Schottel Brandi L, Chifotides Helen T, Shatruk Mikhail, Chouai Abdellatif, Pérez Lisa M, Bacsa John, Dunbar Kim R
Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012, USA.
J Am Chem Soc. 2006 May 3;128(17):5895-912. doi: 10.1021/ja0606273.
Reactions of 3,6-bis(2'-pyridyl)-1,2,4,5-tetrazine (bptz) and 3,6-bis(2'-pyridyl)-1,2-pyridazine (bppn) with the AgX salts (X = [PF6]-, [AsF6]-, [SbF6]-, and [BF4]-) afford complexes of different structural motifs depending on the pi-acidity of the ligand central ring and the outer-sphere anion. The bptz reactions lead to the polymeric [[Ag(bptz)][PF6]]infinity (1) and the dinuclear compounds [Ag2(bptz)2(CH3CN)2][PF6]2 (2) and [Ag2(bptz)2(CH3CN)2][AsF6]2 (3), as well as the propeller-type species [Ag2(bptz)3][AsF6]2 (4) and [Ag2(bptz)3][SbF6]2 (5a and 5b). Reactions of bppn with AgX produce the grid-type structures [Ag4(bppn)4][X]4 (6-9), regardless of the anion present. In 6-9, pi-pi stacking interactions are maximized, whereas multiple and shorter (therefore stronger) anion-pi interactions between the anions and the tetrazine rings are established in 1-5b. These differences reflect the more electron-rich character of the bppn pyridazine ring as compared to the bptz tetrazine ring. The evidence gleaned from the solid-state structures was corroborated by density functional theory calculations. In the electrostatic potential maps of the free ligands, a higher positive charge is present in the bptz as compared to the bppn central ring. Furthermore, the electrostatic potential maps of 3, 4, and 5b indicate an electron density transfer from the anions to the pi-acidic rings. Conversely, upon addition of the [AsF6]- ions to the cation of 7, there is negligible change in the electron density of the central pyridazine ring, which supports the presence of weaker anion-pi interactions in the bppn as compared to the bptz complexes. From the systems studied herein, it is concluded that anion-pi interactions play an important role in the outcome of self-assembly reactions.
3,6-双(2'-吡啶基)-1,2,4,5-四嗪(bptz)和3,6-双(2'-吡啶基)-1,2-哒嗪(bppn)与AgX盐(X = [PF6] -、[AsF6] -、[SbF6] -和[BF4] -)反应，根据配体中心环和外层阴离子的π酸性，生成不同结构模式的配合物。bptz反应生成聚合物[[Ag(bptz)][PF6]]∞(1)、双核化合物[Ag2(bptz)2(CH3CN)2][PF6]2(2)和[Ag2(bptz)2(CH3CN)2][AsF6]2(3)，以及螺旋桨型物种[Ag2(bptz)3][AsF6]2(4)和[Ag2(bptz)3][SbF6]2(5a和5b)。bppn与AgX反应生成网格型结构[Ag4(bppn)4][X]4(6 - 9)，与存在的阴离子无关。在6 - 9中，π-π堆积相互作用最大化，而在1 - 5b中，阴离子与四嗪环之间形成了多个且较短(因此更强)的阴离子-π相互作用。这些差异反映出与bptz四嗪环相比，bppn哒嗪环的富电子特性更强。从固态结构中收集的证据得到了密度泛函理论计算的证实。在游离配体的静电势图中，与bppn中心环相比，bptz中存在更高的正电荷。此外，3、4和5b的静电势图表明有电子密度从阴离子转移到π酸性环上。相反，向7的阳离子中加入[AsF6] -离子后，中心哒嗪环的电子密度变化可忽略不计，这支持了与bptz配合物相比，bppn中阴离子-π相互作用较弱的观点。从本文研究的体系可以得出结论，阴离子-π相互作用在自组装反应的结果中起重要作用。
