Stereochemistry of Seven-Coordinate Main Group and d0 Transition Metal Molecules
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- 作者：Zhenyang Lin and and Ian Bytheway
- 刊名：Inorganic Chemistry
- 出版年：1996
- 出版时间：January 31, 1996
- 年：1996
- 卷：35
- 期：3
- 页码：594 - 603
- 全文大小：367K
- 年卷期：v.35,no.3(January 31, 1996)
- ISSN：1520-510X
文摘
Ab initio quantum chemical calculations have been usedto study the observed preference for the pentagonalbipyramid (PB) geometry in main group heptafluorides (e.g.,TeF7-, IF7, andXeF7+) and main group andtransitionmetal oxofluorides MOF6- (M = I, Re) whilethe capped octahedron (CO) or capped trigonal prism (CTP)geometryis preferred by the analogous transition metal counterparts(e.g., MoF7- andWF7-). An explanation ofthesetrends is provided by a molecular orbital (MO) model which describesthe main group heptafluorides in terms ofthree non- or antibonding MO's localized largely upon the ligandatoms. These MO's are nonbonding for the PBgeometry but slightly antibonding for the CO and CTP geometries becauseof the lower symmetry of thesestereochemistries; thus the PB geometry is predicted for these maingroup molecules. For transition metalheptafluorides, this MO model predicts that two MO's will not beinvolved in M-L bond formation as they arelocalized on the metal atom. Thus for the PB geometry they arenonbonding and slightly antibonding for the COand CTP geometries. A consequence of the antibonding nature ofthese orbitals is the slight stabilization of thebonding orbitals and a preference for the CO and CTP geometries.Ab initio calculations ofMF7- (M = Mo, W)molecules predict that the CO and CTP have approximately the sameenergy and are lower than the PB byapproximately 1-4 kcal mol-1. SimilarMO arguments may be applied to ReOF6- forwhich the PB geometrywas calculated to be lower in energy than the CO and CTP geometries byabout 28 kcal mol-1. Totalelectrondensities (
) of main group and transition metal fluorides andoxofluorides were compared, and strong ioniccharacter was found in both M-F and M-O bonds. Chargeconcentration maxima in the core regions of thecentral atoms were found through analysis of the Laplacian of thecharge density (
2) showing that thecentralatom is distorted by the ligand atoms.
) of main group and transition metal fluorides andoxofluorides were compared, and strong ioniccharacter was found in both M-F and M-O bonds. Chargeconcentration maxima in the core regions of thecentral atoms were found through analysis of the Laplacian of thecharge density (2) showing that thecentralatom is distorted by the ligand atoms.