Trinuclear Cage‐Like Zn II Macrocyclic Complexes: Enantiomeric Recognition and Gas Adsorption Properties

• Published in: Chemistry : a European journal 2016-01, Vol.22 (2), p.598-609
• Main Authors: Janczak, Jan, Prochowicz, Daniel, Lewiński, Janusz, Fairen‐Jimenez, David, Bereta, Tomasz, Lisowski, Jerzy
• Format: Article
• Language: English
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201503479

Three zinc(II) ions in combination with two units of enantiopure [3+3] triphenolic Schiff‐base macrocycles 1 , 2 , 3 , or 4 form cage‐like chiral complexes. The formation of these complexes is accompanied by the enantioselective self‐recognition of chiral macrocyclic units. The X‐ray crystal structures of these trinuclear complexes show hollow metal–organic molecules. In some crystal forms, these barrel‐shaped complexes are arranged in a window‐to‐window fashion, which results in the formation of 1D channels and a combination of both intrinsic and extrinsic porosity. The microporous nature of the [Zn 3 1 2 ] complex is reflected in its N 2 , Ar, H 2 , and CO 2 adsorption properties. The N 2 and Ar adsorption isotherms show pressure‐gating behavior, which is without precedent for any noncovalent porous material. A comparison of the structures of the [Zn 3 1 2 ] and [Zn 3 3 2 ] complexes with that of the free macrocycle H 3 1 reveals a striking structural similarity. In H 3 1 , two macrocyclic units are stitched together by hydrogen bonds to form a cage very similar to that formed by two macrocyclic units stitched together by Zn II ions. This structural similarity is manifested also by the gas adsorption properties of the free H 3 1 macrocycle. Recrystallization of [Zn 3 1 2 ] in the presence of racemic 2‐butanol resulted in the enantioselective binding of ( S )‐2‐butanol inside the cage through the coordination to one of the Zn II ions.