Enantiopure and Racemic Sandwich-like Networks with Dehydration, Readsorption, and Selective Guest-Exchange Phase Transformations
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- 作者：Hong-Qing Hao ; Wen-Ting Liu ; Wei Tan ; Zhuojia Lin ; Ming-Liang Tong
- 刊名：Crystal Growth & Design
- 出版年：2009
- 出版时间：January 7, 2009
- 年：2009
- 卷：9
- 期：1
- 页码：457-465
- 全文大小：520K
- 年卷期：v.9,no.1(January 7, 2009)
- ISSN：1528-7505
文摘
The room-temperature solution reactions of R- or S-H2opa (H2opa = 2-hydroxy-2-phenylacetic acid) with freshly prepared [Ag(NH3)2](OH) in the presence of 1,3-di(4-pyridyl)propane (bpp) yielded two enantiomeric compounds, [Ag2(R-Hopa)(bpp)2](R-Hopa)·3H2O (1·3H2O) and [Ag2(S-Hopa)(bpp)2](S-Hopa)·3H2O (2·3H2O). While a similar solution reaction was carried out with racemic H2opa instead of R- or S-H2opa, a racemic compound [Ag2(R-Hopa)(S-Hopa)(bpp)2]·4H2O (3·4H2O) was formed. When bulk crystals of 3·4H2O were exposed to the air at ambient temperature, a partially dehydrated compound [Ag2(R-Hopa)(S-Hopa)(bpp)2]·H2O (4·H2O) was found, which would transform to [Ag2(R-Hopa)(S-Hopa)(bpp)2]·2MeOH (5·2MeOH) by exposing the crystals of 4·H2O in mixed MeOH−EtOH−DMF solvent or in methanol. Compounds 1−5 have characteristic hydrogen-bonding-directed sandwich-like networks consisting of Ag−bpp layers and Hopa−−ROH chains (R = H for 1−4 and Me for 5). The different structural features come from different hydrogen bonding interactions between Hopa− and the lattice water or MeOH molecules. In 1·3H2O and 2·3H2O, R-Hopa− or S-Hopa− form left-handed or right-handed helices with water molecules running in parallel to the Ag-bpp layers while in 3·4H2O, the centrosymmetric hydrogen bonding chains are composed of two enantiomers of Hopa−. Upon dehydration, the Ag···Ag dimeric units in [Ag2(bpp)2]n2n+ in 3·4H2O were broken and the positions of the Ag-bpp chains were adjusted to form new Hopa−−H2O chains between the silver layers. After absorbing methanol, the Ag-bpp chains restored to their original layer structures and 5·2MeOH is pseudopolymorphic to 3·4H2O. The reversible dehydration, readsorption, and guest-exchange among 3·4H2O, 4·H2O, and 5·2MeOH is an interesting example of phase transformation for racemic coordination polymers. The chirality of 1·3H2O and 2·3H2O was further conformed by solid-state CD spectra.