Department of Chemistry, University of Illinois at Urbana-Champaign, 61801, United States.
J Am Chem Soc. 2011 Sep 7;133(35):14063-70. doi: 10.1021/ja204795q. Epub 2011 Aug 11.
We present a crystallographic study that systematically investigates the effects of the n-alkyl side-chain length on the crystal packing in shape-persistent macrocycles. The solid-state packing of carbazole-ethynylene-containing macrocycles is sensitive to the alkyl-chain length. In macrocycles containing n-alkyl side chains up to nine carbons in length, face-on aromatic π interactions predominate, while the addition of one carbon leads to a completely different packing arrangement. Macrocycles with C(10) or C(11) chains exhibit a novel packing motif wherein the alkyl chains intercalate between macrocycles, leading in one case to continuous solvent-filled channels. When crystals of the C(10) macrocycle are bathed in solvent, the included molecules exchange with the external solvent, and the alkyl chain disorder changes in response to changes in the guest volume in order to retain crystallinity. Powder X-ray diffraction data indicate that alkyl-macrocycle interactions in the longer chains "emulate" the distances typical of face-to-face π interactions, leading to deceptive indicators of π stacking.
我们进行了一项晶体学研究，系统地考察了 n- 烷基侧链长度对形状保持大环晶体堆积的影响。含咔唑乙炔大环的固态堆积对烷基链长度敏感。在含有长达九个碳原子的 n- 烷基侧链的大环中，主要存在面对面的芳香π相互作用，而增加一个碳原子则会导致完全不同的堆积方式。含有 C(10) 或 C(11) 链的大环表现出一种新颖的堆积模式，其中烷基链在大环之间插入，导致一种情况下形成连续充满溶剂的通道。当 C(10) 大环的晶体被溶剂浸泡时，包含的分子与外部溶剂交换，烷基链无序状态会根据客体体积的变化而变化，以保持结晶度。粉末 X 射线衍射数据表明，较长链中的烷基-大环相互作用“模拟”了典型的面对面π相互作用的距离，导致对π 堆积的误导性指标。
