I42+ (three + two bonds), the Se-I -bondedSe2I42+ (four + one bonds), and their higher-energy isomers have been studied using modern DFT and abinitio calculations and theoretical analysis methods: atoms in molecules (AIM), molecular orbital (MO), naturalbond orbital (NBO), and valence bond (VB) analyses, giving their relative energies, theoretical bond orders, andatomic charges. The aim of this work was to seek theory-based answers to four main questions: (1) Are thepreviously proposed simple *-* bonding models valid for S2I42+ and Se2I42+? (2) What accounts for the differencein the structures of S2I42+ and Se2I42+? (3) Why are the classically bonded isolobal P2I4 and As2I4 structures notadopted? (4) Is the high experimentally observed S-S bond order supported by theoretical bond orders, and howdoes it relate to high bond orders between other heavier main group elements? The AIM analysis confirmed thehigh bond orders and established that the weak bonds observed in S2I42+ and Se2I42+ are real and the bonding inthese cations is covalent in nature. The full MO analysis confirmed that S2I42+ contains three and two bonds,that the positive charge is essentially equally distributed over all atoms, that the bonding between S2 and two I2+units in S2I42+ is best described by two mutually perpendicular 4c2e *-* bonds, and that in Se2I42+, two SeI2+moieties are joined by a 6c2e *-* bond, both in agreement with previously suggested models. The VB treatmentprovided a complementary approach to MO analysis and provided insight how the formation of the weak bondsaffects the other bonds. The NBO analysis and the calculated AIM charges showed that the minimization of theelectrostatic repulsion between EI2+ units (E = S, Se) and the delocalization of the positive charge are the mainfactors that explain why the nonclassical structures are favored for S2I42+ and Se2I42+. The difference in the structuresof S2I42+ and Se2I42+ is related to the high strength of the S-S bond compared to the weak S-I bond and theadditional stabilization from increased delocalization of positive charge in the structure of S2I42+ compared to thestructure of Se2I42+. The investigation of the E2X42+ series (E = S, Se, Te; X = Cl, Br, I) revealed that only S2I42+adopts the highly np-np (n 3)-bonded structure, while all other dications favor the -bonded Se2I42+ structure.Theoretical bond order calculations for S2I42+ confirm the previously presented experimentally based bond ordersfor S-S (2.1-2.3) and I-I (1.3-1.5) bonds. The S-S bond is determined to have the highest reported S-S bondorder in an isolated compound and has a bond order that is either similar to or slightly less than the Si-Si bondorder in the proposed triply bonded [(Me3Si)2CH]2(iPr)SiSiSiSi(iPr)[CH(SiMe3)2]2 depending on the definition ofbond orders used.