Large Gas-Solid Structural Differences in Complexes of Haloacetonitriles with Boron Trifluoride

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• 作者：James A. Phillips ; Jason A. Halfen ; John P. Wrass ; Christopher C. Knutson ; and Christopher J. Cramer
• 刊名：Inorganic Chemistry
• 出版年：2006
• 出版时间：January 23, 2006
• 年：2006
• 卷：45
• 期：2
• 页码：722 - 731
• 全文大小：275K
• 年卷期：v.45,no.2(January 23, 2006)
• ISSN：1520-510X

文摘

The structural properties of the singly halogenated derivatives of CH₃CN-BF₃ (X-CH₂CN-BF₃: X = F, Cl, Br, I)have been investigated via single-crystal X-ray crystallography, solid-state infrared spectroscopy, and correlatedelectronic-structure theory. Taken together, these data illustrate large differences between the gas-phase andsolid-state structures of these systems. Calculated gas-phase structures (B3PW91/aug-cc-pVTZ) of FCH₂CN-BF₃,ClCH₂CN-BF₃, and BrCH₂CN-BF₃ indicate that the B-N dative bonds in these systems are quite weak, withdistances of 2.422, 2.374, and 2.341 Å, respectively. However, these distances, as well as other calculated structuralparameters and normal-mode vibrational frequencies, indicate that the dative interactions do become slightly strongerin proceeding from F- to Br-CH₂CN-BF₃. In contrast, solid-state structures for FCH₂CN-BF₃, ClCH₂CN-BF₃, andICH₂CN-BF₃ from X-ray crystallography all have B-N distances that are quite short, about 1.65 Å. Thus, the B-Ndistances of the F- and Cl-containing derivatives contract by over 0.7 Å upon crystallization. Large shifts in thevibrational modes involving motions of the BF₃ subunit parallel these structural changes. An X-ray crystal structurecould not be determined for BrCH₂CN-BF₃(s), but the solid-state IR spectrum is consistent with those obtainedpreviously for related complexes and suggests that the solid-state structure resembles those of the others, and inturn, implicates a large gas-solid structural difference for this species as well.