Factors Controlling Asymmetrization of the Simplest Linear I3鈥?/sup> and I42鈥?/sup> Polyiodides with Implications for the Nature of Halogen Bonding
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- 作者：Gabriele Manca ; Andrea Ienco ; Carlo Mealli
- 刊名：Crystal Growth & Design
- 出版年：2012
- 出版时间：April 4, 2012
- 年：2012
- 卷：12
- 期：4
- 页码：1762-1771
- 全文大小：449K
- 年卷期：v.12,no.4(April 4, 2012)
- ISSN：1528-7505
文摘
This paper investigates geometric and electronic features of linear I3鈥?/sup> and I42鈥?/sup> anions, as building blocks of larger polyiodides. Most experimental structures are quasi D鈭?i>h, although one lateral linkage is occasionally elongated with I路路路I separations approaching those of I路路路I鈥揜鈥?/sup> species, typical of halogen bonding (HalB). Hirshfeld surfaces from crystal data highlight solid state effects depending on the distribution of the counterions around I3鈥?/sup> or I42鈥?/sup> units. Corresponding experimental asymmetries have been mimicked with density functional theory calculations through different surroundings of positive point charges. The consequent deformations are interpreted in terms of the s/p rehybridizations occurring at the central I atom(s) of the populated frontier 蟽* wave functions. The origin is a charge-induced variation of the orbital energies at lateral iodides (electronegativity), hence by their the donor power in a nucleophilic attack. The calculations also provide energy information on I2 + I鈥?/sup> or I2 + 2I鈥?/sup> additions, and, in solvent, the intrinsic energy stability of I42鈥?/sup> is for the first time validated. In the absence of positive charge perturbations, the 1鈥?charge of a remote iodide polarizes I3鈥?/sup> and promotes incipient electrostatic attraction, which is quickly accompanied by electron transfer with a generalized 蟽 delocalization throughout I42鈥?/sup>. Implicit orbital overlap supports a covalent picture, or better to say hypervalency, given the electron richness of the central atoms. Molecular electrostatic potential (MEP) surfaces are expected to show 蟽 holes in support of the purely electrostatic HalB model, typically proposed for I路路路I鈥揜鈥?/sup> systems. However, the computed surfaces show little evidence of 蟽 holes in the equilibrium adducts I3鈥?/sup>, I42鈥?/sup> and I路路路I鈥揜鈥?/sup> suggesting that HalB cannot be purely electrostatic.