同型ハロゲン結合共結結晶におけるディアザビサイクロ[2.2.2]オクタンの回転力学:エントロピックおよびエンタルピック効果
Luca Catalano1,2, Salvador Perez-Estrada1, Hsin-Hua Wang3
1Department of Chemistry and Biochemistry, University of California , Los Angeles, California 90095, United States.
Journal of the American Chemical Society
|December 20, 2016
まとめ
この研究は,ハロゲン結合の共結晶における回転エネルギー障壁に対する明確なエンタルピックとエントロピックの貢献を示している. 研究者は,アンフィダイナミック結晶で報告された最も低い活性化エネルギーを特定し,分子ダイナミクスへの洞察を提供しました.
科学分野:
- クリスタル・エンジニアリング
- 超分子化学
- 固体化学
背景:
- ハロゲン結合 (XB) は,結晶工学の重要な非共性相互作用である.
- 同結晶の回転ダイナミクスを理解することは 分子機械や材料の設計に不可欠です
- トリチルアセチレンハリド (TrX) とディアザビサイクロ[2.2.2]オクタン (dabco) は,制御された分子運動の可能性のある共結晶を形成する.
研究 の 目的:
- XB共結晶の回転自由エネルギーバリアのエンタルピーとエントロピー成分を解明する.
- TrX (X=I, Br, Cl) とダブコの間の1:1共結晶の形成と構造特性を調査する.
- これらの共結晶構造内のDabcoの回転力学と活性化パラメータを決定する.
主な方法:
- 溶媒の蒸発と機械化学的方法による共結結晶合成
- 構造分析のための単一結晶X線微分
- 四極エコー 2H NMRと可変温度 1H NMRのスピン・ラットレス・リラクゼーション (VT 1H T1) を回転動力学研究に使用する.
主要な成果:
- TrI-dabcoとTrBr-dabcoの同型1:1共結晶 (4aと4b) が成功裏に形成されたが,TrClとの共結晶は得られなかった.
- 構造分析は"三脚の上で回転する"モチーフと包装の相互作用の微妙な違いを明らかにしました.
- NMR研究では,低活性化エネルギー (4bのEa = 0.71 kcal mol-1) を有する6倍の潜在エネルギー表面での急速なダブコ回転が示され,これはアンフィダイナミック結晶で報告された最低値である.
- イーリング方程式解析では,小さな負の活性化エントロピー (ΔS‡ = -3.0 kcal mol-1 K-1) と明確な活性化エンタルピー (ΔH‡ for 4a = 0.95 kcal mol-1, 4b = 0.54 kcal mol-1) が得られた.
結論:
- 同型共結晶の回転腔内の微妙なステリック差異は,異なる回転活性化エネルギーを決定する.
- この研究では,XB共結晶の回転障壁に対するエンタルピックとエントロピックの貢献をうまく解明した.
- この発見は,高度な機能的な材料の設計に 関連する固体における分子運動の基本的な理解を提供します.
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